Volley原始碼分析(三)
1.Volley原始碼分析(一)
2.Volley原始碼分析(二)
3.Volley原始碼分析(三)
4.XVolley-基於Volley的封裝的工具類
上一篇分析完了RequestQueue的大部分方法,add執行完後,Volley就會執行執行緒操作了,在第一篇部落格中提到,star方法執行時會建立1個快取執行緒(CacheDispatcher)和4個網路執行緒(NetworkDispatcher),並開始這5個執行緒。這裡我們就先看快取執行緒。
public class CacheDispatcher extends Thread {
private static final boolean DEBUG = VolleyLog.DEBUG;
/** The queue of requests coming in for triage. */
private final BlockingQueue<Request<?>> mCacheQueue;
/** The queue of requests going out to the network. */
private final BlockingQueue<Request<?>> mNetworkQueue;
/** The cache to read from. */
private final Cache mCache;
/** For posting responses. */
private final ResponseDelivery mDelivery;
/** Used for telling us to die. */
private volatile boolean mQuit = false;
/**
* Creates a new cache triage dispatcher thread. You must call {@link #start()}
* in order to begin processing.
*
* @param cacheQueue Queue of incoming requests for triage
* @param networkQueue Queue to post requests that require network to
* @param cache Cache interface to use for resolution
* @param delivery Delivery interface to use for posting responses
*/
public CacheDispatcher(
BlockingQueue<Request<?>> cacheQueue, BlockingQueue<Request<?>> networkQueue,
Cache cache, ResponseDelivery delivery) {
mCacheQueue = cacheQueue;
mNetworkQueue = networkQueue;
mCache = cache;
mDelivery = delivery;
}
/**
* Forces this dispatcher to quit immediately. If any requests are still in
* the queue, they are not guaranteed to be processed.
*/
public void quit() {
mQuit = true;
interrupt();
}
@Override
public void run() {
if (DEBUG) VolleyLog.v("start new dispatcher");
//設定快取執行緒的優先順序
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
// Make a blocking call to initialize the cache.
//初始化快取內容,對應的硬碟快取-DiskBasedCache
mCache.initialize();
while (true) {
try {
// Get a request from the cache triage queue, blocking until
// at least one is available.
//BlockingQueue的take方法,取出佇列中隊首的request,如果沒有則阻塞,等待到有request到來
final Request<?> request = mCacheQueue.take();
request.addMarker("cache-queue-take");
// If the request has been canceled, don't bother dispatching it.
//如果request被取消,則結束當前這次,繼續迴圈
if (request.isCanceled()) {
request.finish("cache-discard-canceled");
continue;
}
// Attempt to retrieve this item from cache.
Cache.Entry entry = mCache.get(request.getCacheKey());
//如果快取裡沒有,則加入請求佇列
if (entry == null) {
request.addMarker("cache-miss");
// Cache miss; send off to the network dispatcher.
mNetworkQueue.put(request);
continue;
}
// If it is completely expired, just send it to the network.
//如果快取過期了,則加入請求佇列
if (entry.isExpired()) {
request.addMarker("cache-hit-expired");
request.setCacheEntry(entry);
mNetworkQueue.put(request);
continue;
}
// We have a cache hit; parse its data for delivery back to the request.
//快取中存在並且沒有過期
request.addMarker("cache-hit");
//將資料包裝成response
Response<?> response = request.parseNetworkResponse(
new NetworkResponse(entry.data, entry.responseHeaders));
request.addMarker("cache-hit-parsed");
if (!entry.refreshNeeded()) {
// Completely unexpired cache hit. Just deliver the response.
//如果快取不需要重新整理,則直接將快取回傳
mDelivery.postResponse(request, response);
} else {
// Soft-expired cache hit. We can deliver the cached response,
// but we need to also send the request to the network for
// refreshing.
request.addMarker("cache-hit-refresh-needed");
request.setCacheEntry(entry);
// Mark the response as intermediate.
response.intermediate = true;
// Post the intermediate response back to the user and have
// the delivery then forward the request along to the network.
