你能给我代码实例吗

当然可以，以下是一个简单的Web缓存程序的Java代码实例：

import java.io.*;
import java.net.*;

public class WebCacheServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        System.out.println("Web Cache Server is running on port 8080...");

        while (true) {
            Socket clientSocket = serverSocket.accept();
            System.out.println("Client connected: " + clientSocket.getInetAddress().getHostAddress());

            BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            String requestLine = in.readLine();
            String[] tokens = requestLine.split("\\s+");
            String method = tokens[0];
            String url = tokens[1];
            String version = tokens[2];

            if (method.equals("GET")) {
                System.out.println("Request: " + url);
                File cacheFile = new File("cache/" + url.replace("/", "_"));

                if (cacheFile.exists() && !isCacheExpired(cacheFile)) {
                    System.out.println("Cache hit: " + url);
                    sendResponse(clientSocket, new FileInputStream(cacheFile));
                } else {
                    System.out.println("Cache miss: " + url);
                    URL remote = new URL(url);
                    HttpURLConnection remoteConn = (HttpURLConnection) remote.openConnection();
                    sendResponse(clientSocket, remoteConn.getInputStream());
                    saveToCache(remoteConn.getInputStream(), cacheFile);
                }
            }

            clientSocket.close();
        }
    }

    private static void saveToCache(InputStream inputStream, File cacheFile) throws IOException {
        OutputStream outputStream = new FileOutputStream(cacheFile);
        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
        }
        outputStream.close();
    }

    private static boolean isCacheExpired(File cacheFile) {
        return (System.currentTimeMillis() - cacheFile.lastModified()) > 86400000; // 1 day
    }

    private static void sendResponse(Socket clientSocket, InputStream inputStream) throws IOException {
        OutputStream outputStream = clientSocket.getOutputStream();
        outputStream.write("HTTP/1.1 200 OK\r\n".getBytes());
        outputStream.write("Content-Type: text/html\r\n".getBytes());
        outputStream.write("\r\n".getBytes());
        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
        }
        inputStream.close();
        outputStream.close();
    }
}

这个程序实现了一个简单的Web缓存服务器，监听8080端口，当客户端发送GET请求时，会先检查是否有该网页的缓存副本，如果有，则直接从缓存中返回数据；如果没有，则向目标网站发出请求，获取数据，并将数据保存到缓存中。程序中缓存的过期时间为1天。你可以根据需要修改程序中的缓存路径、缓存过期时间等参数。