Java.net詳解

Java.net是Java平台提供的用於網路編程的API集合。它提供了在Java應用程序中實現網路連接和通信所需的基本組件和類。Java.net包含了一系列類，如Socket、ServerSocket、URL等，它們可以幫助我們實現網路編程。

一、Socket和ServerSocket

Socket類提供了一種機制，使得兩個進程之間可以進行通信。通過Socket類，可以建立一個客戶端到伺服器的連接。當Socket連接建立後，客戶端和伺服器之間可以發送和接收數據。

ServerSocket類是另一種重要的類，它允許我們創建一個服務端應用程序。服務端應用程序等待客戶端的請求，當有客戶端發起請求後，服務端就可以通過Socket對象與客戶端通信。下面是一個簡單的使用Socket和ServerSocket實現通信的示例代碼。

// 服務端程序
ServerSocket serverSocket = new ServerSocket(8080);
Socket socket = serverSocket.accept();
InputStream inputStream = socket.getInputStream();
OutputStream outputStream = socket.getOutputStream();
inputStream.read();
outputStream.write("Hello World".getBytes());
socket.close();
serverSocket.close();

// 客戶端程序
Socket socket = new Socket("localhost", 8080);
OutputStream outputStream = socket.getOutputStream();
InputStream inputStream = socket.getInputStream();
outputStream.write("Hello Server".getBytes());
inputStream.read();
socket.close();

二、URL和URLConnection

URL類表示一個統一資源定位器，在Java中，我們可以通過URL類來表示網路上的資源。URLConnection類可以通過URL來獲取網路資源的輸入流和輸出流，也可以設置網路連接的各種屬性。下面是一個簡單的URL和URLConnection的實例代碼。

URL url = new URL("http://www.baidu.com");
URLConnection urlConnection = url.openConnection();
InputStream inputStream = urlConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = bufferedReader.readLine()) != null) {
    System.out.println(line);
}
bufferedReader.close();
inputStream.close();

三、DatagramSocket

DatagramSocket類提供了面向數據包的UDP協議的通信功能。它可以用於實現廣播和多播等應用場景。下面是一個簡單的使用DatagramSocket實現UDP通信的示例代碼。

// 服務端程序
DatagramSocket serverSocket = new DatagramSocket(8080);
byte[] buffer = new byte[1024];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
serverSocket.receive(packet);
System.out.println(new String(packet.getData()));
serverSocket.close();

// 客戶端程序
DatagramSocket clientSocket = new DatagramSocket();
byte[] buffer = "Hello Server".getBytes();
InetAddress inetAddress = InetAddress.getByName("localhost");
DatagramPacket packet = new DatagramPacket(buffer, buffer.length, inetAddress, 8080);
clientSocket.send(packet);
clientSocket.close();

四、HttpURLConnection

HttpURLConnection類是URLConnection的子類，它提供了HTTP協議的HTTP/1.1支持。它可以用於實現HTTP客戶端，可以通過HTTP請求獲取HTTP響應。下面是一個簡單的使用HttpURLConnection實現HTTP通信的示例代碼。

// 發起HTTP GET請求
URL url = new URL("http://www.baidu.com");
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.setDoOutput(true);
StringBuilder responseBuilder = new StringBuilder();
BufferedReader reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
String line;
while ((line = reader.readLine()) != null) {
    responseBuilder.append(line);
}
urlConnection.disconnect();
reader.close();

// 發起HTTP POST請求
url = new URL("http://www.baidu.com");
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("POST");
urlConnection.setDoOutput(true);
OutputStreamWriter writer = new OutputStreamWriter(urlConnection.getOutputStream());
writer.write("Hello Server");
writer.flush();
reader = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
responseBuilder = new StringBuilder();
while ((line = reader.readLine()) != null) {
    responseBuilder.append(line);
}
urlConnection.disconnect();
reader.close();
writer.close();

五、SocketChannel和ServerSocketChannel

Java.net提供了使用NIO實現非阻塞I/O的類SocketChannel和ServerSocketChannel。它們可以用於實現高並發的網路編程應用場景。下面是一個簡單的使用SocketChannel和ServerSocketChannel實現非阻塞I/O的示例代碼。

// 服務端程序
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.socket().bind(new InetSocketAddress(8080));
serverSocketChannel.configureBlocking(false);
Selector selector = Selector.open();
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
while (true) {
    int readyChannels = selector.select();
    if (readyChannels == 0) {
        continue;
    }
    Set selectorKeys = selector.selectedKeys();
    Iterator iterator = selectorKeys.iterator();
    while (iterator.hasNext()) {
        SelectionKey selectionKey = iterator.next();
        if (selectionKey.isAcceptable()) {
            SocketChannel socketChannel = serverSocketChannel.accept();
            socketChannel.configureBlocking(false);
            socketChannel.register(selector, SelectionKey.OP_READ);
        } else if (selectionKey.isReadable()) {
            SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
            ByteBuffer buffer = ByteBuffer.allocate(1024);
            socketChannel.read(buffer);
            buffer.flip();
            socketChannel.write(buffer);
        }
        iterator.remove();
    }
}

// 客戶端程序
SocketChannel socketChannel = SocketChannel.open();
socketChannel.connect(new InetSocketAddress("localhost", 8080));
socketChannel.configureBlocking(false);
ByteBuffer buffer = ByteBuffer.wrap("Hello Server".getBytes());
while (buffer.hasRemaining()) {
    socketChannel.write(buffer);
}
buffer.clear();
socketChannel.read(buffer);
socketChannel.close();