java IO笔记(网络中IO的运用)

如今大部分的编程开发都离不开网络，Java IO同样可以基于网络进行开发。事实上网络编程可以看做两个进程之间的通信，我们可以通过java对网络的支持，建立两点的网络连接，连接建立成功之后，就可以看做是本地的文件操作了。前面对于文件进行的类似操作也可以适用在这里。

我们常用的有TCP/UDP建立连接，下面将分别举例说明：

TCPClient:

package NetIo;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.Socket;public class TCPClient {private Socket socket;private boolean connectFlag;private InputStream is;private OutputStream os;private byte[] buffer = new byte[1024];public static void main(String[] args) {TCPClient client = new TCPClient();if (client.initSocket()) {client.execute();} else {System.out.println("the connect has some wrong.");}}private boolean initSocket() {try {socket = new Socket("127.0.0.1", 5008);socket.setSoTimeout(2000);connectFlag = true;} catch (IOException e) {e.printStackTrace();}return connectFlag;}private void execute() {String message = "Hello World!";try {is = socket.getInputStream();os = socket.getOutputStream();int len;os.write(message.getBytes());while (true) {len = is.read(buffer);if (len != -1) {String response = new String(buffer, 0, len);System.out.println("从服务器接收的消息为" + response);break;}}socket.close();} catch (IOException e) {e.printStackTrace();}}}

TCPServer:

package NetIo;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.ServerSocket;import java.net.Socket;public class TCPServer implements Runnable{private ServerSocket serversocket;private Socket socket;private boolean connectFlag;private InputStream is;private OutputStream os;private byte[] buffer = new byte[1024];public TCPServer(){}public TCPServer(Socket socket){this.socket = socket;}public static void main(String[] args) {TCPServer server = new TCPServer();if(server.initServer()){server.execute();}else {System.out.println("there are some mistakes when connect");}}private boolean initServer(){try {serversocket = new ServerSocket(5008);connectFlag = true;} catch (IOException e) {e.printStackTrace();}return connectFlag;}private void execute(){while(true){try {socket = serversocket.accept();new Thread(new TCPServer(socket)).start();} catch (IOException e) {e.printStackTrace();}}}@Overridepublic void run() {try {String host = socket.getInetAddress().toString();int port = socket.getPort();os = socket.getOutputStream();is = socket.getInputStream();while(true){if(socket.isClosed()){return;}int len = is.read(buffer);if(len != -1){System.out.println("从地址为"+host+"端口为"+port+"的客户端发来消息："+new String(buffer,0,len));os.write("服务器已接收消息成功".getBytes());}}} catch (Exception e) {e.printStackTrace();}}}

先执行服务端，在执行客户端代码，可以在控制台看到如下打印：

上面的两个例子模拟了TCP通信，从中可以看出IO在网络编程中也是有着一席之地的。

下面将举例说明基于UDP的网络IO。

UDPClient：

package NetIo;import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;public class UDPClient {public static void main(String[] args) throws IOException {DatagramSocket socket = new DatagramSocket();String message = "Hello World!";byte[] buffer = message.getBytes();InetAddress address = InetAddress.getByName("127.0.0.1");DatagramPacket packet = new DatagramPacket(buffer, buffer.length,address, 5000);socket.send(packet);while (true) {byte[] buf = new byte[1024];DatagramPacket receivePacket = new DatagramPacket(buf, buf.length);socket.receive(receivePacket);String response = new String(receivePacket.getData(), 0,receivePacket.getData().length);if (response != null) {System.out.println("从服务端成功接收消息：" + response);socket.close();break;}}}}

UDPServer:

package NetIo;import java.io.IOException;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import java.util.concurrent.atomic.AtomicInteger;public class UDPServer implements Runnable {private DatagramSocket socket;private DatagramPacket packet;public UDPServer(DatagramSocket socket, DatagramPacket packet) {this.socket = socket;this.packet = packet;}public static void main(String[] args) throws IOException {AtomicInteger numThreads = new AtomicInteger(0);DatagramSocket socket = new DatagramSocket(5000);while (true) {byte[] buf = new byte[1024];DatagramPacket packet = new DatagramPacket(buf, buf.length);socket.receive(packet);Thread thread = new Thread(new UDPServer(socket, packet));thread.start();numThreads.incrementAndGet();}}@Overridepublic void run() {String message = new String(packet.getData(), 0,packet.getData().length);int port = packet.getPort();InetAddress address = packet.getAddress();System.out.println("get a message from address:" + address + " port："+ port + " message:" + message);String respose = "服务器已成功收到消息";DatagramPacket resPacket = new DatagramPacket(respose.getBytes(),respose.getBytes().length, address, port);try {socket.send(resPacket);} catch (IOException e) {e.printStackTrace();}}}

先执行服务端，在执行客户端代码，可以在控制台看到如下打印：

上面的两个例子模拟了UDP简单通信。