问题描述
写了一段服务器端和客户端通信代码，实现以下功能：客户端将文件发送到服务器端，服务器端接收完文件后给客户端发送一个消息。运行代码后出现以下问题不知如何神马原因：客户端文件可以正确地传到服务器端，但是服务器端接收完文件后发送给客户端地确认消息，客户端收不到，报java.net.SocketException: Socket is closed的异常，请各位帮忙看看客户端代码package client;import java.io.*;import java.net.*;public class ClientThread extends Thread{private int hostPort=3000;protected BufferedReader socketReader; protected PrintWriter socketWriter; private BufferedReader streamReader;public ClientThread(){setUpConnection();}public void setUpConnection() { try { Socket client = new Socket("127.0.0.1", hostPort); //socketWriter = new PrintWriter(client.getOutputStream());InputStream inputFromSocket = client.getInputStream();streamReader = new BufferedReader(new InputStreamReader(inputFromSocket));handleConnection(client);} catch (UnknownHostException e) { System.out.println("Error setting up socket connection: unknown host"); } catch (IOException e) { System.out.println("Error setting up socket connection: " + e); } } public void handleConnection(Socket client) {try {File file=new File("a.txt");FileReader fileReader = new FileReader(new File("a.txt"));BufferedReader bufferedFileReader = new BufferedReader(fileReader);PrintWriter streamWriter = new PrintWriter(client.getOutputStream());String line = null;while ((line = bufferedFileReader.readLine()) != null) {streamWriter.println(line);}fileReader.close();streamWriter.close();//////读取服务器收到文件后的返回内容String str=streamReader.readLine();while(str!=null){System.out.println(str);}} catch (Exception e) {System.out.println("Error handling a client: " + e);}} }服务器端代码import java.net.*;import java.io.*;public class ServerThread extends Thread{private int listenPort = 3000;public ServerThread(){acceptConnections();}public void acceptConnections() {try {ServerSocket server = new ServerSocket(listenPort);Socket incomingConnection = null;while (true) {incomingConnection = server.accept();handleConnection(incomingConnection);}} catch (BindException e) {System.out.println("Unable to bind to port " + listenPort);} catch (IOException e) {System.out.println("Unable to instantiate a ServerSocket on port: "+ listenPort);}}public void handleConnection(Socket incomingConnection) {try {BufferedReader socketReader = new BufferedReader( new InputStreamReader(incomingConnection.getInputStream())); String line = null;while ((line = socketReader.readLine()) != null) {//streamWriter.println(line);System.out.println(line);}socketReader.close();/////////接受完服务器发送的文件后给客户端OutputStream os=incomingConnection.getOutputStream();os.write("".getBytes());} catch (Exception e) {System.out.println("Error handling a client: " + e);}}} 问题补充：Rainbow702 写道
解决方案
给你修改了一下，可以正常运行：import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.io.OutputStream;import java.net.BindException;import java.net.ServerSocket;import java.net.Socket;public class ServerThread extends Thread {private int listenPort = 30000;public ServerThread() {acceptConnections();}public void acceptConnections() {try {ServerSocket server = new ServerSocket(listenPort);Socket incomingConnection = null;int i=1;while (true) {System.out.println("i= " + (i++));incomingConnection = server.accept();handleConnection(incomingConnection);}} catch (BindException e) {System.out.println("Unable to bind to port " + listenPort);e.printStackTrace();} catch (IOException e) {System.out.println("Unable to instantiate a ServerSocket on port: "+ listenPort);}}public void handleConnection(Socket incomingConnection) {try {BufferedReader socketReader = new BufferedReader(new InputStreamReader(incomingConnection.getInputStream()));String line = null;while (!