对于android-async-http post请求过程进行简单的源码分析

安卓阵营在Android M版本就放弃org.apache.http.legacy,对于构建在其上面的android-async-http,github也不再更新。虽然其已经退出了历史舞台,但对我这样的仅仅知道调用、调用的码农,尚未知道这个框架是怎么运行的。最近花费时间研究一下,期望可以对自己的分析源码、软件设计有些提升。肯定有多不做之处,期待您的批评。

        asyncHttpClient.post(MainActivity.this.getApplicationContext(), path, stringEntity, "application/json", new AsyncHttpResponseHandler() {

            @Override
            public void onSuccess(int statusCode, Header[] headers, byte[] responseBody) {
                tv.setText(new String(responseBody));
            }

            @Override
            public void onFailure(int statusCode, Header[] headers,
                                  byte[] responseBody, Throwable error) {
                tv.setText(new String(responseBody));

            }
        });

点击post方法进行一步步跟踪到sendRequest

        AsyncHttpRequest request = newAsyncHttpRequest(client, httpContext, uriRequest, contentType, responseHandler, context);
        threadPool.submit(request);

也就是说具体的网络请求是通过在线程池中执行Runnable——AsyncHttpRequest ,完成的。
AsyncHttpRequest.run() -> makeRequestWithRetries() -> makeRequest()

    private void makeRequest() throws IOException {
    ...
        HttpResponse response = client.execute(request, context);//进行具体的网络请求

    ...
        responseHandler.sendResponseMessage(response);
        }

网络请求结果是通过responseHandler处理的,而它恰恰就是我们post传递的参数AsyncHttpResponseHandler。

AsyncHttpResponseHandler.sendResponseMessage

    @Override
    public void sendResponseMessage(HttpResponse response) throws IOException {
    //解析HttpResponse.
    ...
                    sendFailureMessage(status.getStatusCode(), response.getAllHeaders(), responseBody, new HttpResponseException(status.getStatusCode(), status.getReasonPhrase()));
                } else {
                    sendSuccessMessage(status.getStatusCode(), response.getAllHeaders(), responseBody);
                }
            }
        }
    }
    @Override
    final public void sendSuccessMessage(int statusCode, Header[] headers, byte[] responseBytes) {
        sendMessage(obtainMessage(SUCCESS_MESSAGE, new Object[]{statusCode, headers, responseBytes}));
    }

    @Override
    final public void sendFailureMessage(int statusCode, Header[] headers, byte[] responseBody, Throwable throwable) {
        sendMessage(obtainMessage(FAILURE_MESSAGE, new Object[]{statusCode, headers, responseBody, throwable}));
    }
    protected Message obtainMessage(int responseMessageId, Object responseMessageData) {
        return Message.obtain(handler, responseMessageId, responseMessageData);
    }

这里生成的Message就是Android应用开发中常见的Message了。

    protected void sendMessage(Message msg) {

            handler.sendMessage(msg);
        }
    }

这里的handler就是Android应用开发中常见的Handler了。
下面肯定要分析handleMessage方法咯

    /**
     * Avoid leaks by using a non-anonymous handler class.
     */
    private static class ResponderHandler extends Handler {
        private final AsyncHttpResponseHandler mResponder;

        ResponderHandler(AsyncHttpResponseHandler mResponder, Looper looper) {
            super(looper);
            this.mResponder = mResponder;
        }

        @Override
        public void handleMessage(Message msg) {
            mResponder.handleMessage(msg);
        }
    }

这里用到了代理模式,结果又调用了AsyncHttpResponseHandler.handleMessage()

  // Methods which emulate android's Handler and Message methods
    protected void handleMessage(Message message) {
   ...
            switch (message.what) {
                case SUCCESS_MESSAGE:
                 ...
                        onSuccess((Integer) response[0], (Header[]) response[1], (byte[]) response[2]);
                 ...
                    break;
                case FAILURE_MESSAGE:
                   ...
                        onFailure((Integer) response[0], (Header[]) response[1], (byte[]) response[2], (Throwable) response[3]);
                  ...
                    break;
         ...
        }
    }

这里onSuccess && onFailure 就是我们传入post中AsyncHttpResponseHandler对象的方法了。

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