Java 网络编程

java在java.net包提供了丰富的api供网络编程，主要包括了：

URLConnection, HttpURLConnection用于从服务器端获取数据；

ServerSocket和Scoket建立TCP服务器和客户端；

DatagramSocket建立UDP服务器和客户端；

• ServerSocket和Scoket建立TCP／IP连接

首先，我们需要通过ServerSocket建立监听客户端TCP连接请求。当监听到客户端的请求后，Server会分配一个Socket与客户端通信。

 

创建客户端用于发送和接收数据变得相当简单：

Socket socket = new Socket("localhost", 8080);
        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        out.println("test");

        BufferedReader in = new BufferedReader(new InputStreamReader(
                socket.getInputStream()));
        System.out.println(in.readLine()); // 必须输出换行，否则不会输出任何数据给客户

        socket.close();

服务器端也相当简单：

ServerSocket serverSocket = new ServerSocket(8080);
        Socket clientSocket = serverSocket.accept();

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(
                clientSocket.getInputStream()));
        String line;
        while ((line = in.readLine()) != null) {
            out.println("From Server: " + line); // 必须输出换行，否则不会输出任何数据给客户
        }
        clientSocket.close();

        serverSocket.close();

 

 

• DatagramSocket建立UDP连接

与TCP连接不同，UDP并没有严格意义上的服务器端和客户端之分。双方都可以发送数据给对方，接收方不一定接收到数据，发送方也不知道数据是否被接收。发送的数据也不一定按原来的顺序接收。很显然，由于不需要彼此事先建立连接，故而省去了很多不必要的开销。这对于不关心少量数据丢失的应用十分有用，如直播。

public class UDPTest {

    public static void main(String[] args) throws IOException, InterruptedException {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    receive(); // must start a new thread
                } catch (IOException e) {
                    e.printStackTrace();
                }                
            }
        }).start();
        
        send();
    }

    public static void send() throws IOException {
        DatagramSocket datagramSocket = new DatagramSocket();

        byte[] buffer = "test udp".getBytes();
        InetAddress receiverAddress = InetAddress.getLocalHost();

        DatagramPacket packet = new DatagramPacket(buffer, buffer.length,
                receiverAddress, 8800);
        datagramSocket.send(packet); // not block
        datagramSocket.close();
    }

    public static void receive() throws IOException {
        DatagramSocket datagramSocket = new DatagramSocket(8800);

        byte[] buffer = new byte[10];
        DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

        datagramSocket.receive(packet); // it will block until data received
        
        System.out.println(new String(packet.getData()));

        datagramSocket.close();
    }
}

 

•  HttpURLConnection与服务器通信

　　　　GET 

　　　　

URL url = new URL("http://163.com");
        URLConnection conn = url.openConnection();
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(
                conn.getInputStream()));) {
            String line = null;
            while (null != (line = reader.readLine())) {
                System.out.println(line);
            }
        }

　　　　POST

conn.setDoOutput(true); // post
        PrintWriter writer = new PrintWriter(conn.getOutputStream()); //application/x-www-form-urlencoded 
        
        writer.close();

这里有个JarURLConnection类，用于获取jar包相关的信息：

//jar:<url>!/{entry} 
        String urlString = "jar:http://butterfly.jenkov.com/"
                + "container/download/"
                + "jenkov-butterfly-container-2.9.9-beta.jar!/";

        URL jarUrl = new URL(urlString);
        JarURLConnection connection = (JarURLConnection) jarUrl.openConnection();

        Manifest manifest = connection.getManifest();