Android Volley框架全面解析

<uses-permission android:name="android.permission.INTERNET" />

RequestQueue mQueue = Volley.newRequestQueue(context);

/** method：请求方法
url：请求的地址
listener：响应成功的监听器
errorListener：出错时的监听器 **/
public StringRequest(int method, String url, Listener<String> listener, ErrorListener errorListener)
/**不传入method，默认会调用GET方式进行请求**/
public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
this(Method.GET, url, listener, errorListener);
}

StringRequest stringRequest = new StringRequest("http://www.baidu.com",
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
Toast.makeText(MainActivity.this, response, Toast.LENGTH_SHORT).show();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
showlog(error.getMessage());
}
});

StringRequest stringRequest = new StringRequest(Method.POST, url, listener, errorListener) { 
@Override 
protected Map<String, String> getParams() throws AuthFailureError { 
Map<String, String> map = new HashMap<String, String>(); 
map.put("params1", "value1"); 
map.put("params2", "value2"); 
return map; 
} 
};

mQueue.add(stringRequest);

//jsonRequest：POST请求携带的参数，可以为空，表示不携带参数
public JsonObjectRequest(int method, String url, JSONObject jsonRequest, Listener<JSONObject> listener, ErrorListener errorListener) {
super(method, url, (jsonRequest == null) ? null : jsonRequest.toString(), listener, errorListener);
}
//如果jsonRequest为空，默认使用GET请求，否则使用POST
public JsonObjectRequest(String url, JSONObject jsonRequest, Listener<JSONObject> listener, ErrorListener errorListener) {
this(jsonRequest == null ? Method.GET : Method.POST, url, jsonRequest, listener, errorListener);
}

RequestQueue mQueue = Volley.newRequestQueue(context);
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest("http://weather.51wnl.com/weatherinfo/GetMoreWeather?cityCode=101020100&weatherType=0", null, 
new Response.Listener<JSONObject>() { 
@Override 
public void onResponse(JSONObject response) { 
Toast.makeText(MainActivity.this, response.toString(), Toast.LENGTH_SHORT).show();
try {
response = response.getJSONObject("weatherinfo");
showlog("city = " + response.getString("city"));
showlog("weather1 = " + response.getString("weather1"));
} catch (JSONException e) {
e.printStackTrace();
}
} 
}, new Response.ErrorListener() { 
@Override 
public void onErrorResponse(VolleyError error) { 
showlog(error.getMessage()); 
} 
});
mQueue.add(jsonObjectRequest);

Map<String, String> params = new HashMap<String, String>(); 
params.put("name1", "value1"); 
params.put("name2", "value2"); 
JSONObject jsonRequest= new JSONObject(params);
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Method.POST, url, jsonRequest, listener, errorListener)

public ImageRequest(String url, Response.Listener<Bitmap> listener, int maxWidth, int maxHeight, Config decodeConfig, Response.ErrorListener errorListener) {
super(Method.GET, url, errorListener);
setRetryPolicy(new DefaultRetryPolicy(IMAGE_TIMEOUT_MS, IMAGE_MAX_RETRIES, IMAGE_BACKOFF_MULT));
mListener = listener;
mDecodeConfig = decodeConfig;
mMaxWidth = maxWidth;
mMaxHeight = maxHeight;
}

RequestQueue mQueue = Volley.newRequestQueue(context);
ImageRequest imageRequest = new ImageRequest( 
"http://img.my.csdn.net/uploads/201308/31/1377949454_6367.jpg", 
new Response.Listener<Bitmap>() { 
@Override 
public void onResponse(Bitmap response) { 
image.setImageBitmap(response); 
} 
}, 0, 0, Config.RGB_565, new Response.ErrorListener() { 
@Override 
public void onErrorResponse(VolleyError error) { 
image.setImageResource(R.drawable.default_image); 
} 
}); 
mQueue.add(imageRequest);

ImageLoader imageLoader = new ImageLoader(mQueue, new ImageCache() {
@Override
public void putBitmap(String url, Bitmap bitmap) {
}
@Override
public Bitmap getBitmap(String url) {
return null;
}
});

