最近的一次volley整理出下一个。我以前没有再次遭遇了一些小问题，在该记录：
1、HttpUrlConnection DELETE 信息不能加入body问题：java.net.ProtocolException: DELETE does not support writing
这个能够算是一个系统级的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，因此能够试试能不能通过它的其它实现来达到我们的目的。
终于我们决定使用okhttp这个实现。地址为：https://github.com/square/okhttp。
接着我们还得去看看volley的源代码，因为我们的app兼容的最低版本号是4.0。因此我们知道终于调用的是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));
}
}
...
}因此我们仅仅须要将HurlStack的相关代码改动就可以，例如以下：
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));
}
}
...
}/**
* 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：
再次使用到须要使用到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。预计是脑袋进水了。
再来看下这种方法：newRequestQueue(Context context, HttpStack stack)，有两个參数：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);
}
}2、关于（改动）volley的缓存
volley有完整的一套缓存机制。而眼下我们想做个简单的需求：部分界面（差点儿不会改动的）简单的做一定时间的缓存，研究了下代码发现非常easy改动达到自己的目的（有时间在分析下volley的缓存机制，这个一定要做）。简单来说改动一个地方：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改动后的代码例如以下：
/**
* 改动后的。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;
}
...
}此处大家能够发现，我们主要是依据自己定义的变量决定怎样改动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，我们可能会遇到这种问题：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是不是能够呢？查看了下Volley的源代码，在HurlHttp.java中发现例如以下一段：
/* 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.");
}
}这里有一个參考：
https://github.com/adriancole/retrofit/commit/e704b800878b2e37f5ac98b0139cb4994618ace0
以后有其它关于volley它被记录在这个摘要。
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