使用Apache HttpClient的健壮HTTP

下面的部分内容来源于《Unlocking Android》一书：

 

要了解HTTPClient，我们先看一下如何使用核心类来执行HTTP GET和POST方法请求，此处我们结合使用Apache的ResonseHandler和Android的Handler，在与用户界面不同的线程中发起网络请求。

 

 

// new a Handler to receive the response by HTTP request.
private final Handler mHandler = new Handler() {
	public void handleMessage(Message msg) {
		mPrgressDialog.dismiss();
		String result = msg.getData().getString("RESPONSE");
		mOutput.setText(result);
	};
};

@Override
public void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.main);
	mButton = (Button) findViewById(R.id.btn);
	mButton.setOnClickListener(new OnClickListener() {
		public void onClick(View v) {
			mOutput.setText("");
			performRequest(url);
		}
	});
	mOutput = (TextView) findViewById(R.id.output);
}

// perform HTTP request with HttpRequestHelper asynchronously.
private void performRequest(final String url) {
	final ResponseHandler<String> responseHandler = HttpRequestHelper
			.getResponseHandlerInstance(mHandler);
	// show a ProgressDialog to represent that it is woring now, and it
	// will dismiss after receiving response.
	mPrgressDialog = ProgressDialog.show(this, "working...",
			"performing HTTP request");
	new Thread() {
		public void run() {
			HttpRequestHelper helper = new HttpRequestHelper(
					responseHandler);
			// use GET method
			helper.performGet(url, null, null, null);
		};
	}.start();
}

  

/**
 * Helper for HTTP request via GET or POST method.
 */
public final class HttpRequestHelper {

	private static final int POST_TYPE = 1;
	private static final int GET_TYPE = 2;
	public static final String CONTENT_TYPE = "Content-Type";
	public static final String MIME_FORM_ENCODED = "application/x-www-form-urlencoded";
	public static final String MIME_TEXT_PLAIN = "text/plain";
	private final ResponseHandler<String> mResponseHandler;

	public HttpRequestHelper(ResponseHandler<String> responseHandler) {
		mResponseHandler = responseHandler;
	}

	public void performGet(String url, String user, String pwd,
			final Map<String, String> addtionalHeaders) {
		performRequest(null, url, user, pwd, addtionalHeaders, null, GET_TYPE);
	}

	public void performPost(String contentType, String url, String user,
			String pwd, Map<String, String> addtionalHeaders,
			Map<String, String> params) {
		performRequest(contentType, url, user, pwd, addtionalHeaders, params,
				POST_TYPE);
	}

	public void performPost(String url, String user, String pwd,
			Map<String, String> addtionalHeaders, Map<String, String> params) {
		performRequest(MIME_FORM_ENCODED, url, user, pwd, addtionalHeaders,
				params, POST_TYPE);
	}

	private void performRequest(String contentType, String url, String user,
			String pwd, Map<String, String> headers,
			Map<String, String> params, int requestType) {
		DefaultHttpClient client = new DefaultHttpClient();
		if (user != null && pwd != null) {
			client.getCredentialsProvider().setCredentials(AuthScope.ANY,
					new UsernamePasswordCredentials(user, pwd));
		}

		final Map<String, String> sendHeaders = new HashMap<String, String>();
		if (headers != null && !headers.isEmpty()) {
			sendHeaders.putAll(headers);
		}
		if (POST_TYPE == requestType) {
			sendHeaders.put(CONTENT_TYPE, contentType);
		}
		if (!sendHeaders.isEmpty()) {
			client.addRequestInterceptor(new HttpRequestInterceptor() {

				public void process(HttpRequest request, HttpContext context)
						throws HttpException, IOException {
					for (String key : sendHeaders.keySet()) {
						if (!request.containsHeader(key)) {
							request.addHeader(key, sendHeaders.get(key));
						}
					}
				}
			});
		}

		if (POST_TYPE == requestType) {
			HttpPost post = new HttpPost(url);
			List<NameValuePair> nvps = null;
			if (params != null && !params.isEmpty()) {
				nvps = new ArrayList<NameValuePair>();
				for (String key : params.keySet()) {
					nvps.add(new BasicNameValuePair(key, params.get(key)));
				}
			}
			if (nvps != null) {
				try {
					post.setEntity(new UrlEncodedFormEntity(nvps));
				} catch (UnsupportedEncodingException e) {
					// TODO: handle exception
				}
			}
			execute(client, post);
		} else if (GET_TYPE == requestType) {
			execute(client, new HttpGet(url));
		}
	}

	private void execute(HttpClient client, HttpRequestBase method) {
		try {
			client.execute(method, mResponseHandler);
		} catch (Exception e) {
			BasicHttpResponse erroResponse = new BasicHttpResponse(
					new ProtocolVersion("HTTP_ERROR", 1, 1), 500, "ERROR");
			erroResponse.setReasonPhrase(e.getMessage());
			try {
				mResponseHandler.handleResponse(erroResponse);
			} catch (Exception e2) {
				// TODO: handle exception
			}
		}
	}

	public static ResponseHandler<String> getResponseHandlerInstance(
			final Handler handler) {
		return new ResponseHandler<String>() {
			public String handleResponse(HttpResponse response)
					throws ClientProtocolException, IOException {
				Message message = handler.obtainMessage();
				Bundle data = new Bundle();
				HttpEntity entity = response.getEntity();
				String result = null;
				if (entity != null) {
					try {
						result = EntityUtils.toString(entity);
						data.putString("RESPONSE", result);
					} catch (IOException e) {
						data.putString("RESPONSE", "Error - " + e.getMessage());
					}
				} else {
					StatusLine status = response.getStatusLine();
					data.putString("RESPONSE",
							"Error - " + status.getReasonPhrase());
				}
				message.setData(data);
				message.sendToTarget();
				return result;
			}
		};
	}
}