ImageLoader imageLoader = new ImageLoader(mQueue, new BitmapCache());
//BitmapCache的实现类
public class BitmapCache implements ImageCache {
private LruCache<String, Bitmap> mCache;
public BitmapCache() {
int maxSize = 10 * 1024 * 1024;
mCache = new LruCache<String, Bitmap>(maxSize) {
@Override
protected int sizeOf(String key, Bitmap value) {
return value.getRowBytes() * value.getHeight();
}
};
@Override
public Bitmap getBitmap(String url) {
return mCache.get(url);
}
@Override
public void putBitmap(String url, Bitmap bitmap) {
mCache.put(url, bitmap);
}
}

ImageListener listener = ImageLoader.getImageListener(imageView, R.drawable.default_image, R.drawable.fail_image); 

imageLoader.get("http://img.my.csdn.net/uploads/201309/01/1378037128_5291.jpg", listener); 

imageLoader.get("http://img.my.csdn.net/uploads/201309/01/1378037128_5291.jpg", listener, 600, 600); 

public final boolean shouldCache() //查看是否已经做了磁盘缓存。
void setShouldCache(boolean shouldCache)//设置是否运行磁盘缓存，此方法需要在get方法前使用
public boolean isCached(String requestUrl, int maxWidth, int maxHeight)//判断对象是否已经被缓存，传入url，还有图片的最大宽高

创建一个RequestQueue对象。
创建一个ImageLoader对象。
在布局文件中添加一个NetworkImageView控件。
在代码中获取该控件的实例。
设置要加载的图片地址。
<com.android.volley.toolbox.NetworkImageView
android:id="@+id/network_image_view"
android:layout_width="200dp"
android:layout_height="200dp"
android:layout_gravity="center_horizontal" />
/**创建RequestQueue以及ImageLoader对象**/
RequestQueue mQueue = Volley.newRequestQueue(context);
ImageLoader imageLoader = new ImageLoader(mQueue, new BitmapCache()); 
/**获取NetworkImageView控件**/
NetworkImageView networkImageView = (NetworkImageView) findViewById(R.id.network_image_view);
/**设置加载中显示的图片**/
networkImageView.setDefaultImageResId(R.drawable.default_image);
/**加载失败时显示的图片**/
networkImageView.setErrorImageResId(R.drawable.fail_image);
/**设置目标图片的URL地址**/
networkImageView.setImageUrl("http://img.my.csdn.net/uploads/201309/01/1378037151_7904.jpg", imageLoader);

package com.android.volley.toolbox;
public class StringRequest extends Request<String> {
// 建立监听器来获得响应成功时返回的结果
private final Listener<String> mListener; 
// 传入请求方法，url，成功时的监听器，失败时的监听器
public StringRequest(int method, String url, Listener<String> listener, ErrorListener errorListener) {
super(method, url, errorListener);
// 初始化成功时的监听器
mListener = listener;
}
/**
* Creates a new GET request.
* 建立一个默认的GET请求，调用了上面的构造函数
*/
public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
this(Method.GET, url, listener, errorListener);
}
@Override
protected void deliverResponse(String response) {
// 用监听器的方法来传递下响应的结果
mListener.onResponse(response);
}
@Override
protected Response<String> parseNetworkResponse(NetworkResponse response) {
String parsed;
try {
// 调用了new String(byte[] data, String charsetName) 这个构造函数来构建String对象，将byte数组按照特定的编码方式转换为String对象，主要部分是data
parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
} catch (UnsupportedEncodingException e) {
parsed = new String(response.data);
}
return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));
}
}

public class XMLRequest extends Request<XmlPullParser> {
private final Listener<XmlPullParser> mListener;
public XMLRequest(int method, String url, Listener<XmlPullParser> listener, ErrorListener errorListener) {
super(method, url, errorListener);
mListener = listener;
}
public XMLRequest(String url, Listener<XmlPullParser> listener, ErrorListener errorListener) {
this(Method.GET, url, listener, errorListener);
}
@Override
protected Response<XmlPullParser> parseNetworkResponse(NetworkResponse response) {
try {
String xmlString = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
XmlPullParser xmlPullParser = factory.newPullParser();
xmlPullParser.setInput(new StringReader(xmlString));
return Response.success(xmlPullParser, HttpHeaderParser.parseCacheHeaders(response));
} catch (UnsupportedEncodingException e) {
return Response.error(new ParseError(e));
} catch (XmlPullParserException e) {
return Response.error(new ParseError(e));
}
}
@Override
protected void deliverResponse(XmlPullParser response) {
mListener.onResponse(response);
}
}

