Android中 网络框架Volley的用法

Posted 2022-12-14 小威少威

Volley是在Google I/O 2013上发布的一框网络通信http模块，新版本的android已经废除了HttpClient的使用，目前主流的android网络通信库有：Async-Http、NoHttp、xUtil等。本文就自己学习了Volley一些相关知识，基于Volley的部分源码分析，简单描述一下Volley的用法，主要从以下几点进行介绍：

1. Volley源码浅析
2. Volley使用教程
3. 总结

1、Volley源码浅析：
首先，我们先看下Volley.java的整个类代码：

package com.android.volley.toolbox;

import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager.NameNotFoundException;
import android.net.http.AndroidHttpClient;
import android.os.Build;

import com.android.volley.Network;
import com.android.volley.RequestQueue;

import java.io.File;

public class Volley 

    /** Default on-disk cache directory. */
    private static final String DEFAULT_CACHE_DIR = "volley";

    /**
     * Creates a default instance of the worker pool and calls @link RequestQueue#start() on it.
     *
     * @param context A @link Context to use for creating the cache dir.
     * @param stack An @link HttpStack to use for the network, or null for default.
     * @return A started @link RequestQueue instance.
     */
    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) 
        

        if (stack == null) 
            if (Build.VERSION.SDK_INT >= 9) 
                stack = new HurlStack();
             else 
                // Prior to Gingerbread, HttpUrlConnection was unreliable.
                // See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html
                stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));
            
        

        Network network = new BasicNetwork(stack);

        RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
        queue.start();

        return queue;
    

    /**
     * Creates a default instance of the worker pool and calls @link RequestQueue#start() on it.
     *
     * @param context A @link Context to use for creating the cache dir.
     * @return A started @link RequestQueue instance.
     */
    public static RequestQueue newRequestQueue(Context context) 
        return newRequestQueue(context, null);
    

其实可以发现，整个类并不庞大，不到100行的代码量，当我们使用Volley时，我们调用了newRequestQueue(Context context)这个方法来初始化一个请求队列，该方法在源码中调用的是newRequestQueue(Context context, HttpStack stack)这块主体的代码块。
该方法的前面声明了缓存路径，接下来初始化了HttpStack：

if (Build.VERSION.SDK_INT >= 9) 
   stack = new HurlStack();
 

进入HurlStack中我们看下它主要的方法：

@Override
    public HttpResponse performRequest(Request<?> request, Map<String, String> additionalHeaders)
            throws IOException, AuthFailureError 
        String url = request.getUrl();
        HashMap<String, String> map = new HashMap<String, String>();
        map.putAll(request.getHeaders());
        map.putAll(additionalHeaders);
        if (mUrlRewriter != null) 
            String rewritten = mUrlRewriter.rewriteUrl(url);
            if (rewritten == null) 
                throw new IOException("URL blocked by rewriter: " + url);
            
            url = rewritten;
        
        URL parsedUrl = new URL(url);
        HttpURLConnection connection = openConnection(parsedUrl, request);
        for (String headerName : map.keySet()) 
            connection.addRequestProperty(headerName, map.get(headerName));
        
        setConnectionParametersForRequest(connection, request);
        // Initialize HttpResponse with data from the HttpURLConnection.
        ProtocolVersion protocolVersion = new ProtocolVersion("HTTP", 1, 1);
        int responseCode = connection.getResponseCode();
        if (responseCode == -1) 
            // -1 is returned by getResponseCode() if the response code could not be retrieved.
            // Signal to the caller that something was wrong with the connection.
            throw new IOException("Could not retrieve response code from HttpUrlConnection.");
        
        StatusLine responseStatus = new BasicStatusLine(protocolVersion,
                connection.getResponseCode(), connection.getResponseMessage());
        BasicHttpResponse response = new BasicHttpResponse(responseStatus);
        response.setEntity(entityFromConnection(connection));
        for (Entry<String, List<String>> header : connection.getHeaderFields().entrySet()) 
            if (header.getKey() != null) 
                Header h = new BasicHeader(header.getKey(), header.getValue().get(0));
                response.addHeader(h);
            
        
        return response;
    

