Java 使用套接字在客户端和服务器之间进行通信

好的，这是今天早些时候修订的问题，我已经加入了代码来帮助解释这个问题。我正在从客户端向服务器发送两条消息。然后，服务器拾取消息并对其进行处理。服务器最终尝试将消息发送回客户机（请注意服务器代码“testmessage”），这就是我遇到的问题。要么我没有在客户端接收到消息，要么我从服务器端错误地发送了消息

public class ClientConnection {

String address, language, message;
int portNumber;
Socket clientSocket = null;

public ClientConnection(String lan, String mes, String add, int pn) throws IOException{
    address = add;
    portNumber = pn;
    language = lan;
    message = mes;
}
public String createAndSend() throws IOException{
    // Create and connect the socket
    Socket clientSocket = null;
    clientSocket = new Socket(address, portNumber);
    PrintWriter pw = new PrintWriter(clientSocket.getOutputStream(),true);
    BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));     

    // Send first message - Message is being correctly received
    pw.write(language+"\n"); 
    pw.flush(); 
    // Send off the data  

    // Send the second message - Message is being correctly received
    pw.write(message); 
    pw.flush();
    pw.close();
    // Send off the data

    // NOTE: Either I am not receiving the message correctly or I am not sending it from the server properly.
    String translatedMessage = br.readLine();       
    br.close();
    //Log.d("application_name",translatedMessage); Trying to check the contents begin returned from the server.
    return translatedMessage;
}

服务器代码：

public class ServerConnection {

public static void main(String[] args) throws Exception {       
    // Delete - Using while loop to keep connection open permanently.
    boolean status = false;
    while( !status){
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(4444);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 4444.");
            System.exit(1);
        }
        Socket clientSocket = null;
        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }
        // Delete - Working as of here, connection is established and program runs awaiting connection on 4444
        BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));     
        String language = br.readLine();
        String message = br.readLine();
        // Test - Works
        System.out.println(language);      
        // Test - Works
        System.out.println(message);
        // Delete - Working as of here, both messages are passed and applied. Messages are received as sent from client.
        TranslateMessage tm = new TranslateMessage();
        String translatedMessage = tm.translateMessage(language, message);

        // NOTE: This seems to be where I am going wrong, either I am not sending the message correctly or I am not receiving it correctly..
        // PrintWriter writer = new PrintWriter(new BufferedOutputStream(clientSocket.getOutputStream()));
        PrintWriter pw = new PrintWriter(clientSocket.getOutputStream(),true);
        // Send translation back 
        System.out.println(translatedMessage);
        // pw.write(translatedMessage+"\n"); 
        pw.write("Return test"); // Test message!
        pw.flush(); 
        // Send off the data 
        pw.close();
        br.close();
        clientSocket.close();
        serverSocket.close();
    }
}
}

代码有点混乱，我可以看到一些重复的代码，我已经在我感觉到问题的地方发表了评论

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谢谢你的帮助

您正在使用BufferedReader.readLine（）从服务器读取响应，但在测试用例中，您发送的字符串未以\n或\r\n结尾，因此它将无法从文档中获取该行

public String readLine()
            throws IOException

Read a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.

Returns:
    A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached

另一项建议

在编写这样的请求-响应协议时，我不会依赖于行结尾来终止请求或响应。通常我会使用完全格式化的JSON字符串，或者我更喜欢二进制协议，其中所有请求和响应都以二进制计数（通常为4字节bigendian/网络字节顺序）作为前缀。然后客户端和服务器读取4个字节，然后读取后面的字节数。这可以处理通常在网络连接上发生的数据包碎片，还有助于避免恶意用户发送永远不会终止的长字符串进行DOS攻击

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在Java中，可以使用ByteBuffer.order（）来处理bigendian数

嗨，Jim，谢谢你的评论，如果你看上面，我正在使用发送一个变量，\n但是它也不起作用。哦，我看到你在客户端执行readline之前关闭printwriter，这可能不好，因为他们使用的是同一个套接字。我尝试移动pw.close，我运行的android应用程序冻结了。hmmmmDid如果您在发送的测试字符串中添加一个

\n

，它将冻结等待读取整个字符串到\n。此外，我认为没有必要关闭printwriter或bufferedreader。如果您只关闭套接字，我认为这些将被关闭。客户端中的readline返回了什么？它是空的吗？不，它是一个字符串，尽管在本例中它应该是从服务器发送的“字符串测试”。我仍然会在

pw.write（“Return test”）

上粘贴一个\n，只是为了消除它作为一个问题。我做了Jim，但仍然没有用。也许新的一天会产生更好的结果。