Android 网络图片浏览器（ ImageView ）

package cn.lwx.imageview;
import Androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.text.TextUtils;
import android.view.View;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
public class MainActivity extends AppCompatActivity {
    protected static final int CHANGE_UI = 1;
    protected static final int ERROR = 2;
    private EditText et_path;
    private ImageView ivPic;
    // 主线程创建消息处理器
    private Handler handler = new Handler() {
        @Override
        public void handleMessage(android.os.Message msg) {
            if (msg.what == CHANGE_UI) {
                Bitmap bitmap = (Bitmap) msg.obj;
                ivPic.setImageBitmap(bitmap);
            } else if (msg.what == ERROR) {
                Toast.makeText(MainActivity.this, "显示图片错误 !",
                        Toast.LENGTH_SHORT).show();
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        et_path = (EditText) findViewById(R.id.et_path);
        ivPic = (ImageView) findViewById(R.id.iv_pic);
        //et_path.setText("http://www.photophoto.cn/m6/018/030/0180300388.jpg");
        //et_path.setText("图片地址!!!");
        //https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=2834084951,2081126851&fm=11&gp=0.jpg
    }
    public void click(View view) {
        final String path = et_path.getText().toString().trim();
        if (TextUtils.isEmpty(path)) { //判断是否为空串
            Toast.makeText(this, "图片路径不能为空 !", Toast.LENGTH_SHORT).show();
        } else {
            //子线程请求网络,Android4.0以后访问网络不能放在主线程中
            new Thread() { //开启一个线程
                private HttpURLConnection conn;
                private Bitmap bitmap;
                public void run() { //联网操作
                    // 连接服务器 get 请求 获取图片
                    try {
                        // 创建URL对象
                        URL url = new URL(path);
                        // 根据url, 发送http的请求
                        conn = (HttpURLConnection) url.openConnection();
                        // 设置请求的方式
                        conn.setRequestMethod("GET");
                        // 设置超时时间
                        conn.setConnectTimeout(5000);
                        // 得到服务器返回的响应码
                        int code = conn.getResponseCode();
                        // 请求网络成功后, 返回码是200
                        if (code == 200) {
                            //获取输入流
                            InputStream is = conn.getInputStream();
                            //将流转换成Bitmap对象
                            bitmap = BitmapFactory.decodeStream(is);
                            //强制规定：必须在主线程中 更改图片
                            //将更改主界面的消息发送给主线程
                            Message msg = new Message();
                            msg.what = CHANGE_UI;//int型常量,区分不同的消息
                            msg.obj = bitmap;//通过消息携带对应的图片(object类型)
                            handler.sendMessage(msg);//发送消息
                        } else {
                            //返回码不等于200 请求服务器失败
                            Message msg = new Message();
                            msg.what = ERROR;
                            handler.sendMessage(msg);
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                        Message msg = new Message();
                        msg.what = ERROR;
                        handler.sendMessage(msg);
                    }
                    //关闭连接
                    conn.disconnect();
                }
            }.start();
        }
    }
}