Volley源码学习1-Volley类

我们使用Volley时首先会调用这条语句
RequestQueue mQueue = Volley.newRequestQueue(getApplicationContext());
其中返回值为RequestQueue。调用的是volley类里面的静态方法。
首先来看Volley类
它有3个重载的静态方法。
第一个

public static RequestQueue newRequestQueue(Context context) {
        return newRequestQueue(context, (BaseHttpStack) null);
 }

return newRequestQueue(context, (BaseHttpStack) null); 将会调用第二个重载的方法

public static RequestQueue newRequestQueue(Context context, BaseHttpStack stack) {
        BasicNetwork network;
        if (stack == null) {
            if (Build.VERSION.SDK_INT >= 9) {
                network = new BasicNetwork(new HurlStack());
            } else {
                // Prior to Gingerbread, HttpUrlConnection was unreliable.
                // See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html
                // At some point in the future we'll move our minSdkVersion past Froyo and can
                // delete this fallback (along with all Apache HTTP code).
                String userAgent = "volley/0";
                try {
                    String packageName = context.getPackageName();
                    PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);
                    userAgent = packageName + "/" + info.versionCode;
                } catch (NameNotFoundException e) {
                }

                network = new BasicNetwork(
                        new HttpClientStack(AndroidHttpClient.newInstance(userAgent)));
            }
        } else {
            network = new BasicNetwork(stack);
        }

        return newRequestQueue(context, network);
    }

这段代码将会初始化一个BasicNetwork，之后会分析这个类
return newRequestQueue(context, network); 将会调用第三个重载方法

private static RequestQueue newRequestQueue(Context context, Network network) {
        File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);
        RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
        queue.start();
        return queue;
    }

这段代码将会创建一个RequestQueue对象， queue.start();将会使CacheDispatcher、NetworkDispatcher开启线程。这样初始化工作就做好了，RequestQueue队列将会等待队列有请求发出然后进行请求。那么是怎么实现的呢？接下来来看RequestQueue类。