android網絡開源框架volley(五)——volley的一些細節

最近又把volley拿出來整理了下。之前沒有遇到過的一些小問題又來了，在此記錄下：

1、HttpUrlConnection DELETE 方式無法添加body的問題：java.net.ProtocolException: DELETE does not support writing

這個可以算是一個系統級的bug，為什麼這麼說，請看這裡，這個問題在java8中才得以解決。沒辦法直接過去，咱就繞過去。查看HttpUrlConnection，我們發現他是一個抽象類，因此可以試試能不能通過它的其他實現來達到我們的目的。最終我們決定使用okhttp這個實現。地址為：https://github.com/square/okhttp。

接著我們還得去看看volley的源碼，由於我們的app兼容的最低版本是4.0，因此我們知道最終調用的是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));
            }
        }
...
    }

因此我們只需要將HurlStack的相關代碼修改即可，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.");
        }
    }

...
}

2、關於（修改）volley的緩存

volley有完整的一套緩存機制。而目前我們想做個簡單的需求：部分界面（幾乎不會改動的）簡單的做一定時間的緩存，研究了下代碼發現很容易修改達到自己的目的（有時間在分析下volley的緩存機制，這個一定要做）。簡單來說修改一個地方：request.parseNetworkResponse中的

HttpHeaderParser（此處突然感慨volley的設計TMD靈活了，想怎麼改就怎麼改）。HttpHeaderParser修改後的代碼如下：

/**
 * 修改後的，用戶處理緩存
 */
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;
    }
...
}

此處大家可以發現，我們主要是根據自定義的變量決定如何修改cache的TTL來達到自己的目的。

以後有其他關於volley的總結都記錄在此。