(line = socketReader.readLine()).equals("xxx")) {// streamWriter.println(line);System.out.println(line);}//socketReader.close();// ///////接受完服务器发送的文件后给客户端OutputStream os = incomingConnection.getOutputStream();os.write("message arriveredn".getBytes());os.write("n".getBytes());os.flush();System.out.println("handleConnection() is over");} catch (Exception e) {System.out.println("Error handling a client: " + e);}}public static void main(String[] args) {new ServerThread().start();}}import java.io.BufferedReader;import java.io.File;import java.io.FileReader;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.PrintWriter;import java.net.Socket;import java.net.UnknownHostException;public class ClientThread extends Thread{private int hostPort = 30000;protected BufferedReader socketReader;protected PrintWriter socketWriter;private BufferedReader streamReader;public ClientThread() {setUpConnection();}public void setUpConnection() {try {Socket client = new Socket("127.0.0.1", hostPort);// socketWriter = new PrintWriter(client.getOutputStream());InputStream inputFromSocket = client.getInputStream();streamReader = new BufferedReader(new InputStreamReader(inputFromSocket));handleConnection(client);} catch (UnknownHostException e) {System.out.println("Error setting up socket connection: unknown host");} catch (IOException e) {System.out.println("Error setting up socket connection: " + e);}}public void handleConnection(Socket client) {try {File file = new File("src/test.txt");FileReader fileReader = new FileReader(file);BufferedReader bufferedFileReader = new BufferedReader(fileReader);PrintWriter streamWriter = new PrintWriter(client.getOutputStream());String line = null;while ((line = bufferedFileReader.readLine()) != null) {streamWriter.println(line);}streamWriter.println("xxx");streamWriter.flush();fileReader.close();// 此处不能断，否则就断开了与服务器的 socket 连接// streamWriter.close();// ////读取服务器收到文件后的返回内容String str;while ((str = streamReader.readLine()) != null && !str.equals("")) {System.out.println(str);}System.out.println("client thread is over");} catch (Exception e) {System.out.println("Error handling a client: " + e);e.printStackTrace();}}public static void main(String[] args) {new ClientThread().start();}}
解决方案二：
另外判断一个文件是否读完，不能通过是否读取到了 null 来判断，而是应该使用特地的结束符来判断
解决方案三：
引用streamWriter.close();关键是你上面这句代码的问题，通过源码可以看出 public void close() {try { synchronized (lock) {if (out == null) return;out.close();out = null; }}catch (IOException x) { trouble = true;} }会把 out 关闭且置为 null，那么 out 是什么呢？引用PrintWriter streamWriter = new PrintWriter(client.getOutputStream());上面是你的代码。去看一下 PrintWriter 的源码便知：public PrintWriter(OutputStream out) {this(out, false); }public PrintWriter(OutputStream out, boolean autoFlush) {this(new BufferedWriter(new OutputStreamWriter(out)), autoFlush);// save print stream for error propagationif (out instanceof java.io.PrintStream) { psOut = (PrintStream) out;} }public PrintWriter(Writer out, boolean autoFlush) {super(out);this.out = out;this.autoFlush = autoFlush;lineSeparator = (String) java.security.AccessController.doPrivileged( new sun.security.action.GetPropertyAction("line.separator")); }可见，这个 out 就是你通过 socket 得到的 getOutputStream，那么怎么才能将这个 getOutputStream 关闭呢，当然就是断开这个 socket 啦，所以，你会一直得到这个异常
解决方案四：
那把 Thread.sleep(2000); 的时间设置成更大一点。另外，你的 客户端 与 服务端 是分开启动的吧？
解决方案五：
初步推测：引用//////读取服务器收到文件后的返回内容 String str=streamReader.readLine(); while(str!=null){ System.out.println(str); } 这个操作在服务器返回有效结果前已经被执行过，导致客户端的 Thread 的线程执行完毕，从而断开发与服务器的连接（从而可能导致服务器还没有把文件接收结束就已经报了这个异常）。你可以在上面的操作之前加个Thread.sleep(2000);来模拟一下服务器返回结果的延迟效果，看看还能不能收到结果
解决方案六：
引用java.net.SocketException: Socket is closed是哪一行报的错啊？