Andriod- 从网络下载文件保存到SDCARD里

package com.cts.testdwonloadimage.testdwonloadimage;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.renderscript.ScriptGroup;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    private ImageView mImageView;
    private File cache;
    private String imgPath="https://www.cnblogs.com/images/logo_small.gif";


    Handler handler=new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            //显示
            Bitmap b=(Bitmap)msg.obj;
            mImageView.setImageBitmap(b);
            //保存至本地
            File imgFile=new File(cache,"woca.jpg");
            try {
                BufferedOutputStream bos=new BufferedOutputStream(new FileOutputStream(imgFile));
                b.compress(Bitmap.CompressFormat.JPEG,80,bos);
                bos.flush();
                bos.close();
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return false;
        }
    });

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

        mImageView=(ImageView)findViewById(R.id.mImageView);

        cache=new File(Environment.getExternalStorageDirectory(),"Test");
        if(!cache.exists()){
            cache.mkdirs();
        }

        new Thread(){
            @Override
            public void run() {
                super.run();

                HttpURLConnection conn = null;
                InputStream is = null;

                try{
                    URL url = new URL(imgPath);
                    conn=(HttpURLConnection) url.openConnection();
                    conn.setConnectTimeout(5000);
                    conn.setRequestMethod("GET");
                    if(conn.getResponseCode()==200){
                        is=conn.getInputStream();
                        Bitmap b= BitmapFactory.decodeStream(is);
                        //把输入流转化成bitmap格式，以msg形式发送至主线程
                        Message msg=new Message();
                        msg.obj=b;
                        handler.sendMessage(msg);
                    }

                }catch (Exception e){

                    String strEx = e.getMessage();
                    strEx = strEx + "111";
                }finally {
                    //conn.disconnect();
                }

            }
        }.start();

    }
}