深入剖析volley源码：揭秘Android网络

2024-12-28 17:06:25

随着移动互联网的快速发展，越来越多的应用需要通过网络请求获取数据。在Android开发中，网络请求框架的选择至关重要。而volley作为Android平台上的一款高性能网络请求框架，因其简洁易用、性能优异而受到广泛好评。本文将深入剖析volley源码，带您领略其背后的设计理念与实现细节。

一、volley简介

volley是Google官方推出的一个Android网络请求框架，旨在简化网络请求的开发过程，提高网络请求的效率。相比其他网络请求框架，volley具有以下特点：

1.支持同步与异步请求； 2.支持图片加载与缓存； 3.支持文件上传与下载； 4.支持HTTP缓存； 5.支持请求优先级控制。

二、volley源码结构

volley源码主要由以下几个部分组成：

1.RequestQueue：请求队列，负责管理所有网络请求； 2.Request：网络请求实体，包含请求方法、URL、参数、响应解析器等； 3.ResponseDelivery：响应回调，负责将响应结果传递给调用者； 4.ImageRequest：图片请求，负责图片的加载与缓存； 5.DiskCache：磁盘缓存，负责缓存网络请求的数据； 6.HttpStack：HTTP请求栈，负责发送网络请求。

三、volley源码解析

1.RequestQueue

RequestQueue是volley的核心组件，负责管理所有网络请求。其内部使用单例模式，确保全局只有一个RequestQueue实例。

java public static RequestQueue newRequestQueue(Cache cache, int maxRetries, RetryPolicy retryPolicy) { if (cache == null) { cache = new DiskBasedCache(getDiskCacheDir(context, "volley")); } return new RequestQueue(cache, new BasicNetwork(new HurlStack()), maxRetries, retryPolicy); }

RequestQueue内部包含以下成员变量：

Cache：缓存对象，用于存储缓存数据；
ExecutorService：线程池，用于执行网络请求；
List<Request>：请求队列，用于存储待执行的网络请求；
ResponseDelivery：响应回调，用于处理响应结果。

2.Request

Request是网络请求实体，包含请求方法、URL、参数、响应解析器等。

java public class Request<T> { private final String url; private final Map<String, String> headers; private final Map<String, String> params; private final ResponseListener<T> listener; private final int method; private final String tag; private final int sequence; private final Priority priority; private final boolean shouldCache; private final boolean cacheEntry; private final String cacheKey; private final boolean shouldRetryAndRetryAfter; private final RetryPolicy retryPolicy; private final int timeoutMs; private final int socketTimeoutMs; private final int connectTimeoutMs; private final String requestBody; private final MediaType requestContentType; }

3.ResponseDelivery

ResponseDelivery负责将响应结果传递给调用者。它内部使用Handler机制，将响应结果发送到主线程。

`java public class ResponseDelivery { private final Handler handler;

public ResponseDelivery() {
    handler = new Handler(Looper.getMainLooper());
}
public void postResult(Response<?> response) {
    handler.post(new Runnable() {
        @Override
        public void run() {
            deliverResponse(response);
        }
    });
}
public void deliverResponse(Response<?> response) {
    // 处理响应结果
}

} `

4.ImageRequest

ImageRequest负责图片的加载与缓存。它内部使用DiskLruCache实现图片缓存。

java public class ImageRequest implements Request<Bitmap> { private final String url; private final ImageListener listener; private final int maxWidth; private final int maxHeight; private final ScaleType scaleType; private final boolean needCache; private final Bitmap parseBitmap; private final String cacheKey; private final boolean isCacheable; private final String requestUrl; private final String cacheUrl; private final String requestHeaders; private final String cacheHeaders; private final boolean isNetworkAllowed; private final boolean isCacheAllowed; private final String cacheDirectory; private final boolean shouldCacheInMemory; private final boolean shouldCacheOnDisk; private final boolean shouldUseImageDecoder; private final boolean isImageCacheEnabled; private final String bitmapTransform; private final String errorTransform; private final String requestEncoding; private final String cacheEncoding; private final boolean isCacheExpired; private final long cacheLastModified; private final boolean isCacheStale; private final long cacheEntrySize; private final boolean isCacheResponseExpired; private final long cacheResponseLastModified; private final boolean isCacheResponseExpired; private final long cacheResponseEntrySize; }

5.DiskCache

DiskCache负责缓存网络请求的数据。它内部使用DiskLruCache实现数据缓存。

`java public class DiskBasedCache implements Cache { private final String cacheDir; private final DiskLruCache cache;

public DiskBasedCache(String cacheDir) throws IOException {
    this.cacheDir = cacheDir;
    this.cache = DiskLruCache.open(cacheDir, 1, 1, cacheSize);
}
@Override
public void put(String key, ByteBuffer data) throws IOException {
    DiskLruCache.Editor editor = cache.edit(key);
    if (editor != null) {
        try {
            editor.commit();
        } catch (IOException e) {
            editor.abort();
        }
    }
}
@Override
public ByteBuffer get(String key) throws IOException {
    DiskLruCache.Snapshot snapshot = cache.get(key);
    if (snapshot != null) {
        return snapshot.getInputStream(0).getByteBuffer();
    }
    return null;
}
@Override
public void remove(String key) throws IOException {
    cache.remove(key);
}
@Override
public void clear() throws IOException {
    cache.delete();
}

} `

6.HttpStack

HttpStack负责发送网络请求。它内部使用HurlStack实现HTTP请求。

`java public class HurlStack implements HttpStack { private final HttpURLConnectionFactory connectionFactory;

public HurlStack(HttpURLConnectionFactory connectionFactory) {
    this.connectionFactory = connectionFactory;
}
@Override
public Response<String> performRequest(Request<?> request, Map<String, String> additionalHeaders) throws IOException {
    HttpURLConnection connection = null;
    try {
        connection = connectionFactory.newConnection(request.getUrl());
        for (Map.Entry<String, String> entry : additionalHeaders.entrySet()) {
            connection.setRequestProperty(entry.getKey(), entry.getValue());
        }
        connection.setRequestMethod(request.getMethod());
        connection.setConnectTimeout(request.getTimeoutMs());
        connection.setReadTimeout(request.getTimeoutMs());
        return new Response<String>(connection.getResponseCode(), readResponse(connection));
    } finally {
        if (connection != null) {
            connection.disconnect();
        }
    }
}

} `

四、总结

通过对volley源码的剖析，我们可以了解到其内部设计理念与实现细节。volley凭借其简洁易用、性能优异的特点，成为了Android开发中不可或缺的网络请求框架。希望本文能帮助您更好地理解volley，提高网络请求的开发效率。