java—网络编程TCP和UDP
1. Java 网络编程概述
Java 网络编程是通过 java.net 包实现的，Socket 类是用来进行客户端与服务器通信的主要类。服务器端通过 ServerSocket 类来监听客户端的请求，客户端则通过 Socket 类来连接服务器。
2. TCP 网络编程示例
在 TCP 通信中，数据传输是可靠的，确保了数据的顺序和完整性。以下是一个简单的客户端和服务器应用，其中服务器端监听指定端口，客户端向服务器发送消息并接收响应。
2.1 TCP 服务器端
import java.io.*;
import java.net.*;
public class TCPServer {
public static void main(String[] args) {
try {
// 创建ServerSocket对象，监听端口12345
ServerSocket serverSocket = new ServerSocket(12345);
System.out.println("Server is listening on port 12345...");
while (true) {
// 等待客户端连接
Socket clientSocket = serverSocket.accept();
System.out.println("New client connected: " + clientSocket.getInetAddress());
// 创建线程来处理客户端请求
Thread clientThread = new Thread(new ClientHandler(clientSocket));
clientThread.start();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
class ClientHandler implements Runnable {
private Socket clientSocket;
public ClientHandler(Socket socket) {
this.clientSocket = socket;
}
@Override
public void run() {
try {
// 获取客户端输入和输出流
BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
// 读取客户端发送的消息
String message = in.readLine();
System.out.println("Received from client: " + message);
// 发送响应给客户端
out.println("Hello from server!");
// 关闭连接
clientSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
2.2 TCP 客户端
import java.io.*;
import java.net.*;
public class TCPClient {
public static void main(String[] args) {
try {
// 创建Socket对象连接到服务器
Socket socket = new Socket("localhost", 12345);
System.out.println("Connected to the server");
// 获取输入输出流
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
// 向服务器发送消息
out.println("Hello from client!");
// 接收服务器响应
String response = in.readLine();
System.out.println("Received from server: " + response);
// 关闭连接
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
运行步骤：
- 先启动
TCPServer，它将监听端口 12345。 - 然后启动
TCPClient，它将连接到服务器并发送消息。
输出示例：
-
服务器端：
Server is listening on port 12345... New client connected: /127.0.0.1 Received from client: Hello from client!
-
客户端：
Connected to the server Received from server: Hello from server!
3. UDP 网络编程示例
UDP 是一种无连接、不保证可靠性的协议，适用于实时性要求高，但对数据丢失不敏感的场景（如视频流、在线游戏等）。
3.1 UDP 服务器端
import java.net.*;
public class UDPServer {
public static void main(String[] args) {
try {
// 创建UDP服务器端套接字
DatagramSocket serverSocket = new DatagramSocket(12345);
System.out.println("UDP Server is listening on port 12345...");
byte[] receiveData = new byte[1024];
while (true) {
// 创建数据报包来接收客户端消息
DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
// 获取客户端地址和数据
String clientMessage = new String(receivePacket.getData(), 0, receivePacket.getLength());
System.out.println("Received from client: " + clientMessage);
// 发送响应给客户端
InetAddress clientAddress = receivePacket.getAddress();
int clientPort = receivePacket.getPort();
String responseMessage = "Hello from UDP server!";
DatagramPacket sendPacket = new DatagramPacket(responseMessage.getBytes(), responseMessage.length(), clientAddress, clientPort);
serverSocket.send(sendPacket);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
3.2 UDP 客户端
import java.net.*;
public class UDPClient {
public static void main(String[] args) {
try {
// 创建UDP客户端套接字
DatagramSocket clientSocket = new DatagramSocket();
InetAddress serverAddress = InetAddress.getByName("localhost");// 发送消息给服务器
String message = "Hello from UDP client!";
DatagramPacket sendPacket = new DatagramPacket(message.getBytes(), message.length(), serverAddress, 12345);
clientSocket.send(sendPacket);// 接收服务器的响应
byte[] receiveData = new byte[1024];
DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
clientSocket.receive(receivePacket);// 显示服务器响应
String response = new String(receivePacket.getData(), 0, receivePacket.getLength());
System.out.println("Received from server: " + response);// 关闭客户端套接字
clientSocket.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
运行步骤：
- 先启动
UDPServer，它将监听端口 12345。 - 然后启动
UDPClient，它将向服务器发送消息并接收响应。
输出示例：
-
服务器端：
UDP Server is listening on port 12345... Received from client: Hello from UDP client!
-
客户端：
Received from server: Hello from UDP server!
4. 多线程和线程池示例
为了处理多个客户端的连接，可以使用 多线程 来为每个客户端创建独立的处理线程。此外，使用 线程池 可以有效地管理线程，提高服务器的性能。
4.1 使用线程池管理客户端请求
（1）线程池版的 TCP 服务器：
import java.io.*;
import java.net.*;
import java.util.concurrent.*;
public class ThreadPoolTCPServer {
private static final int PORT = 12345;
public static void main(String[] args) {
try {
// 创建线程池
ExecutorService threadPool = Executors.newFixedThreadPool(10);
// 创建ServerSocket并监听端口
ServerSocket serverSocket = new ServerSocket(PORT);
System.out.println("Server is listening on port " + PORT);
while (true) {
// 接受客户端连接
Socket clientSocket = serverSocket.accept();
System.out.println("New client connected: " + clientSocket.getInetAddress());
// 将客户端连接交给线程池处理
threadPool.submit(new ClientHandler(clientSocket));
}
} catch (IOException e) {
e.printStackTrace();
}
}
static class ClientHandler implements Runnable {
private Socket clientSocket;
public ClientHandler(Socket socket) {
this.clientSocket = socket;
}
@Override
public void run() {
try {
// 获取输入输出流
BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
// 处理客户端请求
String message = in.readLine();
System.out.println("Received from client: " + message);
out.println("Hello from server!");
// 关闭连接
clientSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
多线程和线程池的优势：
- 使用 线程池 可以避免频繁创建和销毁线程，从而提升性能。
- 每个客户端连接都会分配一个线程，线程池确保了线程的复用。
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