Java/File Input Output/File Reader
Содержание
- 1 A StraightStreamReader is a bridge from byte streams to character streams
- 2 A word counting utility with FileReader.
- 3 Compare the contents of two Readers to determine if they are equal or not.
- 4 File Locking
- 5 Getting channels from streams
- 6 Indent - prepend leading spaces
- 7 Loading text from a file
- 8 Open File By Name
- 9 Read a file and print, using BufferedReader and System.out
- 10 Read a file containing an offset, and a String at that offset
- 11 Read and return the entire contents of the supplied Reader. This method always closes the reader when finished reading.
- 12 Reader for the ISO-8859-1 encoding.
- 13 Reader for UCS-2 and UCS-4 encodings. (i.e., encodings from ISO-10646-UCS-(2|4)).
- 14 Read file upside down
- 15 Read from Reader and write to Writer until there is no more input from reader.
- 16 Reading Numbers from a Text File
- 17 Reading Numbers from a Text File, Line by Line
- 18 Reads sequentially from multiple sources
- 19 Read the file one buffer at a time
- 20 Testing for end of file while reading a byte at a time
- 21 This class is an part implementation of DataInput. It wraps a Reader object.
- 22 Use a FileReader to display a text file.
A StraightStreamReader is a bridge from byte streams to character streams
<source lang="java">
/*
* An InputStreamReader that does no character encoding translations. * Copyright (C) 2001 Stephen Ostermiller * http://ostermiller.org/contact.pl?regarding=Java+Utilities * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * See COPYING.TXT for details. */
import java.io.*; /**
* A StraightStreamReader is a bridge from byte streams to character streams: It reads bytes * and translates them into characters without using a character encoding. The characters * that a StraightStreamReader returns may not be valid Unicode characters but they are * guaranteed to be in the 0x00 to 0xFF range. * More information about this class is available from .*
* Most of the time you want to do character encoding translation when translating bytes to
* characters. If you are planning on displaying the text, you should always do this and should
* use an InputStreamReader for the purpose. Sometimes it is useful to treat characters as bytes
* with some extra bits. In these cases you would want to use a StraightStreamReader.
* <P>
* For top efficiency, consider wrapping an StraightStreamReader within a BufferedReader. For example:
* BufferedReader in = new BufferedReader(new StraightStreamReader(System.in));
*
* @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
* @since ostermillerutils 1.00.00
*/
public class StraightStreamReader extends Reader{
/**
* The input stream from which all methods in this class read.
*
* @since ostermillerutils 1.00.00
*/
private InputStream in;
/**
* A byte array to be used for calls to the InputStream. This
* is cached as a class variable to avoid object creation and
* deletion each time a read is called. This buffer may be
* null and may not be large enough. Make sure to check i
* before using it.
*
* @since ostermillerutils 1.00.00
*/
private byte[] buffer;
/**
* Create a StraightStreamReader from an InputStream
*
* @param in InputStream to wrap a Reader around.
*
* @since ostermillerutils 1.00.00
*/
public StraightStreamReader(InputStream in) {
this.in = in;
}
/**
* Close the stream.
*
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.00.00
*/
@Override public void close() throws IOException {
in.close();
}
/**
* Mark the present position in the stream. Subsequent calls to reset()
* will attempt to reposition the stream to this point. Not all
* character-input streams support the mark() operation.
*
* @param readAheadLimit Limit on the number of characters that may be read
* while still preserving the mark. After reading this many characters,
* attempting to reset the stream may fail.
* @throws IOException If the stream does not support mark(), or if some other I/O error occurs
*
* @since ostermillerutils 1.00.00
*/
@Override public void mark(int readAheadLimit) throws IOException {
in.mark(readAheadLimit);
}
/**
* Tell whether this stream supports the mark() operation.
*
* @return true if and only if this stream supports the mark operation.
*
* @since ostermillerutils 1.00.00
*/
@Override public boolean markSupported(){
return in.markSupported();
}
/**
* Read a single character. This method will block until a character is available, an
* I/O error occurs, or the end of the stream is reached.
*
* @return The character read, as an integer in the range 0 to 256 (0x00-0xff), or -1 if
* the end of the stream has been reached
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.00.00
*/
@Override public int read() throws IOException {
return in.read();
}
/**
* Read characters into an array. This method will block until some input is available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param cbuf Destination buffer
* @return The number of bytes read, or -1 if the end of the stream has been reached
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.00.00
*/
@Override public int read(char[] cbuf) throws IOException {
return read(cbuf, 0, cbuf.length);
}
/**
* Read characters into an array. This method will block until some input is available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param cbuf Destination buffer
* @param off Offset at which to start storing characters
* @param len Maximum number of characters to read
* @return The number of bytes read, or -1 if the end of the stream has been reached
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.00.00
*/
@Override public int read(char[] cbuf, int off, int len) throws IOException {
// ensure the capacity of the buffer that we will be using
// to read from the input stream
if (buffer == null || buffer.length < len){
buffer = new byte[len];
}
// read from the input stream and copy it to the character array
int length = in.read(buffer, 0, len);
for (int i=0; i<length; i++){
cbuf[off+i] = (char)(0xFF & buffer[i]);
}
return length;
}
/**
* Tell whether this stream is ready to be read.
*
* @return True if the next read() is guaranteed not to block for input, false otherwise.
* Note that returning false does not guarantee that the next read will block.
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.00.00
*/
@Override public boolean ready() throws IOException {
return (in.available() > 0);
}
/**
* Reset the stream. If the stream has been marked, then attempt to reposition it at the mark.
* If the stream has not been marked, then attempt to reset it in some way appropriate to the
* particular stream, for example by repositioning it to its starting point. Not all
* character-input streams support the reset() operation, and some support reset()
* without supporting mark().
*
* @throws IOException If the stream has not been marked, or if the mark has been invalidated,
* or if the stream does not support reset(), or if some other I/O error occurs
*
* @since ostermillerutils 1.00.00
*/
@Override public void reset() throws IOException {
in.reset();
}
/**
* Skip characters. This method will block until some characters are available,
* an I/O error occurs, or the end of the stream is reached.
