直接上干货，实例代码：

import android.annotation.SuppressLint;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.KeyEvent;
import android.view.View;
import android.widget.TextView;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Scanner;


public class MainActivity extends Activity {

    private static final String TAG = "MainActivity";

    private static final int SHOW_RESPONSE = 0;

    @SuppressLint("HandlerLeak")
    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {

            switch (msg.what) {
                case SHOW_RESPONSE:
                    String response = (String) msg.obj;
                    TextView textView = MainActivity.this.findViewById(R.id.response_text);
                    if (null != textView) {
                        textView.setText(response);
                    }
            }

            super.handleMessage(msg);
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onKeyUp(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            moveTaskToBack(true);
        }
        return super.onKeyUp(keyCode, event);
    }

    @Override
    protected void onResume() {
        super.onResume();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
    }

    private String readInStream(InputStream in) {
        Scanner scanner = new Scanner(in).useDelimiter("\\A");
        return scanner.hasNext() ? scanner.next() : "";
    }

    public void sendRequestWithHttpURLConnection(View view) {
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection urlConnection = null;
                try {
                    URL url = new URL("https://www.baidu.com/");
                    urlConnection = (HttpURLConnection)url.openConnection();
                    Message message = new Message();
                    message.what = SHOW_RESPONSE;
                    message.obj =
                            readInStream(new BufferedInputStream(urlConnection.getInputStream()));
                    handler.sendMessage(message);
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    urlConnection.disconnect();
                }
            }
        }).start();
    }
}

布局文件的代码如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:orientation="vertical"
    >

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/send_request_with_http_url_connection"
        android:onClick="sendRequestWithHttpURLConnection"
        />

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/response_text"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="@string/input_some_text_here"
            />
    </ScrollView>

</LinearLayout>

本文参考自 《Android 第一行代码》