XMLRequest xmlRequest = new XMLRequest("http://flash.weather.com.cn/wmaps/xml/china.xml", 
new Response.Listener<XmlPullParser>() { 
@Override 
public void onResponse(XmlPullParser response) { 
try { 
int eventType = response.getEventType(); 
while (eventType != XmlPullParser.END_DOCUMENT) { 
switch (eventType) { 
case XmlPullParser.START_TAG: 
String nodeName = response.getName(); 
if ("city".equals(nodeName)) { 
String pName = response.getAttributeValue(0); 
String cName = response.getAttributeValue(2); 
showlog("省份：" + pName + " 城市：" + cName);
} 
break; 
} 
eventType = response.next(); 
} 
} catch (XmlPullParserException e) { 
e.printStackTrace(); 
} catch (IOException e) { 
e.printStackTrace(); 
} 
} 
}, new Response.ErrorListener() { 
@Override 
public void onErrorResponse(VolleyError error) { 
showlog(error.getMessage()); 
} 
}); 
mQueue.add(xmlRequest);

public class GsonRequest<T> extends Request<T> {
private final Listener<T> mListener;
private Gson mGson;
private Class<T> mClass;
public GsonRequest(int method, String url, Class<T> clazz, Listener<T> listener, ErrorListener errorListener) {
super(method, url, errorListener);
mGson = new Gson();
mClass = clazz;
mListener = listener;
}
public GsonRequest(String url, Class<T> clazz, Listener<T> listener, ErrorListener errorListener) {
this(Method.GET, url, clazz, listener, errorListener);
}
@Override
protected Response<T> parseNetworkResponse(NetworkResponse response) {
try {
String jsonString = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
return Response.success(mGson.fromJson(jsonString, mClass), HttpHeaderParser.parseCacheHeaders(response));
} catch (UnsupportedEncodingException e) {
return Response.error(new ParseError(e));
}
}
@Override
protected void deliverResponse(T response) {
mListener.onResponse(response);
}
}

{"weatherinfo":{"city":"上海","city_en":"","cityid":101020100,"date":"","date_y":"2016年09月20日","fchh":0,"fl1":"","fl2":"","fl3":"","fl4":"","fl5":"","fl6":"","fx1":"","fx2":"","img1":"1","img10":"1","img11":"1","img12":"1","img2":"1","img3":"1","img4":"1","img5":"1","img6":"1","img7":"1","img8":"1","img9":"1","img_single":0,"img_title1":"","img_title10":"","img_title11":"","img_title12":"","img_title2":"","img_title3":"","img_title4":"","img_title5":"","img_title6":"","img_title7":"","img_title8":"","img_title9":"","img_title_single":"","index":"","index48":"","index48_d":"","index48_uv":"","index_ag":"","index_cl":"","index_co":"","index_d":"","index_ls":"","index_tr":"","index_uv":"","index_xc":"","st1":0,"st2":0,"st3":0,"st4":0,"st5":0,"st6":0,"temp1":"20℃~28℃","temp2":"20℃~26℃","temp3":"19℃~26℃","temp4":"21℃~26℃","temp5":"23℃~28℃","temp6":"22℃~27℃","tempF1":"","tempF2":"","tempF3":"","tempF4":"","tempF5":"","tempF6":"","weather1":"多云","weather2":"多云","weather3":"多云","weather4":"多云","weather5":"多云","weather6":"多云","week":"","wind1":"","wind2":"","wind3":"","wind4":"","wind5":"","wind6":""}}

public class Weather {
public WeatherInfo weatherinfo;
}
public class WeatherInfo {
public String city;
public String cityid;
public String date_y;
public String temp1;
public String weather1;
}

GsonRequest<Weather> gsonRequest = new GsonRequest<Weather>(
"http://weather.51wnl.com/weatherinfo/GetMoreWeather?cityCode=101020100&weatherType=0", Weather.class,
new Response.Listener<Weather>() {
@Override
public void onResponse(Weather weather) {
WeatherInfo weatherInfo = weather.weatherinfo;
showlog("city is " + weatherInfo.city);
showlog("cityid is " + weatherInfo.cityid);
showlog("date_y is " + weatherInfo.date_y);
showlog("temp1 is " + weatherInfo.temp1);
showlog("weather1 is " + weatherInfo.weather1);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
showlog(error.getMessage());
}
});
mQueue.add(gsonRequest);

