转自:https://blog.csdn.net/yanmei_yao/article/details/8586199
除了普通的Socket与ServerSocket实现的阻塞式通信外,java提供了非阻塞式通信的NIO API。先看一下NIO的实现原理。
从图中可以看出,服务器上所有Channel(包括ServerSocketChannel和SocketChannel)都需要向Selector注册,而该Selector则负责监视这些Socket的IO状态,当其中任意一个或者多个Channel具有可用的IO操作时,该Selector的select()方法将会返回大于0的整数,该整数值就表示该Selector上有多少个Channel具有可用的IO操作,并提供了selectedKeys()方法来返回这些Channel对应的SelectionKey集合。正是通过Selector,使得服务器端只需要不断地调用Selector实例的select()方法即可知道当前所有Channel是否有需要处理的IO操作。
看个demo
NClient.java
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.Channel;
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;
public class Server {
public static void main(String[] args) {
int port = 8082;
int backlog = 3000;
Charset charSet = Charset.forName("UTF-8");
try {
Selector selector = Selector.open();
ServerSocketChannel channel = ServerSocketChannel.open();
channel.bind(new InetSocketAddress("localhost",port), backlog);
channel.configureBlocking(false);
channel.register(selector, SelectionKey.OP_ACCEPT);
while(selector.select()>0){
for(SelectionKey sk:selector.selectedKeys()){
//移除,TODO
selector.selectedKeys().remove(sk);
if(sk.isAcceptable()){
ServerSocketChannel ssc = (ServerSocketChannel) sk.channel();
//SocketChannel sc = channel.accept();
SocketChannel sc = ssc.accept();
sc.configureBlocking(false);
sc.register(selector, SelectionKey.OP_READ);
sk.interestOps(SelectionKey.OP_ACCEPT);
}
if(sk.isReadable()){
SocketChannel saChannel = (SocketChannel) sk.channel();
ByteBuffer buffer = ByteBuffer.allocate(1024);
String content = "";
while(saChannel.read(buffer)>0){
buffer.flip();
content = content + charSet.decode(buffer);
}
System.out.println("读取到的数据为:"+content);
sk.interestOps(SelectionKey.OP_READ);
if(content!=null&&!"".equals(content)){
for(SelectionKey sko:selector.keys()){
Channel targetChannel = sko.channel();
if(targetChannel instanceof SocketChannel){
SocketChannel tc = (SocketChannel) targetChannel;
tc.write(charSet.encode(content));
}
}
}
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
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import java.io.IOException;
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import java.net.InetSocketAddress;
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import java.nio.ByteBuffer;
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import java.nio.channels.SelectionKey;
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import java.nio.channels.Selector;
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import java.nio.channels.SocketChannel;
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import java.nio.charset.Charset;
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import java.util.Scanner;
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public class NClient {
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//定义检测SocketChannel的Selector对象
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private Selector selector=null;
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//定义处理编码和解码的字符集
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private Charset charset=Charset.forName("UTF-8");
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//客户端SocketChannel
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private SocketChannel sc=null;
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public void init() throws IOException{
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selector=Selector.open();
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InetSocketAddress isa=new InetSocketAddress("127.0.0.1",30000);
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//调用open静态方法创建连接到指定主机的SocketChannel
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sc=SocketChannel.open(isa);
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//设置该sc以非阻塞方式工作
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sc.configureBlocking(false);
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//将Socketchannel对象注册到指定Selector
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sc.register(selector, SelectionKey.OP_READ);
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//启动读取服务器端数据的线程
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new ClientThread().start();
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//创建键盘输入流
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Scanner scan=new Scanner(System.in);
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while(scan.hasNextLine()){
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//读取键盘输入
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String line=scan.nextLine();
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//将键盘输入的内容输出到SocketChannel中
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sc.write(charset.encode(line));
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}
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}
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//定义读取服务器数据的线程
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private class ClientThread extends Thread{
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public void run(){
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try{
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while(selector.select()>0){
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//遍历每个有可用IO操作Channel对应的SelectionKey
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for(SelectionKey sk:selector.selectedKeys()){
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//删除正在处理的SelectionKey
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selector.selectedKeys().remove(sk);
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//如果该SelectionKey对应的Channel中有可读的数据
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if(sk.isReadable()){
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//使用NIO读取channel中的数据
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SocketChannel sc=(SocketChannel) sk.channel();
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ByteBuffer buff=ByteBuffer.allocate(1024);
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String content="";
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while(sc.read(buff)>0){
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//sc.read(buff);
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buff.flip();
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content+=charset.decode(buff);
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}
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//打印输出读取的内容
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System.out.println("聊天信息"+content);
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//为下一次读取做准备
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sk.interestOps(SelectionKey.OP_READ);
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}
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}
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}
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}catch(IOException ex){
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ex.printStackTrace();
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}
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}
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}
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public static void main(String[]args) throws IOException{
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new NClient().init();
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}
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}
NServer.java
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.SocketChannel;
import java.nio.charset.Charset;
import java.util.Scanner;
public class Client {
private static Charset charSet = Charset.forName("UTF-8");
public static void main(String[] args) {
int port = 8082;
try {
Selector selector = Selector.open();
SocketChannel socketChannel = SocketChannel.open();
socketChannel.connect(new InetSocketAddress("localhost", port));
socketChannel.configureBlocking(false);
socketChannel.register(selector, SelectionKey.OP_READ);
Scanner scanner = new Scanner(System.in);
new ReadMsg(selector).start();
while(scanner.hasNextLine()){
String line = scanner.nextLine();
