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。

以上为个人经验，希望能给大家一个参考，也希望大家多多支持。