解决Java中socket使用getInputStream()阻塞问题

socket使用getInputStream()阻塞

今天用socket进行编程练习时，发现程序到了getInputStream(）这里就进行不下去了

Socket socket = new Socket("127.0.0.1", 800);
ObjectInputStream reader = new ObjectInputStream(socket.getInputStream());
System.out.println("a");
ObjectOutputStream writer = new ObjectOutputStream(socket.getOutputStream());

就这样的一个测试代码，a不会打印出来

后来发现是getInputStream(）会一直阻塞在那里阻塞

我把两行代码调了一下就好了，还不太清楚原因，先记下来

Socket socket = new Socket("127.0.0.1", 800);
ObjectOutputStream writer = new ObjectOutputStream(socket.getOutputStream());
System.out.println("a");
ObjectInputStream reader = new ObjectInputStream(socket.getInputStream());

用线程解决Socket的getInputStream阻塞

1.背景

在Socket通信中，当我们希望传输对象时，往往会用到输入/输出对象流。

ObjectInputStream in=new ObjectInputStream(socket.getInputStream());
ObjectOutputStream out=new ObjectOutputStream(socket.getOutputStream());

2.问题

当程序调用socket.getInputStream()程序被被卡住。

3.原因

socket.getInputStream()方法会导致程序阻塞，直到inputStream收到对方发过来的报文消息，程序才会继续往下执行。

public ObjectInputStream(InputStream in) throws IOException的官方API显示：

Creates an ObjectInputStream that reads from the specified InputStream. A serialization stream header is read from the stream and verified. This constructor will block until the corresponding ObjectOutputStream has written and flushed the header. [1]

4.解决办法

用线程的方式处理输入流。以下为示例代码：

//===============客户端代码 SocketClient.java=====================

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import java.net.UnknownHostException;

public class SocketClient {
private Socket socket;
private ObjectOutputStream out;
private ObjectInputStream in;
public SocketClient(){
try {
socket=new Socket("localhost",8081);
out=new ObjectOutputStream(socket.getOutputStream());
ReadThread readThread=new ReadThread();
readThread.start();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}

public void sendMessage(String msg){
System.out.println("send message:"+msg);
try {
out.writeObject(msg);
out.flush();
} catch (IOException e) {
e.printStackTrace();
}
}

class ReadThread extends Thread{
boolean runFlag=true;
public void run(){
try {
in=new ObjectInputStream(socket.getInputStream());
} catch (IOException e1) {
e1.printStackTrace();
}
while(runFlag){
if(socket.isClosed()){
return;
}
try {
Object obj=in.readObject();
if(obj instanceof String){
System.out.println("Client recive:"+obj);
}
}
catch (IOException e) {
e.printStackTrace();
}
catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}

public void exit(){
runFlag=false;
}
}

public static void main(String[] args) {
SocketClient socketClient=new SocketClient();
System.out.println("build socketClient");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
socketClient.sendMessage("Hello first.");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
socketClient.sendMessage("Hello second.");
}
}

//============服务器端代码 SocketService.java===========

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.util.Date;

public class SocketService {
ServerSocket serverSocket;
public SocketService(){
try {
serverSocket=new ServerSocket(8081);
while(true){
Socket socket=serverSocket.accept();
SocketServiceThread sst=new SocketServiceThread(socket);
sst.start();
}
} catch (IOException e) {
e.printStackTrace();
}
}

class SocketServiceThread extends Thread{
Socket socket;
ObjectInputStream in;
ObjectOutputStream out;
boolean runFlag=true;
public SocketServiceThread(Socket socket){
if(null==socket){
runFlag=false;
return;
}
this.socket=socket;
try {
out=new ObjectOutputStream(socket.getOutputStream());
} catch (IOException e) {
e.printStackTrace();
}
}

public void run(){
if(null==socket){
System.out.println("socket is null");
return;
}
try {
in=new ObjectInputStream(socket.getInputStream());
while(runFlag){
if(socket.isClosed()){
System.out.println("socket is closed");
return;
}
try {
String obj=(String)in.readObject();
if(obj instanceof String){
System.out.println("Server recive:"+obj);
Date date=new Date();
out.writeObject("["+date+"]"+obj);
out.flush();
}
else{
System.out.println("Server recive:"+obj);
}
}
catch (ClassNotFoundException e) {
e.printStackTrace();
}
catch (SocketException e){
e.printStackTrace();
return;
}
catch (IOException e){
e.printStackTrace();
}
}
} catch (IOException e1) {
e1.printStackTrace();
return;
} catch (Exception e){
return;
}
}

public void exit(){
runFlag=false;
}
}

public static void main(String[] args) {
System.out.println("===============start service===============");
new SocketService();
}
}

5.Socket通信注意事项

（1）.writeXXX()方法后一般用flush()来把缓存内容发送出去。

（2）.发送对象时，对象必须串行化，即该对象需要实现Serializable接口。

来源：https://blog.csdn.net/godelgnis/article/details/84258285