Question

我正在尝试使用apache httpclient来加载带有缓存的图像。请求后保存文件，但重复相同的请求后，它开始再次下载，新文件保存为缓存。所以缓存的图像不能重复使用。而不是删除。

文件名仅因散列而异 1389449846612.0000000000000001-3f1e8b88.localhost.图像 - 产品 - 212250-7841874.jpg
1389449952782.0000000000000001-5720e341.localhost.图像品-212250-7841874.jpg

我想，即使没有连接到互联网，该图片也会被加载一次，并且能够显示缓存的图像。

这是我的代码

RequestConfig config = RequestConfig.custom()
                .setConnectTimeout(30000)
                .setSocketTimeout(30000)
                .setProxy(getProxy())
                .build();

CacheConfig cacheConfig = CacheConfig.custom()
        .build();

CloseableHttpClient client = CachingHttpClientBuilder.create()
        .setCacheDir(new File("/sdcard/Android/data/com.myapp/cache/"))
        .setCacheConfig(cacheConfig)
        .setDefaultRequestConfig(config)
        .build();

HttpGet request = new HttpGet(imageUri);
HttpCacheContext context = HttpCacheContext.create();
CloseableHttpResponse response = client.execute(request, context);

这是图像响应标题

Cache-Control:max-age=604800
Connection:keep-alive
Content-Length:449512
Content-Type:image/jpeg
Date:Sat, 11 Jan 2014 15:03:21 GMT
Expires:Sat, 18 Jan 2014 15:03:21 GMT
Last-Modified:Tue, 12 Jul 2011 19:40:44 GMT

Answer 1

第一个问题是我每次下载前都会创建新的httpclient，所以每次都创建了HttpCacheStorage的新实例，这就是文件名称不同的原因。其次，默认HttpCacheStorage只在LinkedHashMap中存储下载数据的信息，因此在每次新启动的app cacheStorage之后都不知道上次启动时的缓存数据。
解决方案是创建自己的HttpCacheStorage，它将缓存的数据保存到文件系统，并在从缓存中获取响应时从文件中获取数据。

我刚给CachingHttpClientBuilder添加了一行 - setHttpCacheStorage

CachingHttpClientBuilder.create()
                        .setCacheConfig(cacheConfig)
                        .setHttpCacheStorage(new ImagesCacheStorage(cacheConfig, cacheDir))
                        .setDefaultRequestConfig(config)
                        .build();

并创建了新类FileCacheStorage

import myapp.org.apache.http.client.cache.HttpCacheEntry;
import myapp.org.apache.http.client.cache.HttpCacheUpdateCallback;
import myapp.org.apache.http.impl.client.cache.CacheConfig;
import myapp.org.apache.http.impl.client.cache.ManagedHttpCacheStorage;

public class FileCacheStorage extends ManagedHttpCacheStorage {

    private File mCacheDir;

    public FileCacheStorage(final CacheConfig config, File cacheDir) {
        super(config);
        mCacheDir = cacheDir;
    }

    @Override
    public HttpCacheEntry getEntry(final String url) throws IOException {
        HttpCacheEntry entry = super.getEntry(url);
        if (entry == null) {
            entry = loadCacheEnrty(url);
        }
        return entry;
    }

    @Override
    public void putEntry(final String url, final HttpCacheEntry entry) throws IOException {
        super.putEntry(url, entry);
        saveCacheEntry(url, entry);
    }

    @Override
    public void removeEntry(final String url) throws IOException {
        super.removeEntry(url);
        File cache = getCacheFile(url);
        if (cache != null && cache.exists()) {
            cache.delete();
        }
    }

    @Override
    public void updateEntry(
            final String url,
            final HttpCacheUpdateCallback callback) throws IOException {
        super.updateEntry(url, callback);
        HttpCacheEntry entry = loadCacheEnrty(url);
        if (entry != null) {
            callback.update(entry);
        }
    }

    private void saveCacheEntry(String url, HttpCacheEntry entry) {
        ObjectOutputStream stream = null;
        try {
            File cache = getCacheFile(url);
            stream = new ObjectOutputStream(new FileOutputStream(cache));
            stream.writeObject(entry);
            stream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private HttpCacheEntry loadCacheEnrty(String url) {
        HttpCacheEntry entry = null;
        File cache = getCacheFile(url);
        if (cache != null && cache.exists()) {
            synchronized (this) {
                ObjectInputStream stream = null;
                try {
                    stream = new ObjectInputStream(new FileInputStream(cache));
                    entry = (HttpCacheEntry) stream.readObject();
                    stream.close();
                } catch (ClassNotFoundException e) {
                    e.printStackTrace();
                } catch (StreamCorruptedException e) {
                    e.printStackTrace();
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return entry;
    }

    private File getCacheFile(String url) {
        return new File(mCacheDir, MD5.getHash(url));
    }

}

正如您所看到的，Apache类的包名称带有前缀myapp。我试图使用原始jar文件时遇到错误，我认为这是因为许多类已经存在于Android中。所以我结合了几个来自apache的jar文件，并用它们制作了一个带有该前缀的jar。如果有人有更好的解决方案，请告诉我。希望它对某人有所帮助。

Httpclient没有正确缓存响应

1 个答案: