解決Java中socket使用getInputStream()阻塞問題

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socket使用getInputStream()阻塞

今天用socket進行編程練習時，發現程序到瞭getInputStream(）這裡就進行不下去瞭

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());

就這樣的一個測試代碼，a不會打印出來

後來發現是getInputStream(）會一直阻塞在那裡阻塞

我把兩行代碼調瞭一下就好瞭，還不太清楚原因，先記下來

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());

用線程解決Socket的getInputStream阻塞

1.背景

在Socket通信中，當我們希望傳輸對象時，往往會用到輸入/輸出對象流。

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

2.問題

當程序調用socket.getInputStream()程序被被卡住。

3.原因

socket.getInputStream()方法會導致程序阻塞，直到inputStream收到對方發過來的報文消息，程序才會繼續往下執行。

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

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.解決辦法

用線程的方式處理輸入流。以下為示例代碼：

//===============客戶端代碼 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.");
	} 
}

//============服務器端代碼 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通信註意事項

（1）.writeXXX()方法後一般用flush()來把緩存內容發送出去。

（2）.發送對象時，對象必須串行化，即該對象需要實現Serializable接口。

以上為個人經驗，希望能給大傢一個參考，也希望大傢多多支持WalkonNet。

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