多线程下载图片的简单例子

男娘i 2022-07-15 00:06 200阅读 0赞

[原文][Link 1]

package com.example.kirito.myapplication.testdownload;
    
    import android.os.Environment;
    import android.os.Handler;
    import android.os.Message;
    
    import java.io.File;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.RandomAccessFile;
    import java.net.HttpURLConnection;
    import java.net.MalformedURLException;
    import java.net.URL;
    import java.util.concurrent.Executor;
    import java.util.concurrent.Executors;
    
    /**
     * Created by kirito on 2016.10.25.
     */
    
    public class DownLoadHelp {
        //创建线程池
        private Executor threadPool = Executors.newFixedThreadPool(3);
        private Handler handler;
    
        public DownLoadHelp(Handler handler) {
            this.handler = handler;
        }
    
        static class downRunnable implements Runnable{
            private String url;
            private String filename;
            private long start;
            private long end;
            private Handler handler;
    
            public downRunnable(String url, String filename, long start, long end,Handler handler) {
                this.url = url;
                this.filename = filename;
                this.start = start;
                this.end = end;
                this.handler = handler;
            }
    
            @Override
            public void run() {
                HttpURLConnection con = null;
                try {
                    URL urls = new URL(url);
                    con = (HttpURLConnection) urls.openConnection();
                    con.setRequestMethod("GET");
                    con.setReadTimeout(5000);
                    con.setRequestProperty("Range","bytes="+start+"-" + end);
    
                    RandomAccessFile accessFile = new RandomAccessFile(new File(filename),"rwd");
                    accessFile.seek(start);
    
                    InputStream is = con.getInputStream();
                    byte bt[] = new byte[4 * 1024];
                    int len = 0;
                    while ((len = is.read(bt)) != -1){
                        accessFile.write(bt,0,len);
                    }
                    Message msg = new Message();
                    msg.what = 1;
                    handler.sendMessage(msg);
                    if (accessFile != null){
                        accessFile.close();
                    }
                    if (is != null){
                        is.close();
                    }
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }finally {
                    if (con != null){
                        con.disconnect();
                    }
                }
            }
        }
    
        public void downLoadFile(String purl){
            HttpURLConnection con = null;
            try {
                URL url = new URL(purl);
                con = (HttpURLConnection) url.openConnection();
                con.setRequestMethod("GET");
                con.setReadTimeout(5000);
    
                long length = con.getContentLength();
                long block = length / 3;
    
                String fileName = getFileName(purl);
                File parent = Environment.getExternalStorageDirectory();
                File downLoadFile = new File(parent,fileName);
                /**
                 * 若length = 35,35/3=11
                 * i = 0,0-10
                 * i = 1,11-21
                 * i = 2,22-35(因为有for循环里的if语句)
                 */
                for (int i = 0; i < 3; i++) {
                    long start = i * block;
                    long end = (i + 1) * block - 1;
                    if (i == 2){
                        end = length;
                    }
    
                    downRunnable runnable = new downRunnable(purl,downLoadFile.getAbsolutePath(),start,end,handler);
                    threadPool.execute(runnable);
                }
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }finally {
                if (con != null){
                    con.disconnect();
                }
            }
    
        }
        //获取URL里图片的名字
        private String getFileName(String url){
            return url.substring(url.lastIndexOf('/') + 1);
        }
    }

测试界面

package com.example.kirito.myapplication.testdownload;
    
    import android.os.Bundle;
    import android.os.Handler;
    import android.os.Message;
    import android.support.annotation.Nullable;
    import android.support.v7.app.AppCompatActivity;
    import android.view.View;
    import android.widget.Button;
    import android.widget.TextView;
    
    import com.example.kirito.myapplication.R;
    
    /**
     * Created by kirito on 2016.10.25.
     */
    
    public class TestDownLoad extends AppCompatActivity {
        private Button btn;
        private TextView tv;
        private int count;
        private Handler handler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                count += msg.what;
                if (count == 3){
                    tv.setText("download success!");
                }
            }
        };
    
        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.testgosn);
    
            btn = (Button) findViewById(R.id.td_btn);
            tv = (TextView) findViewById(R.id.td_tv);
            btn.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            DownLoadHelp downLoadHelp = new DownLoadHelp(handler);
                            downLoadHelp.downLoadFile("https://ss1.bdstatic.com/70cFvXSh_Q1YnxGkpoWK1HF6hhy/it/u=2980880098,337923771&fm=116&gp=0.jpg");
                        }
                    }).start();
                }
            });
        }
    }

[Link 1]: http://www.imooc.com/video/8338