Volley简介
Volley 是Google推出的轻量级的异步网络请求、图片请求框架。
主要特点是：
- 扩展性强 ，基于接口实现，可配置性强。
- 符合 Http 规范，包括返回 ResponseCode(2xx、3xx、4xx、5xx）的处理，请求头的处理，缓存机制的支持等。并支持重试及优先级定义。
- 默认 Android2.3 及以上基于 HttpURLConnection，2.3 以下基于 HttpClient 实现（在Android 2.2之前调用HttpURLConnection的close方法会导致连接复用失败，影响连接池。）
- 提供简便的图片加载工具
- 非常适合进行数据量不大，但通信频繁的网络操作
Volley架构图
屏幕快照 2018-01-28 22.41.50.png
Volley 用法
RequestQueue requestQueue = Volley.newRequestQueue(this);
String url = "http://www.google.com";
// StringRequest GET请求示例
StringRequest stringquest = new StringRequest(Request.Method.GET,
url, new Response.Listener<String>() {
@Override
public void onResponse(String s) {
Log.d("LOG","result : "+s);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError volleyError) {
Log.d("LOG","error : "+volleyError.getMessage());
}
});
//StringRequest POST请求示例
String url="http://api.k780.com:88/?app=phone.get";
StringRequest request= new StringRequest(Request.Method.POST, url,
new Response.Listener<String>() {
@Override
public void onResponse(String s) {
Log.d("success", s);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError volleyError) {
Log.d("error", s);
}
}){
@Override
protected Map<String, String> getParams() throws AuthFailureError {
Map<String,String> map=new HashMap<>();
map.put("phone", "13800138000");
map.put("appkey", "10003");
map.put("sign", "b59bc3ef6191eb9f747dd4e83c99f2a4");
map.put("format", "json");
map.put("idcard", "110101199001011114");
return map;
}
};
//JsonObjectRequest GET请求
String url="http://api.k780.com:88/?app=phone.get&phone=13800138000&appkey=10003&sign=b59bc3ef6191eb9f747dd4e83c99f2a4&format=json";
JsonObjectRequest request=new JsonObjectRequest(url, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject jsonObject) {
Log.e("success", jsonObject.toString());
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError volleyError) {}
});
requestQueue.add(stringquest);
// 使用ImageLoader加载图片
ImageView imageView;
RequestQueue mQueue = Volley.newRequestQueue(getApplicationContext());
ImageLoader imageLoader = new ImageLoader(mQueue, new BitmapCache());
ImageLoader.ImageListener listener = ImageLoader.getImageListener(iv_image,R.drawable.ico_default, R.drawable.ico_default);
imageLoader.get("http://img.my.csdn.net/uploads/201603/26/1458988468_5804.jpg", listener);
// 使用NetworkImageView加载图片
<com.android.volley.toolbox.NetworkImageView
android:id="@+id/nv_image"
android:layout_width="200dp"
android:layout_height="200dp"
android:layout_centerHorizontal="true"
android:layout_below="@id/iv_image"
android:layout_marginTop="20dp" />
iv_image = (ImageView) this.findViewById(R.id.iv_image);
RequestQueue mQueue = Volley.newRequestQueue(getApplicationContext());
ImageLoader imageLoader = new ImageLoader(mQueue, new BitmapCache());
nv_image.setDefaultImageResId(R.drawable.ico_default);
nv_image.setErrorImageResId(R.drawable.ico_default);
nv_image.setImageUrl("http://img.my.csdn.net/uploads/201603/26/1458988468_5804.jpg",imageLoader);
下面，通过Volley源码来简单了解一下其内部结构吧。
屏幕快照 2018-01-28 19.01.51.png
【1】首先来看看Volley这类。
public class Volley {
private static final String DEFAULT_CACHE_DIR = "volley";
public static RequestQueue newRequestQueue(Context context) {
return newRequestQueue(context, null);
}
public static RequestQueue newRequestQueue(Context context, HttpStack stack) {
//缓存文件
File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);
String userAgent = "volley/0";
try {
String packageName = context.getPackageName();
PackageInfo info = context.getPackageManager()
.getPackageInfo(packageName, 0);
userAgent = packageName + "/" + info.versionCode;
} catch (NameNotFoundException e) {
}
//策略模式
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;
}
}
【2】RequestQueue
屏幕快照 2018-01-28 19.09.13.png
public class RequestQueue {
public void start() {
stop(); // Make sure any currently running dispatchers are stopped.
// 创建一个缓存调度线程并使之运行
mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery);
mCacheDispatcher.start();
// 默认创建4个网络调度线程并运行
for (int i = 0; i < mDispatchers.length; i++) {
NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork,
mCache, mDelivery);
mDispatchers[i] = networkDispatcher;
networkDispatcher.start();
}
}
public <T> Request<T> add(Request<T> request) {
// Tag the request as belonging to this queue and add it to the set of current requests.
request.setRequestQueue(this);
synchronized (mCurrentRequests) {
mCurrentRequests.add(request);
}
// Process requests in the order they are added.
request.setSequence(getSequenceNumber());
request.addMarker("add-to-queue");
// If the request is uncacheable, skip the cache queue and go straight to the network.
if (!request.shouldCache()) {
mNetworkQueue.add(request);
return request;
}
//之前是否有执行相同的请求且还没有返回结果的，如果有的话将此请求加入mWaitingRequests队列，不再重复请求
synchronized (mWaitingRequests) {
String cacheKey = request.getCacheKey();
if (mWaitingRequests.containsKey(cacheKey)) {
// There is already a request in flight. Queue up.
Queue<Request<?>> stagedRequests = mWaitingRequests.get(cacheKey);
if (stagedRequests == null) {
stagedRequests = new LinkedList<Request<?>>();
}
stagedRequests.add(request);
mWaitingRequests.put(cacheKey, stagedRequests);
if (VolleyLog.DEBUG) {
VolleyLog.v("Request for cacheKey=%s is in flight, putting on hold.", cacheKey);
}
} else {
//没有的话就将请求加入缓存队列mCacheQueue，同时加入mWaitingRequests中用来做下次同样请求来时的重复判断依据
mWaitingRequests.put(cacheKey, null);
mCacheQueue.add(request);
}
return request;
}
}
}
【3】CacheDispatcher 缓存调度线程
public class CacheDispatcher extends Thread {
@Override
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();
request.addMarker("cache-queue-take");
// If the request has been canceled, don't bother dispatching it.
if (request.isCanceled()) {
request.finish("cache-discard-canceled");
continue;
}
// 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.
mNetworkQueue.put(request);
continue;
}
// If it is completely expired, just send it to the network.
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.
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;
// 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;
}
}
}
}
【4】NetworkDispatcher网络调度线程
public class NetworkDispatcher extends Thread {
@Override
public void run() {
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
Request<?> request;
while (true) {
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);
} catch (VolleyError volleyError) {
parseAndDeliverNetworkError(request, volleyError);
} catch (Exception e) {
VolleyLog.e(e, "Unhandled exception %s", e.toString());
mDelivery.postError(request, new VolleyError(e));
}
}
}
}
