Java入门系列-25-NIO(实现非阻塞网络通讯)

还记得以前介绍NIO时对比传统IO的一大特色吗？就是NIO是非阻塞式的，这篇文章带你们来看一下非阻塞的网络操做。

补充：以数组的形式使用缓冲区

package testnio;

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

public class TestBufferArray {

    public static void main(String[] args) throws IOException {
        RandomAccessFile raf1=new RandomAccessFile("D:/1.txt","rw");
        
        //1.获取通道
        FileChannel channel1=raf1.getChannel();
        
        //2.建立缓冲区数组
        ByteBuffer buf1=ByteBuffer.allocate(512);
        ByteBuffer buf2=ByteBuffer.allocate(512);
        ByteBuffer[] bufs= {buf1,buf2};
        //3.将数据读入缓冲区数组
        channel1.read(bufs);
        
        for (ByteBuffer byteBuffer : bufs) {
            byteBuffer.flip();
        }
        System.out.println(new String(bufs[0].array(),0,bufs[0].limit()));
        System.out.println("-----------");
        System.out.println(new String(bufs[1].array(),0,bufs[1].limit()));
        
        //写入缓冲区数组到通道中
        RandomAccessFile raf2=new RandomAccessFile("D:/2.txt","rw");
        FileChannel channel2=raf2.getChannel();
        channel2.write(bufs);
        
    }
}

使用NIO实现阻塞式网络通讯

TCP协议的网络通讯传统实现方式是经过套接字编程(Socket和ServerSocket)，NIO实现TCP网络通讯须要用到 Channel 接口的两个实现类：SocketChannel和ServerSocketChannel

使用NIO实现阻塞式网络通讯

客户端

package com.jikedaquan.blockingnio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.SocketChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class Client {

    public static void main(String[] args) {

        SocketChannel sChannel=null;

        FileChannel inChannel=null;
        try {
            //一、获取通道
            sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 1666));
            //用于读取文件            
            inChannel = FileChannel.open(Paths.get("F:/a.jpg"), StandardOpenOption.READ);

            //二、分配指定大小的缓冲区
            ByteBuffer buf=ByteBuffer.allocate(1024);

            //三、读取本地文件，发送到服务器端

            while(inChannel.read(buf)!=-1) {
                buf.flip();
                sChannel.write(buf);
                buf.clear();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            //关闭通道
            if (inChannel!=null) {
                try {
                    inChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            if(sChannel!=null) {
                try {
                    sChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

new InetSocketAddress("127.0.0.1", 1666) 用于向客户端套接字通道(SocketChannel)绑定要链接地址和端口

服务端

package com.jikedaquan.blockingnio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class Server {

    public static void main(String[] args) {

        ServerSocketChannel ssChannel=null;

        FileChannel outChannel=null;

        SocketChannel sChannel=null;
        try {
            //一、获取通道
            ssChannel = ServerSocketChannel.open();
            //用于保存文件的通道
            outChannel = FileChannel.open(Paths.get("F:/b.jpg"), StandardOpenOption.WRITE,StandardOpenOption.CREATE);

            //二、绑定要监听的端口号
            ssChannel.bind(new InetSocketAddress(1666));
            //三、获取客户端链接的通道
            sChannel = ssChannel.accept();

            //四、分配指定大小的缓冲区
            ByteBuffer buf=ByteBuffer.allocate(1024);

            //五、接收客户端的数据，并保存到本地
            while(sChannel.read(buf)!=-1) {
                buf.flip();
                outChannel.write(buf);
                buf.clear();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            //六、关闭通道
            if(sChannel!=null) {
                try {
                    sChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(outChannel!=null) {
                try {
                    outChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(ssChannel!=null) {
                try {
                    ssChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }   
            }       
        }
    }   
}

服务端套接字仅绑定要监听的端口便可 ssChannel.bind(new InetSocketAddress(1666));

上面的代码使用NIO实现的网络通讯，可能有同窗会问，没有看到阻塞效果啊，确实是阻塞式的看不到效果，由于客户端发送一次数据就结束了，服务端也是接收一次数据就结束了。那若是服务端接收完成数据后，再向客户端反馈呢？