socketChannel.write(charSet.encode(line));
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
class ReadMsg extends Thread{
private static Charset charSet = Charset.forName("UTF-8");
private Selector selector;
public ReadMsg(Selector selector){
this.selector = selector;
}
@Override
public void run() {
try {
while(selector.select()>0){
for(SelectionKey sk:selector.selectedKeys()){
selector.selectedKeys().remove(sk);
if(sk.isConnectable()){
SocketChannel channel = (SocketChannel) sk.channel();
if(channel.isConnectionPending()){
channel.finishConnect();
}
channel.configureBlocking(false);
channel.register(selector, SelectionKey.OP_READ);
sk.interestOps(SelectionKey.OP_READ);
}
if(sk.isReadable()){
String content = "";
ByteBuffer buffer = ByteBuffer.allocate(1024);
SocketChannel channel = (SocketChannel) sk.channel();
while(channel.read(buffer)>0){
buffer.flip();
content = content+charSet.decode(buffer);
}
System.out.println("接收到的信息:"+content);
sk.interestOps(SelectionKey.OP_READ);
}
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
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import java.io.IOException;
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import java.net.InetSocketAddress;
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import java.nio.ByteBuffer;
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import java.nio.channels.Channel;
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import java.nio.channels.SelectionKey;
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import java.nio.channels.Selector;
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import java.nio.channels.ServerSocketChannel;
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import java.nio.channels.SocketChannel;
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import java.nio.charset.Charset;
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public class NServer {
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//用于检测所有Channel状态的Selector
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private Selector selector=null;
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//定义实现编码、解码的字符集对象
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private Charset charset=Charset.forName("UTF-8");
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public void init() throws IOException{
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selector=Selector.open();
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//通过open方法来打开一个未绑定的ServerSocketChannel实例
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ServerSocketChannel server=ServerSocketChannel.open();
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InetSocketAddress isa=new InetSocketAddress("127.0.0.1",30000);
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//将该ServerSocketChannel绑定到指定ip地址
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server.socket().bind(isa);
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//设置ServerSocket以非阻塞方式工作
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server.configureBlocking(false);
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//将server注册到指定Selector对象
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server.register(selector, SelectionKey.OP_ACCEPT);
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while(selector.select()>0){
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//依次处理selector上的每个已选择的SelectionKey
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for(SelectionKey sk:selector.selectedKeys()){
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//从selector上的已选择Key集中删除正在处理的SelectionKey
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selector.selectedKeys().remove(sk);
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//如果sk对应的通信包含客户端的连接请求
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if(sk.isAcceptable()){
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//调用accept方法接受连接,产生服务器端对应的SocketChannel
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SocketChannel sc=server.accept();
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//设置采用非阻塞模式
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sc.configureBlocking(false);
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sc.register(selector, SelectionKey.OP_READ);
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//将sk对应的Channel设置成准备接受其他请求
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sk.interestOps(SelectionKey.OP_ACCEPT);
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}
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//如果sk对应的通道有数据需要读取
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if(sk.isReadable()){
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//获取该SelectionKey对应的Channel,该Channel中有可读的数据
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SocketChannel sc=(SocketChannel) sk.channel();
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//定义准备之星读取数据的ByteBuffer
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ByteBuffer buff=ByteBuffer.allocate(1024);
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String content="";
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//开始读取数据
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try{
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while(sc.read(buff)>0){
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buff.flip();
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content+=charset.decode(buff);
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}
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//打印从该sk对应的Channel里读到的数据
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System.out.println("=========="+content);
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//将sk对应的Channel设置成准备下一次读取
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sk.interestOps(SelectionKey.OP_READ);
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//如果捕捉到该sk对应的channel出现异常,即表明该channel对应的client出现了
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//异常,所以从selector中取消sk的注册
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}catch(IOException e){
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//从Selector中删除指定的SelectionKey
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sk.cancel();
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if(sk.channel()!=null){
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sk.channel().close();
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}
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}
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//如果content的长度大于0,即聊天信息不为空
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if(content.length()>0){
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//遍历该selector里注册的所有SelectKey
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for(SelectionKey key:selector.keys()){
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//选取该key对应的Channel
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Channel targetChannel=key.channel();
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//如果该channel是SocketChannel对象
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if(targetChannel instanceof SocketChannel){
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//将独到的内容写入该Channel中
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SocketChannel dest=(SocketChannel) targetChannel;
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dest.write(charset.encode(content));
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}
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}
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}
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}
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}
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}
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}
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public static void main(String[]args) throws IOException{
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new NServer().init();
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}
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}
通过java提供的NIO实现非阻塞Socket通信,大大提高了网络服务器的性能。