*
* @param n The number of characters to skip
* @return The number of characters actually skipped
* @throws IllegalArgumentException If n is negative
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.00.00
*/
@Override public long skip(long n) throws IOException {
return in.skip(n);
}
}
</source>
A word counting utility with FileReader.
<source lang="java">
import java.io.FileReader; class WordCount {
public static void main(String args[]) throws Exception {
int words = 0;
int lines = 0;
int chars = 0;
FileReader fr = new FileReader("yourFile.txt");
int c = 0;
boolean lastWhite = true;
String whiteSpace = " \t\n\r";
while ((c = fr.read()) != -1) {
chars++;
if (c == "\n") {
lines++;
}
int index = whiteSpace.indexOf(c);
if (index == -1) {
if (lastWhite == true) {
++words;
}
lastWhite = false;
} else {
lastWhite = true;
}
}
if (chars != 0) {
++lines;
}
}
}
</source>
Compare the contents of two Readers to determine if they are equal or not.
<source lang="java">
/*
* Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */
import java.io.BufferedReader; import java.io.IOException; import java.io.Reader; /** * Origin of code: Apache Avalon (Excalibur)
* * @author Peter Donald * @author Jeff Turner * @author Matthew Hawthorne * @author Stephen Colebourne * @author Gareth Davis * @version CVS $Revision$ $Date$*/
public class Main {
/**
* Compare the contents of two Readers to determine if they are equal or not.
* <p>
* This method buffers the input internally using BufferedReader if they are not
* already buffered.
*
* @param input1
* the first reader
* @param input2
* the second reader
* @return true if the content of the readers are equal or they both don"t exist, false
* otherwise
* @throws NullPointerException
* if either input is null
* @throws IOException
* if an I/O error occurs
* @since 1.1
*/
public static boolean contentEquals(Reader input1, Reader input2) throws IOException
{
if (!(input1 instanceof BufferedReader))
{
input1 = new BufferedReader(input1);
}
if (!(input2 instanceof BufferedReader))
{
input2 = new BufferedReader(input2);
}
int ch = input1.read();
while (-1 != ch)
{
int ch2 = input2.read();
if (ch != ch2)
{
return false;
}
ch = input1.read();
}
int ch2 = input2.read();
return (ch2 == -1);
}
}
</source>
File Locking
<source lang="java">
// : c12:FileLocking.java // {Clean: file.txt} // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. import java.io.FileOutputStream; import java.nio.channels.FileLock; public class FileLocking {
public static void main(String[] args) throws Exception {
FileOutputStream fos = new FileOutputStream("file.txt");
FileLock fl = fos.getChannel().tryLock();
if (fl != null) {
System.out.println("Locked File");
Thread.sleep(100);
fl.release();
System.out.println("Released Lock");
}
fos.close();
}
} ///:~
</source>
Getting channels from streams
<source lang="java">
// : c12:GetChannel.java // Getting channels from streams // {Clean: data.txt} // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.RandomAccessFile; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; public class GetChannel {
private static final int BSIZE = 1024;
public static void main(String[] args) throws Exception {
// Write a file:
FileChannel fc = new FileOutputStream("data.txt").getChannel();
fc.write(ByteBuffer.wrap("Some text ".getBytes()));
fc.close();
// Add to the end of the file:
fc = new RandomAccessFile("data.txt", "rw").getChannel();
fc.position(fc.size()); // Move to the end
fc.write(ByteBuffer.wrap("Some more".getBytes()));
fc.close();
// Read the file:
fc = new FileInputStream("data.txt").getChannel();
ByteBuffer buff = ByteBuffer.allocate(BSIZE);
fc.read(buff);
buff.flip();
while (buff.hasRemaining())
System.out.print((char) buff.get());
}
} ///:~
</source>
Indent - prepend leading spaces
<source lang="java">
/*
* Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002. * All rights reserved. Software written by Ian F. Darwin and others. * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $ * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS"" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s, * pioneering role in inventing and promulgating (and standardizing) the Java * language and environment is gratefully acknowledged. * * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for * inventing predecessor languages C and C++ is also gratefully acknowledged. */
import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.IOException; import java.io.InputStreamReader; /**
* Indent - prepend leading spaces * * @author Ian F. Darwin, http://www.darwinsys.ru/ * @version $Id: Indent.java,v 1.3 2004/02/09 03:34:03 ian Exp $ */
public class Indent {
/** the default number of spaces. */
static int nSpaces = 10;
public static void main(String[] av) {
Indent c = new Indent();
switch (av.length) {
case 0:
c.process(new BufferedReader(new InputStreamReader(System.in)));
break;
default:
for (int i = 0; i < av.length; i++)
try {
c.process(new BufferedReader(new FileReader(av[i])));
} catch (FileNotFoundException e) {
System.err.println(e);
}
}
}
/** print one file, given an open BufferedReader */
public void process(BufferedReader is) {
try {
String inputLine;
//+
while ((inputLine = is.readLine()) != null) {
for (int i = 0; i < nSpaces; i++)
System.out.print(" ");
System.out.println(inputLine);
}
//-
is.close();
} catch (IOException e) {
System.out.println("IOException: " + e);
}
}
}
</source>
Loading text from a file
<source lang="java">
import java.io.BufferedReader; import java.io.File; import java.io.FileReader; public class Main {
public static void main(String[] argv) throws Exception {
File f = new File("C:\\test.txt");
FileReader fr = new FileReader(f);
BufferedReader br = new BufferedReader(fr);
StringBuffer sb = new StringBuffer();
String eachLine = br.readLine();
while (eachLine != null) {
sb.append(eachLine);
sb.append("\n");
eachLine = br.readLine();
}
System.out.println(sb.toString());
}
}
</source>
Open File By Name
<source lang="java">
/*
* Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002. * All rights reserved. Software written by Ian F. Darwin and others. * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $ * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS"" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s, * pioneering role in inventing and promulgating (and standardizing) the Java * language and environment is gratefully acknowledged. * * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for * inventing predecessor languages C and C++ is also gratefully acknowledged. */
import java.io.*; public class OpenFileByName {
public static void main(String[] args) throws IOException {
BufferedReader is = new BufferedReader(new FileReader("myFile.txt"));
BufferedOutputStream bytesOut = new BufferedOutputStream(
new FileOutputStream("bytes.dat"));
// Code here to read from is, write to bytesOut
