教你利用JAVA实现可以自行关闭服务器的方法
JAVA实现可以自行关闭的服务器
普通实现的服务器都无法关闭自身,只有依靠操作系统来强行终止服务程序。这种强行终止服务程序的方式尽管简单方便,但会导致服务器中正在执行的任务突然中断。如果服务器处理的任务非常重要,不允许被突然中断,应该由服务器自身在恰当的时刻关闭自己
代码如下:
- EchoServer类
package ShutdownServer; import java.io.*; import java.net.ServerSocket; import java.net.Socket; import java.net.SocketException; import java.net.SocketTimeoutException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.RejectedExecutionException; import java.util.concurrent.TimeUnit; public class EchoServer { private int port=8000; private ServerSocket serverSocket; private ExecutorService executorService; //线程池 private final int POOL_SIZE=4; //单个CPU时线程池中工作线程的数目 private int portForShutdown=8001; //用于监听关闭服务器命令的端口 private ServerSocket serverSocketShutdown; private boolean isShutdown=false; //服务器是否已经关闭 private Thread shutdownThread=new Thread(){ //负责关闭服务器的线程 public void run(){ while(!isShutdown){ Socket socketForShutdown=null; try{ socketForShutdown=serverSocketShutdown.accept(); BufferedReader br=new BufferedReader( new InputStreamReader(socketForShutdown.getInputStream()) ); String command=br.readLine(); if (command.equals("shutdown")){ long beginTime=System.currentTimeMillis(); socketForShutdown.getOutputStream().write("服务器正在关闭\r\n".getBytes()); isShutdown=true; //请求关闭线程池 //线程池不再接收新的任务,但会继续执行完工作队列中现有的任务 executorService.shutdown(); //等待关闭线程池,每次等待的超时时间为30s //当使用awaitTermination时,主线程会处于一种等待的状态,等待线程池中所有的线程都运行完毕后才继续运行。 //如果等待的时间超过指定的时间,但是线程池中的线程运行完毕,那么awaitTermination()返回true。执行分线程已结束 //如果等待的时间超过指定的时间,但是线程池中的线程未运行完毕,那么awaitTermination()返回false。不执行分线程已结束 //如果等待时间没有超过指定时间,等待! //可以用awaitTermination()方法来判断线程池中是否有继续运行的线程。 while(!executorService.isTerminated()) executorService.awaitTermination(30, TimeUnit.SECONDS); //关闭与EchoClient客户通信的ServerSocket serverSocket.close(); long endTime=System.currentTimeMillis(); socketForShutdown.getOutputStream().write(("服务器关闭,"+"关闭服务器用了"+(endTime-beginTime)+"ms\r\n").getBytes()); socketForShutdown.close(); serverSocketShutdown.close(); System.out.println("服务器关闭"); } else { socketForShutdown.getOutputStream().write("错误的命令\r\n".getBytes()); socketForShutdown.close(); } } catch (Exception e) { e.printStackTrace(); } } } }; public EchoServer() throws IOException { serverSocket=new ServerSocket(port); //设定等待客户连接的超时时间为60s serverSocket.setSoTimeout(60000); serverSocketShutdown=new ServerSocket(portForShutdown); //创建线程池 executorService= Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors() * POOL_SIZE); shutdownThread.start(); System.out.println("服务器启动"); } public void service(){ while(!isShutdown){ Socket socket=null; try { //可能会抛出SocketTimeoutException和SocketException socket=serverSocket.accept(); //把等待客户发送数据的超时时间设为60s socket.setSoTimeout(60000); //可能会抛出RejectedExecutionException executorService.execute(new Handler(socket)); }catch (SocketTimeoutException e){ //不必处理等待客户连接时出现的异常 }catch (RejectedExecutionException e) { try { if (socket != null) socket.close(); } catch (IOException ex) { return; } }catch (SocketException e){ if (e.getMessage().indexOf("socket closed")!=-1) return; }catch (IOException e){ e.printStackTrace(); } } } public static void main(String[] args) throws IOException { //main方法抛出异常,异常直接交给虚拟机,虚拟机直接结束异常 new EchoServer().service(); } } //负责与单个客户通信的任务 class Handler implements Runnable{ private Socket socket; public Handler(Socket socket){ this.socket=socket; } private PrintWriter getWriter(Socket socket) throws IOException{ OutputStream socketOut=socket.getOutputStream(); return new PrintWriter(socketOut,true); } private BufferedReader getReader(Socket socket) throws IOException{ InputStream socketIn=socket.getInputStream(); return new BufferedReader(new InputStreamReader(socketIn)); } public String echo(String msg){ return "echo: "+msg; } @Override public void run() { try{ System.out.println("New connection accepted "+socket.getInetAddress()+":"+socket.getPort()); BufferedReader br=getReader(socket); PrintWriter pw=getWriter(socket); String msg=null; //接收和发送数据,直到通信结束 while((msg=br.readLine())!