//快取需要重新整理的話,先將快取傳回給客戶,然後在將請求交給佇列
mDelivery.postResponse(request, response, new Runnable() {
@Override
public void run() {
try {
mNetworkQueue.put(request);
} catch (InterruptedException e) {
// Not much we can do about this.
}
}
});
}
} catch (InterruptedException e) {
// We may have been interrupted because it was time to quit.
if (mQuit) {
return;
}
}
}
}
}
首先從繼承關係我們就可以看出,建立的是個執行緒。既然是個執行緒,無可厚非,肯定是看它的run方法,從原始碼我們也可以看出,這裡面除了構造方法就兩個方法,quit和run,quit就不用說了,這裡重點看一下run方法。
可以看到第51行先設定了當前執行緒的優先順序,保證執行緒的順利進行。
第55行,初始化了快取,這裡要說明一下,Volley現在預設使用的是硬碟快取,這一點從初始化requestqueue時就可以看出來。
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
後面可以看到,是個死迴圈,保證快取執行緒一直執行。
第62行,可以看到從mCacheQueue.take取出請求。這裡說明一下:
mCacheQueue是一個BlockingQueue,它的take方法,取出佇列中隊首的request,如果沒有則阻塞,等待到有request到來
下面就是幾種情況的判斷:
1)如果該請求被取消——————->結束當前這次迴圈
2)如果快取中不存在這個請求————>結束當前這次迴圈,並將請求加入網路請求佇列
3)如果快取過期了———————>結束當前這次迴圈,並將請求加入網路請求佇列
當以上幾種情況都不存在時,第95行,便要將快取中這個request對應的請求結果封裝成response
後面這個判斷很奇妙,我一開始半天沒理解,後來才懂了
這裡判斷快取是否需要重新整理,如果快取不需要重新整理,則將response回撥給UI執行緒,如果需要重新整理,同樣先將response回撥給UI執行緒,然後再將這個請求放入網路佇列,進行請求並重新整理快取
快取執行緒到這裡基本上就看完了,現在來看網路執行緒
NetworkDispatcher。
public class NetworkDispatcher extends Thread {
/** The queue of requests to service. */
private final BlockingQueue<Request<?>> mQueue;
/** The network interface for processing requests. */
private final Network mNetwork;
/** The cache to write to. */
private final Cache mCache;
/** For posting responses and errors. */
private final ResponseDelivery mDelivery;
/** Used for telling us to die. */
private volatile boolean mQuit = false;
/**
* Creates a new network dispatcher thread. You must call {@link #start()}
* in order to begin processing.
*
* @param queue Queue of incoming requests for triage
* @param network Network interface to use for performing requests
* @param cache Cache interface to use for writing responses to cache
* @param delivery Delivery interface to use for posting responses
*/
public NetworkDispatcher(BlockingQueue<Request<?>> queue,
Network network, Cache cache,
ResponseDelivery delivery) {
mQueue = queue;
mNetwork = network;
mCache = cache;
mDelivery = delivery;
}
/**
* Forces this dispatcher to quit immediately. If any requests are still in
* the queue, they are not guaranteed to be processed.
*/
public void quit() {
mQuit = true;
interrupt();
}
@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)
private void addTrafficStatsTag(Request<?> request) {
// Tag the request (if API >= 14)
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
TrafficStats.setThreadStatsTag(request.getTrafficStatsTag());
}
}
@Override
public void run() {
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
while (true) {
//記錄開始時間
long startTimeMs = SystemClock.elapsedRealtime();
Request<?> request;
try {
// Take a request from the queue.
//從隊首拿一個請求
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.
//如果被取消則結束當前這次迴圈
if (request.isCanceled()) {
request.finish("network-discard-cancelled");
continue;
}
//新增流量統計標籤
addTrafficStatsTag(request);
// Perform the network request.
