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第一步MainActivity.javapackage com.example.myoo;import android.app.Activity;import android.os.Bundle;import android.os.Handler;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;public class MainActivity extends Activity {
   //android:usesCleartextTraffic="true"   这句话非常重要    private Button btnsave;    private EditText editurl;    Handler handler = new Handler()    {
           public void handleMessage(android.os.Message msg)        {
               if(msg.what == 0x123)            {
                   Toast.makeText(getApplicationContext(), "开始下载", Toast.LENGTH_SHORT).show();            }        };    };    @Override    protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        btnsave = (Button) findViewById(R.id.btnsave);        editurl = (EditText) findViewById(R.id.editurl);        btnsave.setOnClickListener(new OnClickListener() {
               @Override            public void onClick(View v) {
                   new Thread()                {
                       @Override                    public void run() {
                           String path = editurl.getText().toString();                        try {
                               DownLoadService.downLoad(path, MainActivity.this);                        } catch (Exception e) {
   e.printStackTrace();}                        handler.sendEmptyMessage(0x123);                    }                }.start();            }        });    }}第二步activity-main.xml
   
       
        
        
    
   第三步 androidManifest.xml    
       
       
           android:usesCleartextTraffic="true"第四步：package com.example.myoo;import java.io.InputStream;import java.io.OutputStream;import java.net.URL;import android.content.Context;import android.widget.Toast;public class DownLoadService {
       public static void downLoad(String path,Context context)throws Exception    {
           URL url = new URL(path);        InputStream is = url.openStream();        //截取最后的文件名        String end = path.substring(path.lastIndexOf("."));        //打开手机对应的输出流,输出到文件中        OutputStream os = context.openFileOutput("Cache_"+System.currentTimeMillis()+end, Context.MODE_PRIVATE);        byte[] buffer = new byte[1024];        int len = 0;        //从输入六中读取数据,读到缓冲区中        while((len = is.read(buffer)) > 0)        {
               os.write(buffer,0,len);        }        //关闭输入输出流        is.close();        os.close();    }}

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