前言：

1.代码摘要只有主线,提供一般流程

2.为了易于理解，码变量名，而是类名的驼峰式写法。如源代码中：WorkRunnable mWorker，在本文中为 workRunnable

3.须要配合看Xutils的源代码，能够让你看Xutils源代码时降低一定的难度

代码主干：

HttpFragment:

//HttpFragment是Xutils自带样例中的一个类
httpUtils = new HttpUtils();

httpUtils.send(mthord, url, params, callback{ onStart(), onLoading(), onSuccess(), onFailure, })

HttpUtils:

httpRequest = new HttpRequest(method, url);

httpUtils.sendRequest(request, params, callback);

httpHandler = new Handler<T>(httpClient, httpContext, resoponseTextCharset, callBack);

httpRequest.setRequestParams(params, httpHandler);

httpHandler.executeOnExcutor(priorityExecutor, request);

PriorityAsynTask == HttpHandler:
//HttpHandler extends PriorityAsyncTask，故下面方法实际上调用的是HttpHandler中的方法

//Thread能够运行的有两类接口 1.Runable()接口 2.Callable接口

//差别是分别调用run()、call()开线程;后者有返回值，可取消作业，能够返回异常

//然而想要用Thread调用Callable须要用FutreTask包装。FutureTask实现了Runable接口,done()方法在作业结束后运行，可用来推断下载成功、取消等状态；

//以下两行代码是初始化。不在运行顺序中

workRunnable{ call(){ return postResult(doInBackground(parmas)}};

futureTask = new FutureTask<Result>(workRunnable){ done( postResultIfNotInvoke())};

workRunnable.mParams = params;

priorityExecutor.execute(new PriorityRunnable(priority, futureTask));

PriorityExecutor:

//用线程池来开线程

threadPoolExecutor.execute(new PriorityRunnable(priority, futrueTask))

PriorityRunnable:

//futureTask是workRunnable包装类，调用的是workRunnable里的方法，即postResult(doInBackground(parmas);
futrueTask.run();

HttpHandler:

//最终执行HttpHandler的doInBackground了

httpHandler.doInBackground();

httpHandler.sendRequest(httpRequest);

httpResponse = client.execute(httpRequest, context);

handleResponse(httpResponse);

fileDownloadHandler.handleEntity(httpEntity, httpHandler, charset);

StringDownloadHandler:

//最终到下载处理阶段了。

O(∩_∩)O哈哈~

while ((line = reader.readLine()) != null) {

httpHandler.updateProgress(total, current, false)

}

HttpHandler:

httpHandler.publishProgress(UPDATE_LOADING, total, current);

//values = new Progress[]{UPDATE_LOADING, total, current}; 利用Java的不确定数量的形參机制，即(Profress... )

//利用Handler机制通信

handler.obtainMessage(MESSAGE_POST_PROGRESS,

new AsyncTaskResult<Progress>(this, values))

//priorityAsyncTask就是httpHandler

asyncTaskResult.priorityAsyncTask.onProgressUpdate(values);

//依据values[0]推断为正在下载

requestCallBack.onLoading(

Long.valueOf(String.valueOf(values[1])),//文件总大小

Long.valueOf(String.valueOf(values[2])),//已下载大小

isUploading);

//好了到这里就结束了，其它的開始下载、下载完、下载失败的回调函数的逻辑于此类似。