android单线程，多线程下载

单线程下载很简单，就是开启一个线程去下载资源再进行本地保存；

多线程下载是通过RandomAccessFile（随机文件读写操作类）来设置每个线程读取文件的起始点位置，起始点之间的长度即为该线程需要下载的文件大小

下载开始位置：线程id*每条线程下载的数据长度 = ?

下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

这样比如文件大小：size，线程数：threads，则每个线程的下载量：size/threads；但是这是整除的情况，如果考虑到不能整除的情况：则前threads-1个线程下载量为size/threads，最后一个线程的下载量：size/threads+size%threads
File_downactivity.java代码
package file.down;

import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;

import javax.security.auth.PrivateCredentialPermission;

import android.R.integer;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewDebug.FlagToString;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;

public class File_downActivity extends Activity {
    private Button but1,but2;
    private EditText etUrl;
    private ProgressBar bar1,bar2;
    private TextView tv1,tv2;
    private boolean flag = true;
    private int temp = 0;
    private int downLoadedSize = 0;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        etUrl = (EditText) findViewById(R.id.downloadUrl);

        but1 = (Button) findViewById(R.id.but1);
        but2 = (Button) findViewById(R.id.but2);

        bar1 = (ProgressBar) findViewById(R.id.downloadProgressBar1);
        bar2 = (ProgressBar) findViewById(R.id.downloadProgressBar2);

        tv1 = (TextView) findViewById(R.id.tv1);
        tv2 = (TextView) findViewById(R.id.tv2);


        //单线程下载
        but1.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                if(DownUtil.isExistSdCard()){
                    if(DownUtil.checkNet(File_downActivity.this)){
                        if(DownUtil.creatDir(DownUtil.path1)){
                            thread.start();
                        }
                    }
                }
            }
        });
        //多线程下载
        but2.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                mulThread.start();
            }
        });
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        DownUtil.downLoadSize = 0;
    }
    /**
     * 单线程下载
     */
    private Thread thread = new Thread(new Runnable() {

        @Override
        public void run() {

                DownUtil.fileDown1(etUrl.getText().toString(), DownUtil.savePath1, handler);
                bar1.setMax(DownUtil.fileSize);
        }
    });
    /**
     * 多线程下载(主线程类)
     */
    private Thread mulThread = new Thread(new Runnable() {
        private int blockSize,downLoadSizeMore;
        private int threadNum = 5;//线程数

        @Override
        public void run() {
//          MulDownThread[] threads = new MulDownThread[threadNum];
            try {
                URL url = new URL(etUrl.getText().toString()); 补充：移动开发 , Android ,