volley，应该是Android开源框架中最简单的框架了，同时它也是最具有代表性的框架。如果你吃透了它，那么你看其他的开源框架也会容易很多。
先上图：
这里写图片描述
从上图中可以看出，Volley创建了RequestQueue，RequestQueue执行Cache和NetWork两个转发器，
最终执行ExecutorDelivery
下面一步一步开始分析
1.Volley执行newRequestQueue
public static RequestQueue newRequestQueue(Context context, HttpStack stack) {
File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);
.......
// 根据版本不同之行不同当网络请求
if (stack == null) {
if (Build.VERSION.SDK_INT >= 9) {
stack = new HurlStack();
} else {
stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));
}
}
Network network = new BasicNetwork(stack);
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
queue.start();
return queue;
}
RequestQueue里持有两个队列：一个是缓存队列，一个是网络队列
/** The cache triage queue. */
private final PriorityBlockingQueue> mCacheQueue =
new PriorityBlockingQueue>();
/** The queue of requests that are actually going out to the network. */
private final PriorityBlockingQueue> mNetworkQueue =
new PriorityBlockingQueue>();
Volley调用了start方法，创建了者两个队列，并同时执行
public void start() {
stop(); // Make sure any currently running dispatchers are stopped.
// Create the cache dispatcher and start it.
mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery);
mCacheDispatcher.start();
// Create network dispatchers (and corresponding threads) up to the pool size.
for (int i = 0; i < mDispatchers.length; i++) {
NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork,
mCache, mDelivery);
mDispatchers[i] = networkDispatcher;
networkDispatcher.start();
}
}
我们先看缓存转发器里主要做了什么
//首先它是继承Thread
CacheDispatcher extends Thread
在run方法里执行了：
一直在循环
while (true) {
try {
// Get a request from the cache triage queue, blocking until
// 不停的从Cache队列里取出请求
final Request request = mCacheQueue.take();
Cache.Entry entry = mCache.get(request.getCacheKey());
// 如果从缓存里取不到，则把他放到NetWork队列
if (entry == null) {
request.addMarker("cache-miss");
mNetworkQueue.put(request);
continue;
}
// 如果从缓存里取出则返回
request.addMarker("cache-hit");
Response response = request.parseNetworkResponse(
new NetworkResponse(entry.data, entry.responseHeaders));
request.addMarker("cache-hit-parsed");
if (!entry.refreshNeeded()) {
mDelivery.postResponse(request, response);
} else {
request.addMarker("cache-hit-refresh-needed");
request.setCacheEntry(entry);
// Mark the response as intermediate.
mDelivery.postResponse(request, response, new Runnable() {
@Override
public void run() {
try {
mNetworkQueue.put(request);
} catch (InterruptedException e) {
// Not much we can do about this.
}
}
});
}
NetWorkDispatch,实际就是发起请求返回结果
while (true) {
long startTimeMs = SystemClock.elapsedRealtime();
Request request;
try {
// Take a request from the queue.
request = mQueue.take();
} catch (InterruptedException e) {
// We may have been interrupted because it was time to quit.
if (mQuit) {
return;
}
continue;
}
try {
request.addMarker("network-queue-take");
// If the request was cancelled already, do not perform the
// network request.
if (request.isCanceled()) {
request.finish("network-discard-cancelled");
continue;
}
addTrafficStatsTag(request);
// Perform the network request.
NetworkResponse networkResponse = mNetwork.performRequest(request);
request.addMarker("network-http-complete");
// If the server returned 304 AND we delivered a response already,
// we're done -- don't deliver a second identical response.
if (networkResponse.notModified && request.hasHadResponseDelivered()) {
request.finish("not-modified");
continue;
}
// Parse the response here on the worker thread.
Response response = request.parseNetworkResponse(networkResponse);
request.addMarker("network-parse-complete");
// Write to cache if applicable.
// TODO: Only update cache metadata instead of entire record for 304s.
if (request.shouldCache() && response.cacheEntry != null) {
mCache.put(request.getCacheKey(), response.cacheEntry);
request.addMarker("network-cache-written");
}
// Post the response back.
request.markDelivered();
mDelivery.postResponse(request, response);
从上面两个Dispatcher中最后都由mDelivery. postResponse
那么它是什么尼？
mDelivery ＝ new ExecutorDelivery(new Handler(Looper.getMainLooper()))
mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, runnable));
private class ResponseDeliveryRunnable implements Runnable {
private final Request mRequest;
private final Response mResponse;
private final Runnable mRunnable;
public ResponseDeliveryRunnable(Request request, Response response, Runnable runnable) {
mRequest = request;
mResponse = response;
mRunnable = runnable;
}
@SuppressWarnings("unchecked")
@Override
public void run() {
// 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();
}
}
}