Volley源码分析 （三）：如何分发结果

首先是将请求组装成NetWorkResponse，这里有两种情况，一种是经过网络请求的，一种是取得缓存的，最后统一经过ExecutorDelively。

首先是网络请求：

longrequestStart = SystemClock.elapsedRealtime();
while ( true) {
    HttpResponse httpResponse = null;
    byte[] responseContents =null;
    Map<String , String> responseHeaders =newHashMap<String,String>();
    try {
        // Gather headers.
        Map<String , String> headers = new HashMap<String , String>();
        addCacheHeaders(headers,request.getCacheEntry());
        httpResponse = mHttpStack .performRequest(request,headers);
        StatusLine statusLine = httpResponse.getStatusLine();
        int statusCode = statusLine.getStatusCode();

        responseHeaders = convertHeaders(httpResponse.getAllHeaders());
        // Handle cache validation.
        if (statusCode == HttpStatus.SC_NOT_MODIFIED) {
            return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED,
                    request.getCacheEntry().data,responseHeaders, true);
        }

        // Some responses such as 204s do not have content.  We must check.
        if (httpResponse.getEntity() !=null) {
          responseContents = entityToBytes(httpResponse.getEntity());
        } else {
          // Add 0 byte response as a way of honestly representing a
          // no-content request.
          responseContents =new byte[0];
        }

        // if the request is slow, log it.
        long requestLifetime = SystemClock.elapsedRealtime() - requestStart;
        logSlowRequests(requestLifetime,request,responseContents,statusLine);

        if (statusCode < 200 || statusCode > 299 ) {
            throw new IOException();
        }

       return newNetworkResponse(statusCode,responseContents,responseHeaders, false );

如果没有修改就传入request的缓存，否则就取response的内容来组成NetWorkResponse;

如果是缓存的就直接在CacheDispather:

request.addMarker("cache-hit");
Response<?> response = request.parseNetworkResponse(
        new NetworkResponse(entry.data,entry.responseHeaders));

request.addMarker("cache-hit-parsed");

最后是分发：

// If this request has canceled, finish it and don't deliver.
if(mRequest.isCanceled()) {
    mRequest .finish("canceled-at-delivery");
    return;
}

// Deliver a normal response or error, depending.
if(mResponse.isSuccess()) {
    mRequest .deliverResponse(mResponse.result);
}else{
    mRequest .deliverError(mResponse.error);
}

// If this is an intermediate response, add a marker, otherwise we're done
// and the request can be finished.
if(mResponse.intermediate) {
    mRequest .addMarker("intermediate-response");
}else{
    mRequest .finish("done");
}

// If we have been provided a post-delivery runnable, run it.
if(mRunnable!=null) {
    mRunnable .run();

}

如果请求取消了就直接finish，如果成功了，就交给自己重写的listener，如果是需要再请求的，用于这个请求是不需要立即刷新，但可以立即返回缓存结果，之后再刷新的。这也是上篇讲的内容。