MainActivity.java代码：

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
    public void accessNet(View view) {
      new Thread(){
          @Override
          public void run() {
              try {
//                  URL url = new URL("http://www.lnfvc.edu.cn/newweb/index.asp");
//                  URL url = new URL("https://www.baidu.com");
                 URL url = new URL("https://www.jianshu.com/p/cbbe59893263"); //进入网站
                  HttpURLConnection connection = (HttpURLConnection) url.openConnection();  //发送HTTP请求
                  connection.setRequestMethod("GET"); //GET表示从服务器哪里获取数据   POST 表示提交数据给服务器
                  connection.connect();
                  InputStream inputStream=connection.getInputStream();
                  int length=connection.getContentLength();
                  byte[] buf=new byte[9000];
                  int len=0;
                  while ((len=inputStream.read(buf))!=-1){
                      Log.i("len:",len+"......\r\n");
                      Log.i("html",new String(buf,0,len,"UTF-8")+"\n");
                  }
                  inputStream.close();
                  connection.disconnect();
              } catch (IOException e) {
                  e.printStackTrace();
              } finally {
              }
          }
      }.start();
    }
}

AndroidManifest.xml : 获取权限

uses-permission android:name="android.permission.INTERNET"></uses-permission>

activity_main

<LinearLayout xmlns: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="com.lnjr.httpdemo.MainActivity"
    android:orientation="horizontal">
<button 用于发送HTTP请求>    
<Button
        android:id="@+id/accessNet"
        android:onClick="accessNet"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />


</LinearLayout>