java socket通讯乱码问题的解决

使用socket通讯经常会遇到客户端、服务器端字符编码不一致的情况，如果传输的信息包含中文，这时我们可能就需要对传输的信息的按照指定的字符集进行解码

关于乱码的问题，最关键的要明白接受到的信息是什么编码的，就需要用什么字符集进行解码。

首先我们了解jdk api中的几个基本的概念

String类

public String(byte[] bytes,
              String charsetName)
       throws UnsupportedEncodingException

getBytes

public byte[] getBytes()

getBytes

public byte[] getBytes(String charsetName)
                throws UnsupportedEncodingException

在项目开发中遇到这种情况对方系统的编码为gb18030，而我们系统的编码为utf-8，两个系统直接使用socket进行通讯

在通讯过程中我们系统作为客户端需要按照gb18030进行报文发送，而当接受到对方系统的报文时我们需要将报文按照gb18030进行解码

具体测试代码如下：

socket服务端：

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class SocketServer {
    
    /**
     * @throws Exception
     */
    public void startServer(int port) throws Exception {
        ServerSocket serverSocket = new ServerSocket(port);
        Socket server = null;
        try {
            while (true) {
                server = serverSocket.accept();
                System.out.println("socket服务端启动……");
                try {
                    BufferedReader input = new BufferedReader(new InputStreamReader(new ByteArrayInputStream("服务端发给客户端的信息".getBytes())));
                    BufferedInputStream in = new BufferedInputStream(server.getInputStream());
                    PrintWriter out = new PrintWriter(new OutputStreamWriter(server.getOutputStream()));
                    
                    String serverstring = null;
                    String clientstring = null;
                    out.println("欢迎客户端连入");
                    out.flush();
                    while (true) {
                        byte[] buf = new byte[10000];
                        int size=0;
                        if ((size=in.read(buf))!=-1) {
                            clientstring = new String(buf,0,size,"GB18030");
                            if (clientstring != null) {
                                System.out.println("client:" + clientstring);
                            }
                        }    
                        serverstring = input.readLine();
                        out.println(serverstring);
                        out.flush();
                        break;
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    server.close();
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            serverSocket.close();
        }
    }
    
    public static void main(String[] args) {
        SocketServer ss = new SocketServer();
        int port = 8888;
        try {
            ss.startServer(port);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

socket客户端

import java.io.BufferedInputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;


public class SocketClient {
    
    /**
     * @throws Exception
     */
    public void makeConn(String ip, int port) throws Exception {
        Socket client = new Socket(ip, port);
        try {
//            BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
//            BufferedReader input = new BufferedReader(new InputStreamReader(new ByteArrayInputStream("客户端发给服务器端的信息".getBytes())));
            BufferedInputStream in = new BufferedInputStream(client.getInputStream());
            PrintWriter out = new PrintWriter(new OutputStreamWriter(client.getOutputStream(),"GB18030"));
            
            String clientString = null;
            String serverString = null;
            while (true) {
                byte[] buf = new byte[10000];
                int size=0;
                if ((size=in.read(buf))!=-1) {
                    serverString = new String(buf,0,size,"GB18030");
                    if (serverString != null) {
                        System.out.println("server:" + serverString);
                    }
                }
//                clientString = input.readLine();
                clientString = "客户端发给服务器端的信息";
                if (clientString != null) {
                    out.println(clientString);
                    out.flush();
                    break;
                }
            }
            in.close();
            out.close();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            client.close();
        }
    }
    
    public static void main(String[] args) {
        SocketClient sc = new SocketClient();
        int port = 8888;
        try {
            sc.makeConn("localhost", port);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

上述代码的关键在于以下几部分：

由于socket服务端的编码是gb18030的，因此在接受到socket服务端的报文后我们需要按照gb18030进行解码

clientstring = new String(buf,0,size,"GB18030");

而socket客户端因为编码是utf-8的，而socket服务端只能识别gb18030的编码，所以socket客户端在发送报文时需要做转换

 PrintWriter out = new PrintWriter(new OutputStreamWriter(client.getOutputStream(),"GB18030"));

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