Android网络技术（三）——网络编程的最佳实践

一、HttpURLConnection封装Http

public class HttpUtil {
    public static String sendHttpRequest(String address){
        HttpURLConnection connection = null;
        try {
            URL url = new URL(address);
            connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setConnectTimeout(8000);
            connection.setDoInput(true);
            connection.setDoOutput(true);
            InputStream in = connection.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(in));
            StringBuilder response = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null){
                response.append(line);
            }
            return response.toString();
        }catch (Exception e){
            e.printStackTrace();
            return e.getMessage();
        }finally {
            if(connection != null){
                connection.disconnect();
            }
        }
    }
}

发起HTTP请求就这样写：

String address = "http://www.baidu.com";
String response = HttpUtil.sendHttpRequest(address);

为了避免耗时操作阻塞主线程，我们需要使用JAVA的回调机制：
首先需要定义一个接口，命名为HttpCallbackListener:

public interface HttpCallbackListener {
    void onFinish(String response);
    
    void onError(Exception e);
}

然后修改HttpUtil的代码：

public class HttpUtil {
    public static void sendHttpRequest(final String address, final HttpCallbackListener listener){
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                try {
                    URL url = new URL(address);
                    connection = (HttpURLConnection) url.openConnection();
                    connection.setRequestMethod("GET");
                    connection.setConnectTimeout(8000);
                    connection.setDoInput(true);
                    connection.setDoOutput(true);
                    InputStream in = connection.getInputStream();
                    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null){
                        response.append(line);
                    }
                    if (listener != null){
                        listener.onFinish(response.toString());
                    }
                }catch (Exception e){
                    e.printStackTrace();
                    if (listener != null){
                        listener.onError(e);
                    }
                }finally {
                    if(connection != null){
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }
}

通过开启一个子线程将数据或异常原因传入了HttpCallbackListener的方法中，之后就可以这么调用：

HttpUtil.sendHttpRequest(address, new HttpCallbackListener(){
	@Override
	public void onFinish(String response){
		// 这里写返回内容的执行逻辑
	}
	@Override
	public void onError(Exception e){
		// 这里对异常情况进行处理
	}
});

二、OkHttp封装Http

public class HttpUtil {
    public static void sendHttpRequest(String address, okhttp3.Callback callback){
        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder()
                .url(address)
                .build();
        client.newCall(request).enqueue(callback);
    }
}

okhttp3.Callback这个参数就是OkHttp库中自带的回调接口，类似于上文的HttpCallbackListener
之后也没有调用.execute()，而是调用.enqueue()，这个方法在内部会开好子线程，并将结果回调到okhttp3.Callback中
所以之后要这么调用：

HttpUtil.sendOkHttpRequest("http://www.baidu.com", new okhttp3.Callback(){
	@Override
	public void onResponse(Call call, Response response)throws IOException{
		// 得到服务器返回的具体内容
		String responseData = response.body().String();
	}
	@Override
	public void onFailure(Call call, IOException e){
		// 对异常情况处理
	}
});

三、总结

需要注意的是，以上两种方法都是在子线程中运行的，因此我们不可以在这里执行任何UI操作，除非借助runOnUiThread()方法进行线程转换。