关于回答网友有关servlet和servlet之间通信的问题（建议放入精华区）-JSP教程,Jsp/Servlet

以下是几种常调用的方法
     servlet to servlet communication
    
     listing 1: servletbase
     public class servletbase extends httpservlet{
     static connection databaseconnection = null;
     public void init(servletconfig _config) throws servletexception{
     super.init(_config);
     if ( databaseconnection == null )
     //- open up the database connection
     }
     protected boolean isloggedon( string _username ){
     return true;
     }
     protected boolean loguseron( string _username ){
     return true;
     }
     }
     listing 2: using the newserletbase class
     public class logonservlet extends servletbase{
     public void service(httpservletrequest _req, httpservletre-
     sponse _res) throws servletexception{
     if ( isloggedon( _req.getparameter(襏sername? ){
     //- display a message indicating they are already logged on
     }else{
     loguseron( _req.getparameter(襏sername? );
     }
     }
     }
     listing 3: storing an object
     public class logonservlet extends httpservlet{
     public void service(httpservletrequest _req, httpservletre-
     sponse _res) throws servletexception{
     servletcontext thiscontext = getservletcontext();
     //– assume some method creates a new connection class
     connection newconnection = createconnection();
     thiscontext.setattribute( database.connection? newconnection );
     //– return some output to the client
     }
     }
     listing 4: retrieving an object
     public class logoffservlet extends httpservlet{
     public void service(httpservletrequest _req, httpservletre-
     sponse _res) throws servletexception{
     servletcontext thiscontext = getservletcontext();
     //– assume some method creates a new connection class
     connection newconnection = thiscontext.getattribute(
     database.connection?;
     if ( newconnection == null )
     //- database has not been opened yet
     //– return some output to the client
     }
     }
     listing 5: looking at all the objects
     public class allservlet extends httpservlet{
     public void service(httpservletrequest _req, httpservletre-
     sponse _res) throws servletexception{
     servletcontext thiscontext = getservletcontext();
     //– assume some method creates a new connection class
     enumeration e = thiscontext.getattributenames();
     while ( e.hasmoreelements() ){
     string name = (string)e.nextelement();
     system.out.println( "object: " + name );
     }
     }
     }
     listing 6: retrieving remote contexts
     public class otherservlet extends httpservlet{
     public void service(httpservletrequest _req, httpservletre-
     sponse _res) throws servletexception{
     servletcontext othercontext =
     getservletcontext(http://<otherdomain>/servlet/allservlet?;
     //– assume some method creates a new connection class
     enumeration e = othercontext.getattributenames();
     while ( e.hasmoreelements() ){
     string name = (string)e.nextelement();
     system.out.println( "object: " + name );
     }
     }
     }
     listing 7: forwarding a request
     public class forwardservlet extends httpservlet{
     public void service(httpservletrequest _req, httpservletre-
     sponse _res) throws servletexception{
     servletcontext xt = getservletcontext();
     requestdispatcher xyzservlet =
     xt.getrequestdispatcher(http://<domain>/servlet/xyzservlet?;
     //- do any preliminary processing
     _req.setattribute( database.results? new results() );
     xyzservlet.forward( _req, _res );
     }
     }
     listing 8: inserting content
     public class insertservlet extends httpservlet{
     public void service(httpservletrequest _req, httpservletre-
     sponse _res) throws servletexception{
     servletcontext xt = getservletcontext();
     requestdispatcher xyzservlet =
     xt.getrequestdispatcher(http://<domain>/servlet/xyzservlet?;
     printwriter out = _res.getwriter();
     out.println( this is from the insertservlet ?);
     for(int x=0; x < 10; x++ )
     xyzservlet.insert( _req, _res );
     out.println( this is the end of the print servlet ?);
     }
     }