就是涉及跟网络通信交互的方式，基于了HttpURLConnection 的实现。回到Volley类中，接下来就是这几句代码：

RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);
queue.start();
return queue;

我们的请求队列就是在这里生成的。这边就涉及到了RequestQueue这个类，我们还是先看下这个类的构造方法吧，下面方法块是最终在类内部调用的最终构造方法：

/**
     * Creates the worker pool. Processing will not begin until @link #start() is called.
     *
     * @param cache A Cache to use for persisting responses to disk
     * @param network A Network interface for performing HTTP requests
     * @param threadPoolSize Number of network dispatcher threads to create
     * @param delivery A ResponseDelivery interface for posting responses and errors
     */
    public RequestQueue(Cache cache, Network network, int threadPoolSize,
            ResponseDelivery delivery) 
        mCache = cache;
        mNetwork = network;
        mDispatchers = new NetworkDispatcher[threadPoolSize];
        mDelivery = delivery;
    

那我们知道了，初始化queue主要跟以下几个对象有关：Cache 、Network 、ResponseDelivery 、NetworkDispatcher、CacheDispatcher

之后便是queue.start()方法：

/**
     * Starts the dispatchers in this queue.
     */
    public void start() 
        stop();  // Make sure any currently running dispatchers are stopped.
        // Create the cache dispatcher and start it.
        mCacheDispatcher = new CacheDispatcher(mCacheQueue, mNetworkQueue, mCache, mDelivery);
        mCacheDispatcher.start();

        // Create network dispatchers (and corresponding threads) up to the pool size.
        for (int i = 0; i < mDispatchers.length; i++) 
            NetworkDispatcher networkDispatcher = new NetworkDispatcher(mNetworkQueue, mNetwork,
                    mCache, mDelivery);
            mDispatchers[i] = networkDispatcher;
            networkDispatcher.start();
        
    

至此，便返回一个请求队列，完成queue的初始化工作。

最后，我们这个队列可以添加request，完成访问网络的工作。我们也还是贴下add方法的源码进行看下先：

/**
     * Adds a Request to the dispatch queue.
     * @param request The request to service
     * @return The passed-in request
     */
    public Request add(Request 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.
        //设置序列号，按顺序执行请求
        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;
        

        // Insert request into stage if there's already a request with the same cache key in flight.
         // 表示这个请求可以去先去缓存中获取数据。
        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 
                // Insert 'null' queue for this cacheKey, indicating there is now a request in
                // flight.
                mWaitingRequests.put(cacheKey, null);
                mCacheQueue.add(request);
            
            return request;
        

当mCacheQueue或者mNetworkQueue的add方法添加请求之后，我们运行的线程就会接收到请求，从而去处理相对应的请求，最后将处理的结果由mDelivery来发送到主线程进行更新。到这里，我们的请求就会在缓存线程或者网络线程中去处理了，在以上步骤完成之后，request会调用自身的finish()方法，表示结束整个请求：

/**
     * Called from @link Request#finish(String), indicating that processing of the given request
     * has finished.
     *
     * <p>Releases waiting requests for <code>request.getCacheKey()</code> if
     *      <code>request.shouldCache()</code>.</p>
     */
    void finish(Request request) 
        // Remove from the set of requests currently being processed.
        synchronized (mCurrentRequests) 
            mCurrentRequests.remove(request);
        

        if (request.shouldCache()) 
            synchronized (mWaitingRequests) 
                String cacheKey = request.getCacheKey();
                Queue<Request> waitingRequests = mWaitingRequests.remove(cacheKey);
                if (waitingRequests != null) 
                    if (VolleyLog.DEBUG) 
                        VolleyLog.v("Releasing %d waiting requests for cacheKey=%s.",
                                waitingRequests.size(), cacheKey);
                    