bytesOut.close();
}
}
</source>
Read a file and print, using BufferedReader and System.out
<source lang="java">
/*
* Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002. * All rights reserved. Software written by Ian F. Darwin and others. * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $ * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS"" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s, * pioneering role in inventing and promulgating (and standardizing) the Java * language and environment is gratefully acknowledged. * * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for * inventing predecessor languages C and C++ is also gratefully acknowledged. */
import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.IOException; import java.io.InputStreamReader; /**
* Read a file and print, using BufferedReader and System.out */
public class CatFile {
public static void main(String[] av) {
CatFile c = new CatFile();
if (av.length == 0)
c.process(new BufferedReader(new InputStreamReader(System.in)));
else
for (int i = 0; i < av.length; i++)
try {
c.process(new BufferedReader(new FileReader(av[i])));
} catch (FileNotFoundException e) {
System.err.println(e);
}
}
/** print one file, given an open BufferedReader */
public void process(BufferedReader is) {
try {
String inputLine;
while ((inputLine = is.readLine()) != null) {
System.out.println(inputLine);
}
is.close();
} catch (IOException e) {
System.out.println("IOException: " + e);
}
}
}
</source>
Read a file containing an offset, and a String at that offset
<source lang="java">
/*
* Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002. * All rights reserved. Software written by Ian F. Darwin and others. * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $ * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS"" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s, * pioneering role in inventing and promulgating (and standardizing) the Java * language and environment is gratefully acknowledged. * * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for * inventing predecessor languages C and C++ is also gratefully acknowledged. */
import java.io.IOException; import java.io.RandomAccessFile; /**
* Read a file containing an offset, and a String at that offset. * * @author Ian F. Darwin, http://www.darwinsys.ru/ * @version $Id: ReadRandom.java,v 1.6 2004/03/07 17:30:35 ian Exp $ */
public class RandomRead {
final static String FILENAME = "random.dat";
protected String fileName;
protected RandomAccessFile seeker;
public static void main(String[] argv) throws IOException {
RandomRead r = new RandomRead(FILENAME);
System.out.println("Offset is " + r.readOffset());
System.out.println("Message is \"" + r.readMessage() + "\".");
}
/** Constructor: save filename, construct RandomAccessFile */
public RandomRead(String fname) throws IOException {
fileName = fname;
seeker = new RandomAccessFile(fname, "r");
}
/** Read the Offset field, defined to be at location 0 in the file. */
public int readOffset() throws IOException {
seeker.seek(0); // move to very beginning
return seeker.readInt(); // and read the offset
}
/** Read the message at the given offset */
public String readMessage() throws IOException {
seeker.seek(readOffset()); // move to the offset
return seeker.readLine(); // and read the String
}
}
</source>
Read and return the entire contents of the supplied Reader. This method always closes the reader when finished reading.
<source lang="java">
/*
* JBoss DNA (http://www.jboss.org/dna) * See the COPYRIGHT.txt file distributed with this work for information * regarding copyright ownership. Some portions may be licensed * to Red Hat, Inc. under one or more contributor license agreements. * See the AUTHORS.txt file in the distribution for a full listing of * individual contributors. * * JBoss DNA is free software. Unless otherwise indicated, all code in JBoss DNA * is licensed to you under the terms of the GNU Lesser General Public License as * published by the Free Software Foundation; either version 2.1 of * the License, or (at your option) any later version. * * JBoss DNA is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this software; if not, write to the Free * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA * 02110-1301 USA, or see the FSF site: http://www.fsf.org. */
import java.io.IOException; import java.io.Reader; /**
* @author Randall Hauch */
public class Main {
/**
* Read and return the entire contents of the supplied {@link Reader}. This method always closes the reader when finished
* reading.
*
* @param reader the reader of the contents; may be null
* @return the contents, or an empty string if the supplied reader is null
* @throws IOException if there is an error reading the content
*/
public static String read( Reader reader ) throws IOException {
if (reader == null) return "";
StringBuilder sb = new StringBuilder();
boolean error = false;
try {
int numRead = 0;
char[] buffer = new char[1024];
while ((numRead = reader.read(buffer)) > -1) {
sb.append(buffer, 0, numRead);
}
} catch (IOException e) {
error = true; // this error should be thrown, even if there is an error closing reader
throw e;
} catch (RuntimeException e) {
error = true; // this error should be thrown, even if there is an error closing reader
throw e;
} finally {
try {
reader.close();
} catch (IOException e) {
if (!error) throw e;
}
}
return sb.toString();
}
}
</source>
Reader for the ISO-8859-1 encoding.
<source lang="java">
/*
* Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */
import java.io.IOException; import java.io.InputStream; import java.io.Reader; /**
* <p> * Reader for the ISO-8859-1 encoding.*
* * @xerces.internal * * @author Michael Glavassevich, IBM * * @version $Id: Latin1Reader.java 446716 2006-09-15 20:28:48Z mrglavas $ */
public class Latin1Reader extends Reader {
//
// Constants
//
/** Default byte buffer size (2048). */
public static final int DEFAULT_BUFFER_SIZE = 2048;
//
// Data
//
/** Input stream. */
protected final InputStream fInputStream;
/** Byte buffer. */
protected final byte[] fBuffer;
//
// Constructors
//
/**
* Constructs an ISO-8859-1 reader from the specified input stream using the
* default buffer size.
*
* @param inputStream
* The input stream.
*/
public Latin1Reader(InputStream inputStream) {
this(inputStream, DEFAULT_BUFFER_SIZE);
} // <init>(InputStream)
/**
* Constructs an ISO-8859-1 reader from the specified input stream and buffer
* size.
*
* @param inputStream
* The input stream.
* @param size
* The initial buffer size.
*/
public Latin1Reader(InputStream inputStream, int size) {
this(inputStream, new byte[size]);
} // <init>(InputStream, int)
/**
* Constructs an ISO-8859-1 reader from the specified input stream and buffer.
*
* @param inputStream
* The input stream.
* @param buffer
* The byte buffer.
