Java Tutorial/Log/Log Handler

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Add Multiple Handlers to a logger

   <source lang="java">

import java.util.logging.ConsoleHandler; import java.util.logging.FileHandler; import java.util.logging.Logger; public class MainClass { 

 private static Logger logger = Logger.getLogger("MultipleHandlers2");
 public static void main(String[] args) throws Exception {
   FileHandler logFile = new FileHandler("MultipleHandlers2.xml");
   logger.addHandler(logFile);
   logger.addHandler(new ConsoleHandler());
   logger.setUseParentHandlers(false);
   logger.warning("Output to multiple handlers");
 }

}</source>





A file handler that appends.

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Logger; public class Main { 

 public static void main(String[] argv) throws Exception {
   boolean append = true;
   FileHandler handler = new FileHandler("my.log", append);
   Logger logger = Logger.getLogger("com.mycompany");
   logger.addHandler(handler);
 }

}</source>





Alternate XML by using FileHandler

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Level; import java.util.logging.Logger; public class Main { 

 public static void main(String[] argv) throws Exception {
   FileHandler handler = new FileHandler("alterxml.xml");
   Logger logger = Logger.getLogger("your.logging");
   logger.addHandler(handler);
   logger.log(Level.INFO, "alternative xml");
 }

}</source>





Create a memory handler with a memory of 100 records and dumps the records into the file my.log

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Level; import java.util.logging.LogRecord; import java.util.logging.Logger; import java.util.logging.MemoryHandler; public class Main { 

 public static void main(String[] argv) throws Exception {
   FileHandler fhandler = new FileHandler("my.log");
   int numRec = 100;
   MemoryHandler mhandler = new MemoryHandler(fhandler, numRec, Level.OFF) {
     public synchronized void publish(LogRecord record) {
       super.publish(record);
       push();
     }
   };
   Logger logger = Logger.getLogger("com.mycompany");
   logger.addHandler(mhandler);
 }

}</source>





Flush File Handler and Logger

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Level; import java.util.logging.LogRecord; import java.util.logging.Logger; public class Main { 

 public static void main(String[] args) throws Exception {
   FileHandler handler = null;
   Logger logger = Logger.getLogger("logging");
   handler = new FileHandler("pattern", 1000, 2);
   logger.addHandler(handler);
   LogRecord record = new LogRecord(Level.INFO, "Logged in a file...");
   logger.log(record);
   handler.flush();
   handler.close();
 }

}</source>





How to write custom handler

   <source lang="java">

import java.util.ArrayList; import java.util.List; import java.util.logging.Handler; import java.util.logging.LogRecord; import java.util.logging.Logger; public class MainClass { 

 private static Logger logger = Logger.getLogger("CustomHandler");
 private static List strHolder = new ArrayList();
 public static void main(String[] args) {
   logger.addHandler(new Handler() {
     public void publish(LogRecord logRecord) {
       strHolder.add(logRecord.getLevel() + ":");
       strHolder.add(logRecord.getSourceClassName() + ":");
       strHolder.add(logRecord.getSourceMethodName() + ":");
       strHolder.add("<" + logRecord.getMessage() + ">");
       strHolder.add("\n");
     }
     public void flush() {
     }
     public void close() {
     }
   });
   logger.warning("Logging Warning");
   logger.info("Logging Info");
   System.out.print(strHolder);
 }

}</source>





Limiting the Size of a Log by Using a Rotating Sequence of Files

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Logger; public class Main { 

 public static void main(String[] argv) throws Exception {
   // Create a file handler that uses 3 logfiles, each with a limit of 1Mbyte
   String pattern = "my%g.log";
   int limit = 1000000; // 1 Mb
   int numLogFiles = 3;
   FileHandler fh = new FileHandler(pattern, limit, numLogFiles);
   // Add to logger
   Logger logger = Logger.getLogger("com.mycompany");
   logger.addHandler(fh);
 }

}</source>





Limiting the Size of a Log File

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Logger; public class Main { 

 public static void main(String[] argv) throws Exception {
   // Create a file handler with a limit of 1 megabytes
   String pattern = "my.log";
   int limit = 1000000; // 1 Mb
   FileHandler fh = new FileHandler("my.log", limit, 1);
   // Add to logger
   Logger logger = Logger.getLogger("com.mycompany");
   logger.addHandler(fh);
 }

