解析Android框架之Volley源碼
Volley簡單使用
我這裡是以依賴架包的形式 ，大傢也可以以gradle的形式進行依賴。
好瞭，接下來上代碼瞭…..
//獲取volley的請求對象
RequestQueue requestQueue = Volley.newRequestQueue(getApplicationContext());
StringRequest stringRequest = new StringRequest(StringRequest.Method.GET, "http://www.baidu.com", new Response.Listener<String>() {
@Override
public void onResponse(String s) {
Log.d("MainActivity", "----->" + s);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError volleyError) {
Log.d("MainActivity", "---volleyError-->" + volleyError);
}
});
requestQueue.add(stringRequest);
從代碼可以看出，首先newRequestQueue來獲取到一個請求隊列，然後在將StringRequest這個請求添加到請求隊列中，就可以瞭，就是這麼簡單。當然請求不值StringRequest，還有JsonObjectRequest ，ImageRequest等等但是用法都是一樣的，這裡就不貼代碼瞭。Volley的簡單使用就這樣可以進行請求瞭。是不是很簡單
Volley執行原理
但是這個不是本篇的重點，重點是分析一下這些是怎麼執行的。先上一張圖
我們先看看newRequestQueue這個內部是怎麼執行的，代碼一開始連續執行瞭幾個重載方法，最後走到newRequestQueue
public static RequestQueue newRequestQueue(Context context, HttpStack stack, int maxDiskCacheBytes) {
File cacheDir = new File(context.getCacheDir(), "volley");
String userAgent = "volley/0";
try {
String packageName = context.getPackageName();
PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);
userAgent = packageName + "/" + info.versionCode;
} catch (NameNotFoundException var7) {
;
}
//這裡進行瞭一個版本的判斷 2.3之前用的是HTTPClient，2.3之後使用的是HttpURLConnection
if (stack == null) {
if (VERSION.SDK_INT >= 9) {
stack = new HurlStack();
} else {
stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));
}
}
Network network = new BasicNetwork((HttpStack)stack);
RequestQueue queue;
if (maxDiskCacheBytes <= -1) {
queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
} else {
queue = new RequestQueue(new DiskBasedCache(cacheDir, maxDiskCacheBytes), network);
}
queue.start();
return queue;
}
在這裡，我們看到瞭一個版本判斷，是不是瞬間感覺有點熟悉，沒錯，我們前面說的，volley2.3之前用的是HTTPClient，2.3之後使用的是HttpURLConnection就是在這裡進行判斷的。接著看queue.start();
public void start() {
this.stop();
this.mCacheDispatcher = new CacheDispatcher(this.mCacheQueue, this.mNetworkQueue, this.mCache, this.mDelivery);
this.mCacheDispatcher.start();
for(int i = 0; i < this.mDispatchers.length; ++i) {
NetworkDispatcher networkDispatcher = new NetworkDispatcher(this.mNetworkQueue, this.mNetwork, this.mCache, this.mDelivery);
this.mDispatchers[i] = networkDispatcher;
networkDispatcher.start();
}
}
mCacheDispatcher是緩存調度線程，NetworkDispatcher是網絡調度線程，而這個this.mDispatchers.length系統默認的大小為4，也就是說，在這裡總共啟動瞭5個線程在後臺運行。
好瞭，到這裡，就可以瞭，看源碼不要每一行都弄懂，不然，出不來瞭。到這裡就拿到瞭這個RequestQueue對象。回過頭來看前面使用的代碼
//獲取volley的請求對象
RequestQueue requestQueue = Volley.newRequestQueue(getApplicationContext());
StringRequest stringRequest = new StringRequest(StringRequest.Method.GET, "http://www.baidu.com", new Response.Listener<String>() {
@Override
public void onResponse(String s) {
Log.d("MainActivity", "----->" + s);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError volleyError) {
Log.d("MainActivity", "---volleyError-->" + volleyError);
}
});
requestQueue.add(stringRequest);
我們拿到這個RequestQueue對象以後，然後就把這個請求通過add方法添加到隊列中，我們看看這個add()方法是怎麼執行的。
public <T> Request<T> add(Request<T> request) {
request.setRequestQueue(this);
Set var2 = this.mCurrentRequests;
synchronized(this.mCurrentRequests) {
this.mCurrentRequests.add(request);
}
request.setSequence(this.getSequenceNumber());
request.addMarker("add-to-queue");
if (!request.shouldCache()) { //如果不能緩存
this.mNetworkQueue.add(request);
return request;
} else {
Map var7 = this.mWaitingRequests;
synchronized(this.mWaitingRequests) {
String cacheKey = request.getCacheKey();
if (this.mWaitingRequests.containsKey(cacheKey)) { //判斷之前是否執行過，但是還沒有返回結果
Queue<Request<?>> stagedRequests = (Queue)this.mWaitingRequests.get(cacheKey);
if (stagedRequests == null) {
stagedRequests = new LinkedList();
}
((Queue)stagedRequests).add(request);
this.mWaitingRequests.put(cacheKey, stagedRequests);
if (VolleyLog.DEBUG) {