*/
public Latin1Reader(InputStream inputStream, byte[] buffer) {
fInputStream = inputStream;
fBuffer = buffer;
} // <init>(InputStream, byte[])
//
// Reader methods
//
/**
* Read a single character. This method will block until a character is
* available, an I/O error occurs, or the end of the stream is reached.
*
* * Subclasses that intend to support efficient single-character input should * override this method. * * @return The character read, as an integer in the range 0 to 255 (0x00-0xff), * or -1 if the end of the stream has been reached * * @exception IOException * If an I/O error occurs */ public int read() throws IOException { return fInputStream.read(); } // read():int /** * Read characters into a portion of an array. This method will block until * some input is available, an I/O error occurs, or the end of the stream is * reached. * * @param ch * Destination buffer * @param offset * Offset at which to start storing characters * @param length * Maximum number of characters to read * * @return The number of characters read, or -1 if the end of the stream has * been reached * * @exception IOException * If an I/O error occurs */ public int read(char ch[], int offset, int length) throws IOException { if (length > fBuffer.length) { length = fBuffer.length; } int count = fInputStream.read(fBuffer, 0, length); for (int i = 0; i < count; ++i) { ch[offset + i] = (char) (fBuffer[i] & 0xff); } return count; } // read(char[],int,int) /** * Skip characters. This method will block until some characters are * available, an I/O error occurs, or the end of the stream is reached. * * @param n * The number of characters to skip * * @return The number of characters actually skipped * * @exception IOException * If an I/O error occurs */ public long skip(long n) throws IOException { return fInputStream.skip(n); } // skip(long):long /** * Tell whether this stream is ready to be read. * * @return True if the next read() is guaranteed not to block for input, false * otherwise. Note that returning false does not guarantee that the * next read will block. * * @exception IOException * If an I/O error occurs */ public boolean ready() throws IOException { return false; } // ready() /** * Tell whether this stream supports the mark() operation. */ public boolean markSupported() { return fInputStream.markSupported(); } // markSupported() /** * Mark the present position in the stream. Subsequent calls to reset() will * attempt to reposition the stream to this point. Not all character-input * streams support the mark() operation. * * @param readAheadLimit * Limit on the number of characters that may be read while still * preserving the mark. After reading this many characters, * attempting to reset the stream may fail. * * @exception IOException * If the stream does not support mark(), or if some other I/O * error occurs */ public void mark(int readAheadLimit) throws IOException { fInputStream.mark(readAheadLimit); } // mark(int) /** * Reset the stream. If the stream has been marked, then attempt to reposition * it at the mark. If the stream has not been marked, then attempt to reset it * in some way appropriate to the particular stream, for example by * repositioning it to its starting point. Not all character-input streams * support the reset() operation, and some support reset() without supporting * mark(). * * @exception IOException * If the stream has not been marked, or if the mark has been * invalidated, or if the stream does not support reset(), or if * some other I/O error occurs */ public void reset() throws IOException { fInputStream.reset(); } // reset() /** * Close the stream. Once a stream has been closed, further read(), ready(), * mark(), or reset() invocations will throw an IOException. Closing a * previously-closed stream, however, has no effect. * * @exception IOException * If an I/O error occurs */ public void close() throws IOException { fInputStream.close(); } // close() } // class Latin1Reader </source>
Reader for UCS-2 and UCS-4 encodings. (i.e., encodings from ISO-10646-UCS-(2|4)).
<source lang="java">
/*
* Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */
import java.io.IOException; import java.io.InputStream; import java.io.Reader; /**
* Reader for UCS-2 and UCS-4 encodings. (i.e., encodings from * ISO-10646-UCS-(2|4)). * * @xerces.internal * * @author Neil Graham, IBM * * @version $Id: UCSReader.java 449317 2006-09-23 22:12:30Z mrglavas $ */
public class UCSReader extends Reader {
//
// Constants
//
/**
* Default byte buffer size (8192, larger than that of ASCIIReader since it"s
* reasonable to surmise that the average UCS-4-encoded file should be 4 times
* as large as the average ASCII-encoded file).
*/
public static final int DEFAULT_BUFFER_SIZE = 8192;
public static final short UCS2LE = 1;
public static final short UCS2BE = 2;
public static final short UCS4LE = 4;
public static final short UCS4BE = 8;
//
// Data
//
/** Input stream. */
protected final InputStream fInputStream;
/** Byte buffer. */
protected final byte[] fBuffer;
// what kind of data we"re dealing with
protected final short fEncoding;
//
// Constructors
//
/**
* Constructs a UCS reader from the specified input stream using the default
* buffer size. The Endian-ness and whether this is UCS-2 or UCS-4 needs also
* to be known in advance.
*
* @param inputStream
* The input stream.
* @param encoding
* One of UCS2LE, UCS2BE, UCS4LE or UCS4BE.
*/
public UCSReader(InputStream inputStream, short encoding) {
this(inputStream, DEFAULT_BUFFER_SIZE, encoding);
} // <init>(InputStream, short)
/**
* Constructs a UCS reader from the specified input stream and buffer size.
* The Endian-ness and whether this is UCS-2 or UCS-4 needs also to be known
* in advance.
*
* @param inputStream
* The input stream.
* @param size
* The initial buffer size.
* @param encoding
* One of UCS2LE, UCS2BE, UCS4LE or UCS4BE.
*/
public UCSReader(InputStream inputStream, int size, short encoding) {
this(inputStream, new byte[size], encoding);
} // <init>(InputStream,int,short)
/**
* Constructs a UCS reader from the specified input stream and buffer. The
* Endian-ness and whether this is UCS-2 or UCS-4 needs also to be known in
* advance.
*
* @param inputStream
* The input stream.
* @param buffer
* The byte buffer.
* @param encoding
* One of UCS2LE, UCS2BE, UCS4LE or UCS4BE.
*/
public UCSReader(InputStream inputStream, byte[] buffer, short encoding) {
fInputStream = inputStream;
fBuffer = buffer;
fEncoding = encoding;
} // <init>(InputStream,int,short)
//
// Reader methods
//
/**
* Read a single character. This method will block until a character is
* available, an I/O error occurs, or the end of the stream is reached.
*
* <p>
* Subclasses that intend to support efficient single-character input should
* override this method.
