问题背景

oracle jdk默认的socket通信发送int类型数据高位优先。下面是jdk包内部相关源码。(模拟)

os.write((len >>> 24) & 0xFF);

os.write((len >>> 16) & 0xFF);

os.write((len >>> 8) & 0xFF);

os.write((len >>> 0) & 0xFF);

可以很明显的看出写入流时，先右移了24位。因为int类型的数据在jdk中是以4个字节表示的。1个字节有拥有8位。这是如果按照这个顺序与C++通信会发生误读情况，转成10进制以后，数字完全变了。故而要调整jdk源码。如下方法所示：

/**

* 字节序转换发送到server

* 针对发送int类型数据

*/

public void intTrans(int length, OutputStream os) throws IOException {

os.write((length >>> 0) & 0xFF);

os.write((length >>> 8) & 0xFF);

os.write((length >>> 16) & 0xFF);

os.write((length >>> 24) & 0xFF);

}

其他整型可类比。long型是8字节。

当然，同时做socket通信时，服务端接收时，协议所定义的包头大小很显然也是要做同样的大小端问题处理。原理一样。下面贴出了我的服务端代码：

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import org.springframework.beans.factory.annotation.Value;

import org.springframework.boot.ApplicationArguments;

import org.springframework.boot.ApplicationRunner;

import org.springframework.core.annotation.Order;

import org.springframework.stereotype.Component;

import java.io.*;

import java.net.ServerSocket;

import java.net.Socket;

/**

* @author Jerry

* @date 2018/11/6

*/

@Component

@Order(value = 1)

public class SocketServer implements ApplicationRunner {

private static Logger logger = LoggerFactory.getLogger(SocketServer.class);

/**

* 取到客户端发来的int类型的消息头，并且解决JDK大小端问题

* @param b

* @return

*/

private static int byteArrayToInt(byte[] b){

return b[0]&0xFF | (b[1]&0xFF) << 8 | (b[2]&0xFF) << 16 | (b[3]&0xFF) << 24;

}

@Value("${pixelMaster.listen.port}")

private int port;

public void startSocketServer() throws IOException {

ServerSocket serverSocket = new ServerSocket(port);

while (true){

Socket client = serverSocket.accept();

new HandlerThread(client);

}

}

private class HandlerThread implements Runnable{

private Socket socket;

private HandlerThread(Socket client){

socket = client;

new Thread(this).start();

}

@Override

public void run() {

try{

InputStream input = socket.getInputStream();

byte[] datalen = new byte[4];

input.read(datalen);

int length = byteArrayToInt(datalen);

logger.info("客户端发来的消息长度是:"+length);

byte[] data = new byte[length];

input.read(data);

String recvMsg = new String(data);//将获得数据转为字符串类型

logger.info("客户端发来的信息是:"+recvMsg);

input.close();

}catch (Exception e){

e.printStackTrace();

logger.error("获取客户端信息异常");

}

}

}

@Override

public void run(ApplicationArguments args) throws IOException {

startSocketServer();

}

}

顺便也贴出客户端代码留作记录。

import com.mcwl.pixelmaster.utils.ByteOrderTransAndSend;

import org.springframework.beans.factory.annotation.Value;

import org.springframework.stereotype.Component;

import java.io.IOException;

import java.io.OutputStream;

import java.io.PrintWriter;

import java.net.Socket;

/**

* @author Jerry

* @date 2018/11/1

* 描述：socket连接客户端

*/

@Component

public class Client {

//服务器地址

@Value(value = "${pixelMaster.server.url}")

private String ipAddr;

//服务器端口

@Value(value = "${pixelMaster.server.port}")

private int port;

public void send(String message)throws IOException{

Socket socket = new Socket(ipAddr,port);

OutputStream os = socket.getOutputStream();

ByteOrderTransAndSend trans = new ByteOrderTransAndSend();

trans.intTrans(message.getBytes().length,os);

PrintWriter writer = new PrintWriter(os);

writer.write(message);

writer.flush();

socket.shutdownOutput();

}

}