Volley is an HTTP library that makes networking for Android apps easier and most importantly, faster. Volley is available through the open AOSP repository.

Volley 是一个HTTP库。它使得android app的网络传输数据更简单，更快。

Volley的设计目标就是很适合去进行数据量不大，但通信频繁的网络操作，而对于大数据量的网络操作。比方说下载文件，流视频操作等。Volley的表现就会很糟糕。我一般考虑DownloadManager。

Volley源代码下载地址：

git clone https://android.googlesource.com/platform/frameworks/volley

我们把代码下载下来。參考Android working with Volley Library，我们能够生成volley.jar，我们在项目中，能够直接使用volley.jar包。

2. StringRequest

我们先从最简单的StringRequest開始。介绍一下怎样使用Volley去发起string的请求：

public class Lesson01Activity extends Activity {

    public static final String TAG = "Lesson01Activity";
    private StringRequest stringRequest; 
    private RequestQueue mRequestQueue;  
    private TextView mTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_01);
        init();
    }

    private void init() {
        // TODO Auto-generated method stub
        mTextView = (TextView) findViewById(R.id.text);     
        mRequestQueue = Volley.newRequestQueue(this);
        String url ="http://www.baidu.com";
        stringRequest = new StringRequest(Request.Method.GET, url,
                    new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                // Display the first 500 characters of the response string.
                mTextView.setText("Response is: "+ response.substring(0,500));
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                mTextView.setText("That didn't work!");
            }
        }); 
        // Set the tag on the request.
        stringRequest.setTag(TAG);      
        // Add the request to the RequestQueue.
        mRequestQueue.add(stringRequest);
    }

    @Override
    protected void onStop() {
        // TODO Auto-generated method stub
        super.onStop();
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(TAG);
        }
    }
}

最后。一定要AndroidManifest.xml中添加 INTERNET Permission：

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

3. cache–缓存的使用

volley支持cache，以下是一个使用cache的例子：

mTextView = (TextView) findViewById(R.id.text); 
Cache cache = new DiskBasedCache(getCacheDir(), 1024 * 1024); // 1MB cap
Network network = new BasicNetwork(new HurlStack());
mRequestQueue = new RequestQueue(cache, network);
mRequestQueue.start();
String url ="http://www.myurl.com";
// Request a string response from the provided URL.
stringRequest = new StringRequest(
   Request.Method.GET, 
   url,
   new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
        mTextView.setText("Response is: "+ response.substring(0,500));
            }
        }, 
    new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
            mTextView.setText("That didn't work!");
    }
}); 
stringRequest.setTag(TAG);
mRequestQueue.add(stringRequest);

4. 使用单例模式应用volley

MySingleton ——单例模式类

import android.content.Context;
import android.graphics.Bitmap;
import android.util.LruCache;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.Volley;

public class MySingleton {  
    private static MySingleton mInstance;
    private RequestQueue mRequestQueue;
    private ImageLoader mImageLoader;
    private static Context mCtx;

    private MySingleton(Context context) {
        mCtx = context;
        mRequestQueue = getRequestQueue();
        mImageLoader = new ImageLoader(mRequestQueue,
                new ImageLoader.ImageCache() {
            private final LruCache<String, Bitmap>
                    cache = new LruCache<String, Bitmap>(20);
            @Override
            public Bitmap getBitmap(String url) {
                return cache.get(url);
            }
            @Override
            public void putBitmap(String url, Bitmap bitmap) {
                cache.put(url, bitmap);
            }
        });
    }

    public static synchronized MySingleton getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new MySingleton(context);
        }
        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        if (mRequestQueue == null) {
// getApplicationContext() is key, it keeps you from leaking the
// Activity or BroadcastReceiver if someone passes one in.
            mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
        }
        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req) {
        getRequestQueue().add(req);
    }

    public ImageLoader getImageLoader() {
        return mImageLoader;
    }   
}

使用例子：

mTextView = (TextView) findViewById(R.id.text);
mRequestQueue = MySingleton.getInstance(this.getApplicationContext()).
                getRequestQueue();  
String url ="http://www.baidu.com";
stringRequest = new StringRequest(
    Request.Method.GET, 
    url,
    new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
        mTextView.setText("Response is: "+ response.substring(0,500));
            }
        }, 
    new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
         mTextView.setText("That didn't work!");
    }
});
stringRequest.setTag(TAG);              
MySingleton.getInstance(this).addToRequestQueue(stringRequest);

5.ImageRequest + ImageView

ImageRequest 就是Image的请求:

ImageView mImageView;
String url = "http://i.imgur.com/7spzG.png";
mImageView = (ImageView) findViewById(R.id.myImage);
...