//此處執行網路請求
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.
//如果伺服器返回的304或者request已經存在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.
//設定request已經返回response
request.markDelivered();
mDelivery.postResponse(request, response);
} catch (VolleyError volleyError) {
volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
parseAndDeliverNetworkError(request, volleyError);
} catch (Exception e) {
VolleyLog.e(e, "Unhandled exception %s", e.toString());
VolleyError volleyError = new VolleyError(e);
volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
mDelivery.postError(request, volleyError);
}
}
}
private void parseAndDeliverNetworkError(Request<?> request, VolleyError error) {
error = request.parseNetworkError(error);
mDelivery.postError(request, error);
}
}
同樣,這裡重點看run方法。
和快取執行緒一樣,這裡先設定了執行緒的優先順序,保證執行緒的進行,並且利用死迴圈,使執行緒一直進行,不會被回收。
第58行,首先從隊首拿了一個請求。
第61行,這裡就是java常用的中斷執行緒的方式。
第73行,如果請求被取消的話,則結束當前這次迴圈。
這裡重點說明,第82行,這裡就是我們整個Volley真正執行網路請求的地方。
NetworkResponse networkResponse = mNetwork.performRequest(request);
可以看到,這裡request被當做引數傳入,最後返回了一個response。而方法是屬於mNetwork,這個mNetwork是在volley初始化requestqueue時傳入的。
/**
* 建立一個網路請求
*/
Network network = new BasicNetwork(stack);
/**
* 這裡每次都會建立一個請求佇列,可以優化,只建立一個全域性佇列嗎
*/
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
還記得這裡嗎,第一篇部落格的時候說過,後面會介紹這個Network,這裡就很好理解了,這個mNetwork就是在這裡傳入,真正執行網路請求就是在這個類中,而這個類的建構函式需要我們傳入一個HttpStack物件,這裡就是我們最開始說版本判斷策略模式那裡。這裡我們可以進入BasicNetwork類中,看一下performRequest方法,來驗證我們的想法。
@Override
public NetworkResponse performRequest(Request<?> request) throws VolleyError {
long requestStart = SystemClock.elapsedRealtime();
while (true) {
HttpResponse httpResponse = null;
byte[] responseContents = null;
Map<String, String> responseHeaders = Collections.emptyMap();
try {
// Gather headers.
Map<String, String> headers = new HashMap<String, String>();
addCacheHeaders(headers, request.getCacheEntry());
//執行網路請求
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) {
Entry entry = request.getCacheEntry();
if (entry == null) {
return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, null,
responseHeaders, true,
SystemClock.elapsedRealtime() - requestStart);
}
// A HTTP 304 response does not have all header fields. We
// have to use the header fields from the cache entry plus
// the new ones from the response.
// http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5
entry.responseHeaders.putAll(responseHeaders);
return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, entry.data,
entry.responseHeaders, true,
SystemClock.elapsedRealtime() - requestStart);
}
// 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 new NetworkResponse(statusCode, responseContents, responseHeaders, false,
SystemClock.elapsedRealtime() - requestStart);
} catch (SocketTimeoutException e) {
attemptRetryOnException("socket", request, new TimeoutError());
} catch (ConnectTimeoutException e) {
attemptRetryOnException("connection", request, new TimeoutError());
} catch (MalformedURLException e) {
throw new RuntimeException("Bad URL " + request.getUrl(), e);
} catch (IOException e) {
int statusCode;
if (httpResponse != null) {
statusCode = httpResponse.getStatusLine().getStatusCode();
} else {
throw new NoConnectionError(e);
}
VolleyLog.e("Unexpected response code %d for %s", statusCode, request.getUrl());
NetworkResponse networkResponse;
if (responseContents != null) {
networkResponse = new NetworkResponse(statusCode, responseContents,
responseHeaders, false, SystemClock.elapsedRealtime() - requestStart);
if (statusCode == HttpStatus.SC_UNAUTHORIZED ||
statusCode == HttpStatus.SC_FORBIDDEN) {
attemptRetryOnException("auth",
request, new AuthFailureError(networkResponse));
} else if (statusCode >= 400 && statusCode <= 499) {
// Don't retry other client errors.