                    // Process all queued up requests. They won't be considered as in flight, but
                    // that's not a problem as the cache has been primed by 'request'.
                    mCacheQueue.addAll(waitingRequests);
                
            
        
    

干完了源码分析的工作，接下来我们就实际操刀一下：

2、使用教程：

1、AndroidManifest中添加访问网络的权限，不用说都知道。

2、引入Volley包。这里大家可以去搜一下。

3、代码编写。

按我自己的代码风格，喜欢先封装一下VolleyUtil的工具类，写了部分代码，不打完善，大家可以自行补充。：VolleyUtil .java

import android.content.Context;

import com.android.volley.NetworkResponse;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.HttpHeaderParser;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONObject;

import java.io.UnsupportedEncodingException;

/**
 * 作者：viviant on 2016/6/30 14:08
 * 描述：Volley封装类
 */
public class VolleyUtil 

    private static RequestQueue mQueue; // volley的请求队列
    private static VolleyUtil instance;
    private static Context context;

    private VolleyUtil(Context context) 
        this.context = context;
    

    public static VolleyUtil getInstance() 
            synchronized (VolleyUtil.class) 
                if (instance == null) 
                    instance = new VolleyUtil(context);
                
            
        return instance;
    

    /**
     * get方式请求
     */
    public void get(Context context, String url, Response.Listener<String> listener, Response.ErrorListener errorListener) 
        mQueue = Volley.newRequestQueue(context);
        mQueue.add(new MyStringRequest(Request.Method.GET, url, listener, errorListener));
    

    /**
     * get方式请求
     */
    public void get(Context context, String url, JSONObject jsonObject, Response.Listener<JSONObject> listener, Response.ErrorListener errorListener) 
        mQueue = Volley.newRequestQueue(context);
        mQueue.add(new JsonObjectRequest(Request.Method.GET, url, jsonObject, listener, errorListener));
    

    /**
     * post方式请求
     */
    public void post(Context context, String url, Response.Listener<String> listener, Response.ErrorListener errorListener) 
        mQueue = Volley.newRequestQueue(context);
        mQueue.add(new MyStringRequest(Request.Method.POST, url, listener, errorListener));
    

    /**
     * post方式请求
     */
    public void put(Context context, String url, Response.Listener<String> listener, Response.ErrorListener errorListener) 
        mQueue = Volley.newRequestQueue(context);
        mQueue.add(new MyStringRequest(Request.Method.PUT, url, listener, errorListener));
    

    /**
     * post方式请求
     */
    public void delete(Context context, String url, Response.Listener<String> listener, Response.ErrorListener errorListener) 
        mQueue = Volley.newRequestQueue(context);
        mQueue.add(new MyStringRequest(Request.Method.DELETE, url, listener, errorListener));
    


    /**
     * get by tag方式请求
     */
    public void getByTag(Context context, String url, Response.Listener<String> listener, Response.ErrorListener errorListener, Object tag) 
        mQueue = Volley.newRequestQueue(context);
        MyStringRequest request = new MyStringRequest(Request.Method.GET, url, listener, errorListener);
        request.setTag(tag);
        mQueue.add(request);

    

    /**
     * 根据tag取消请求
     * @param tag
     */
    public void cancleRequests(Object tag) 
        if (mQueue != null) 
            mQueue.cancelAll(tag);
        
    

    /**
     * 取消所有的请求
     */
    public void onStop() 
        if (mQueue != null) 
            mQueue.cancelAll(new RequestQueue.RequestFilter() 
                @Override
                public boolean apply(Request<?> request) 
                    // do I have to cancel this?
                    return true; // -> always yes
                
            );
        
    

    public class MyStringRequest extends StringRequest 

        public MyStringRequest(int method, String url, Response.Listener<String> listener,Response.ErrorListener errorListener) 
            super(method, url, listener, errorListener);
        