// Retrieves an image specified by the URL, displays it in the UI.
ImageRequest request = new ImageRequest(url,
    new Response.Listener<Bitmap>() {
        @Override
        public void onResponse(Bitmap bitmap) {
            mImageView.setImageBitmap(bitmap);
        }
    }, 0, 0, null,
    new Response.ErrorListener() {
        public void onErrorResponse(VolleyError error) {
            mImageView.setImageResource(R.drawable.image_load_error);
        }
    });
// Access the RequestQueue through your singleton class.
MySingleton.getInstance(this).addToRequestQueue(request);

6.ImageLoader + ImageView

ImageLoader mImageLoader;
ImageView mImageView;
// The URL for the image that is being loaded.
private static final String IMAGE_URL =
    "http://developer.android.com/images/training/system-ui.png";
...
mImageView = (ImageView) findViewById(R.id.regularImageView);

// Get the ImageLoader through your singleton class.
mImageLoader = MySingleton.getInstance(this).getImageLoader();
mImageLoader.get(IMAGE_URL, ImageLoader.getImageListener(mImageView,
         R.drawable.def_image, R.drawable.err_image));

7.ImageLoader+NetworkImageView

在ListView中。对于有效的显示多张图片，我们能够採用NetworkImageView 和 ImageLoader来处理。
xml布局文件：

<com.android.volley.toolbox.NetworkImageView
        android:id="@+id/networkImageView"
        android:layout_width="150dp"
        android:layout_height="170dp"
        android:layout_centerHorizontal="true" />

使用例子：

ImageLoader mImageLoader;
NetworkImageView mNetworkImageView;
private static final String IMAGE_URL =
    "http://developer.android.com/images/training/system-ui.png";
...

// Get the NetworkImageView that will display the image.
mNetworkImageView = (NetworkImageView) findViewById(R.id.networkImageView);

// Get the ImageLoader through your singleton class.
mImageLoader = MySingleton.getInstance(this).getImageLoader();

// Set the URL of the image that should be loaded into this view, and
// specify the ImageLoader that will be used to make the request.
mNetworkImageView.setImageUrl(IMAGE_URL, mImageLoader);

8.图片显示的一个综合例子

8.1LruBitmapCache.java

import android.content.Context;
import android.graphics.Bitmap;
import android.support.v4.util.LruCache;
import android.util.DisplayMetrics;
import com.android.volley.toolbox.ImageLoader.ImageCache;

public class LruBitmapCache extends LruCache<String, Bitmap>
        implements ImageCache {

    public LruBitmapCache(int maxSize) {
        super(maxSize);
    }

    public LruBitmapCache(Context ctx) {
        this(getCacheSize(ctx));
    }

    @Override
    protected int sizeOf(String key, Bitmap value) {
        return value.getRowBytes() * value.getHeight();
    }

    @Override
    public Bitmap getBitmap(String url) {
        return get(url);
    }

    @Override
    public void putBitmap(String url, Bitmap bitmap) {
        put(url, bitmap);
    }

    // Returns a cache size equal to approximately three screens worth of images.
    public static int getCacheSize(Context ctx) {
        final DisplayMetrics displayMetrics = ctx.getResources().
                getDisplayMetrics();
        final int screenWidth = displayMetrics.widthPixels;
        final int screenHeight = displayMetrics.heightPixels;
        // 4 bytes per pixel
        final int screenBytes = screenWidth * screenHeight * 4;
        return screenBytes * 3;
    }
}

8.2 activity_main_04.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".Lesson01Activity" >

    <TextView 
        android:id="@+id/tv01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="ImageView"
        />

    <ImageView
        android:id="@+id/myImage"
        android:layout_below="@id/tv01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <TextView 
        android:id="@+id/tv02"
        android:layout_below="@id/myImage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="NetworkImageView"
        />

    <com.android.volley.toolbox.NetworkImageView
        android:id="@+id/networkImageView"
        android:layout_below="@id/tv02"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@drawable/ic_launcher" />