public class User {
private String name; 
private int age; 
}

public class GsonRequestWithAuth<T> extends Request<T> { 
private final Gson gson = new Gson(); 
private final Class<T> clazz; 
private final Listener<T> listener; 
private Map<String, String> mHeader = new HashMap<String, String>(); 
private String mBody;
/** http请求编码方式 */ 
private static final String PROTOCOL_CHARSET = "utf-8"; 
/** 设置访问自己服务器时必须传递的参数，密钥等 */ 
static 
{ 
mHeader.put("APP-Key", "Key"); 
mHeader.put("APP-Secret", "Secret"); 
} 
/** 
* @param url 
* @param clazz 我们最终的转化类型 
* @param listener 
* @param appendHeader 附加头数据 
* @param body 请求附带消息体 
* @param errorListener 
*/ 
public GsonRequestWithAuth(String url, Class<T> clazz, Listener<T> listener, Map<String, String> appendHeader, String body, ErrorListener errorListener) { 
super(Method.POST, url, errorListener); 
this.clazz = clazz; 
this.listener = listener;
mHeader.putAll(appendHeader); 
mBody = body; 
} 
@Override 
public Map<String, String> getHeaders() throws AuthFailureError { 
// 默认返回 return Collections.emptyMap(); 
return mHeader;
} 
@Override 
public byte[] getBody() {
try { 
return mBody == null ? null : mBody.getBytes(PROTOCOL_CHARSET); 
} catch (UnsupportedEncodingException uee) { 
VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s", mUserName, PROTOCOL_CHARSET); 
return null; 
} 
}
@Override 
protected void deliverResponse(T response) { 
listener.onResponse(response); 
} 
@Override 
protected Response<T> parseNetworkResponse(NetworkResponse response) { 
try 
{ 
/** 得到返回的数据 */ 
String jsonStr = new String(response.data, HttpHeaderParser.parseCharset(response.headers)); 
/** 转化成对象 */ 
return Response.success(gson.fromJson(jsonStr, clazz), HttpHeaderParser.parseCacheHeaders(response)); 
} catch (UnsupportedEncodingException e) 
{ 
return Response.error(new ParseError(e)); 
} catch (JsonSyntaxException e) 
{ 
return Response.error(new ParseError(e)); 
} 
} 
}

public class TestServlet extends HttpServlet { 
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
this.doPost(request, response); 
} 
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
request.setCharacterEncoding("utf-8"); 
/**获取APP-Key和APP-Secret */ 
String appKey = request.getHeader("APP-Key"); 
String appSecret = request.getHeader("APP-Secret"); 
/**获取用户名、密码 */ 
String username = request.getHeader("username"); 
String password = request.getHeader("password"); 
/**获取消息体 */
int size = request.getContentLength();
InputStream is = request.getInputStream();
byte[] reqBodyBytes = readBytes(is, size);
String body = new String(reqBodyBytes);
if ("admin".equals(username) && "123".equals(password) && "getUserInfo".equals(body)) { 
response.setContentType("text/plain;charset=utf-8"); 
PrintWriter out = response.getWriter(); 
out.print("{\"name\":\"Watson\",\"age\":28}"); 
out.flush(); 
} 
} 
}

Map<String, String> appendHeader = new HashMap<String, String>(); 
appendHeader.put("username", "admin"); 
appendHeader.put("password", "123");
String url = "http://172.27.35.1:8080/webTest/TestServlet"; 
GsonRequestWithAuth<User> userRequest = new GsonRequestWithAuth<User>(url, User.class, new Listener<User>() { 
@Override 
public void onResponse(User response) 
{ 
Log.e("TAG", response.toString()); 
} 
}, appendHeader, "getUserInfo", null); 
mQueue.add(userRequest);

response.setContentType("text/plain;charset=utf-8");

public class CharsetStringRequest extends StringRequest {
public CharsetStringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
super(url, listener, errorListener);
}
public CharsetStringRequest(int method, String url, Listener<String> listener, ErrorListener errorListener) {
super(method, url, listener, errorListener);
}
@Override
protected Response<String> parseNetworkResponse(NetworkResponse response) {
String str = null;
try {
str = new String(response.data,"utf-8"); //在此处强制utf-8编码
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return Response.success(str, HttpHeaderParser.parseCacheHeaders(response));
}
}

