java - 多线程 Java 代理服务器

Question

我对 Stack Overflow 还不太熟悉，所以如果我做错了什么，请随时告诉我。我还没有找到另一篇文章以对我来说有意义的方式解决这个问题。

所以我的最终目标是用 Java 编写一个多线程 HTTP 代理服务器，但作为第一步，我只是尝试将通过浏览器建立的连接的输入流写入窗口。

这是我的代码:

private static ServerSocket welcomeSocket;
private static Socket connectionSocket;

private static Socket clientSocket;

private static OutputStream clientOutput;
private static InputStream proxyInput;

private static BufferedReader reader;

private static InetSocketAddress clientStream;

public static void main(String[] args) throws IOException, URISyntaxException {

    // Create socket, port 12345, for incoming request
    welcomeSocket = new ServerSocket(12345);
    while(true){
        try(Socket clientSocket = welcomeSocket.accept()){
        BufferedReader reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()));

        Thread t = new Thread(){  
            public void run(){
                System.out.println("running\n");
                try{
                    System.out.println("trying\n");
                    String lineIn;
                    while((lineIn = reader.readLine()) != null){
                        System.out.println("writing\n");
                        writer.write(lineIn);
                        writer.newLine();
                    }
                }
                catch(IOException i){
                    try {                            
                        Logger.getLogger(EECS325_Project1.class.getName()).log(Level.SEVERE, null, i);
                        throw i;
                    } catch (IOException ex) {
                        Logger.getLogger(EECS325_Project1.class.getName()).log(Level.SEVERE, null, ex);
                    }
                }
            }
        };
        t.start();
        }
    }

}

但是，当我在浏览器中访问 localhost:12345 时，出现以下异常:

     Nov 04, 2015 9:53:44 AM eecs325_project1.EECS325_Project1$1 run
     SEVERE: null
     java.net.SocketException: socket closed
     at java.net.SocketInputStream.socketRead0(Native Method)
     at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
     at java.net.SocketInputStream.read(SocketInputStream.java:170)
     at java.net.SocketInputStream.read(SocketInputStream.java:141)
     at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
     at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
     at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
     at java.io.InputStreamReader.read(InputStreamReader.java:184)
     at java.io.BufferedReader.fill(BufferedReader.java:161)
     at java.io.BufferedReader.readLine(BufferedReader.java:324)
     at java.io.BufferedReader.readLine(BufferedReader.java:389)
     at eecs325_project1.EECS325_Project1$1.run(EECS325_Project1.java:46)

大多数帖子都说，当关闭读取器/写入器时会发生此异常，从而有效地关闭套接字。但是，我绝不会关闭读取器、写入器或套接字。

任何帮助将不胜感激!

Answer 1

您的 try-with-resources block 在线程执行之前关闭客户端套接字 - 这意味着当线程尝试使用它们时，reader 和 writer 引用关闭的底层流.

解决此问题的方法是将 try-with-resources block 移至线程内部:

final Socket clientSocket = welcomeSocket.accept();
Thread t = new Thread(){  
  @Override public void run(){
    // BufferedReader/Writer close the underlying stream when they
    // are closed, so the socket will be closed when this
    // try-with-resources block finishes.
    try (BufferedReader reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())));
         BufferedWriter writer = ...) {
      // Do whatever.
    } catch (IOException e) {
      // Handle the exception.
    }
  }
};
t.start();

这意味着在线程运行之前，更具体地说，在您完成 reader 和 writer 的操作之后，关闭才会发生。

注意:您必须小心确保套接字始终关闭:如果在创建线程或创建 BufferedReader 时出现异常，则不会发生这种情况。这些情况有点糟糕，并且涉及一些额外的 try/catch/finally block ；我不想将这些添加到答案中，因为我认为它们只是模糊了主要思想。