当遇到并发服务场景时,咱们能够采取如下措施:
一、同步阻塞 IO 实现
public class DemoServer extends Thread {
private ServerSocket serverSocket;
public int getPort() {return serverSocket.getLocalPort();
}
public void run() {
try {serverSocket = new ServerSocket(0);
while (true) {
// 十分占用内存资源,每个客户端启用一个线程,非常不合理
Socket socket = serverSocket.accept();
RequesHandler requesHandler = new RequesHandler(socket);
requesHandler.start();}
} catch (IOException e) {e.printStackTrace();
} finally {if (serverSocket != null) {
try {serverSocket.close();
} catch (IOException e) {e.printStackTrace();
}
;
}
}
}
public static void main(String[] args) throws IOException {DemoServer server = new DemoServer();
server.start();
try (Socket client = new Socket(InetAddress.getLocalHost(), server.getPort())) {BufferedReader buferedReader = new BufferedReader(new InputStreamReader(client.getInputStream()));
buferedReader.lines().forEach(s -> System.out.println(s));
}
}
}
// 简化实现,不做读取,间接发送字符串
class RequesHandler extends Thread {
private Socket socket;
RequesHandler(Socket socket) {this.socket = socket;}
@Override
public void run() {try (PrintWriter out = new PrintWriter(socket.getOutputStream());) {out.println("Hello world!");
out.flush();} catch (Exception e) {e.printStackTrace();
}
}
}
每次 new 一个线程或者销毁一个线程是有显著的开销的,每个线程都有独自的线程构造,十分占用内存资源,每个客户端启用一个线程是非常不合理的,因而能够采纳线程池的形式进行优化。
// 也是阻塞 IO,采纳线程池的形式解决申请,当来一个新的客户端连贯时,// 将申请 Socket 封装成一个 task,放到线程池中取执行。serverSocket = new ServerSocket(0);
executor = Executors.newFixedThreadPool(8);
while (true) {Socket socket = serverSocket.accept();
RequesHandler requesHandler = new RequesHandler(socket);
executor.execute(requesHandler);
}
二、NIO 实现
NIO(非阻塞 IO)多路复用机制
public class NIOServer extends Thread {public void run() {try (Selector selector = Selector.open(); ServerSocketChannel serverSocket = ServerSocketChannel.open();) {// 创立 Selector 和 Channel
serverSocket.bind(new InetSocketAddress(InetAddress.getLocalHost(), 8888));
serverSocket.configureBlocking(false);
// 注册到 Selector,并阐明关注点
serverSocket.register(selector, SelectionKey.OP_ACCEPT);
while (true) {selector.select();// 阻塞期待就绪的 Channel,这是关键点之一
Set<SelectionKey> selectedKeys = selector.selectedKeys();
Iterator<SelectionKey> iter = selectedKeys.iterator();
while (iter.hasNext()) {SelectionKey key = iter.next();
// 生产零碎中个别会额定进行就绪状态查看
sayHelloWorld((ServerSocketChannel) key.channel());
iter.remove();}
}
} catch (IOException e) {e.printStackTrace();
}
}
private void sayHelloWorld(ServerSocketChannel server) throws IOException {try (SocketChannel client = server.accept();) {ByteBuffer readBuffer = ByteBuffer.allocate(32);
client.read(readBuffer);
System.out.println("Server received :" + new String(readBuffer.array()));
ByteBuffer writeBuffer = ByteBuffer.allocate(128);
writeBuffer.put("hello xiaoming".getBytes());
writeBuffer.flip();
client.write(writeBuffer);
//client.write(Charset.defaultCharset().encode("Hello world!"));
}
}
public static void main(String[] args) throws IOException {NIOServer server = new NIOServer();
server.start();
try {SocketChannel socketChannel = SocketChannel.open();
socketChannel.connect(new InetSocketAddress(InetAddress.getLocalHost(), 8888));
ByteBuffer writeBuffer = ByteBuffer.allocate(32);
ByteBuffer readBuffer = ByteBuffer.allocate(32);
writeBuffer.put("hello".getBytes());
writeBuffer.flip();
while (true) {writeBuffer.rewind();
socketChannel.write(writeBuffer);
// readBuffer.clear();
socketChannel.read(readBuffer);
System.out.println("Client received :" + new String(readBuffer.array()));
}
} catch (IOException e) {}}
/**
* @return
*/
private int getPort() {return 8888;}
三、总结
在后面两个例子中: 阻塞 IO 和伪异步 IO,一个是应用 new 线程的形式,另外一个是采纳线程池治理的形式,IO 都是同步阻塞模式,所以须要多线程以实现多任务处理。
而 NIO 则是利用了单线程轮询事件的机制,通过高效地定位就绪的 Channel,来决定做什么,仅仅 select 阶段是阻塞的,能够无效防止大量客户端连贯时频繁线程切换带来的问题,利用的扩大能力有了十分大的进步。