随着分布式技术的普及和海量数据的增长，io的能力越来越重要，java提供的io模块提供了足够的扩展性来适应。

我是李福春，我在准备面试，今天的问题是：

java中的io有哪几种？

java中的io分3类：

1，BIO ,即同步阻塞IO,对应java.io包提供的工具；基于流模型，虽然直观，代码实现也简单，但是扩展性差，消耗资源大，容易成为系统的瓶颈；

2，NIO，同步非阻塞io,对应java.nio包提供的工具，基于io多路复用；
核心类： Channel ,Selector , Buffer , Charset  
selector是io多路复用的基础，实现了一个线程高效管理多个客户端连接，通过事件监听处理感兴趣的事件。

3，AIO,即异步非阻塞io, 基于事件和回调

io的类层级

java各种IO的例子

java.io客户端连接服务端例子

package org.example.mianshi.io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * 说明：传统流式io 客户端连接服务端例子
 * @author carter
 * 创建时间： 2020年03月25日 9:58 下午
 **/

public class JavaIOApp {

    public static void main(String[] args) {

        final Server server = new Server();
        new Thread(server).start();

        try (
                Socket socket = new Socket(InetAddress.getLocalHost(), server.getPort());
        ) {
            final BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            bufferedReader.lines().forEach(System.out::println);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static class Server implements Runnable {

        private ServerSocket serverSocket;

        public int getPort() {
            return serverSocket.getLocalPort();
        }

        @Override
        public void run() {

            try (ServerSocket serverSocket = new ServerSocket(0);) {

                this.serverSocket = serverSocket;
                while (true) {
                    final Socket socket = serverSocket.accept();
                    new RequestHandler(socket).start();
                }

            } catch (IOException e) {
                e.printStackTrace();
            }

        }

        private class RequestHandler extends Thread {
            private Socket socket;

            public RequestHandler(Socket socket) {
                this.socket = socket;
            }

            @Override
            public void run() {
                try (
                        final PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
                ) {

                    printWriter.write("hello world");
                    printWriter.flush();

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

使用连接池优化

package org.example.mianshi.io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 说明：传统流式io 客户端连接服务端例子
 * @author carter
 * 创建时间： 2020年03月25日 9:58 下午
 **/

public class ThreadPoolJavaIOApp {

    public static void main(String[] args) {

        final Server server = new Server();
        new Thread(server).start();

        try (
                Socket socket = new Socket(InetAddress.getLocalHost(), server.getPort());
        ) {
            final BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            bufferedReader.lines().forEach(System.out::println);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static class Server implements Runnable {

        private ExecutorService threadPool = Executors.newFixedThreadPool(4);

        private ServerSocket serverSocket;

        public int getPort() {
            return serverSocket.getLocalPort();
        }

        @Override
        public void run() {

            try (ServerSocket serverSocket = new ServerSocket(0);) {

                this.serverSocket = serverSocket;
                while (true) {
                    final Socket socket = serverSocket.accept();

                    threadPool.submit(new RequestHandler(socket));
                }

            } catch (IOException e) {
                e.printStackTrace();
            }finally {
                threadPool.shutdown();
            }

        }

        private class RequestHandler implements Runnable {
            private Socket socket;

            public RequestHandler(Socket socket) {
                this.socket = socket;
            }

            @Override
            public void run() {
                try (
                        final PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
                ) {

                    printWriter.write("hello world");
                    printWriter.flush();

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

java.nio例子

package org.example.mianshi.io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;

/**
 * 说明：nio的客户端连接服务端例子
 * @author carter
 * 创建时间： 2020年03月25日 10:32 下午
 **/

public class JavaNioApp {

    public static void main(String[] args) {

        new Server().start();

        try (
                Socket socket = new Socket(InetAddress.getLocalHost(), 8888);
        ) {
            final BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            bufferedReader.lines().forEach(System.out::println);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static class Server extends Thread {

        @Override
        public void run() {

            try {
                ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();

                serverSocketChannel.bind(new InetSocketAddress(InetAddress.getLocalHost(), 8888));

                serverSocketChannel.configureBlocking(false);

                final Selector selector = Selector.open();

                serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

                while (true) {

                    selector.select();
                    selector.selectedKeys().forEach(selectionKey -> {
                        sayHelloWorld((ServerSocketChannel) selectionKey.channel());
                    });

                }

            } catch (IOException e) {
                e.printStackTrace();
            }

        }

        private void sayHelloWorld(ServerSocketChannel channel) {

            try (SocketChannel socketChannel = channel.accept()) {

                socketChannel.write(Charset.defaultCharset().encode("hello world nio"));

            } catch (IOException e) {
                e.printStackTrace();
            }

        }
    }

}


java.nio2例子

package org.example.mianshi.io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.nio.charset.Charset;

/**
 * 说明：TODO
 * @author carter
 * 创建时间： 2020年03月25日 10:54 下午
 **/

public class JavaNio2App {

    public static void main(String[] args) {

        new Server().start();

        try (
                Socket socket = new Socket(InetAddress.getLocalHost(), 9999);
        ) {
            final BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            bufferedReader.lines().forEach(System.out::println);

        } catch (IOException e) {
            e.printStackTrace();
        }


    }

    public static class Server extends Thread {


        @Override
        public void run() {

            try {
                AsynchronousServerSocketChannel serverSocketChannel = AsynchronousServerSocketChannel.open()
                        .bind(new InetSocketAddress(InetAddress.getLocalHost(), 9999));

                serverSocketChannel.accept(serverSocketChannel, new CompletionHandler<AsynchronousSocketChannel, AsynchronousServerSocketChannel>() {
                    @Override
                    public void completed(AsynchronousSocketChannel socketChannel,
                                          AsynchronousServerSocketChannel serverSocketChannel1) {
//                        serverSocketChannel1.accept(socketChannel, this);

                        socketChannel.write(Charset.defaultCharset().encode("hello world nio2 "));

                        try {
                            socketChannel.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }

                    @Override
                    public void failed(Throwable exc, AsynchronousServerSocketChannel attachment) {
                        exc.printStackTrace();
                    }
                });

            } catch (IOException e) {
                e.printStackTrace();
            }


        }
    }

}

本例子暂时无法运行。只为展示过程；

小结

本篇主要介绍了java提供的3中io，即 BIO,NIO,AIO ; 并提供了一些示例代码辅助理解。

原创不易，转载请注明出处。