*
* @return The character read, as an integer in the range 0 to 127 (0x00-0x7f),
* or -1 if the end of the stream has been reached
*
* @exception IOException
* If an I/O error occurs
*/
public int read() throws IOException {
int b0 = fInputStream.read() & 0xff;
if (b0 == 0xff) {
return -1;
}
int b1 = fInputStream.read() & 0xff;
if (b1 == 0xff) {
return -1;
}
// UCS-4
if (fEncoding >= 4) {
int b2 = fInputStream.read() & 0xff;
if (b2 == 0xff) {
return -1;
}
int b3 = fInputStream.read() & 0xff;
if (b3 == 0xff) {
return -1;
}
if (fEncoding == UCS4BE) {
return (b0 << 24) + (b1 << 16) + (b2 << 8) + b3;
}
return (b3 << 24) + (b2 << 16) + (b1 << 8) + b0;
}
// UCS-2
if (fEncoding == UCS2BE) {
return (b0 << 8) + b1;
}
return (b1 << 8) + b0;
} // read():int
/**
* Read characters into a portion of an array. This method will block until
* some input is available, an I/O error occurs, or the end of the stream is
* reached.
*
* @param ch
* Destination buffer
* @param offset
* Offset at which to start storing characters
* @param length
* Maximum number of characters to read
*
* @return The number of characters read, or -1 if the end of the stream has
* been reached
*
* @exception IOException
* If an I/O error occurs
*/
public int read(char ch[], int offset, int length) throws IOException {
int byteLength = length << ((fEncoding >= 4) ? 2 : 1);
if (byteLength > fBuffer.length) {
byteLength = fBuffer.length;
}
int count = fInputStream.read(fBuffer, 0, byteLength);
if (count == -1)
return -1;
// try and make count be a multiple of the number of bytes we"re looking for
if (fEncoding >= 4) { // BigEndian
// this looks ugly, but it avoids an if at any rate...
int numToRead = (4 - (count & 3) & 3);
for (int i = 0; i < numToRead; i++) {
int charRead = fInputStream.read();
if (charRead == -1) { // end of input; something likely went wrong!A Pad
// buffer with nulls.
for (int j = i; j < numToRead; j++) {
fBuffer[count + j] = 0;
}
break;
}
fBuffer[count + i] = (byte) charRead;
}
count += numToRead;
} else {
int numToRead = count & 1;
if (numToRead != 0) {
count++;
int charRead = fInputStream.read();
if (charRead == -1) { // end of input; something likely went wrong!A Pad
// buffer with nulls.
fBuffer[count] = 0;
} else {
fBuffer[count] = (byte) charRead;
}
}
}
// now count is a multiple of the right number of bytes
int numChars = count >> ((fEncoding >= 4) ? 2 : 1);
int curPos = 0;
for (int i = 0; i < numChars; i++) {
int b0 = fBuffer[curPos++] & 0xff;
int b1 = fBuffer[curPos++] & 0xff;
// UCS-4
if (fEncoding >= 4) {
int b2 = fBuffer[curPos++] & 0xff;
int b3 = fBuffer[curPos++] & 0xff;
if (fEncoding == UCS4BE) {
ch[offset + i] = (char) ((b0 << 24) + (b1 << 16) + (b2 << 8) + b3);
} else {
ch[offset + i] = (char) ((b3 << 24) + (b2 << 16) + (b1 << 8) + b0);
}
} else { // UCS-2
if (fEncoding == UCS2BE) {
ch[offset + i] = (char) ((b0 << 8) + b1);
} else {
ch[offset + i] = (char) ((b1 << 8) + b0);
}
}
}
return numChars;
} // read(char[],int,int)
/**
* Skip characters. This method will block until some characters are
* available, an I/O error occurs, or the end of the stream is reached.
*
* @param n
* The number of characters to skip
*
* @return The number of characters actually skipped
*
* @exception IOException
* If an I/O error occurs
*/
public long skip(long n) throws IOException {
// charWidth will represent the number of bits to move
// n leftward to get num of bytes to skip, and then move the result
// rightward
// to get num of chars effectively skipped.
// The trick with &"ing, as with elsewhere in this dcode, is
// intended to avoid an expensive use of / that might not be optimized
// away.
int charWidth = (fEncoding >= 4) ? 2 : 1;
long bytesSkipped = fInputStream.skip(n << charWidth);
if ((bytesSkipped & (charWidth | 1)) == 0)
return bytesSkipped >> charWidth;
return (bytesSkipped >> charWidth) + 1;
} // skip(long):long
/**
* Tell whether this stream is ready to be read.
*
* @return True if the next read() is guaranteed not to block for input, false
* otherwise. Note that returning false does not guarantee that the
* next read will block.
*
* @exception IOException
* If an I/O error occurs
*/
public boolean ready() throws IOException {
return false;
} // ready()
/**
* Tell whether this stream supports the mark() operation.
*/
public boolean markSupported() {
return fInputStream.markSupported();
} // markSupported()
/**
* Mark the present position in the stream. Subsequent calls to reset() will
* attempt to reposition the stream to this point. Not all character-input
* streams support the mark() operation.
*
* @param readAheadLimit
* Limit on the number of characters that may be read while still
* preserving the mark. After reading this many characters,
* attempting to reset the stream may fail.
*
* @exception IOException
* If the stream does not support mark(), or if some other I/O
* error occurs
*/
public void mark(int readAheadLimit) throws IOException {
fInputStream.mark(readAheadLimit);
} // mark(int)
/**
* Reset the stream. If the stream has been marked, then attempt to reposition
* it at the mark. If the stream has not been marked, then attempt to reset it
* in some way appropriate to the particular stream, for example by
* repositioning it to its starting point. Not all character-input streams
* support the reset() operation, and some support reset() without supporting
* mark().
*
* @exception IOException
* If the stream has not been marked, or if the mark has been
* invalidated, or if the stream does not support reset(), or if
* some other I/O error occurs
*/
public void reset() throws IOException {
fInputStream.reset();
} // reset()
/**
* Close the stream. Once a stream has been closed, further read(), ready(),
* mark(), or reset() invocations will throw an IOException. Closing a
* previously-closed stream, however, has no effect.