}</source>





Memory Handler Demo

   <source lang="java">

import java.util.logging.ConsoleHandler; import java.util.logging.Level; import java.util.logging.LogRecord; import java.util.logging.Logger; import java.util.logging.MemoryHandler; public class Main { 

 public static void main(String args[]) throws Exception {
   Logger logger = Logger.getLogger("your.logging");
   ConsoleHandler handler = new ConsoleHandler();
   MemoryHandler mHandler = new MemoryHandler(handler, 10, Level.ALL);
   logger.addHandler(mHandler);
   logger.setUseParentHandlers(false);
   LogRecord record1 = new LogRecord(Level.SEVERE, "This is SEVERE level message");
   LogRecord record2 = new LogRecord(Level.WARNING, "This is WARNING level message");
   logger.log(record1);
   logger.log(record2);
 }

}</source>





Socket Handler Demo

   <source lang="java">

import java.util.logging.Logger; import java.util.logging.SocketHandler; public class Main { 

 public static void main(String args[]) throws Exception{
   SocketHandler handler = null;
   Logger logger = Logger.getLogger("your.logging");
   handler = new SocketHandler("127.0.0.1", 8080);
   logger.addHandler(handler);
   logger.warning("SocketHandler is working...");
 }

}</source>





Stream Handler

   <source lang="java">

import java.io.OutputStream; import java.util.logging.Logger; import java.util.logging.SimpleFormatter; import java.util.logging.StreamHandler; public class Main { 

 public static void main(String[] args) {
   Logger logger = Logger.getLogger("logging");
   OutputStream outStream = System.out;
   StreamHandler handler = new StreamHandler(outStream, new SimpleFormatter());
   logger.addHandler(handler);
   logger.setUseParentHandlers(false);
   logger.info("StreamHandler is working�");
 }

}</source>





The Patterns in FileHandler

   <source lang="java">

Expression Meaning / The path separator of the local OS %t A directory suitable for storing temporary logging files, such as the temp directory of the OS %h A directory such as the "user.home" location, which is suitable to store user-specific data in the system %g A log generation number to rotate log files %u A number to make a log file unique to avoid any conflicts %% A literal percent sign</source>





Use ConsoleHandler

   <source lang="java">

import java.util.logging.ConsoleHandler; import java.util.logging.FileHandler; import java.util.logging.Logger; public class MainClass { 

 private static Logger logger = Logger.getLogger("MultipleHandlers");
 public static void main(String[] args) throws Exception {
   FileHandler logFile = new FileHandler("MultipleHandlers.xml");
   logger.addHandler(logFile);
   logger.addHandler(new ConsoleHandler());
   logger.warning("Output to multiple handlers");
 }

}</source>





Use Logger with simple formatter and FileHander

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Level; import java.util.logging.Logger; import java.util.logging.SimpleFormatter; public class Main { 

 public static void main(String[] args) throws Exception {
   Logger logger = Logger.getLogger("MyLog");
   FileHandler fh;
   fh = new FileHandler("c:\\MyLogFile.log", true);
   logger.addHandler(fh);
   logger.setLevel(Level.ALL);
   SimpleFormatter formatter = new SimpleFormatter();
   fh.setFormatter(formatter);
   logger.log(Level.WARNING, "My first log");
 }

}</source>





Using FileHandler to log a message

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Level; import java.util.logging.LogManager; import java.util.logging.Logger; import java.util.logging.XMLFormatter; public class LoggingExample1 { 

 public static void main(String args[])  {
   try {
     LogManager lm = LogManager.getLogManager();
     Logger logger;
     FileHandler fh = new FileHandler("log_test.txt");
     logger = Logger.getLogger("LoggingExample1");
     lm.addLogger(logger);
     logger.setLevel(Level.INFO);
     fh.setFormatter(new XMLFormatter());
     logger.addHandler(fh);
      //logger.setUseParentHandlers(false);
     logger.log(Level.INFO, "test 1");
     logger.log(Level.INFO, "test 2");
     logger.log(Level.INFO, "test 3");
     fh.close();
   } catch (Exception e) {
     System.out.println("Exception thrown: " + e);
     e.printStackTrace();
   }
 }