可以看到阻塞效果的网络通讯

客户端

package com.jikedaquan.blockingnio2;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.SocketChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class Client {

    public static void main(String[] args) {
        SocketChannel sChannel=null;
        FileChannel inChannel=null;
        try {
            sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1", 1666));
            inChannel = FileChannel.open(Paths.get("F:/a.jpg"), StandardOpenOption.READ);

            ByteBuffer buf=ByteBuffer.allocate(1024);

            while(inChannel.read(buf)!=-1) {
                buf.flip();
                sChannel.write(buf);
                buf.clear();
            }
            
            //sChannel.shutdownOutput();//去掉注释掉将不会阻塞

            //接收服务器端的反馈
            int len=0;
            while((len=sChannel.read(buf))!=-1) {
                buf.flip();
                System.out.println(new String(buf.array(),0,len));
                buf.clear();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(inChannel!=null) {
                try {
                    inChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(sChannel!=null) {
                try {
                    sChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

服务端

package com.jikedaquan.blockingnio2;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class Server {

    public static void main(String[] args) {

        ServerSocketChannel ssChannel=null;
        FileChannel outChannel=null;
        SocketChannel sChannel=null;
        try {
            ssChannel = ServerSocketChannel.open();
            outChannel = FileChannel.open(Paths.get("F:/a.jpg"),StandardOpenOption.WRITE,StandardOpenOption.CREATE);

            ssChannel.bind(new InetSocketAddress(1666));
            sChannel = ssChannel.accept();
            ByteBuffer buf=ByteBuffer.allocate(1024);

            while(sChannel.read(buf)!=-1) {
                buf.flip();
                outChannel.write(buf);
                buf.clear();
            }

            //发送反馈给客户端
            buf.put("服务端接收数据成功".getBytes());
            buf.flip();
            sChannel.write(buf);
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(sChannel!=null) {
                try {
                    sChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(outChannel!=null) {
                try {
                    outChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(ssChannel!=null) {
                try {
                    ssChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

服务端将向客户端发送两次数据

选择器(Selector)

想要实现非阻塞的IO，必需要先弄懂选择器。Selector 抽象类，可经过调用此类的 open 方法建立选择器，该方法将使用系统的默认选择器提供者建立新的选择器。

将通道设置为非阻塞以后，须要将通道注册到选择器中，注册的同时须要指定一个选择键的类型 (SelectionKey)。

选择键(SelectionKey)能够认为是一种标记，标记通道的类型和状态。

SelectionKey的静态字段：
OP_ACCEPT：用于套接字接受操做的操做集位
OP_CONNECT：用于套接字链接操做的操做集位
OP_READ：用于读取操做的操做集位
OP_WRITE：用于写入操做的操做集位

用于检测通道状态的方法：

方法名称	说明
isAcceptable()	测试此键的通道是否已准备好接受新的套接字链接
isConnectable()	测试此键的通道是否已完成其套接字链接操做
isReadable()	测试此键的通道是否已准备好进行读取
isWritable()	测试此键的通道是否已准备好进行写入

将通道注册到选择器：

ssChannel.register(selector, SelectionKey.OP_ACCEPT);

IO操做准备就绪的通道大于0，轮询选择器

while(selector.select()>0) {
    //获取选择键，根据不一样的状态作不一样的操做
}

实现非阻塞式TCP协议网络通讯

非阻塞模式：channel.configureBlocking(false);

客户端

package com.jikedaquan.nonblockingnio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;
import java.util.Date;
import java.util.Scanner;

public class Client {

    public static void main(String[] args) {
        SocketChannel sChannel=null;
        try {
            //一、获取通道
            sChannel = SocketChannel.open(new InetSocketAddress("127.0.0.1",1666));
            
            //二、切换非阻塞模式
            sChannel.configureBlocking(false);
            
            //三、分配指定大小的缓冲区
            ByteBuffer buf=ByteBuffer.allocate(1024);
            //四、发送数据给服务端
            Scanner scanner=new Scanner(System.in);
            //循环从控制台录入数据发送给服务端
            while(scanner.hasNext()) {
                
