volley-request.png
Volley的工作原理
- 线程管理
- 缓存的管理
- 发送网络请求过程
- 在主线程把请求加入请求队列
- 缓存线程查询请求是否有缓存，如果有缓存，则从缓存中获取数据解析返回给主线程，如果没有缓存，把请求分发给网络线程
- 网络线程发送请求，从服务器获取数据，解析后返回给主线程
Volley源码分析
首先,从创建请求队列开始看
Volley.newRequestQueue(context);
点击进去跳到Volley类,然后就会跳到这个方法里面.
public static RequestQueue newRequestQueue(Context context, HttpStack stack) {
File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR); //这里创建了一个缓存目录,具体路径在data/data/包名/cache/DEFAULT_CACHE_DIR所指向的文件名里面
String userAgent = "volley/0";
try {
String packageName = context.getPackageName();
PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);
userAgent = packageName + "/" + info.versionCode;
} catch (NameNotFoundException e) {
}
if (stack == null) {
if (Build.VERSION.SDK_INT >= 9) { //如果当前的构建版本大于SDK9 就用HurlStack为HttpStack赋值,HttpStack内部用HttpUrlConnection来创建网络连接
stack = new HurlStack();
} else { //否则就用HttpClientStack来为HttpStack赋值,HttpClientStack里面使用HttpClient来创建网络连接
// Prior to Gingerbread, HttpUrlConnection was unreliable.
// See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html
stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));
}
}
Network network = new BasicNetwork(stack);
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
queue.start();
return queue;
}
我们进去看一下HttpStack类
public interface HttpStack {
/**
* Performs an HTTP request with the given parameters.
*
* A GET request is sent if request.getPostBody() == null. A POST request is sent otherwise,
* and the Content-Type header is set to request.getPostBodyContentType().
*
* @param request the request to perform
* @param additionalHeaders additional headers to be sent together with
* {@link Request#getHeaders()}
* @return the HTTP response
*/
public HttpResponse performRequest(Request request, Map additionalHeaders)
throws IOException, AuthFailureError;
}
发现这是一个接口,那就看一下他的实现类HurlStack,查看该类的实现方法
public HttpResponse performRequest(Request request, Map additionalHeaders)
throws IOException, AuthFailureError {
String url = request.getUrl();
HashMap map = new HashMap();
map.putAll(request.getHeaders());
map.putAll(additionalHeaders);
if (mUrlRewriter != null) {
String rewritten = mUrlRewriter.rewriteUrl(url);
if (rewritten == null) {
throw new IOException("URL blocked by rewriter: " + url);
}
url = rewritten;
}
URL parsedUrl = new URL(url);
HttpURLConnection connection = openConnection(parsedUrl, request); //使用HttpURLConnection来打开网络连接
for (String headerName : map.keySet()) {
connection.addRequestProperty(headerName, map.get(headerName));
}
setConnectionParametersForRequest(connection, request);
// Initialize HttpResponse with data from the HttpURLConnection.
ProtocolVersion protocolVersion = new ProtocolVersion("HTTP", 1, 1);
int responseCode = connection.getResponseCode();
if (responseCode == -1) {
// -1 is returned by getResponseCode() if the response code could not be retrieved.
// Signal to the caller that something was wrong with the connection.
throw new IOException("Could not retrieve response code from HttpUrlConnection.");
}
StatusLine responseStatus = new BasicStatusLine(protocolVersion,
connection.getResponseCode(), connection.getResponseMessage());
BasicHttpResponse response = new BasicHttpResponse(responseStatus);
if (hasResponseBody(request.getMethod(), responseStatus.getStatusCode())) {
response.setEntity(entityFromConnection(connection));
}
for (Entry> header : connection.getHeaderFields().entrySet()) {
if (header.getKey() != null) {
Header h = new BasicHeader(header.getKey(), header.getValue().get(0));
response.addHeader(h);
}
}
return response;
}
我们发现这个方法主要是在构建网络连接,里面是使用HttpURLConnection来网络连接,然后返回HttpResponse响应.
继续回到newRequestQueue方法里面
Network network = new BasicNetwork(stack);
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
queue.start();
代码执行到这里了,我们看一下这行代码,这里传入了两个参数,一个是基于磁盘的缓存,一个是网络连接.进去DiskBasedCache类看一下
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
public DiskBasedCache(File rootDirectory) {
this(rootDirectory, DEFAULT_DISK_USAGE_BYTES);
}
可以看出这里设置了缓存的目录以及默认使用缓存的大小
private static final int DEFAULT_DISK_USAGE_BYTES = 5 * 1024 * 1024;
默认缓存的大小为5M.
我们最后进入RequestQueue里面看一下构造方法做了一些什么事情
public RequestQueue(Cache cache, Network network) {
this(cache, network, DEFAULT_NETWORK_THREAD_POOL_SIZE);
}
继续点击进去,
public RequestQueue(Cache cache, Network network, int threadPoolSize) {
this(cache, network, threadPoolSize,
new ExecutorDelivery(new Handler(Looper.getMainLooper())));
}
再次点击进去,最终是调用这个构造方法
public RequestQueue(Cache cache, Network network, int threadPoolSize,
ResponseDelivery delivery) {
mCache = cache; //根据上面封装的构造方法,这里传进来的是new DiskBasedCache(cacheDir)
mNetwork = network;//这里传进来的是new BasicNetwork(stack)
mDispatchers = new NetworkDispatcher[threadPoolSize];//threadPoolSize传进来的是 DEFAULT_NETWORK_THREAD_POOL_SIZE,根据查看源码得知这个值是为4
//private static final int DEFAULT_NETWORK_THREAD_POOL_SIZE = 4;
mDelivery = delivery;
//这里传进来的是
//new ExecutorDelivery(new Handler(Looper.getMainLooper())));
//这里做的是,将子线程切换到主线程
}
我们最终是初始化了以上这些类,我们点击NetworkDispatcher进去看一下,里面做了一些什么事情
发现NetworkDispatcher是继承了Thread类的,就说明,上面初始化的时候,初始化了4个线程.