}</source>





Using Regular Expressions based on StreamHandler

   <source lang="java">

import java.util.logging.Handler; import java.util.logging.Level; import java.util.logging.LogRecord; import java.util.logging.Logger; import java.util.logging.StreamHandler; import java.util.regex.Matcher; import java.util.regex.Pattern; public class MainClass { 

 public static void main(String args[]) {
   Logger log = Logger.getAnonymousLogger();
   setLoggerhandler(log);
   log.finest(new Exception().toString());
 }
 public static void setLoggerhandler(Logger logger) {
   Handler handler = new ExceptionHandler();
   logger.addHandler(handler);
   logger.setLevel(Level.ALL);
 }

} class ExceptionHandler extends StreamHandler { 

 public void publish(LogRecord record) {
   String msg = record.getMessage();
   int exceptionIndex = msg.indexOf("Exception");
   if (exceptionIndex > -1) {
     Pattern pattern = Pattern.rupile("(.*Exception.*)");
     Matcher matcher = pattern.matcher(msg);
     if (matcher != null && matcher.find()) {
       String err = "EXCEPTION FOUND " + matcher.group(1);
       System.out.println(err);
     }
   }
 }

}</source>





Window Handler: display log message in a window(JFrame)

   <source lang="java">

import java.util.logging.ErrorManager; import java.util.logging.Filter; import java.util.logging.Formatter; import java.util.logging.Handler; import java.util.logging.Level; import java.util.logging.LogManager; import java.util.logging.LogRecord; import java.util.logging.Logger; import java.util.logging.SimpleFormatter; import javax.swing.JFrame; import javax.swing.JScrollPane; import javax.swing.JTextArea; class LogWindow extends JFrame { 

 private JTextArea textArea = new JTextArea();
 public LogWindow() {
   super("");
   setSize(300, 300);
   add(new JScrollPane(textArea));
   setVisible(true);
 }
 public void showInfo(String data) {
   textArea.append(data);
   this.validate();
 }

} class WindowHandler extends Handler { 

 private LogWindow window = null;
 private Formatter formatter = null;
 private Level level = null;
 private static WindowHandler handler = null;
 private WindowHandler() {
   LogManager manager = LogManager.getLogManager();
   String className = this.getClass().getName();
   String level = manager.getProperty(className + ".level");
   setLevel(level != null ? Level.parse(level) : Level.INFO);
   if (window == null)
     window = new LogWindow();
 }
 public static synchronized WindowHandler getInstance() {
   if (handler == null) {
     handler = new WindowHandler();
   }
   return handler;
 }
 public synchronized void publish(LogRecord record) {
   String message = null;
   if (!isLoggable(record))
     return;
   message = getFormatter().format(record);
   window.showInfo(message);
 }
 public void close() {
 }
 public void flush() {
 }

} public class Main { 

 private WindowHandler handler = null;
 private Logger logger = null;
 public Main() {
   handler = WindowHandler.getInstance();
   logger = Logger.getLogger("logging.handler");
   logger.addHandler(handler);
 }
 public void logMessage() {
   logger.info("Hello from ...");
 }
 public static void main(String args[]) {
   Main demo = new Main();
   demo.logMessage();
   WindowHandler h = WindowHandler.getInstance();
   LogRecord r = new LogRecord(Level.WARNING, "The Handler publish method...");
   h.publish(r);
 }

}</source>





Writing Log Records Only After a Condition Occurs

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Level; import java.util.logging.Logger; import java.util.logging.MemoryHandler; public class Main { 

 public static void main(String[] argv) throws Exception {
   FileHandler fhandler = new FileHandler("my.log");
   int numRec = 100;
   MemoryHandler mhandler = new MemoryHandler(fhandler, numRec, Level.SEVERE);
   Logger logger = Logger.getLogger("com.mycompany");
   logger.addHandler(mhandler);
 }

}</source>





Writing Log Records to a Log File

   <source lang="java">

import java.util.logging.FileHandler; import java.util.logging.Logger; public class Main { 

 public static void main(String[] argv) throws Exception {
   FileHandler handler = new FileHandler("my.log");
   Logger logger = Logger.getLogger("com.mycompany");
   logger.addHandler(handler);
 }

}</source>





Writing Log Records to Standard Error

   <source lang="java">

import java.util.logging.ConsoleHandler; import java.util.logging.Logger; public class Main { 

 public static void main(String[] argv) throws Exception {
   ConsoleHandler handler = new ConsoleHandler();
   // Add to logger
   Logger logger = Logger.getLogger("com.mycompany");
   logger.addHandler(handler);
 }

}</source>


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