使用Java通過套接字接收python json

Question

我一直在遵循多個教程，通過套接字將Java代碼連接到python。

使用json數組，從Java發送到python效果很好。 但是，我似乎無法用Java接收東西。 我不太了解應該如何進行聆聽。 現在，我只是在15秒的while循環中進行監聽（python應該在收到輸入后立即發送），但是我感覺自己在做一些嚴重的錯誤。 也許有人有主意？

client.py：

import socket
import sys
import numpy as np
import json

# Create a TCP/IP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Bind the socket to the port
server_address = ('localhost', 10004)
print >>sys.stderr, 'starting up on %s port %s' % server_address
sock.bind(server_address)

# Listen for incoming connections
sock.listen(1)

def mysum(x):
    return np.sum(x)

while True:
    # Wait for a connection
    print >>sys.stderr, 'waiting for a connection'
    connection, client_address = sock.accept()
    infile = sock.makefile();

    try:
        print >>sys.stderr, 'connection from', client_address

        # Receive the data in small chunks and retransmit it
        data = b''
        while True:
             new_data = connection.recv(16)
             if new_data:
                 # connection.sendall(data)
                 data += new_data
             else:
                 data += new_data[:]
                 print >>sys.stderr, 'no more data from', client_address
                 break
        data= data.strip('\n');
        print("data well received!: ")
        print(data,)
        print(np.array(json.loads(data)));

        #send a new array back

        sendArray =  np.array( [ (1.5,2,3), (4,5,6) ] );
        print("Preparing to send this:");
        print(sendArray);
        connection.send(json.dumps(sendArray.tolist()));

    except Exception as e:
        print(e)
        connection.close()
        print("closed");
    finally:
        # Clean up the connection
        connection.close()
        print("closed");

server.java：

import java.io.*;
import java.net.Socket;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;

import org.json.*;

import java.net.ServerSocket;

public class SocketTest {

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


        String hostName = "localhost";
        int portNumber = 10004;

        try (

                //open a socket
                Socket clientSocket = new Socket(hostName, portNumber);

                BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
                PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);


        ) {

            System.out.println("Connected");
            Double[][] test2 = new Double[5][2];
            test2[1][1] = 0.1;
            test2[1][0] = 0.2;
            test2[2][1] = 0.2;
            test2[2][0] = 0.2;
            test2[3][1] = 0.1;
            test2[3][0] = 0.2;
            test2[4][1] = 0.2;
            test2[4][0] = 0.2;
            test2[0][1] = 0.2;
            test2[0][0] = 0.2;


            System.out.println("A");
            out.println(new JSONArray(test2).toString());
            System.out.println("B");


            long t = System.currentTimeMillis();
            long end = t + 15000;


            while (System.currentTimeMillis() < end) {
                String response;
                while ((response = in.readLine()) != null) {
                    System.out.println("receiving");
                    System.out.println( response );

                }


            }


            //listen for input continuously? 


            //clientSocket.close();
        } catch (JSONException e) {
            e.printStackTrace();
        }


    }


}

python的輸出是：

data well received!: 
('[[0.2,0.2],[0.2,0.1],[0.2,0.2],[0.2,0.1],[0.2,0.2]]',)
[[ 0.2  0.2]
 [ 0.2  0.1]
 [ 0.2  0.2]
 [ 0.2  0.1]
 [ 0.2  0.2]]
Preparing to send this:
[[ 1.5  2.   3. ]
 [ 4.   5.   6. ]]
closed
waiting for a connection
connection from ('127.0.0.1', 40074)

來自Java的輸出：

A
B

問題是sendArray = np.array（[（1.5,2,3），（4,5,6）]）; 永遠不會被Java接收。 我覺得我缺少使聽的簡單方法了……感謝您的幫助。

Answer 1

發生這種情況是因為您的Java代碼被阻止。 看看B如何不打印到您的日志中？ 那是因為由於這部分正在等待刷新命令，所以它不執行： out.println(new JSONArray(test2).toString()); 。 您需要做的是out.flush(); 如此下去。

Answer 2

您的代碼有多個問題。

1. Client.py和Server.java都在等待接收數據，這會導致死鎖。

當True時 ，Client.py被阻止，一直在等待新數據。
Server.java已發送長度為51的JSONArray（test2）.toString（） 。然后繼續在in.readLine（）中等待。

請參見如何在java中識別InputStream的結尾 。 相同的想法適用於python。 最好知道要讀取多少個字節。

更改：因為JSONArray（test2）.toString（）的長度為51，所以您將其替換

    while True:
         new_data = connection.recv(16)
         if new_data:
             # connection.sendall(data)
             data += new_data
         else:
             data += new_data[:]
             print >>sys.stderr, 'no more data from', client_address
             break

同

 data = connection.recv(51)

2. Server.java調用in.readLine（） 。 但是Client.py永遠不會發送'\\ n'並過早關閉套接字。 它導致in.readLine（）拋出異常。

更改：發送'\\ n'，以便Server.java可以成功讀取一行。

    connection.send(json.dumps(sendArray.tolist()));
    connection.send("\n");

3. Client.py關閉套接字，這將導致無限的in.readLine（）引發“連接重置”異常。

更改：確保雙方不再發送/接收數據，然后合上插座。

1＆2更改后的代碼。 （需要更多的精力來解決3，這不是這個問題的重點）：

public class Server {

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


    String hostName = "localhost";
    int portNumber = 10004;

    try (

        //open a socket
        Socket clientSocket = new Socket(hostName, portNumber);

        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);


    ) {

      System.out.println("Connected");
      Double[][] test2 = new Double[5][2];
      test2[1][1] = 0.1;
      test2[1][0] = 0.2;
      test2[2][1] = 0.2;
      test2[2][0] = 0.2;
      test2[3][1] = 0.1;
      test2[3][0] = 0.2;
      test2[4][1] = 0.2;
      test2[4][0] = 0.2;
      test2[0][1] = 0.2;
      test2[0][0] = 0.2;


      System.out.println("A");
      out.println(new JSONArray(test2).toString());
      System.out.println("B");


      long t = System.currentTimeMillis();
      long end = t + 15000;


      while (System.currentTimeMillis() < end) {
        String response;
        while ((response = in.readLine()) != null) {
          System.out.println("receiving");
          System.out.println( response );

        }
      }
      //listen for input continuously?
      //clientSocket.close();
    } catch (JSONException e) {
      e.printStackTrace();
    }
  }
}

Client.py輸出：

starting up on localhost port 10004
waiting for a connection
connection from ('127.0.0.1', 53388)
data well received!: 
('[[0.2,0.2],[0.2,0.1],[0.2,0.2],[0.2,0.1],[0.2,0.2]]',)
[[ 0.2  0.2]
 [ 0.2  0.1]
 [ 0.2  0.2]
 [ 0.2  0.1]
 [ 0.2  0.2]]
Preparing to send this:
[[ 1.5  2.   3. ]
 [ 4.   5.   6. ]]
closed

Server.java輸出：

Connected
A
B
receiving
[[1.5, 2.0, 3.0], [4.0, 5.0, 6.0]]
Exception in thread "main" java.net.SocketException: Connection reset
    at java.net.SocketInputStream.read(SocketInputStream.java:209)
    at java.net.SocketInputStream.read(SocketInputStream.java:141)