Java/Servlets/Context
Содержание
Context accessor
<source lang="java">
import java.util.Collections; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class ContextAccessor extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException {
//get a servlet context attribute
ContextObject contextObj = (ContextObject) getServletContext()
.getAttribute("com.jexp.ContextObject");
if (contextObj != null)
contextObj.put(request.getRemoteAddr(), "" + new java.util.Date());
//display
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter();
out
.println("<html><head><title>Servlet Context Attribute</title></head><body>");
if (contextObj != null) {
out.println("Servlet Context Attribute Values
"); out.println(contextObj.getValues());
} else {
out.println("Servlet Context Attribute is Null
"); }
out.println("</body></html>");
} //end doGet
} //ContextObject.java class ContextObject {
private Map map;
public ContextObject() {
map = Collections.synchronizedMap(new HashMap());
}
public void put(Object key, Object value) {
if (key == null || value == null)
throw new IllegalArgumentException(
"Invalid parameters passed to ContextObject.put");
map.put(key, value);
}
public Map getMap() {
return map;
}
public String getValues() {
StringBuffer buf = new StringBuffer("");
Set set = map.keySet();
synchronized (map) {
Iterator i = set.iterator();
while (i.hasNext())
buf.append((String) i.next() + "
");
}
return buf.toString();
}
public String toString() {
return getClass().getName() + "[ " + map + " ]";
}
}
</source>
Context Attributes Servlet
<source lang="java">
import java.io.PrintWriter; import java.io.IOException; import java.util.Date; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; public class SessionTracker2 extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse res)throws ServletException, IOException
{
res.setContentType("text/html");
PrintWriter out = res.getWriter();
HttpSession session = req.getSession(true);
Integer totalCount = (Integer) getServletContext().getAttribute("total");
if (totalCount == null)
{
totalCount = new Integer(1);
}
else
{
totalCount = new Integer(totalCount.intValue() + 1);
}
Integer count = (Integer) session.getAttribute("count");
if (count == null) {
count = new Integer(1);
} else {
count = new Integer(count.intValue() + 1);
}
session.setAttribute("count", count);
getServletContext().setAttribute("total", totalCount);
out.println("<html><head><title>SessionSnoop</title></head>");
out.println("<body>Session Details
"); out.println("You"ve visited this page " + count + ((count.intValue() == 1) ? " time." : " times.") + "
");
out.println("Total number of visits: " + totalCount + "
");
out.println("Details of this session:
"); out.println("Session id: " + session.getId() + "
");
out.println("New session: " + session.isNew() + "
");
out.println("Timeout: " + session.getMaxInactiveInterval() + "
");
out.println("Creation time: " + new Date(session.getCreationTime()) + "
");
out.println("Last access time: " + new Date(session.getLastAccessedTime()) + "
");
out.println("</body></html>");
}
}
</source>
Context binder
<source lang="java">
import java.util.Collections; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class ContextBinder extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException {
//bind an object to the servlet context
getServletContext().setAttribute("com.jexp.ContextObject",
new ContextObject());
//better display something
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter();
out
.println("<html><head><title>Servlet Context Attribute</title></head><body>");
out.println("Servlet Context Attribute Bound
"); out.println("Object: "
+ getServletContext().getAttribute("com.jexp.ContextObject"));
out.println("</body></html>");
} //end doGet
} //ContextObject.java class ContextObject {
private Map map;
public ContextObject() {
map = Collections.synchronizedMap(new HashMap());
}
public void put(Object key, Object value) {
if (key == null || value == null)
throw new IllegalArgumentException(
"Invalid parameters passed to ContextObject.put");
map.put(key, value);
}
public Map getMap() {
return map;
}
public String getValues() {
StringBuffer buf = new StringBuffer("");
Set set = map.keySet();
synchronized (map) {
Iterator i = set.iterator();
while (i.hasNext())
