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();
}
}
