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背景
Volley网络框架，是谷歌13开发给开发的一套网络请求加载框架，这个框架比较适合于请求数据量比较小，但是请求比较频繁的情况下使用，对于数据量比较大的这个框架就不是很适合， 因为底层是用请求队列的形式，因为本身比较小，不会加大App本身的大小所以很多人选择，我们有必要了解这个网络请求框架的执行流程。
一、Volley框架的简单使用
private void getStringRequest() {
String url="http://api.k780.com:88/?app=phone.get&phone=13800138000&appkey=10003&sign=b59bc3ef6191eb9f747dd4e83c99f2a4&format=json";
RequestQueue queue= Volley.newRequestQueue(this);
StringRequest request=new StringRequest(url, new Response.Listener<String>() {
@Override
public void onResponse(String s) {
Log.e("success",s);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError volleyError) {
}
});
queue.add(request);
}二、代码源码分析
RequestQueue queue= Volley.newRequestQueue(this);对应源码
public static RequestQueue newRequestQueue(Context context, BaseHttpStack stack) {
BasicNetwork network;
if (stack == null) {
if (Build.VERSION.SDK_INT >= 9) { //如果版本小于9
network = new BasicNetwork(new HurlStack());
} else {
// Prior to Gingerbread, HttpUrlConnection was unreliable.
// See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html
// At some point in the future we'll move our minSdkVersion past Froyo and can
// delete this fallback (along with all Apache HTTP code).
//生成一个
String userAgent = "volley/0";
try {
String packageName = context.getPackageName();
PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);
userAgent = packageName + "/" + info.versionCode;
} catch (NameNotFoundException e) {
}
network = new BasicNetwork(
new HttpClientStack(AndroidHttpClient.newInstance(userAgent)));
}
} else {
network = new BasicNetwork(stack);
}
return newRequestQueue(context, network);
}
/**
* Creates a default instance of the worker pool and calls {@link RequestQueue#start()} on it.
*
* @param context A {@link Context} to use for creating the cache dir.
* @param stack An {@link HttpStack} to use for the network, or null for default.
* @return A started {@link RequestQueue} instance.
* @deprecated Use {@link #newRequestQueue(Context, BaseHttpStack)} instead to avoid depending
* on Apache HTTP. This method may be removed in a future release of Volley.
*/
@Deprecated
@SuppressWarnings("deprecation")
public static RequestQueue newRequestQueue(Context context, HttpStack stack) {
if (stack == null) {
return newRequestQueue(context, (BaseHttpStack) null);
}
return newRequestQueue(context, new BasicNetwork(stack));
}
private static RequestQueue newRequestQueue(Context context, Network network) {
File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
queue.start();
return queue;
}
/**
* 最初始传入的方法
*/
public static RequestQueue newRequestQueue(Context context) {
return newRequestQueue(context, (BaseHttpStack) null);
}
}接下来我们看一下StringRequest这个类
public class StringRequest extends Request<String> {
/** Lock to guard mListener as it is cleared on cancel() and read on delivery. */
private final Object mLock = new Object();
// @GuardedBy("mLock")
private Listener<String> mListener;
/**
*创建一个stringRequest;
* @param method the request {@link Method} to use
* @param url URL to fetch the string at
* @param listener Listener to receive the String response
* @param errorListener Error listener, or null to ignore errors
*/
public StringRequest(int method, String url, Listener<String> listener,
ErrorListener errorListener) {
super(method, url, errorListener);
mListener = listener;
}
/**
* Creates a new GET request.
*
* @param url URL to fetch the string at
* @param listener Listener to receive the String response
* @param errorListener Error listener, or null to ignore errors
*/
public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
this(Method.GET, url, listener, errorListener);
}
//取消这个请求
@Override
public void cancel() {
super.cancel();
synchronized (mLock) {
mListener = null;
}
}
//分发响应
@Override
protected void deliverResponse(String response) {
Response.Listener<String> listener;
synchronized (mLock) {
listener = mListener;
}
if (listener != null) {
listener.onResponse(response);
}
}
//解析响应
@Override
protected Response<String> parseNetworkResponse(NetworkResponse response) {
String parsed;
try {
parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
} catch (UnsupportedEncodingException e) {
parsed = new String(response.data);
}
return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));
}
} /**
* 开始分发队列
*/
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();
}
}对于缓存分发器
final Request<?> request = mCacheQueue.take();
request.addMarker("cache-queue-take");
// If the request has been canceled, don't bother dispatching it.
if (request.isCanceled()) {
request.finish("cache-discard-canceled");
return;
}
// Attempt to retrieve this item from cache.
Cache.Entry entry = mCache.get(request.getCacheKey());
if (entry == null) {
request.addMarker("cache-miss");
// Cache miss; send off to the network dispatcher.
//如果缓存找不到 那么去网络下载
if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
mNetworkQueue.put(request);
}
return;
}
// If it is completely expired, just send it to the network.
//如果有但是过期了 那么请求放到网络队列中
if (entry.isExpired()) {
request.addMarker("cache-hit-expired");
request.setCacheEntry(entry);
if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
mNetworkQueue.put(request);
}
return;
}
// We have a cache hit; parse its data for delivery back to the request.
//如果中 那么解析数据
request.addMarker("cache-hit");
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.
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;
if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
// Post the intermediate response back to the user and have
// the delivery then forward the request along to the network.
mDelivery.postResponse(request, response, new Runnable() {
@Override
public void run() {
try {
mNetworkQueue.put(request);
} catch (InterruptedException e) {
// Restore the interrupted status
Thread.currentThread().interrupt();
}
}
});
} else {
// request has been added to list of waiting requests
// to receive the network response from the first request once it returns.
mDelivery.postResponse(request, response);
}
}网络请求队列
private void processRequest() throws InterruptedException {
// Take a request from the queue.
Request<?> request = mQueue.take();//拿到一个请求
long startTimeMs = SystemClock.elapsedRealtime();//记录开始
try {
request.addMarker("network-queue-take");//添加标识
// If the request was cancelled already, do not perform the
// network request.
if (request.isCanceled()) {//请求是否被取消
request.finish("network-discard-cancelled");//
request.notifyListenerResponseNotUsable();
return;
}
addTrafficStatsTag(request);
// Perform the network request.
NetworkResponse networkResponse = mNetwork.performRequest(request);//拿到响应
request.addMarker("network-http-complete");//添加标识
// 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");
request.notifyListenerResponseNotUsable();
return;
}//
// Parse the response here on the worker thread.
Response<?> response = request.parseNetworkResponse(networkResponse);
request.addMarker("network-parse-complete");//解析完成
// Write to cache if applicable.
// TODO: Only update cache metadata instead of entire record for 304s.
if (request.shouldCache() && response.cacheEntry != null) {//放到缓存中
mCache.put(request.getCacheKey(), response.cacheEntry);
request.addMarker("network-cache-written");
}
// Post the response back.
request.markDelivered();
mDelivery.postResponse(request, response);
request.notifyListenerResponseReceived(response);
} catch (VolleyError volleyError) {
volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
parseAndDeliverNetworkError(request, volleyError);
request.notifyListenerResponseNotUsable();
} 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);
request.notifyListenerResponseNotUsable();
}
}