重温JAVA网络编程之BIO

Love The Way You Lie 2021-12-07 12:47 253阅读 0赞

**BIO:**即为同步阻塞式编程，最常用的就是Socket。

先从最简单的例子开始：

**客户端与服务端进行通信**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2h1YWl4aWFvaGFpXzE_size_16_color_FFFFFF_t_70][]

代码实现：

//服务端
    public class Service {
    	public static void main(String[] args) {
    		try {
    			ServerSocket serversocket = new ServerSocket(8888);
    			Socket socket=serversocket.accept();
    			InputStream in = socket.getInputStream();
    			InputStreamReader read = new InputStreamReader(in);
    			BufferedReader br = new BufferedReader(read);
    			String info=null;
    			while((info=br.readLine())!=null) {
    				System.out.println(info);
    			}
    			socket.shutdownInput();
    			OutputStream out = socket.getOutputStream();
    			PrintWriter pw = new PrintWriter(out);
    			pw.write("哈哈哈");
    			pw.flush();
    			socket.shutdownOutput();
    			in.close();
    			br.close();
    			read.close();
    			pw.close();
    			out.close();
    			socket.close();
    			serversocket.close();
    		} catch (IOException e) {
    			e.printStackTrace();
    		}
    	}
    }

//用户端
    public class Client {
    	public static void main(String[] args) {
    		try {
    			Socket socket = new Socket("localhost",8888);
    			OutputStream out = socket.getOutputStream();
    			PrintWriter pw =new PrintWriter(out);
    			pw.write("嘿嘿嘿");
    			pw.flush();
    			socket.shutdownOutput();
    			InputStream in = socket.getInputStream();
    			InputStreamReader read = new InputStreamReader(in);
    			BufferedReader bf = new BufferedReader(read);
    			String info=null;
    			while((info=bf.readLine())!=null) {
    				System.out.println(info);
    			}
    			socket.shutdownInput();
    			bf.close();
    			read.close();
    			in.close();
    			pw.close();
    			out.close();
    			socket.close();
    		} catch (UnknownHostException e) {
    			e.printStackTrace();
    		} catch (IOException e) {
    			e.printStackTrace();
    		}
    	}
    }

说明：**服务端监听一个地址，通accept()方法一直进行等待。直到有客户端进行连接。然后开始通过IO进行通信。这样一次通信就完成了。**

缺点：**如果我有多个用户请求连接服务端，并且IO操作时非常费时的，这样就会造成大量用户等待。**

解决方法：**通过采用多线程的方式去进行IO操作。**

//服务端
    public class Sercice {
    public static void main(String[] args) throws IOException {
    	Socket socket;
    	ServerSocket service = new ServerSocket(8888);
    	while(true) {
    		socket=service.accept();
    		new ThreadService(socket).start(); 
    		}
    	}
    }

//服务端IO处理
    public class ThreadService extends Thread {
    	private Socket socket = null;
    
    	public ThreadService(Socket socket) {
    		this.socket = socket;
    	}
    
    	@Override
    	public void run() {
    		InputStream in = null;
    		InputStreamReader ir = null;
    		BufferedReader br = null;
    		PrintWriter pw =null;
    		OutputStream out =null;
    		try {
    			in = socket.getInputStream();
    			ir = new InputStreamReader(in);
    			br = new BufferedReader(ir);
    			String str = null;
    			while ((str = br.readLine()) != null) {
    				System.out.println(str);
    			}
    			socket.shutdownInput();
    			
    			out=socket.getOutputStream();
    			pw = new PrintWriter(out);
    			pw.write("欢迎你");
    			pw.flush();
    			
    			socket.shutdownOutput();
    
    		} catch (IOException e) {
    			e.printStackTrace();
    		}finally {
    			try {
    				br.close();
    				ir.close();
    				in.close();
    				pw.close();
    				out.close();
    				socket.close();
    			} catch (IOException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    }

//客户端
    public class Client {
    	public static void main(String[] args) throws UnknownHostException, IOException {
    		Socket socket = new Socket("localhost",8888);
    		OutputStream out=socket.getOutputStream();
    		PrintWriter pw = new PrintWriter(out);
    		pw.write("嘿嘿");
    		pw.flush();
    		socket.shutdownOutput();
    		
    		InputStream in = socket.getInputStream();
    		InputStreamReader ir = new InputStreamReader(in);
    		BufferedReader bf = new BufferedReader(ir);
    		String str=null;
    		while((str=bf.readLine())!=null) {
    			System.out.println(str);
    		}
    		socket.shutdownInput();
    		pw.close();
    		out.close();
    		bf.close();
    		ir.close();
    		in.close();
    	}
    }

说明：通过把每次IO操作都采用开启新的线程去执行来减少一次通信的时间。

缺点：**当我连接数很多时，这样每一个连接数都对应一个线程，window的最大线程1000左右，linux加倍，那么这样的消耗也是消耗不起的，并且线程的建立与销毁都是非常消耗性能的。**

解决办法：采用连接池的当时，指定连接数，保持线程长期存活。

//客户端
    public class Sercice {
    	public static void main(String[] args) throws IOException {
    		Socket socket;
    		ServerSocket service = new ServerSocket(8888);
    		ExecutorService pool = new ThreadPoolExecutor(50, 1000, 120L, TimeUnit.SECONDS,
    				new ArrayBlockingQueue<Runnable>(1000));
    		while (true) {
    			socket = service.accept();
    			pool.execute(new ThreadService(socket)); 
    		}
    	}
    }

//IO操作执行类
    public class ThreadService implements Runnable{
    	private Socket socket = null;
    
    	public ThreadService(Socket socket) {
    		this.socket = socket;
    	}
    
    	@Override
    	public void run() {
    		InputStream in = null;
    		InputStreamReader ir = null;
    		BufferedReader br = null;
    		PrintWriter pw =null;
    		OutputStream out =null;
    		try {
    			in = socket.getInputStream();
    			ir = new InputStreamReader(in);
    			br = new BufferedReader(ir);
    			String str = null;
    			while ((str = br.readLine()) != null) {
    				System.out.println(str);
    			}
    			socket.shutdownInput();
    			
    			out=socket.getOutputStream();
    			pw = new PrintWriter(out);
    			pw.write("欢迎你");
    			pw.flush();
    			
    			socket.shutdownOutput();
    
    		} catch (IOException e) {
    			e.printStackTrace();
    		}finally {
    			try {
    				br.close();
    				ir.close();
    				in.close();
    				pw.close();
    				out.close();
    				socket.close();
    			} catch (IOException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    }

说明：**我们通过线程池的方式达到了伪异步的方式，但这并不是真正的异步。没有从根本上解决阻塞的问题。**

### **那么阻塞到底阻塞到哪了？** ###

**阻塞在了IO的read()以及write()方法上了。**

**read方法除了下面三个情况会一直阻塞着：**

**1.有数据可读**

**2.可用数据读取完毕**

**3.发生空指针IO异常**

**比如我要向服务端发消息（10字节），那么当网络比较慢的时候，开始只发过来8个字节，那么服务器会一直等待我，直到我所有的消息发送完，才会进行下一步处理。**

那么我们该怎么处理这个问题呢？请看一下篇。

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