                String str=scanner.next();
                buf.put((new Date().toString()+"\n"+str).getBytes());
                buf.flip();
                sChannel.write(buf);
                buf.clear();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            //五、关闭通道
            if(sChannel!=null) {
                try {
                    sChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

服务端

package com.jikedaquan.nonblockingnio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;

public class Server {

    public static void main(String[] args) throws IOException {
        
        //一、获取通道
        ServerSocketChannel ssChannel=ServerSocketChannel.open();
        //二、切换非阻塞模式
        ssChannel.configureBlocking(false);
        //三、绑定监听的端口号
        ssChannel.bind(new InetSocketAddress(1666));
        //四、获取选择器
        Selector selector=Selector.open();
        //五、将通道注册到选择器上，并指定“监听接收事件”
        ssChannel.register(selector, SelectionKey.OP_ACCEPT);
        
        //六、轮询式的获取选择器上已经 “准备就绪”的事件
        while(selector.select()>0) {
            //七、获取当前选择器中全部注册的“选择键(已就绪的监听事件)”
            Iterator<SelectionKey> it=selector.selectedKeys().iterator();
            while(it.hasNext()) {
                //八、获取准备就绪的事件
                SelectionKey sk=it.next();
                //九、判断具体是什么事件准备就绪
                if(sk.isAcceptable()) {
                    //十、若“接收就绪”，获取客户端链接
                    SocketChannel sChannel=ssChannel.accept();
                    //十一、切换非阻塞模式
                    sChannel.configureBlocking(false);
                    //十二、将该通道注册到选择器上
                    sChannel.register(selector, SelectionKey.OP_READ);
                }else if(sk.isReadable()) {
                    //1三、获取当前选择器上“读就绪”状态的通道
                    SocketChannel sChannel=(SocketChannel)sk.channel();
                    //1四、读取数据
                    ByteBuffer buf=ByteBuffer.allocate(1024);
                    int len=0;
                    while((len=sChannel.read(buf))>0) {
                        buf.flip();
                        System.out.println(new String(buf.array(),0,len));
                        buf.clear();
                    }
                }
                //1五、取消选择键 SelectionKey
                it.remove();
            }
            
        }
    }
}

服务端接收客户端的操做须要在判断 isAcceptable() 方法内将就绪的套接字通道以读操做注册到 选择器中

在判断 isReadable() 内从通道中获取数据

实现非阻塞式UDP协议网络通讯

发送端

package com.jikedaquan.nonblockingnio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
import java.util.Scanner;

public class TestDatagramSend {

    public static void main(String[] args) throws IOException {
        //获取通道
        DatagramChannel dChannel=DatagramChannel.open();
        //非阻塞
        dChannel.configureBlocking(false);
        ByteBuffer buf=ByteBuffer.allocate(1024);
        Scanner scanner=new Scanner(System.in);
        while(scanner.hasNext()) {
            String str=scanner.next();
            buf.put(str.getBytes());
            buf.flip();
            //发送数据到目标地址和端口
            dChannel.send(buf,new InetSocketAddress("127.0.0.1", 1666));
            buf.clear();
        }
        dChannel.close();
    }
}

接收端

package com.jikedaquan.nonblockingnio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.util.Iterator;

public class TestDatagramReceive {
    public static void main(String[] args) throws IOException {
        //获取通道
        DatagramChannel dChannel=DatagramChannel.open();
        dChannel.configureBlocking(false);
        //绑定监听端口
        dChannel.bind(new InetSocketAddress(1666));
        //获取选择器
        Selector selector=Selector.open();
        //读操做注册通道
        dChannel.register(selector, SelectionKey.OP_READ);
        while(selector.select()>0) {
            Iterator<SelectionKey> it=selector.selectedKeys().iterator();
            //迭代选择键
            while(it.hasNext()) {
                SelectionKey sk=it.next();
                //通道可读
                if(sk.isReadable()) {
                    ByteBuffer buf=ByteBuffer.allocate(1024);
                    //接收数据存入缓冲区
                    dChannel.receive(buf);
                    buf.flip();
                    System.out.println(new String(buf.array(),0,buf.limit()));
                    buf.clear();
                }
            }
            
            it.remove();
        }
    }
}