buf.append((String) i.next() + "
");
}
return buf.toString();
}
public String toString() {
return getClass().getName() + "[ " + map + " ]";
}
}
</source>
Context Parameters Servlet
Get settings from ServletContext
<source lang="java">
import java.io.IOException; import java.io.PrintWriter; import java.util.Enumeration; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class WebAppProperties extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException,
IOException {
resp.setContentType("text/html");
PrintWriter out = resp.getWriter();
ServletContext context = getServletContext();
String displayName = context.getServletContextName();
if (displayName == null) {
displayName = "(no display-name element defined)";
}
out.println("<html>");
out.println("<body>");
out.println("
Name: " + displayName);
out.println("
Context: " + req.getContextPath());
out.println("");
out.println("Initialization Parameters
");
out.println("
");
out.println("| " + name + " | "); out.println("" + context.getInitParameter(name) + " | "); out.println("
out.println("</body>");
out.println("</html>");
out.flush();
}
}
</source>
Servlets Context Sample
Set the context parameters in web.xml
<source lang="java">
// web.xml /* <?xml version="1.0" encoding="ISO-8859-1"?> <web-app xmlns="http://java.sun.ru/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.ru/xml/ns/j2ee http://java.sun.ru/xml/ns/j2ee/web-app_2_4.xsd" version="2.4"> <context-param> <param-name>name</param-name> <param-value>Joe</param-value> </context-param> <context-param> <param-name>password</param-name> <param-value>password</param-value> </context-param> <servlet> <servlet-name>ParameterServlet</servlet-name> <servlet-class>ParameterServlet</servlet-class> <init-param> <param-name>name</param-name> <param-value>Joe</param-value> </init-param> <init-param> <param-name>password</param-name> <param-value>password</param-value> </init-param> </servlet>
</web-app>
- /
import java.io.IOException; import javax.servlet.ServletConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class ParameterServlet extends HttpServlet {
private String dbName = "";
private String dbPassword = "";
public void init(ServletConfig config) throws ServletException {
super.init(config);
ServletContext context = getServletContext();
dbName = context.getInitParameter("name");
dbPassword = context.getInitParameter("password");
}
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws IOException {
ServletOutputStream out = res.getOutputStream();
res.setContentType("text/html");
out.println("<html><head><title>Basic Servlet</title></head>");
out.println("<body>Database username is " + dbName);
out.println("
Database password is " + dbPassword + "");
out.println("</body></html>");
}
}
</source>
Using Contexts Servlet
<source lang="java">
import java.io.*; import java.util.*; import javax.servlet.*; import javax.servlet.http.*; public class UsingContexts extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
HttpSession session = request.getSession(true);
Integer counter2 = (Integer) getServletContext().getAttribute ("counter2");
if (counter2 == null) {
counter2 = new Integer(1);
} else {
counter2 = new Integer(counter2.intValue() + 1);
}
getServletContext().setAttribute("counter2", counter2);
Integer counter = (Integer) session.getAttribute("counter");
if (counter == null) {
counter = new Integer(1);
} else {
counter = new Integer(counter.intValue() + 1);
}
session.setAttribute("counter", counter);
out.println("<HTML>");
out.println("<HEAD>");
out.println("<TITLE>");
out.println("Using Contexts");
out.println("</TITLE>");
out.println("</HEAD>");
out.println("<BODY>");
out.println("Using Contexts
"); out.println("Welcome! You have been here " + counter + " times.
");
out.println("Total page accesses: " + counter2 + "
");
if(session.isNew()){
out.println("This is a new session.
");
} else {
out.println("This is not a new session.
");
}
out.println("The session ID: " + session.getId() + "
");
out.println("Last time accessed: " + new Date(session.getLastAccessedTime()) + "
");
out.println("Creation time: " + new Date(session.getCreationTime()) + "
");
out.println("Timeout length: " + session.getMaxInactiveInterval() + " seconds
");
out.println("</BODY>");
out.println("</HTML>");
}
}
</source>
