package net.webjoy.jackluo.android_json;

/**

 *  1.http Range "bytes="+  start+end

 *  2.RandomAccessFile设置写入的位置

 *  3开启多线程下载

 *

 * Created by jackluo on 9/30/15.

 */

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;

/**

 * 多线程下载

 */

public class DownLoad {

    //创建一个线程池      创建三个线程

    private Executor threadPool = Executors.newFixedThreadPool(3);

    private Handler handler;

    public DownLoad(Handler handler){

        this.handler = handler;

    }

    //创建一个线程池对象

    static class DownLoadRunnable implements Runnable{

        private String url;

        private String fileName;

        private long start ;//开始位置

        private long end;//结束位置

        private Handler handler;

        public DownLoadRunnable(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() {

            try {

                URL httpUrl = new URL(url);

                HttpURLConnection connection = (HttpURLConnection) httpUrl.openConnection();

                connection.setRequestMethod("GET");

                connection.setReadTimeout(5000);

                //设置下载位置  向服务器拿到指定的流信息

                connection.setRequestProperty("Range", "bytes=" + start + "-" + end);

                //创建一个文件  根据指定位置写入信息

                RandomAccessFile accessFile = new RandomAccessFile(new File(fileName),"rwx");

                accessFile.seek(start);//设置读写的位置

                InputStream inputStream = connection.getInputStream();

                byte[] b = new byte[1024*4];//设置缓冲区的大小存

                int len=0;

                while ((len = inputStream.read(b))!=-1){

                    accessFile.write(b,0,len);

                }

                if (accessFile !=null){

                    accessFile.close();

                }

                if (inputStream !=null){

                    inputStream.close();

                }

                //给主线程发送一个消息

                Message message = new Message();

                message.what = 1;

                handler.sendMessage(message);

            } catch (MalformedURLException e) {

                e.printStackTrace();

            } catch (IOException e) {

                e.printStackTrace();

            }

        }

    }

    public void downLoadFile(String url){

        try {

            URL httpUrl = new URL(url);

            HttpURLConnection connection = (HttpURLConnection) httpUrl.openConnection();

            connection.setRequestMethod("GET");

            connection.setReadTimeout(5000);

            int count = connection.getContentLength();//获取了图片的大小

            int block = count/3;

            //算线程的启始位置

            String fileName = getFileName(url);

            File parent = Environment.getExternalStorageDirectory();

            File fileDownLoad = new File(parent,fileName);

            /**

             * 11 / 3 = 每个下载 3个字节3 还余出2个字节空间

             * 第一个线程 0-2

             * 第二个线程 3-5

             * 第三个线程 6-10

             *

             *

             */

            for (int i=0;i<3;i++){

                long start = i*block;

                long end = (i+1)*block -1;

                if (i==2){

                    end = count;

                }

                DownLoadRunnable runnable = new DownLoadRunnable(url, fileDownLoad.getAbsolutePath(),start,end,handler);

                //提交任务

                threadPool.execute(runnable);

            }

        } catch (MalformedURLException e) {

            e.printStackTrace();

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

    /**

     * 获取 URL后缀名

     */

    public String getFileName(String url){

        return url.substring(url.lastIndexOf("/")+1);

    }

}

package net.webjoy.jackluo.android_json;

import android.os.Bundle;

import android.os.Handler;

import android.os.Message;

import android.support.v7.app.AppCompatActivity;

import android.view.View;

import android.widget.Button;

import android.widget.TextView;

public class DownLoadActivity extends AppCompatActivity {

    private Button button;

    private TextView textView;

    private int count =1;

    private Handler handler = new Handler(){

        @Override

        public void handleMessage(Message msg) {

            //super.handleMessage(msg);

            int result = msg.what;

            count +=result;

            if (count==3){

                textView.setText("download success");

            }

        }

    };

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_down_load);

        button = (Button) findViewById(R.id.downlad_btn);

        textView = (TextView) findViewById(R.id.textView);

        button.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                new Thread(){

                    @Override

                    public void run() {

                        DownLoad load = new DownLoad(handler);

                        load.downLoadFile("http://news.jsyks.com/photo/img1a.xgo-img.com.cn/pics/737/736406.jpg");

                    }

                }.start();

            }

        });

    }

}