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