Java 库的建立方法及其实例（3）

Java 库的建立方法及其实例（3）

下面的例子说明了这一技术。使用者的代码使用Server.setDebugStream(),指定一个PrintStream对 象。然后，调试信息就被输出到这个流中。



// set this to a print stream if you want debug info

// sent to it; otherwise, leave it null

static private PrintStream debugStream;



// call this to send the debugging output somewhere

static public void setDebugStream( PrintStream ps ) {

debugStream = ps;

}

当使用者使用了调试的流的时候，你的库代码可以打印错误：



// send debug info to the print stream, if there is one

static public void debug( String s ) {

if (debugStream != null)

debugStream.println( s );

}


下面，来完整的看一看这个具体的例子：

EchoServer

// $Id$



import java.io.*;

import java.net.*;

import mylib.*;



public class EchoServer extends Server

{

public EchoServer( int port ) {

// The superclass knows what to do with the port number, we

// don´t have to care about it

super( port );

}



// This is called by the Server class when a connection

// comes in. "in" and "out" come from the incoming socket

// connection

public void handleConnection( Socket socket ) {

try {

InputStream in = socket.getInputStream();

OutputStream out = socket.getOutputStream();



// just copy the input to the output

while (true)

out.write( in.read() );



} catch( IOException ie ) {

System.out.println( ie );

}

}

protected void cleanUp() {

System.out.println( "Cleaning up" );

}



static public void main( String args[] ) throws Exception {

// Grab the port number from the command-line

int port = Integer.parseInt( args[0] );



// Have debugging info sent to standard error stream

Server.setDebugStream( System.err );



// Create the server, and it´s up and running

new EchoServer( port );

}

}

mylib.Server


// $Id$



package mylib;



import java.io.*;

import java.net.*;



abstract public class Server implements Runnable

{

// the port we´ll be listening on

private int port;



// how many connections we´ve handled

int numConnections;



// the Reporter that´s reporting on this Server

private Reporter reporter;



// set this to true to tell the thread to stop accepting

// connections

private boolean mustQuit = false;



public Server( int port ) {

// remember the port number so the thread can

// listen on it

this.port = port;



// the constructor starts a background thread

new Thread( this ).start();



// and start a reporter

reporter = new Reporter( this );

}



// this is our background thread

public void run() {

ServerSocket ss = null;

try {



// get ready to listen

ss = new ServerSocket( port );



while( !mustQuit ) {



// give out some debugging info

debug( "Listening on "+port );



// wait for an incoming connection

Socket s = ss.accept();



// record that we got another connection

numConnections++;



// more debugging info

debug( "Got connection on "+s );



// process the connection -- this is implemented

// by the subclass

handleConnection( s );

}

} catch( IOException ie ) {

debug( ie.toString() );

}



debug( "Shutting down "+ss );



cleanUp();

}



// the default implementation does nothing

abstract public void handleConnection( Socket s );



// tell the thread to stop accepting connections

public void close() {

mustQuit = true;

reporter.close();

}



// Put any last-minute clean-up stuff in here

protected void cleanUp() {

}



// everything below provides a simple debug system for

// this package



// set this to a print stream if you want debug info

// sent to it; otherwise, leave it null

static private PrintStream debugStream;



// we have two versions of this ...

static public void setDebugStream( PrintStream ps ) {

debugStream = ps;

}



// ... just for convenience

static public void setDebugStream( OutputStream out ) {

debugStream = new PrintStream( out );

}



// send debug info to the print stream, if there is one

static public void debug( String s ) {

if (debugStream != null)

debugStream.println( s );

}

}

mylib.Reporter


// $Id$



package mylib;



class Reporter implements Runnable

{

// the Server we are reporting on

private Server server;



// our background thread

private Thread thread;



// set this to true to tell the thread to stop accepting

// connections

private boolean mustQuit = false;



Reporter( Server server ) {

this.server = server;



// create a background thread

thread = new Thread( this );

thread.start();

}



public void run() {

while (!mustQuit) {

// do the reporting

Server.debug( "server has had "+server.numConnections+" connections" );



// then pause a while

try {

Thread.sleep( 5000 );

} catch( InterruptedException ie ) {}

}

}



// tell the background thread to quit

public void close() {

mustQuit = true;

}

} （未完待续）

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