android网络开源框架volley(五)——volley的一些细节

    最近又把volley拿出来整理了下。之前没有遇到过的一些小问题又来了，在此记录下：

1、HttpUrlConnection DELETE 方式无法添加body的问题：java.net.ProtocolException: DELETE does not support writing

    这个可以算是一个系统级的bug，为什么这么说，请看这里，这个问题在java8中才得以解决。没办法直接过去，咱就绕过去。查看HttpUrlConnection，我们发现他是一个抽象类，因此可以试试能不能通过它的其他实现来达到我们的目的。最终我们决定使用okhttp这个实现。地址为：https://github.com/square/okhttp。

接着我们还得去看看volley的源码，由于我们的app兼容的最低版本是4.0，因此我们知道最终调用的是HurlStack：

    public static RequestQueue newRequestQueue(Context context, HttpStack stack) {...        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));            }        }...    }

因此我们只需要将HurlStack的相关代码修改即可，如下：

volley.java

public static RequestQueue newRequestQueue(Context context, HttpStack stack) {...        if (stack == null) {            if (Build.VERSION.SDK_INT >= 9) {                // old way: stack = new HurlStack();            // http://square.github.io/okhttp/                stack = new HurlStack(null, null, new OkUrlFactory(new OkHttpClient()));            } 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));            }        }...    }

HurlStack.java

/** * An {@link HttpStack} based on {@link HttpURLConnection}. */public class HurlStack implements HttpStack {    private final OkUrlFactory mOkUrlFactory;     /**     * @param urlRewriter Rewriter to use for request URLs     * @param sslSocketFactory SSL factory to use for HTTPS connections     * @param okUrlFactory solution delete body(https://github.com/square/okhttp)     */    public HurlStack(UrlRewriter urlRewriter, SSLSocketFactory sslSocketFactory, OkUrlFactory okUrlFactory) {        mUrlRewriter = urlRewriter;        mSslSocketFactory = sslSocketFactory;        mOkUrlFactory = okUrlFactory;    }    /**     * Create an {@link HttpURLConnection} for the specified {@code url}.     */    protected HttpURLConnection createConnection(URL url) throws IOException {if(null != mOkUrlFactory){return mOkUrlFactory.open(url);}        return (HttpURLConnection) url.openConnection();    }    @SuppressWarnings("deprecation")    /* package */     static void setConnectionParametersForRequest(HttpURLConnection connection,            Request<?> request) throws IOException, AuthFailureError {        switch (request.getMethod()) {            ...            case Method.DELETE:                connection.setRequestMethod("DELETE");                addBodyIfExists(connection, request);                break;            ...            default:                throw new IllegalStateException("Unknown method type.");        }    }...}

2015-04-26更新：

再次使用到需要使用到okhttp，回头看下上面的代码，不知道当时怎么想的，使用这么复杂的方法引入Okhttp，估计是脑袋进水了。再来看下这个方法：newRequestQueue(Context context, HttpStack stack)，有两个参数：context和HttpStack，这里是要传入自己的HttpStack就好了。那么我们用OKhttp的实现：

/** * An {@link com.android.volley.toolbox.HttpStack HttpStack} implementation which * uses OkHttp as its transport. */public class OkHttpStack extends HurlStack {  private final OkHttpClient client;   public OkHttpStack() {    this(new OkHttpClient());  }   public OkHttpStack(OkHttpClient client) {    if (client == null) {      throw new NullPointerException("Client must not be null.");    }    this.client = client;  }   @Override protected HttpURLConnection createConnection(URL url) throws IOException {    return client.open(url);  }   }

参考：https://gist.github.com/JakeWharton/5616899

2、关于（修改）volley的缓存

    volley有完整的一套缓存机制。而目前我们想做个简单的需求：部分界面（几乎不会改动的）简单的做一定时间的缓存，研究了下代码发现很容易修改达到自己的目的（有时间在分析下volley的缓存机制，这个一定要做）。简单来说修改一个地方：request.parseNetworkResponse中的