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
queue.start();
可以看出RequestQueue初始化做了一下事情:
- 初始化磁盘缓存
- 初始化了网络连接
- 创建了4个网络线程
- 初始化了一个将执行结果发送到主线程的传递器
继续点击进去看start方法做了什么事情
public void start() {
stop(); // Make sure any currently running dispatchers are stopped.
// Create the cache dispatcher and start it.
//首先创建了缓存分发器
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();
}
}
通过这个方法我们可以知道,首先创建了缓存分发器.首先检查缓存中是否有数据,我们进去CacheDispatcher类查看
这是一个继承了Thread的类,
public void run() {
if (DEBUG) VolleyLog.v("start new dispatcher");
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
// Make a blocking call to initialize the cache.
mCache.initialize();
while (true) {
try {
// Get a request from the cache triage queue, blocking until
// at least one is available.
final Request request = mCacheQueue.take(); //这里不断地往缓存队列中拿数据
request.addMarker("cache-queue-take"); //并且为请求添加标记
// If the request has been canceled, don't bother dispatching it.
if (request.isCanceled()) { //判断请求是否已经取消
request.finish("cache-discard-canceled");
continue;
}
// Attempt to retrieve this item from cache.
Cache.Entry entry = mCache.get(request.getCacheKey());
//内存中找不到请求,就从磁盘中查找缓存
if (entry == null) { //如果找不到缓存
request.addMarker("cache-miss"); //则为这个请求打上"缓存丢失的标记"
// Cache miss; send off to the network dispatcher.
mNetworkQueue.put(request); //找不到缓存,就会往网络队列中寻找缓存
continue;
}
// If it is completely expired, just send it to the network.
if (entry.isExpired()) { //判断缓存是否过期
request.addMarker("cache-hit-expired"); //过期了就,为缓存打上"缓存过期" 的标记
request.setCacheEntry(entry); //并重新设置缓存
mNetworkQueue.put(request); //向网络请求队列中加入缓存
continue;
}
// We have a cache hit; parse its data for delivery back to the request.
request.addMarker("cache-hit"); //如果有缓存,就打上"找到缓存"的标记
Response response = request.parseNetworkResponse(
new NetworkResponse(entry.data, entry.responseHeaders));
//读取缓存并解析缓存
request.addMarker("cache-hit-parsed"); //为请求打上"缓存被解析"的标记
if (!entry.refreshNeeded()) {//判断数据是否需要刷新
// Completely unexpired cache hit. Just deliver the response.
mDelivery.postResponse(request, response); //传递器将响应从子线程传递到主线程
} else {
//如果数据需要重新刷新,就需要重新加入网络请求队列中,发送网络请求
// 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.
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;
}
continue;
}
}
}
看完这里,可以知道,首先在内存中寻找缓存,如果没有就到磁盘中寻找缓存,如果没有,再发送网络请求获取数据.
volley-request.png
和上面这个图的工作原理一样.数据加入网络请求队列之后,继续往下看
for (int i = 0; i < mDispatchers.length; i++) {
NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork,
mCache, mDelivery);
mDispatchers[i] = networkDispatcher;
networkDispatcher.start();
}
这里添加了四个线程给网络分发器,对应上图.
我们进去NetworkDispatcher里面看
public void run() {
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
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); //发送响应到主线程
} 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);
}
}
}
工作原理和上面的缓存队列工作原理相似.
mDelivery.postResponse(request, response); //发送响应到主线程
继续往下查看
@Override
public void postResponse(Request request, Response response, Runnable runnable) {
request.markDelivered();
request.addMarker("post-response");
mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, runnable));
}
这里执行了ResponseDeliveryRunnable,继续查看
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()) { //响应成功
mRequest.deliverResponse(mResponse.result);
} else { //响应失败
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();
}
}
响应成功或者失败都会回调监听
响应成功:
@Override
protected void deliverResponse(T response) {
mListener.onResponse(response);
}
响应失败:
public void deliverError(VolleyError error) {
if (mErrorListener != null) {
mErrorListener.onErrorResponse(error);
}
}
因为本人这里是使用JsonRequest,所以这里会响应JsonRequest的请求,监听器就有数据过来了
private NetWorkListener mListener=new NetWorkListener()
{
@Override
public void onResponse(NewsListBean response) {
//保存新闻列表数据
mNews = response.getData().getNews();
//保存轮播图数据
mTopNews = response.getData().getTopnews();
//刷新新闻列表
mAdapter.notifyDataSetChanged();
//保存more字段,加载更多
mMore = response.getData().getMore();
List urls = new ArrayList();
mTopNews = response.getData().getTopnews();
//遍历轮播图的数据，构建图片url集合
for (int i = 0; i NetWorkListener是我自己写的,实现了Response.Listener,Response.ErrorListener接口
public class NetWorkListener implements Response.Listener,Response.ErrorListener{
@Override
public void onErrorResponse(VolleyError error) {
}
@Override
public void onResponse(T response) {
}
}