throw new ClientError(networkResponse);
} else if (statusCode >= 500 && statusCode <= 599) {
if (request.shouldRetryServerErrors()) {
attemptRetryOnException("server",
request, new ServerError(networkResponse));
} else {
throw new ServerError(networkResponse);
}
} else {
// 3xx? No reason to retry.
throw new ServerError(networkResponse);
}
} else {
attemptRetryOnException("network", request, new NetworkError());
}
}
}
}
可以看到,使用的其實也是Android原生的網路請求方式,只不過加入很多判斷。
現在接著看NetworkDispatcher的run方法。
第88行,這裡如果伺服器返回了304,或者這個request已經返回了response則同樣結束這次迴圈。
Response<?> response = request.parseNetworkResponse(networkResponse);
第94行,這裡也是一個重點的地方,看到方法你會不會眼熟哪?如果你是熟練使用volley的話,你會發現這個方法就是我們自定義request中需要重寫的方法。將網路請求返回的reponse封裝轉換為我們需要的response物件。
第99行,將請求的結果加入快取,很好理解。
第106行,這裡設定該request已經放回了response,對應的就是前面第88行的判斷。
第107行,這裡是我們介面回撥的地方。這裡需要詳細看下mDelivery物件。
public RequestQueue(Cache cache, Network network, int threadPoolSize) {
this(cache, network, threadPoolSize,
//Looper.getMainLooper()對應主執行緒,所以請求成功後的介面回撥對應是在主執行緒中執行。
new ExecutorDelivery(new Handler(Looper.getMainLooper())));
}
可以看到,在requestqueue的建構函式中,預設初始化了ExecutorDelivery類,這裡需要注意一個地方Looper.getMainLooper()對應主執行緒,所以請求成功後的介面回撥對應是在主執行緒中執行。
public ExecutorDelivery(final Handler handler) {
// Make an Executor that just wraps the handler.
mResponsePoster = new Executor() {
@Override
public void execute(Runnable command) {
handler.post(command);
}
};
}
可以看到,這裡handler對應的是UI執行緒,執行的Runable。
@Override
public void postResponse(Request<?> request, Response<?> response, Runnable runnable) {
request.markDelivered();
request.addMarker("post-response");
mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, runnable));
}
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()) {
//請求成功,介面回撥
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) {
//這裡當請求成功後,對應情況:需要重新整理快取,先將快取返回成response後,再非同步請求,重新整理快取。
mRunnable.run();
}
}
這裡只需要注意兩個地方,首先介面回撥的地方,可以看到deliverResponse這個方法是不是也很熟悉,自定義Request的時候,需要重寫這個方法,執行我們的回撥。
mRequest.deliverResponse(mResponse.result);
這裡附上StringRequest的deliverResponse方法。
@Override
protected void deliverResponse(String response) {
if (mListener != null) {
mListener.onResponse(response);
}
}
這樣一看就很清楚了。
最後需要注意的一點:
if (mRunnable != null) {
//這裡當請求成功後,對應情況:需要重新整理快取,先將快取返回成response後,再非同步請求,重新整理快取。
mRunnable.run();
}
這裡會的對應情況是什麼那,還記不記得當我們快取需要重新整理時,會怎麼做,Volley會先將快取的response返回,然後執行一個網路請求,並重新整理快取。
//快取需要重新整理的話,先將快取傳回給客戶,然後在將請求交給佇列
mDelivery.postResponse(request, response, new Runnable() {
@Override
public void run() {
try {
mNetworkQueue.put(request);
} catch (InterruptedException e) {
// Not much we can do about this.
}
}
});