[Java知识库]Java BIO 使用socket实现服务端与客户端长连接

Client端

package com.athairen.bio;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.util.Locale;
import java.util.Scanner;
import java.util.Stack;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;

public class BioClient {

    private static final String EXIT_STR="exit";

    public static void main(String[] args) throws IOException {
        ExecutorService threadPool= Executors.newCachedThreadPool();
        Socket socket=new Socket("127.0.0.1",6666);
        OutputStream outputStream = socket.getOutputStream();
        InputStream inputStream = socket.getInputStream();


        threadPool.execute(new Runnable() {
            @Override
            public void run() {
                byte[] buffer=new byte[1024];
                int length;
                try {
                    while ((length=inputStream.read(buffer))!=-1) {
                        String s=new String(buffer,0, length);
                        System.out.println(s);
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }

            }
        });
        System.out.println("输入消息：");
        String inputStr="";
        while (!inputStr.toLowerCase(Locale.ROOT).equals(EXIT_STR)){
            Scanner scanner=new Scanner(System.in);
            inputStr = scanner.next();
            outputStream.write(inputStr.getBytes(StandardCharsets.UTF_8));
            outputStream.flush();
        }

        inputStream.close();
        outputStream.close();
        socket.shutdownInput();
        socket.shutdownOutput();
        if(!socket.isClosed()){
            socket.close();
        }
        System.out.println("client programe exit");

    }

}

server端

package com.athairen.bio;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class BioServer {

    public static void main(String[] args) throws IOException {
        //create a thread pool
        ExecutorService threadPool = Executors.newCachedThreadPool();
        ServerSocket serverSocket = new ServerSocket(6666);
        System.out.println("server start");
        while (true) {
            final Socket client = serverSocket.accept();
            System.out.println("one client connected server");
            threadPool.execute(new Runnable() {
                @Override
                public void run() {
                    try {
                        handler(client);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            });
        }
    }


    public static void handler(Socket client) throws IOException {

        if(!client.isConnected()){
            client.shutdownInput();
            client.shutdownOutput();
            if(!client.isClosed()){
                client.close();
            }
        }
        System.out.println("thread:: " + Thread.currentThread().getId() + " -- " + Thread.currentThread().getName());
        OutputStream outputStream = client.getOutputStream();
        InputStream inputStream = client.getInputStream();
        byte[] buffer = new byte[1024];
        int len;
        while ((len = inputStream.read(buffer)) != -1) {
            String s=new String(buffer, 0, len);
            System.out.println(s);
            outputStream.write(("hello,client,welcome!! your send content is: " + s).getBytes(StandardCharsets.UTF_8));
            outputStream.flush();
        }


    }

}

需要注意的地方：

短连接与长连接的不同：短连接将在shutdow流之后对应的socket也将会被关闭，所以我们在使用短连接时应该在流和socket关闭后，重新连接即new 一个新的socket，而长连接不应该关闭流和socket对象也不能shutdown流，而应该在写buffer时flush output流，注意！！，因此长连接的内存占用会高一些，也由于BIO的同步阻塞导致我们的服务器不能处理大量并发，因此更推荐使用NIO（同步非阻塞）框架netty，或AIO（异步非阻塞）。

注：

NIO更适合处理大量请求且少量资源（处理高并发字符串消息）的情况

AIO更适合处理大量请求且大量资源的情况（处理高并发且处理图片数据）的情况，但目前尚不成熟。

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