volley3--Volley类

 1 public class Volley {  
 2   
 3     /**  
 4      * Default on-disk cache directory. 
 5      * 默认缓存目录名  
 6      */  
 7     private static final String DEFAULT_CACHE_DIR = "volley";  
 8   
 9     /** 
10      * Creates a default instance of the worker pool and calls {@link RequestQueue#start()} on it. 
11      * You may set a maximum size of the disk cache in bytes. 
12      * 创建一个默认工作池，并且启动请求队列 
13      * @param context A {@link Context} to use for creating the cache dir.用于创建缓存目录 
14      * @param stack An {@link HttpStack} to use for the network, or null for default. 
15      * @param maxDiskCacheBytes the maximum size of the disk cache, in bytes. Use -1 for default size. 
16      * 硬盘缓存最大值，-1则默认 
17      * @return A started {@link RequestQueue} instance. 
18      */  
19     public static RequestQueue newRequestQueue(Context context, HttpStack stack, int maxDiskCacheBytes) {  
20         File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);//缓存队列  
21   
22         String userAgent = "volley/0";  
23         try {  
24             String packageName = context.getPackageName();//包名  
25             PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);  
26             userAgent = packageName + "/" + info.versionCode;  
27         } catch (NameNotFoundException e) {  
28         }  
29   
30         if (stack == null) {//如果没有限定stack  
31             if (Build.VERSION.SDK_INT >= 9) {//adk版本在9或者以上  
32                 stack = new HurlStack();  
33             } else {  
34                 // Prior to Gingerbread, HttpUrlConnection was unreliable.  
35                 // See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html  
36                 stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));  
37             }  
38         }  
39   
40         Network network = new BasicNetwork(stack);  
41           
42         RequestQueue queue;  
43         if (maxDiskCacheBytes <= -1)//小于等于-1,则默认值  
44         {  
45             // No maximum size specified  
46             queue = new RequestQueue(new DiskBasedCache(cacheDir), network);  
47         }  
48         else  
49         {  
50             // Disk cache size specified  
51             queue = new RequestQueue(new DiskBasedCache(cacheDir, maxDiskCacheBytes), network);  
52         }  
53   
54         queue.start();  
55   
56         return queue;  
57     }