=null){ System.out.println("from "+socket.getInetAddress()+":"+socket.getPort()+">"+msg); pw.println(echo(msg)); if (msg.equals("bye")) break; } } catch (IOException e) { e.printStackTrace(); }finally{ try{ if (socket!=null) socket.close(); }catch (IOException e){ e.printStackTrace(); } } } }
- AdminClient类(负责向EchoServer发送“shutdown”命令,关闭服务器)
package ShutdownServer; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.io.OutputStream; import java.net.Socket; public class AdminClient { public static void main(String[] args){ Socket socket=null; try{ socket=new Socket("localhost",8001); //发送关闭命令 OutputStream socketOut=socket.getOutputStream(); //Scanner scanner=new Scanner(System.in); //String order=scanner.next(); socketOut.write("shutdown\r\n".getBytes()); //接收服务器反馈 BufferedReader br=new BufferedReader(new InputStreamReader(socket.getInputStream())); String msg=null; while ((msg=br.readLine())!=null){ System.out.println(msg); } } catch (Exception e) { e.printStackTrace(); }finally { try{ if (socket!=null) socket.close(); } catch (IOException e) { e.printStackTrace(); } } } }
- Client类(客户,与服务器进行通讯)
package ShutdownServer; import java.io.*; import java.net.Socket; public class Client { private String host="localhost"; private int port=8000; private Socket socket; public Client() throws IOException { socket=new Socket(host,port); } private PrintWriter getWriter(Socket socket) throws IOException{ OutputStream socketOut=socket.getOutputStream(); return new PrintWriter(socketOut,true); } private BufferedReader getReader(Socket socket) throws IOException{ InputStream socketIn=socket.getInputStream(); return new BufferedReader(new InputStreamReader(socketIn)); } public void talk() throws IOException{ try{ BufferedReader br=getReader(socket); PrintWriter pw=getWriter(socket); BufferedReader localReader=new BufferedReader(new InputStreamReader(System.in)); String msg=null; while((msg=localReader.readLine()) != null){ pw.println(msg); System.out.println(br.readLine()); if (msg.equals("bye")){ break; } } }catch (IOException e){ e.printStackTrace(); } finally { try{ socket.close(); }catch (IOException e){ e.printStackTrace(); } } } public static void main(String args[]) throws IOException { new Client().talk(); } }
shutdownThread线程负责关闭服务器,它一直监听8001端口,如果接收到了AdminClient发送的“shutdown”命令,就把isShutdown设置为true。
在关闭服务器时,我们使用了最常用的方法,先调用线程池的shutdown()方法,接着调用线程池的awaitTermination()方法。
executorService.shutdown(); //等待关闭线程池,每次等待的超时时间为30s //当使用awaitTermination时,主线程会处于一种等待的状态,等待线程池中所有的线程都运行完毕后才继续运行。 //如果等待的时间超过指定的时间,但是线程池中的线程运行完毕,那么awaitTermination()返回true。执行分线程已结束 //如果等待的时间超过指定的时间,但是线程池中的线程未运行完毕,那么awaitTermination()返回false。不执行分线程已结束 //如果等待时间没有超过指定时间,等待! //可以用awaitTermination()方法来判断线程池中是否有继续运行的线程。 while(!executorService.isTerminated()) executorService.awaitTermination(30, TimeUnit.SECONDS);
在线程池执行了shutdown()方法后,线程池不会在接收新的任务,同时该线程因为调用awaitTermination()方法而发生阻塞,直到线程池中所有线程的任务执行完毕,该线程才会继续向下
运行结果
先运行EchoServer,Client,AdminClient后,再开启一客户程序Client1,显示Client1无法被加入线程池
- EchoServer(只显示连接了Client,未连接Client1)
- Client
- Client2(向服务器发送消息,收到null)
- AdminClient(在Client没有运行结束时,被阻塞)
当Client输入“bye”结束运行后,AdminClient关闭服务器
- Client类
- EchoServer类
- AdminClient类
参考Java网络编程核心技术详解
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