Picasso加载网络图片失败，提示decodestream时返回null

最近遇到一个问题，项目用的图片加载框架是Picasso，网络加载框架是okhttp，项目在加载轮播图时有时可以正常加载，有时，会加载失败，提示decodestream时返回null。

首先，需要确定是哪个环节出了问题。

网上搜了很多关于“decodestream时返回null”的问题，都说需要在decodestream之前reset stream。不过，由于用的是Picasso，不太方便改代码，再换个思路看一下。

要确认是否是Picasso的问题，那我就用其他图片加载框架替换Picasso，这里，我使用Glide替换Picasso。

替换之后，运行程序，图片加载没有任何问题。

由此，可以确认，问题出在Picasso身上。

于是，我又在网上搜索关于Picasso的这类问题，在百度上，完全没有类似问题，google上倒是可以找到几个类似问题，百度在这方面还需要加油啊。。。

google上搜到的都是GitHub上Picasso使用者提的issue，这里也是说是decodestream调用两次的问题。

于是我查看源码：

 static Bitmap decodeStream(InputStream stream, Request request) throws IOException {
    MarkableInputStream markStream = new MarkableInputStream(stream);
    stream = markStream;

    long mark = markStream.savePosition(65536); // TODO fix this crap.

    final BitmapFactory.Options options = RequestHandler.createBitmapOptions(request);
    final boolean calculateSize = RequestHandler.requiresInSampleSize(options);

    boolean isWebPFile = Utils.isWebPFile(stream);
    markStream.reset(mark);
    // When decode WebP network stream, BitmapFactory throw JNI Exception and make app crash.
    // Decode byte array instead
    if (isWebPFile) {
      byte[] bytes = Utils.toByteArray(stream);
      if (calculateSize) {
        BitmapFactory.decodeByteArray(bytes, 0, bytes.length, options);
        RequestHandler.calculateInSampleSize(request.targetWidth, request.targetHeight, options,
            request);
      }
      return BitmapFactory.decodeByteArray(bytes, 0, bytes.length, options);
    } else {
      if (calculateSize) {
        BitmapFactory.decodeStream(stream, null, options);
        RequestHandler.calculateInSampleSize(request.targetWidth, request.targetHeight, options,
            request);

        markStream.reset(mark);
      }
      Bitmap bitmap = BitmapFactory.decodeStream(stream, null, options);
      if (bitmap == null) {
        // Treat null as an IO exception, we will eventually retry.
        throw new IOException("Failed to decode stream.");
      }
      return bitmap;
    }
  }

View Code

并定位到这个地方，进行单步调试，发现decodestream确实调用了两次，但是，jack已经进行了reset操作。这个地方不应该会出现问题。

继续找资料，在Github找到一个解决方案：在url后面加上“？”+System.currentTimeMillis()。

url加时间戳后每次都从网络下载图片，没加的话会从缓存中加载图片。

.memoryPolicy(MemoryPolicy.NO_CACHE)
.networkPolicy(NetworkPolicy.NO_CACHE)

再次调试，发现可以正常加载图片。
由此可以确定：是缓存问题导致加载图片失败。
嗯，接下去该自定义缓存试一下了。
再次到网上搜索资料（爱分享的程序员/媛就是这么招人喜欢）
参考http://www.jianshu.com/p/6241950f9daf写了个自定义缓存。
贴几处关键代码：

OkHttpClient client = new OkHttpClient .Builder() .cache(new Cache(BaseApplication.getContext().getCacheDir(), 1000 * 1024)) .addInterceptor(new CaheInterceptor(BaseApplication.getContext())) .addNetworkInterceptor(new CaheInterceptor(BaseApplication.getContext())) .build(); mPicasso = new Picasso.Builder(BaseApplication.getContext()) .downloader(new ImageDownLoader(client)) .build(); mPicasso.with(BaseApplication.getContext()).setIndicatorsEnabled(true);//左上角标出颜色，红色为从网络获取，绿色为从内存中获取，蓝色为从硬盘中获取

public class ImageDownLoader implements Downloader { OkHttpClient client = null; public ImageDownLoader(OkHttpClient client) { this.client = client; } @Override public Response load(Uri uri, int networkPolicy) throws IOException { CacheControl cacheControl = null; if (networkPolicy != 0) { if (NetworkPolicy.isOfflineOnly(networkPolicy)) { cacheControl = CacheControl.FORCE_CACHE; } else { CacheControl.Builder builder = new CacheControl.Builder(); if (!NetworkPolicy.shouldReadFromDiskCache(networkPolicy)) { builder.noCache(); } if (!NetworkPolicy.shouldWriteToDiskCache(networkPolicy)) { builder.noStore(); } cacheControl = builder.build(); } } Request.Builder builder = new Request.Builder().url(uri.toString()); if (cacheControl != null) { builder.cacheControl(cacheControl); } okhttp3.Response response = client.newCall(builder.build()).execute(); int responseCode = response.code(); if (responseCode >= 300) { response.body().close(); throw new ResponseException(responseCode + " " + response.message(), networkPolicy, responseCode); } boolean fromCache = response.cacheResponse() != null; ResponseBody responseBody = response.body(); return new Response(responseBody.byteStream(), fromCache, responseBody.contentLength()); } @Override public void shutdown() { Cache cache = client.cache(); if (cache != null) { try { cache.close(); } catch (IOException ignored) { } } } }

public class CaheInterceptor implements Interceptor { private Context context; public CaheInterceptor(Context context) { this.context = context; } @Override public Response intercept(Chain chain) throws IOException { Request request = chain.request(); if (NetStateUtil.isNetworkAvailable(context)) { Response response = chain.proceed(request); // read from cache for 60 s int maxAge = 300; String cacheControl = request.cacheControl().toString(); Log.e("Tamic", maxAge + "s load cahe:" + cacheControl); return response.newBuilder() .removeHeader("Pragma") .removeHeader("Cache-Control") .header("Cache-Control", "public, max-age=" + maxAge) .build(); } else { Log.e("Tamic", " no network load cahe"); request = request.newBuilder() .cacheControl(CacheControl.FORCE_CACHE) .build(); Response response = chain.proceed(request); //set cahe times is 3 days int maxStale = 60 * 60 * 24 * 3; return response.newBuilder() .removeHeader("Pragma") .removeHeader("Cache-Control") .header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale) .build(); } } }

Picasso加载网络图片失败，提示decodestream时返回null

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