*
* @exception IOException
* If an I/O error occurs
*/
public void close() throws IOException {
fInputStream.close();
} // close()
} // class UCSReader
</source>
Read file upside down
<source lang="java">
import java.io.File; import java.io.FileReader; public class Main {
public static void main(String[] args) throws Exception {
File f = new File("hello.txt");
FileReader fr = new FileReader(f);
char[] c = new char[(int) f.length()];
char[] cnew = new char[(int) f.length()];
StringBuffer sbuf = new StringBuffer();
fr.read(c, 0, (int) f.length());
int len = (int) f.length();
for (int i = 0, j = len - 1; i < len; i++, j--) {
cnew[i] = c[j];
sbuf.append(cnew[i]);
}
System.out.println(sbuf.toString());
fr.close();
}
}
</source>
Read from Reader and write to Writer until there is no more input from reader.
<source lang="java">
import java.io.IOException; import java.io.Reader; import java.io.Writer; public class Main {
/**
* Read input from reader and write it to writer until there is no more
* input from reader.
*
* @param reader the reader to read from.
* @param writer the writer to write to.
* @param buf the char array to use as a bufferx
*/
public static void flow( Reader reader, Writer writer, char[] buf )
throws IOException {
int numRead;
while ( (numRead = reader.read(buf) ) >= 0) {
writer.write(buf, 0, numRead);
}
}
}
</source>
Reading Numbers from a Text File
<source lang="java">
import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; import java.io.Reader; import java.io.StreamTokenizer; // The buffering makes the program more than 20 times faster. public class SumFile {
public static void main(String[] a) throws IOException {
sumfile("file.txt");
}
static void sumfile(String filename) throws IOException {
Reader r = new BufferedReader(new FileReader(filename));
StreamTokenizer stok = new StreamTokenizer(r);
stok.parseNumbers();
double sum = 0;
stok.nextToken();
while (stok.ttype != StreamTokenizer.TT_EOF) {
if (stok.ttype == StreamTokenizer.TT_NUMBER)
sum += stok.nval;
else
System.out.println("Nonnumber: " + stok.sval);
stok.nextToken();
}
System.out.println("The file sum is " + sum);
}
}
</source>
Reading Numbers from a Text File, Line by Line
<source lang="java">
import java.io.FileReader; import java.io.IOException; import java.io.LineNumberReader; import java.io.StreamTokenizer; public class SumLine {
public static void main(String[] a)throws IOException {
sumLines("file.txt");
}
static void sumLines(String filename) throws IOException {
LineNumberReader lnr = new LineNumberReader(new FileReader(filename));
lnr.setLineNumber(1);
StreamTokenizer stok = new StreamTokenizer(lnr);
stok.parseNumbers();
stok.eolIsSignificant(true);
stok.nextToken();
while (stok.ttype != StreamTokenizer.TT_EOF) {
int lineno = lnr.getLineNumber();
double sum = 0;
while (stok.ttype != StreamTokenizer.TT_EOL) {
if (stok.ttype == StreamTokenizer.TT_NUMBER)
sum += stok.nval;
stok.nextToken();
}
System.out.println("Sum of line " + lineno + " is " + sum);
stok.nextToken();
}
}
}
</source>
Reads sequentially from multiple sources
<source lang="java">
/*
* Copyright (C) 2004 Stephen Ostermiller * http://ostermiller.org/contact.pl?regarding=Java+Utilities * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * See COPYING.TXT for details. */
import java.io.*; import java.util.ArrayList; /**
* A reader which reads sequentially from multiple sources. * More information about this class is available from . * * @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities * @since ostermillerutils 1.04.00 */
public class ConcatReader extends Reader {
/**
* Current index to readerQueue
*
* @since ostermillerutils 1.04.01
*/
private int readerQueueIndex = 0;
/**
* Queue of readers that have yet to be read from.
*
* @since ostermillerutils 1.04.01
*/
private ArrayList<Reader> readerQueue = new ArrayList<Reader>();
/**
* A cache of the current reader from the readerQueue
* to avoid unneeded access to the queue which must
* be synchronized.
*
* @since ostermillerutils 1.04.01
*/
private Reader currentReader = null;
/**
* true iff the client may add more readers.
*
* @since ostermillerutils 1.04.01
*/
private boolean doneAddingReaders = false;
/**
* Causes the addReader method to throw IllegalStateException
* and read() methods to return -1 (end of stream)
* when there is no more available data.
* <p>
* Calling this method when this class is no longer accepting
* more readers has no effect.
*
* @since ostermillerutils 1.04.01
*/
public void lastReaderAdded(){
doneAddingReaders = true;
}
/**
* Add the given reader to the queue of readers from which to
* concatenate data.
*
* @param in Reader to add to the concatenation.
* @throws IllegalStateException if more readers can"t be added because lastReaderAdded() has been called, close() has been called, or a constructor with reader parameters was used.
*
* @since ostermillerutils 1.04.01
*/
public void addReader(Reader in){
synchronized(readerQueue){
if (in == null) throw new NullPointerException();
if (closed) throw new IllegalStateException("ConcatReader has been closed");
if (doneAddingReaders) throw new IllegalStateException("Cannot add more readers - the last reader has already been added.");
readerQueue.add(in);
}
}
/**
* Add the given reader to the queue of readers from which to
* concatenate data.
*
* @param in Reader to add to the concatenation.
* @throws IllegalStateException if more readers can"t be added because lastReaderAdded() has been called, close() has been called, or a constructor with reader parameters was used.
* @throws NullPointerException the array of readers, or any of the contents is null.
*
* @since ostermillerutils 1.04.01
*/
public void addReaders(Reader[] in){
for (Reader element: in) {
addReader(element);
}
}
/**
* Gets the current reader, looking at the next
* one in the list if the current one is null.
*
* @since ostermillerutils 1.04.01
*/
private Reader getCurrentReader(){
if (currentReader == null && readerQueueIndex < readerQueue.size()){
synchronized(readerQueue){
// reader queue index is advanced only by the nextReader()
// method. Don"t do it here.
currentReader = readerQueue.get(readerQueueIndex);
}
}
return currentReader;
}
/**
* Indicate that we are done with the current reader and we should
* advance to the next reader.