        /**
         * 重写以解决乱码问题
         */
        @Override
        protected Response<String> parseNetworkResponse(NetworkResponse response) 
            String str = null;
            try 
                str = new String(response.data, "utf-8");
             catch (UnsupportedEncodingException e) 
                e.printStackTrace();
            
            return Response.success(str,  HttpHeaderParser.parseCacheHeaders(response));
        
    

以上也包含了一个填坑操作，我们使用StringRequest 时返回来的数据会乱码，这边我在网上查了别人的解决方案，重写了一个类。

下面是我的二次封装代码：VolleyNetManager.java

import android.content.Context;
import android.util.Log;

import com.android.volley.Response;
import com.android.volley.VolleyError;

import org.json.JSONObject;

import viviant.cn.weeklyplan.common.util.VolleyUtil;

/**
 * 作者：viviant on 2016/6/30 14:18
 * 描述：
 */
public class VolleyNetManager 

    /**
     * 根据标签取消请求
     * @param tag
     */
    public static void cancleRequests (Object tag) 
        VolleyUtil.getInstance().cancleRequests(tag);
    

    /**
     * 取消所有请求
     */
    public static void cancleAllRequests () 
        VolleyUtil.getInstance().onStop();
    

    /**
     * Volley Get 方法测试方法
     */
    public static void TestVolleyGet(Context context, String url) 
        VolleyUtil.getInstance().get(context, url,new Response.Listener<String>() 

            @Override
            public void onResponse(String arg0) 
//                Toast.makeText(getActivity(), arg0, Toast.LENGTH_LONG).show();
                Log.d("weiwei", arg0);
            
        , new Response.ErrorListener() 

            @Override
            public void onErrorResponse(VolleyError arg0) 
//                Toast.makeText(getActivity(), arg0.toString(), Toast.LENGTH_LONG).show();
                Log.d("weiwei", "error : " + arg0.toString());
            
        );
    

    /**
     * Volley Get JSONObject 方法测试方法
     */
    public static void TestVolley(Context context, String url) 
        VolleyUtil.getInstance().get(context, url, null, new Response.Listener<JSONObject>() 

            @Override
            public void onResponse(JSONObject jsonObject) 
//                Toast.makeText(getActivity(), arg0, Toast.LENGTH_LONG).show();
                Log.d("weiwei", jsonObject.toString());
            
        , new Response.ErrorListener() 

            @Override
            public void onErrorResponse(VolleyError arg0) 
//                Toast.makeText(getActivity(), arg0.toString(), Toast.LENGTH_LONG).show();
                Log.d("weiwei", "error : " + arg0.toString());
            
        );
    


    /**
     * VolleyPost方法测试方法
     */
    public static void TestVolleyPost(Context context, String url) 

        VolleyUtil.getInstance().post(context, url, new Response.Listener<String>() 

            @Override
            public void onResponse(String arg0) 
//                Toast.makeText(getActivity(), arg0, Toast.LENGTH_LONG).show();
                Log.d("weiwei", arg0);
            
        , new Response.ErrorListener() 

            @Override
            public void onErrorResponse(VolleyError arg0) 
//                Toast.makeText(getActivity(), arg0.toString(), Toast.LENGTH_LONG).show();
                Log.d("weiwei", "error : " + arg0.toString());
            
        );
    

我们在activity中可以调用：

private static final String URL = "http://www.baidu.com/";
VolleyNetManager.TestVolleyGet(getContext(), URL);

然后就可以在VolleyNetManager 得到我们返回来的数据。

3、总结：

这边画了个草图，梳理下RequestQueue的主要方法：

总得来说，volley是一个很优秀的框架，比较简洁。好歹是谷歌自己出的。
以上是我对自己使用时做的一个小小的总结，有不好的地方欢迎提出意见。