一、布局：
<Button
android:layout_width="100dp"
android:layout_height="wrap_content"
android:id="@+id/get"
android:text="获取数据"
android:layout_alignParentTop="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true" />

<ScrollView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@+id/get"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true">
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/text"
        android:layout_below="@+id/get"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />
</ScrollView>

二、在主线程中
public class MainActivity extends AppCompatActivity {
private TextView textView;
private String path;
private Handler handler;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    textView = (TextView) findViewById(R.id.text);
    path = "http://www.baidu.com";
    Button get = (Button) findViewById(R.id.get);
    get.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            getHttpurlConnection();
            handler = new Handler() {//更新主线程UI
                @Override
                public void handleMessage(Message msg) {
                    if(msg.what == 1) {
                        textView.setText(msg.obj.toString());
                    }
                }
            };
        }
    });
}

三、子线程中
private void getHttpurlConnection() {
new Thread(new Runnable() {//创建线程
@Override
public void run() {
try {
URL url = new URL(path);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();//与百度首页链接
connection.setRequestMethod("GET");
connection.setConnectTimeout(200);
BufferedReader br = new BufferedReader(new InputStreamReader(connection.getInputStream()));获取百度首页源代码并封装成BufferedReader
String s1;
StringBuilder s =new StringBuilder();//使用StringBuilder可以拼接获取的字符
while ((s1 = br.readLine()) != null) {
Message msg = new Message();
msg.what = 1;
s.append(s1);
msg.obj=s;
handler.sendMessage(msg);//发送msg给主线程
}
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
}
}