</RelativeLayout>

8.3 使用例子

public class Lesson04Activity extends Activity {

    public static final String TAG = "Lesson04Activity";
    private static final String IMAGE_URL =     "http://developer.android.com/images/training/system-ui.png";
    private String url = "http://i.imgur.com/7spzG.png";
    private ImageRequest request; 
    private RequestQueue mRequestQueue; 
    private ImageView myImage;  
    private NetworkImageView networkImageView;
    private ImageLoader imageLoader;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_04);
        init();
    }
    private void init() {
        // TODO Auto-generated method stub  
        mRequestQueue = MySingleton.getInstance(this.getApplicationContext()).
                getRequestQueue();          
        networkImageView = (NetworkImageView) findViewById(R.id.networkImageView);
    networkImageView.setImageResource(R.drawable.ic_launcher);      
        //imageLoader = MySingleton.getInstance(this).getImageLoader();
        imageLoader = new ImageLoader(mRequestQueue, new LruBitmapCache(
                LruBitmapCache.getCacheSize(this)));    
        //imageLoader.get(url, ImageLoader.getImageListener(networkImageView,
        //         R.drawable.ic_launcher, R.drawable.ic_launcher));        
        //networkImageView.setImageUrl(IMAGE_URL, imageLoader); 
        networkImageView.setImageUrl(url, imageLoader);

        myImage = (ImageView) findViewById(R.id.myImage);
        myImage.setImageResource(R.drawable.ic_launcher);   
        request = new ImageRequest(url, 
                new Response.Listener<Bitmap>() {
                    @Override
                    public void onResponse(Bitmap bitmap) {
                        // TODO Auto-generated method stub
                        myImage.setImageBitmap(bitmap);
                    }
                }, 0, 0, null, 
                new Response.ErrorListener() {

                    @Override
                    public void onErrorResponse(VolleyError arg0) {
                        // TODO Auto-generated method stub
                        myImage.setImageResource(R.drawable.ic_launcher);
                    }
                });
        request.setTag(TAG);        
    MySingleton.getInstance(this).addToRequestQueue(request);
    }

    @Override
    protected void onStop() {
        // TODO Auto-generated method stub
        super.onStop();
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(TAG);
        }
    }
}

效果图：

9.JSON requests

Volley provides the following classes for JSON requests:

JsonArrayRequest—A request for retrieving a JSONArray response body at a given URL.
JsonObjectRequest—A request for retrieving a JSONObject response body at a given URL, allowing for an optional JSONObject to be passed in as part of the request body.
Both classes are based on the common base class JsonRequest.

使用例子：

mTextView = (TextView) findViewById(R.id.text);     
mRequestQueue = Volley.newRequestQueue(this);               
//String url = "http://my-json-feed";
String url = "http://api.androidhive.info/volley/person_object.json";
JsonObjectRequest jsObjRequest = new JsonObjectRequest(
Request.Method.GET, 
url, 
null, 
new Response.Listener<JSONObject>() {
    @Override
    public void onResponse(JSONObject response) {
    // TODO Auto-generated method stub
    mTextView.setText("Response: " + response.toString());
    }
}, 
new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError response) {
    // TODO Auto-generated method stub
    mTextView.setText("Response: " + response.toString());
    }
});
MySingleton.getInstance(this).addToRequestQueue(jsObjRequest);

.10 自己定义Response

For cases where you do need to implement a custom request, this is all you need to do:

1.Extend the Request class, where represents the type of parsed response the request expects. So if your parsed response is a string, for example, create your custom request by extending Request. See the Volley toolbox classes StringRequest and ImageRequest for examples of extending Request.

2.Implement the abstract methods parseNetworkResponse() and deliverResponse(), described in more detail below.

一个例子：

public class GsonRequest<T> extends Request<T> {
    private final Gson gson = new Gson();
    private final Class<T> clazz;
    private final Map<String, String> headers;
    private final Listener<T> listener;

    /**
     * Make a GET request and return a parsed object from JSON.
     *
     * @param url URL of the request to make
     * @param clazz Relevant class object, for Gson's reflection
     * @param headers Map of request headers
     */
    public GsonRequest(String url, Class<T> clazz, Map<String, String> headers,
            Listener<T> listener, ErrorListener errorListener) {
        super(Method.GET, url, errorListener);
        this.clazz = clazz;
        this.headers = headers;
        this.listener = listener;
    }

    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        return headers != null ? headers : super.getHeaders();
    }

    @Override
    protected void deliverResponse(T response) {
        listener.onResponse(response);
    }

    @Override
    protected Response<T> parseNetworkResponse(NetworkResponse response) {
        try {
            String json = new String(
                    response.data,
                    HttpHeaderParser.parseCharset(response.headers));
            return Response.success(
                    gson.fromJson(json, clazz),
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        } catch (JsonSyntaxException e) {
            return Response.error(new ParseError(e));
        }
    }
}

源代码下载地址

http://download.csdn.net/detail/hfreeman2008/8917631

參考资料

1. https://developer.android.com/intl/zh-cn/training/volley/index.html
   Transmitting Network Data Using Volley
   2.http://www.androidhive.info/2014/05/android-working-with-volley-library-1/
   Android working with Volley Library