java - 无法在 Java 中使用 cachingHttpClient 缓存 HttpResponse？

Question

我尝试使用 cachingHttpClient 来缓存 HTTP 响应，但没有成功。这是我引用此链接整理的演示，http://hc.apache.org/httpcomponents-client-ga/tutorial/html/caching.html

  public class CacheDemo {

    public static void main(String[] args) {
        CacheConfig cacheConfig = new CacheConfig();
        cacheConfig.setMaxCacheEntries(1000);
        cacheConfig.setMaxObjectSizeBytes(1024 * 1024);

        HttpClient cachingClient = new CachingHttpClient(new DefaultHttpClient(), cacheConfig);

        HttpContext localContext = new BasicHttpContext();

        sendRequest(cachingClient, localContext);
        CacheResponseStatus responseStatus = (CacheResponseStatus) localContext.getAttribute(
                CachingHttpClient.CACHE_RESPONSE_STATUS);
        checkResponse(responseStatus);


        sendRequest(cachingClient, localContext);
        responseStatus = (CacheResponseStatus) localContext.getAttribute(
                CachingHttpClient.CACHE_RESPONSE_STATUS);
        checkResponse(responseStatus);
    }

    static void sendRequest(HttpClient cachingClient, HttpContext localContext) {
        HttpGet httpget = new HttpGet("http://www.mydomain.com/content/");
        HttpResponse response = null;
        try {
            response = cachingClient.execute(httpget, localContext);
        } catch (ClientProtocolException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
        HttpEntity entity = response.getEntity();
        try {
            EntityUtils.consume(entity);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    static void checkResponse(CacheResponseStatus responseStatus) {
        switch (responseStatus) {
            case CACHE_HIT:
                System.out.println("A response was generated from the cache with no requests "
                        + "sent upstream");
                break;
            case CACHE_MODULE_RESPONSE:
                System.out.println("The response was generated directly by the caching module");
                break;
            case CACHE_MISS:
                System.out.println("The response came from an upstream server");
                break;
            case VALIDATED:
                System.out.println("The response was generated from the cache after validating "
                        + "the entry with the origin server");
                break;
        }
    }

  }

这是一个简单的程序，但我不知道哪里出错了。您的帮助将不胜感激。谢谢。

Answer 1

带有 url http://www.mydomain.com/content/ 的 GET 请求将以 Http 404 代码(未找到)结束。此结果很可能无法缓存，所以我猜这就是它对您不起作用的原因。

更新:必须满足某些条件才能提供来自缓存的响应。您应该启用 apache http 客户端的日志记录(例如 http://hc.apache.org/httpclient-3.x/logging.html )。比您可以调试正在发生的事情以及为什么其他 URL 缓存未命中。您可能还应该下载该库的源代码并在那里查看 (http://hc.apache.org/downloads.cgi)。您尤其会对 org.apache.http.impl.client.cache.CachedResponseSuitabilityChecker 类感兴趣。这也应该有助于您使用库进行后续开发。

顺便说一句。 http://muvireviews.com/celebrity/full_view/41/Shahrukh-khan返回此 header :

Cache-Control:no-store, no-cache, must-revalidate, post-check=0, pre-check=0, max-age=0, no-cache, no-store

并且由于 CachedResponseSuitabilityChecker 中的 if 语句:

            if (HeaderConstants.CACHE_CONTROL_NO_CACHE.equals(elt.getName())) {
                log.trace("Response contained NO CACHE directive, cache was not suitable");
                return false;
            }

不会使用缓存。

祝你好运;)