VolleyLog.v("Request for cacheKey=%s is in flight, putting on hold.", new Object[]{cacheKey});
}
} else {
//沒有的話就將請求加入緩存隊列mCacheQueue，同時加入mWaitingRequests中用來做下次同樣請求來時的重復判斷依據
this.mWaitingRequests.put(cacheKey, (Object)null);
this.mCacheQueue.add(request);
}
return request;
}
}
}
從代碼中可以看出，首先判斷是否可以緩存，當然，默認是可以緩存的。如果不能緩存的話，則通過this.mNetworkQueue.add(request);將請求添加到網絡請求隊列中。如果可以緩存，則還會判斷一次這個請求是否請求，如果執行過就就通過this.mWaitingRequests.put(cacheKey, stagedRequests);添加到mWaitingRequests隊列，不在重復請求。否則就加入到緩存隊列。
大體的流程是這樣。現在我們看看緩存的，和網絡的是怎麼執行的。我們找到start()方法
public void start() {
this.stop();
this.mCacheDispatcher = new CacheDispatcher(this.mCacheQueue, this.mNetworkQueue, this.mCache, this.mDelivery);
this.mCacheDispatcher.start();
for(int i = 0; i < this.mDispatchers.length; ++i) {
NetworkDispatcher networkDispatcher = new NetworkDispatcher(this.mNetworkQueue, this.mNetwork, this.mCache, this.mDelivery);
this.mDispatchers[i] = networkDispatcher;
networkDispatcher.start();
}
}
先看CacheDispatcher，找到run()方法
public void run() {
if (DEBUG) {
VolleyLog.v("start new dispatcher", new Object[0]);
}
Process.setThreadPriority(10);
this.mCache.initialize();
while(true) {
while(true) {
while(true) {
while(true) {
try {
while(true) {
final Request<?> request = (Request)this.mCacheQueue.take(); //從緩存隊列中獲取到一個請求
request.addMarker("cache-queue-take");
if (request.isCanceled()) { //判斷請求是否取消，如果取消瞭，那就將該請求finish掉
request.finish("cache-discard-canceled");
} else {
Entry entry = this.mCache.get(request.getCacheKey());
if (entry == null) {//如果從緩存中取出來的內容為空，則將請求加入到網絡線程中再次請求
request.addMarker("cache-miss");
this.mNetworkQueue.put(request);
} else if (entry.isExpired()) { //如果請求過期瞭，則將請求加入到網絡線程中再次請求
request.addMarker("cache-hit-expired");
request.setCacheEntry(entry);
this.mNetworkQueue.put(request);
} else { //將數據回調到主線程
request.addMarker("cache-hit");
Response<?> response = request.parseNetworkResponse(new NetworkResponse(entry.data, entry.responseHeaders));
request.addMarker("cache-hit-parsed");
if (entry.refreshNeeded()) {
request.addMarker("cache-hit-refresh-needed");
request.setCacheEntry(entry);
response.intermediate = true;
this.mDelivery.postResponse(request, response, new Runnable() {
public void run() {
try {
CacheDispatcher.this.mNetworkQueue.put(request);
} catch (InterruptedException var2) {
;
}
}
});
} else {
this.mDelivery.postResponse(request, response);
}
}
}
}
} catch (InterruptedException var4) {
if (this.mQuit) {
return;
}
}
}
}
}
}
}
這裡嵌套瞭幾個循環，有點凌亂啊，但是慢慢分析的話，就會發現，其實很清晰。我在註釋上面寫瞭，這裡就不重復瞭
我們在看看NetworkDispatcher，看看網絡線程是怎麼執行的。一樣找到run()方法
public void run() {
Process.setThreadPriority(10);
while(true) {
long startTimeMs;
Request request;
while(true) {
startTimeMs = SystemClock.elapsedRealtime();
try {
request = (Request)this.mQueue.take(); //獲取到一個請求
break;
} catch (InterruptedException var6) {
if (this.mQuit) {
return;
}
}
}
try {
request.addMarker("network-queue-take");
if (request.isCanceled()) { //如果請求取消瞭，則將請求finish掉
request.finish("network-discard-cancelled");
} else {//進行網絡請求
this.addTrafficStatsTag(request);
NetworkResponse networkResponse = this.mNetwork.performRequest(request);
request.addMarker("network-http-complete");
if (networkResponse.notModified && request.hasHadResponseDelivered()) {
request.finish("not-modified");
} else {
Response<?> response = request.parseNetworkResponse(networkResponse);
request.addMarker("network-parse-complete");
if (request.shouldCache() && response.cacheEntry != null) {
this.mCache.put(request.getCacheKey(), response.cacheEntry);
request.addMarker("network-cache-written");
}
request.markDelivered();
this.mDelivery.postResponse(request, response);
}
}
} catch (VolleyError var7) {
var7.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
this.parseAndDeliverNetworkError(request, var7);
} catch (Exception var8) {
VolleyLog.e(var8, "Unhandled exception %s", new Object[]{var8.toString()});
VolleyError volleyError = new VolleyError(var8);
volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
this.mDelivery.postError(request, volleyError);
}
}
}
代碼比較多，我們直接找到NetworkResponse networkResponse = this.mNetwork.performRequest(request);這句代碼，這句代碼就是請求網絡的代碼，最核心的。performRequest是一個接口，我們看看這個performRequest()方法。Network在最開始說版本判斷的時候裡面有一句代碼Network network = new BasicNetwork((HttpStack)stack); 從這句代碼，我們可以知道BasicNetwork才是最終實現網絡請求的類，我們找到performRequest方法
public NetworkResponse performRequest(Request<?> request) throws VolleyError {
long requestStart = SystemClock.elapsedRealtime();
while(true) {
HttpResponse httpResponse = null;
byte[] responseContents = null;
Map responseHeaders = Collections.emptyMap();
try {
Map<String, String> headers = new HashMap();
this.addCacheHeaders(headers, request.getCacheEntry());
httpResponse = this.mHttpStack.performRequest(request, headers);
StatusLine statusLine = httpResponse.getStatusLine();
int statusCode = statusLine.getStatusCode();
responseHeaders = convertHeaders(httpResponse.getAllHeaders());
if (statusCode == 304) {
Entry entry = request.getCacheEntry();
if (entry == null) {
return new NetworkResponse(304, (byte[])null, responseHeaders, true, SystemClock.elapsedRealtime() - requestStart);
}
entry.responseHeaders.putAll(responseHeaders);
return new NetworkResponse(304, entry.data, entry.responseHeaders, true, SystemClock.elapsedRealtime() - requestStart);
}
if (statusCode == 301 || statusCode == 302) {
String newUrl = (String)responseHeaders.get("Location");
request.setRedirectUrl(newUrl);
}
byte[] responseContents;
if (httpResponse.getEntity() != null) {
responseContents = this.entityToBytes(httpResponse.getEntity());
} else {
responseContents = new byte[0];
}
long requestLifetime = SystemClock.elapsedRealtime() - requestStart;
this.logSlowRequests(requestLifetime, request, responseContents, statusLine);
if (statusCode >= 200 && statusCode <= 299) {
return new NetworkResponse(statusCode, responseContents, responseHeaders, false, SystemClock.elapsedRealtime() - requestStart);
}
throw new IOException();
} catch (SocketTimeoutException var12) {
attemptRetryOnException("socket", request, new TimeoutError());
} catch (ConnectTimeoutException var13) {
attemptRetryOnException("connection", request, new TimeoutError());
} catch (MalformedURLException var14) {
throw new RuntimeException("Bad URL " + request.getUrl(), var14);
} catch (IOException var15) {
int statusCode = false;
NetworkResponse networkResponse = null;
if (httpResponse == null) {
throw new NoConnectionError(var15);
}
int statusCode = httpResponse.getStatusLine().getStatusCode();
if (statusCode != 301 && statusCode != 302) {
VolleyLog.e("Unexpected response code %d for %s", new Object[]{statusCode, request.getUrl()});
} else {
VolleyLog.e("Request at %s has been redirected to %s", new Object[]{request.getOriginUrl(), request.getUrl()});
}
if (responseContents == null) {
throw new NetworkError(networkResponse);
}
networkResponse = new NetworkResponse(statusCode, (byte[])responseContents, responseHeaders, false, SystemClock.elapsedRealtime() - requestStart);
if (statusCode != 401 && statusCode != 403) {
if (statusCode != 301 && statusCode != 302) {
throw new ServerError(networkResponse);
}
attemptRetryOnException("redirect", request, new AuthFailureError(networkResponse));
} else {
attemptRetryOnException("auth", request, new AuthFailureError(networkResponse));
}
}
}
}
代碼比較多，但是大多數代碼是判斷狀態返回碼的，不需要理會。
我們直接看httpResponse = this.mHttpStack.performRequest(request, headers);這一句代碼，HttpStack這個有沒有很熟悉。沒有？？沒關系我在復制一次代碼
if (stack == null) {
if (VERSION.SDK_INT >= 9) {
stack = new HurlStack();
} else {
stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));
}
}
還是在這個版本判斷這裡，這裡就是HurlStack就是真正的網絡請求的類瞭，網絡請求，就是寫在這個類裡面的。好瞭，volley整個流程大概就是這樣瞭。現在大傢回過頭看最初的哪一張圖，是不是明瞭很多。
以上就是解析Android框架之Volley源碼的詳細內容，更多關於Android框架之Volley源碼的資料請關註WalkonNet其它相關文章！
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