Android 模拟多线程下载

 以下是一个多线程下载的例子，见代码：

1、首先是布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">


    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="下载"
        android:id="@+id/btnDownLoad" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="New Text"
        android:id="@+id/tv"
        android:layout_gravity="center_vertical" />
</LinearLayout>

　　2、然后是对应的Activity文件

import android.app.Activity;
import android.os.Handler;
import android.os.Message;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import com.yt.httpstudy.util.Download;


public class DownLoadActivity extends Activity {
    private Button btnDown;
    private TextView textView;
    private int count = 0;
    private Handler handler = new Handler(){
        //接收信息并且处理
        public void handleMessage(Message message){
            int result = message.what;
            count += result;
           if(count ==3){
               //下载完成后刷新页面
                textView.setText("下载完成！"+count);
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_down_load);
        btnDown = (Button) findViewById(R.id.btnDownLoad);
        textView = (TextView) findViewById(R.id.tv);

        btnDown.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                new Thread(){
                    @Override
                    public void run() {
                        super.run();
                        Download download = new Download(handler);
                        //下载资源的地址
                        download.downLoadFile("http://192.168.1.123:8080/test/asd.jpg");
                    }
                }.start();
            }
        });
    }
}

     3、处理多线程下载

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
 */
public class Download {


    public   Handler handler;
    //创建线程池
    private Executor threadPool = Executors.newFixedThreadPool(3);

    //构造器
    public Download(Handler handler){
        this.handler = handler;
    }

    //线程池对象
    static class DownLoadRunnable implements  Runnable{
        //指定成员变量
        private String url;
        private String fileName;
        private long start,end;
        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() {

            HttpURLConnection conn = null;
            try {
                URL httpUrl = new URL(url);
                conn = (HttpURLConnection) httpUrl.openConnection();
                conn.setRequestProperty("Range", "bytes=" + start + "-" + end);
                conn.setRequestMethod("GET");
                conn.setReadTimeout(5000);

                //往本地写文件
                RandomAccessFile access = new RandomAccessFile(new File(fileName),"rwd");
                access.seek(start);
                //读取数据流
                InputStream in = conn.getInputStream();

                //创建缓冲区
                byte[] b = new byte[1024*4];
                int len = 0;
                while ((len = in.read(b)) !=-1){
                    access.write(b,0,len);
                }
                if(access !=null){
                    access.close();
                }
                if(in !=null){
                    in.close();
                }

                //发送消息
                Message message = new Message();
                message.what =1;
                handler.sendMessage(message);
            } catch (IOException e) {
                e.printStackTrace();
            }

        }
    }

    public void downLoadFile(String url){
        try {
            URL httpUrl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection) httpUrl.openConnection();
            conn.setRequestMethod("GET");
            conn.setReadTimeout(5000);

            //获取下载内容长度
            int count = conn.getContentLength();
            int bloack = count/3;

            //获取文件名
            String fileName = getFileName(url);

            //获取外部设备名称
            File parent  = Environment.getExternalStorageDirectory();
            File fileDownLoad = new File(parent,fileName);

            for(int i=0;i<3;i++){
                long start = i*bloack;
                long end = (i+1)*bloack-1;
                //第三个线程需要包括完最后的数据，否则不完整
                if(i==2){
                    end = count;
                }

                DownLoadRunnable runnable =
                        new DownLoadRunnable(url,
                                fileDownLoad.getAbsolutePath(),
                                start,end,handler);
                //线程池提交任务
                threadPool.execute(runnable);
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //根据URL取出文件名
    public String getFileName(String url){
        return url.substring(url.lastIndexOf("/")+1);
    }
}