<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayoutxmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<Button
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/btn_send"
android:text="HTTP获取数据"/>
<TextView
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:id="@+id/text_response"
app:layout_constraintTop_toBottomOf="@id/btn_send"/>
</android.support.constraint.ConstraintLayout>

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private Button btnSend;
    private TextViewresponseText;

    @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnSend = findViewById(R.id.btn_send);
responseText= findViewById(R.id.text_response);
btnSend.setOnClickListener(MainActivity.this);
}

public void onClick(View v) {
   if (v.getId()==R.id.btn_send){
httpGetMsg();
    }
 }

 private void httpGetMsg(){
  new Thread(new Runnable() {
     @Override
     public void run() {
HttpURLConnection connection = null;
BufferedReader reader = null;
       try {
           URL url = new URL("https://www.baidu.com");
           connection = (HttpURLConnection)url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(10000);
connection.setReadTimeout(10000);
InputStream in = connection.getInputStream();

reader = new BufferedReader(new InputStreamReader(in));
StringBuilder response = new StringBuilder();
           String line;
           while ((line = reader .readLine())!=null){
response.append(line);
            }
showResponse(response.toString());
        }catch (Exception e){
e.printStackTrace();
        }finally {
             if (reader!=null){
                try {
reader.close();
                }catch (IOException e){
e.printStackTrace();
                }
              }
             if (connection!=null){
connection.disconnect();
             }
          }
         }
      }).start();
   }
 private void showResponse(final String response){
runOnUiThread(new Runnable() {
     @Override
 public void run() {
responseText.setText(response);
 }
    });
  }
}