*
* @since ostermillerutils 1.04.01
*/
private void advanceToNextReader(){
currentReader = null;
readerQueueIndex++;
}
/**
* True iff this the close() method has been called on this stream.
*
* @since ostermillerutils 1.04.00
*/
private boolean closed = false;
/**
* Create a new reader that can dynamically accept new sources.
* <p>
* New sources should be added using the addReader() method.
* When all sources have been added the lastReaderAdded() should
* be called so that read methods can return -1 (end of stream).
* <p>
* Adding new sources may by interleaved with read calls.
*
* @since ostermillerutils 1.04.01
*/
public ConcatReader(){
// Empty Constructor
}
/**
* Create a new reader with one source.
* <p>
* When using this constructor, more readers cannot
* be added later, and calling addReader() will
* throw an illegal state Exception.
*
* @param in reader to use as a source.
*
* @throws NullPointerException if in is null
*
* @since ostermillerutils 1.04.00
*/
public ConcatReader(Reader in){
addReader(in);
lastReaderAdded();
}
/**
* Create a new reader with two sources.
* <p>
* When using this constructor, more readers cannot
* be added later, and calling addReader() will
* throw an illegal state Exception.
*
* @param in1 first reader to use as a source.
* @param in2 second reader to use as a source.
*
* @throws NullPointerException if either source is null.
*
* @since ostermillerutils 1.04.00
*/
public ConcatReader(Reader in1, Reader in2){
addReader(in1);
addReader(in2);
lastReaderAdded();
}
/**
* Create a new reader with an arbitrary number of sources.
* <p>
* When using this constructor, more readers cannot
* be added later, and calling addReader() will
* throw an illegal state Exception.
*
* @param in readers to use as a sources.
*
* @throws NullPointerException if the input array on any element is null.
*
* @since ostermillerutils 1.04.00
*/
public ConcatReader(Reader[] in){
addReaders(in);
lastReaderAdded();
}
/**
* Read a single character. This method will block until a
* character is available, an I/O error occurs, or the end of all underlying
* streams are reached.
* <p>
* If this class in not done accepting readers and the end of the last known
* stream is reached, this method will block forever unless another thread
* adds a reader or interrupts.
*
* @return The character read, as an integer in the range 0 to 65535 (0x00-0xffff),
* or -1 if the end of the stream has been reached
*
* @throws IOException - If an I/O error occurs
*
* @since ostermillerutils 1.04.00
*/
@Override public int read() throws IOException {
if (closed) throw new IOException("Reader closed");
int r = -1;
while (r == -1){
Reader in = getCurrentReader();
if (in == null){
if (doneAddingReaders) return -1;
try {
Thread.sleep(100);
} catch (InterruptedException iox){
throw new IOException("Interrupted");
}
} else {
r = in.read();
if (r == -1) advanceToNextReader();
}
}
return r;
}
/**
* Read characters into an array. This method will block until some input is available, an
* I/O error occurs, or the end of all underlying
* streams are reached.
* <p>
* If this class in not done accepting readers and the end of the last known
* stream is reached, this method will block forever unless another thread
* adds a reader or interrupts.
*
* @param cbuf - Destination buffer
* @return The number of characters read, or -1 if the end of the stream has been reached
*
* @throws IOException - If an I/O error occurs
* @throws NullPointerException - If the buffer is null.
*
* @since ostermillerutils 1.04.00
*/
@Override public int read(char[] cbuf) throws IOException {
return read(cbuf, 0, cbuf.length);
}
/**
* Read characters into a portion of an array. This method will block until
* some input is available, an I/O error occurs, or the end of all underlying
* streams are reached.
* <p>
* If this class in not done accepting readers and the end of the last known
* stream is reached, this method will block forever unless another thread
* adds a reader or interrupts.
*
* @param cbuf Destination buffer
* @param off Offset at which to start storing characters
* @param len Maximum number of characters to read
* @return The number of characters read, or -1 if the end of the stream has been reached
*
* @throws IOException - If an I/O error occurs
* @throws NullPointerException - If the buffer is null.
* @throws IndexOutOfBoundsException - if length or offset are not possible.
*
* @since ostermillerutils 1.04.00
*/
@Override public int read(char[] cbuf, int off, int len) throws IOException {
if (off < 0 || len < 0 || off + len > cbuf.length) throw new IndexOutOfBoundsException();
if (closed) throw new IOException("Reader closed");
int r = -1;
while (r == -1){
Reader in = getCurrentReader();
if (in == null){
if (doneAddingReaders) return -1;
try {
Thread.sleep(100);
} catch (InterruptedException iox){
throw new IOException("Interrupted");
}
} else {
r = in.read(cbuf, off, len);
if (r == -1) advanceToNextReader();
}
}
return r;
}
/**
* Skip characters. This method will block until some characters are
* available, an I/O error occurs, or the end of the stream is reached.
* <p>
* If this class in not done accepting readers and the end of the last known
* stream is reached, this method will block forever unless another thread
* adds a reader or interrupts.
*
* @param n the number of characters to skip
* @return The number of characters actually skipped
*
* @throws IllegalArgumentException If n is negative.
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.04.00
*/
@Override public long skip(long n) throws IOException {
if (closed) throw new IOException("Reader closed");
if (n <= 0) return 0;
long s = -1;
while (s <= 0){
Reader in = getCurrentReader();
if (in == null){
if (doneAddingReaders) return 0;
try {
Thread.sleep(100);
} catch (InterruptedException iox){
throw new IOException("Interrupted");
}
} else {
s = in.skip(n);
// When nothing was skipped it is a bit of a puzzle.
// The most common cause is that the end of the underlying
// stream was reached. In which case calling skip on it
// will always return zero. If somebody were calling skip
// until it skipped everything they needed, there would
// be an infinite loop if we were to return zero here.
// If we get zero, let us try to read one character so
// we can see if we are at the end of the stream. If so,
// we will move to the next.
if (s <= 0) {
// read() will advance to the next stream for us, so don"t do it again
s = ((read()==-1)?-1:1);
}
}
}
return s;
}
/**
* Tell whether this stream is ready to be read.