HttpHeaderParser（此处突然感慨volley的设计TMD灵活了，想怎么改就怎么改）。HttpHeaderParser修改后的代码如下：

/** * 修改后的，用户处理缓存 */public class BHHttpHeaderParser {    /**     * Extracts a {@link Cache.Entry} from a {@link NetworkResponse}.     *     * @param response The network response to parse headers from     * @return a cache entry for the given response, or null if the response is not cacheable.     */    public static Cache.Entry parseCacheHeaders(NetworkResponse response, boolean isCustomCache) {...        if(isCustomCache){        softExpire = now + Config.HTTP_CACHE_TTL;        } else {        if (hasCacheControl) {            softExpire = now + maxAge * 1000;        } else if (serverDate > 0 && serverExpires >= serverDate) {            // Default semantic for Expire header in HTTP specification is softExpire.            softExpire = now + (serverExpires - serverDate);        }        }                Cache.Entry entry = new Cache.Entry();        entry.data = response.data;        entry.etag = serverEtag;        entry.softTtl = softExpire;        entry.ttl = entry.softTtl;        entry.serverDate = serverDate;        entry.responseHeaders = headers;        return entry;    }...}

此处大家可以发现，我们主要是根据自定义的变量决定如何修改cache的TTL来达到自己的目的。

3、HttpUrlConnection与PATCH（2015-04-26）

在使用Volley发送PATCH请求的时候，我们可能会遇到这样的问题：Unknown method 'PATCH'; must be one of [OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE]。这个时候你的第一反应是什么呢？是Volley不支持PATCH请求吗？换成OkHttp是不是可以呢？查看了下Volley的源码，在HurlHttp.java中发现如下一段：

/* package */ static void setConnectionParametersForRequest(HttpURLConnection connection,            Request<?> request) throws IOException, AuthFailureError {        switch (request.getMethod()) {            case Method.DEPRECATED_GET_OR_POST:                // This is the deprecated way that needs to be handled for backwards compatibility.                // If the request's post body is null, then the assumption is that the request is                // GET.  Otherwise, it is assumed that the request is a POST.                byte[] postBody = request.getPostBody();                if (postBody != null) {                    // Prepare output. There is no need to set Content-Length explicitly,                    // since this is handled by HttpURLConnection using the size of the prepared                    // output stream.                    connection.setDoOutput(true);                    connection.setRequestMethod("POST");                    connection.addRequestProperty(HEADER_CONTENT_TYPE,                            request.getPostBodyContentType());                    DataOutputStream out = new DataOutputStream(connection.getOutputStream());                    out.write(postBody);                    out.close();                }                break;            case Method.GET:                // Not necessary to set the request method because connection defaults to GET but                // being explicit here.                connection.setRequestMethod("GET");                break;            case Method.DELETE:                connection.setRequestMethod("DELETE");                break;            case Method.POST:                connection.setRequestMethod("POST");                addBodyIfExists(connection, request);                break;            case Method.PUT:                connection.setRequestMethod("PUT");                addBodyIfExists(connection, request);                break;            case Method.HEAD:                connection.setRequestMethod("HEAD");                break;            case Method.OPTIONS:                connection.setRequestMethod("OPTIONS");                break;            case Method.TRACE:                connection.setRequestMethod("TRACE");                break;            case Method.PATCH:                connection.setRequestMethod("PATCH");                addBodyIfExists(connection, request);                break;            default:                throw new IllegalStateException("Unknown method type.");        }    }

通过这段代码，我们知道，Volley对PATCH还是支持的。在细看下错误这个是有HttpUrlConnection抛出的。因此我们需要在这方面下手。这里有一个参考：

https://github.com/adriancole/retrofit/commit/e704b800878b2e37f5ac98b0139cb4994618ace0

以后有其他关于volley的总结都记录在此。