如何用Java实现简单CDN缓存机制 Java设置请求缓存策略示例

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SimpleCacheFilter implements Filter {

    private static final Map<String, CachedResponse> cache = new HashMap<>();

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // 初始化操作，可以读取配置文件等
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        String url = httpRequest.getRequestURL().toString();

        // 检查缓存
        CachedResponse cachedResponse = cache.get(url);

        if (cachedResponse != null && !isExpired(cachedResponse)) {
            // 缓存命中
            System.out.println("Cache hit for URL: " + url);
            cachedResponse.applyTo(httpResponse);
        } else {
            // 缓存未命中或已过期
            System.out.println("Cache miss for URL: " + url);

            // 创建一个包装的响应对象
            ResponseWrapper responseWrapper = new ResponseWrapper(httpResponse);

            // 执行请求链
            chain.doFilter(request, responseWrapper);

            // 将响应内容存入缓存
            byte[] content = responseWrapper.getContent();
            String contentType = responseWrapper.getContentType();
            if (content != null && contentType != null) {
                cache.put(url, new CachedResponse(content, contentType, System.currentTimeMillis()));
            }

            // 将响应内容返回给客户端
            responseWrapper.copyTo(httpResponse);
        }
    }

    private boolean isExpired(CachedResponse cachedResponse) {
        // 缓存过期时间，例如 10 秒
        long expirationTime = 10 * 1000;
        return (System.currentTimeMillis() - cachedResponse.getTimestamp()) > expirationTime;
    }


    @Override
    public void destroy() {
        // 销毁操作，释放资源
    }

    // 内部类，用于包装响应内容
    private static class ResponseWrapper {
        private HttpServletResponse response;
        private byte[] content;
        private String contentType;

        public ResponseWrapper(HttpServletResponse response) {
            this.response = response;
        }

        public byte[] getContent() {
            return content;
        }

        public String getContentType() {
            return contentType;
        }

        public void setContent(byte[] content, String contentType) {
            this.content = content;
            this.contentType = contentType;
        }

        public void copyTo(HttpServletResponse response) throws IOException {
            if (content != null) {
                response.setContentType(contentType);
                response.setContentLength(content.length);
                response.getOutputStream().write(content);
            }
        }
    }

    // 内部类，用于存储缓存的响应
    private static class CachedResponse {
        private byte[] content;
        private String contentType;
        private long timestamp;

        public CachedResponse(byte[] content, String contentType, long timestamp) {
            this.content = content;
            this.contentType = contentType;
            this.timestamp = timestamp;
        }

        public byte[] getContent() {
            return content;
        }

        public String getContentType() {
            return contentType;
        }

        public long getTimestamp() {
            return timestamp;
        }

        public void applyTo(HttpServletResponse response) throws IOException {
            response.setContentType(contentType);
            response.setContentLength(content.length);
            response.getOutputStream().write(content);
        }
    }
}

HttpServletResponse response = (HttpServletResponse) servletResponse;
response.setHeader("Cache-Control", "public, max-age=3600");
response.setDateHeader("Expires", System.currentTimeMillis() + (3600 * 1000)); // 设置1小时后过期