*
* @return True if the next read() is guaranteed not to block for input,
* false otherwise. Note that returning false does not guarantee that the next
* read will block.
*
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.04.00
*/
@Override public boolean ready() throws IOException {
if (closed) throw new IOException("Reader closed");
Reader in = getCurrentReader();
if (in == null) return false;
return in.ready();
}
/**
* Close the stream and any underlying streams.
* Once a stream has been closed, further read(), ready(), mark(), or reset()
* invocations will throw an IOException. Closing a previously-closed stream,
* however, has no effect.
*
* @throws IOException If an I/O error occurs
*
* @since ostermillerutils 1.04.00
*/
@Override public void close() throws IOException {
if (closed) return;
for (Reader reader: readerQueue) {
reader.close();
}
closed = true;
}
/**
* Mark not supported.
*
* @throws IOException because mark is not supported.
*
* @since ostermillerutils 1.04.00
*/
@Override public void mark(int readlimit) throws IOException {
throw new IOException("Mark not supported");
}
/**
* Reset not supported.
*
* @throws IOException because reset is not supported.
*
* @since ostermillerutils 1.04.00
*/
@Override public void reset() throws IOException {
throw new IOException("Reset not supported");
}
/**
* Mark not supported.
*
* @return false
*
* @since ostermillerutils 1.04.00
*/
@Override public boolean markSupported(){
return false;
}
}
</source>
Read the file one buffer at a time
<source lang="java">
import java.io.FileReader; public class Main {
public static void main(String[] argv) throws Exception {
FileReader fr = new FileReader("text.txt");
int count;
char chrs[] = new char[80];
do {
count = fr.read(chrs);
for (int i = 0; i < count; i++)
System.out.print(chrs[i]);
} while (count != -1);
}
}
</source>
Testing for end of file while reading a byte at a time
<source lang="java">
// : c12:TestEOF.java // Testing for end of file while reading a byte at a time. // From "Thinking in Java, 3rd ed." (c) Bruce Eckel 2002 // www.BruceEckel.ru. See copyright notice in CopyRight.txt. import java.io.BufferedInputStream; import java.io.DataInputStream; import java.io.FileInputStream; import java.io.IOException; public class TestEOF {
// Throw exceptions to console:
public static void main(String[] args) throws IOException {
DataInputStream in = new DataInputStream(new BufferedInputStream(
new FileInputStream("TestEOF.java")));
while (in.available() != 0)
System.out.print((char) in.readByte());
}
} ///:~
</source>
This class is an part implementation of DataInput. It wraps a Reader object.
<source lang="java">
/* Copyright (c) 2001-2009, The HSQL Development Group
* All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions are met: * * Redistributions of source code must retain the above copyright notice, this * list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright notice, * this list of conditions and the following disclaimer in the documentation * and/or other materials provided with the distribution. * * Neither the name of the HSQL Development Group nor the names of its * contributors may be used to endorse or promote products derived from this * software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG, * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
import java.io.DataInput; import java.io.EOFException; import java.io.IOException; import java.io.Reader; /**
* This class is an part implementation of DataInput. It wraps a Reader object. * * @author Fred Toussi (fredt@users dot sourceforge.net) * @version 1.9.0 * @since 1.9.0 */
public class ReaderDataInput implements DataInput {
protected Reader reader;
protected int pos;
int lastChar = -1;
public ReaderDataInput(Reader reader) {
this.reader = reader;
this.pos = 0;
}
// methods that implement java.io.DataInput
public final void readFully(byte[] b) throws IOException {
readFully(b, 0, b.length);
}
public final void readFully(byte[] bytes, int off,
int len) throws IOException {
if (len < 0) {
throw new IndexOutOfBoundsException();
}
int n = 0;
while (n < len) {
int b = read();
if (b < 0) {
throw new EOFException();
}
bytes[off + n++] = (byte) b;
}
}
public final boolean readBoolean() throws IOException {
int b = read();
if (b < 0) {
throw new EOFException();
}
return (b != 0);
}
public final byte readByte() throws IOException {
int b = read();
if (b < 0) {
throw new EOFException();
}
return (byte) b;
}
public final int readUnsignedByte() throws IOException {
int b = read();
if (b < 0) {
throw new EOFException();
}
return b;
}
public short readShort() throws IOException {
int b1 = read();
if (b1 < 0) {
throw new EOFException();
}
int b2 = read();
if (b2 < 0) {
throw new EOFException();
}
return (short) ((b1 << 8) | b2);
}
public final int readUnsignedShort() throws IOException {
int b1 = read();
int b2 = read();
if ((b1 | b2) < 0) {
throw new EOFException();
}
return ((b1 << 8) + (b2));
}
public final char readChar() throws IOException {
int b1 = read();
int b2 = read();
if ((b1 | b2) < 0) {
throw new EOFException();
}
return (char) ((b1 << 8) + (b2));
}
public int readInt() throws IOException {
throw new java.lang.RuntimeException("not implemented.");
}
public long readLong() throws IOException {
throw new java.lang.RuntimeException("not implemented.");
}
public final float readFloat() throws IOException {
throw new java.lang.RuntimeException("not implemented.");
}
public final double readDouble() throws IOException {
throw new java.lang.RuntimeException("not implemented.");
}
public int skipBytes(int n) throws IOException {
throw new java.lang.RuntimeException("not implemented.");
}
public String readLine() throws IOException {
throw new java.lang.RuntimeException("not implemented.");
}
public String readUTF() throws IOException {
throw new java.lang.RuntimeException("not implemented.");
}
public int read() throws IOException {
if (lastChar >= 0) {
int val = lastChar & 0xff;
lastChar = -1;
pos++;
return val;
}
lastChar = reader.read();
if (lastChar < 0) {
return lastChar;
}
pos++;
return lastChar >> 8;
}
}
</source>
Use a FileReader to display a text file.
<source lang="java">
import java.io.FileReader; public class Main {
public static void main(String[] argv) throws Exception {
FileReader fr = new FileReader("text.txt");
int ch;
do {
ch = fr.read();
if (ch != -1)
System.out.println((char) ch);
} while (ch != -1);
fr.close();
}
}
</source>