CharsetStringRequest stringRequest = new CharsetStringRequest("http://www.weather.com.cn/data/sk/101010100.html",
new Response.Listener<String>() {
@Override
public void onResponse(String response) {
showlog(response);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
showlog(error.getMessage());
}
});
mQueue.add(userRequest);

public static RequestQueue newRequestQueue(Context context) { 
return newRequestQueue(context, null); 
} 
public static RequestQueue newRequestQueue(Context context, HttpStack stack) { 
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) { 
} 
//如果stack是等于null的，则去创建一个HttpStack对象,手机系统版本号是大于9的，则创建一个HurlStack的实例，否则就创建一个HttpClientStack的实例,HurlStack的内部就是使用HttpURLConnection进行网络通讯的，而HttpClientStack的内部则是使用HttpClient进行网络通讯的
if (stack == null) { 
if (Build.VERSION.SDK_INT >= 9) { 
stack = new HurlStack(); 
} else { 
stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent)); 
} 
} 
//创建了一个Network对象，它是用于根据传入的HttpStack对象来处理网络请求的
Network network = new BasicNetwork(stack); 
RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network); 
queue.start(); 
return queue; 
}

public void start() { 
stop(); // Make sure any currently running dispatchers are stopped. 
//先是创建了一个CacheDispatcher的实例，然后调用了它的start()方法
mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery); 
mCacheDispatcher.start(); 
//for循环创建NetworkDispatcher的实例，并分别调用它们的start()方法 
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"); 
//判断当前的请求是否可以缓存，如果不能缓存则直接将这条请求加入网络请求队列
if (!request.shouldCache()) { 
mNetworkQueue.add(request); 
return request; 
} 
// Insert request into stage if there's already a request with the same cache key in flight. 
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 { 
//当前的请求可以缓存的话则将这条请求加入缓存队列
mWaitingRequests.put(cacheKey, null); 
mCacheQueue.add(request); 
} 
return request; 
} 
}

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; 
} 
//尝试从缓存当中取出响应结果 
Cache.Entry entry = mCache.get(request.getCacheKey()); 
if (entry == null) { 
request.addMarker("cache-miss"); 
// 如何为空的话则把这条请求加入到网络请求队列中
mNetworkQueue.put(request); 
continue; 
} 
// 如果不为空的话再判断该缓存是否已过期，如果已经过期了则同样把这条请求加入到网络请求队列中
if (entry.isExpired()) { 
request.addMarker("cache-hit-expired"); 
request.setCacheEntry(entry); 
mNetworkQueue.put(request); 
continue; 
} 
//没有过期就认为不需要重发网络请求，直接使用缓存中的数据即可 
request.addMarker("cache-hit"); 
//对数据进行解析 
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; 
} 
} 
} 
}

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); 
//调用Network的performRequest()方法来去发送网络请求 
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. 
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)); 
} 
} 
} 
}

public class BasicNetwork implements Network { 
…… 
@Override 
public NetworkResponse performRequest(Request<?> request) throws VolleyError { 
long requestStart = SystemClock.elapsedRealtime(); 
while (true) { 
HttpResponse httpResponse = null; 
byte[] responseContents = null; 
Map<String, String> responseHeaders = new HashMap<String, String>(); 
try { 
// Gather headers. 
Map<String, String> headers = new HashMap<String, String>(); 
addCacheHeaders(headers, request.getCacheEntry()); 
//调用了HttpStack的performRequest()方法，这里的HttpStack就是在一开始调用newRequestQueue()方法是创建的实例，默认情况下如果系统版本号大于9就创建的HurlStack对象，否则创建HttpClientStack对象 
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) { 
//将服务器返回的数据组装成一个NetworkResponse对象进行返回
return new NetworkResponse(HttpStatus.SC_NOT_MODIFIED, 
request.getCacheEntry() == null ? null : request.getCacheEntry().data, 
responseHeaders, true); 
} 
// 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); 
} catch (Exception e) { 
…… 
} 
} 
} 
}

public void postResponse(Request<?> request, Response<?> response, Runnable runnable) { 
request.markDelivered(); 
request.addMarker("post-response"); 
mResponsePoster.execute(new ResponseDeliveryRunnable(request, response, runnable)); 
}

private class ResponseDeliveryRunnable implements Runnable { 
private final Request mRequest; 
private final Response mResponse; 
private final Runnable mRunnable; 
public ResponseDeliveryRunnable(Request request, Response response, Runnable runnable) { 
mRequest = request; 
mResponse = response; 
mRunnable = runnable; 
} 
@SuppressWarnings("unchecked") 
@Override 
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()) { 
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) { 
mRunnable.run(); 
} 
} 
}