Android 使用HttpURLConnection实现多线程下载 笔记

参考阅读文章：

http://www.tuicool.com/articles/7bEJFv

使用HttpURLConnection实现多线程下载  核心步骤：

*****************源代码及注释****************

DownUtil.java

package com.example.multithreaddown;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;public class DownUtil {private String path;private String targetFile;private int ThreadNum;private DownThread[] threads;//downthread object  arrayprivate int total_filesize;//get length  , calculate down percentage public DownUtil(String path,String targetFile,int ThreadNum){//outclass constructorthis.path = path;this.targetFile = targetFile;this.ThreadNum = ThreadNum;threads = new DownThread[ThreadNum];//initial download object array}//main download method  create each downthread objectpublic void download() throws Exception{URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection)url.openConnection();//conn.setConnectTimeout(5 * 1000);conn.setRequestMethod("GET");conn.setRequestProperty("Accept","image/gif, image/jpeg, image/pjpeg, image/pjpeg, "+ "application/x-shockwave-flash, application/xaml+xml, "+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "+ "application/x-ms-application, application/vnd.ms-excel, "+ "application/vnd.ms-powerpoint, application/msword, */*");conn.setRequestProperty("Accept-Language", "zh-CN");conn.setRequestProperty("Charset", "UTF-8");//**UTF-8***in android platform conn.setRequestProperty("Connection", "Keep-Alive");//total_filesize = conn.getContentLength();conn.disconnect();RandomAccessFile file = new RandomAccessFile(targetFile,"rw");file.setLength(total_filesize);file.close();int currentPartSize = total_filesize/ThreadNum + 1;int startPos = 0;//create each download threadfor(int i = 0;i<ThreadNum;i++){startPos = i*currentPartSize;//***RandomAccessFile currentPart = new RandomAccessFile(targetFile,"rw");currentPart.seek(startPos);threads[i] = new DownThread(startPos,currentPartSize,currentPart);//threads[i].start();//}}public double getCompleteRate(){int sumSize = 0;for(int i = 0;i<ThreadNum;i++){//calculate the already download amount of each threadsumSize += threads[i].download_length;}return (sumSize*1.0)/total_filesize;}//Inner thread classprivate class DownThread extends Thread{//private int startPos;private int currentPartSize;private RandomAccessFile currentPart;public int download_length = 0;//calculate percentage in outer class method//inner class constructorpublic DownThread(int startPos,int currentPartSize,RandomAccessFile currentPart){this.startPos = startPos;this.currentPartSize = currentPartSize;this.currentPart = currentPart;}@Overridepublic void run(){try{URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection)url.openConnection();//conn.setConnectTimeout(5 * 1000);conn.setRequestMethod("GET");conn.setRequestProperty("Accept","image/gif, image/jpeg, image/pjpeg, image/pjpeg, "+ "application/x-shockwave-flash, application/xaml+xml, "+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "+ "application/x-ms-application, application/vnd.ms-excel, "+ "application/vnd.ms-powerpoint, application/msword, */*");conn.setRequestProperty("Accept-Language", "zh-CN");conn.setRequestProperty("Charset", "UTF-8");conn.setRequestProperty("Connection", "Keep-Alive");//InputStream inStream = conn.getInputStream();inStream.skip(startPos);//byte []buffer = new byte[1024];int hasRead = 0;////while((download_length<=currentPartSize)&&(hasRead = inStream.read(buffer))!=-1){while((download_length<currentPartSize)&&(hasRead = inStream.read(buffer))!=-1){currentPart.write(buffer, 0, hasRead);//download_length += hasRead;}currentPart.close();inStream.close();}catch(Exception e){e.printStackTrace();}}}}

MultiThreadDown.java

package com.example.multithreaddown;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;public class DownUtil {private String path;private String targetFile;private int ThreadNum;private DownThread[] threads;//downthread object  arrayprivate int total_filesize;//get length  , calculate down percentage public DownUtil(String path,String targetFile,int ThreadNum){//outclass constructorthis.path = path;this.targetFile = targetFile;this.ThreadNum = ThreadNum;threads = new DownThread[ThreadNum];//initial download object array}//main download method  create each downthread objectpublic void download() throws Exception{URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection)url.openConnection();//conn.setConnectTimeout(5 * 1000);conn.setRequestMethod("GET");conn.setRequestProperty("Accept","image/gif, image/jpeg, image/pjpeg, image/pjpeg, "+ "application/x-shockwave-flash, application/xaml+xml, "+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "+ "application/x-ms-application, application/vnd.ms-excel, "+ "application/vnd.ms-powerpoint, application/msword, */*");conn.setRequestProperty("Accept-Language", "zh-CN");conn.setRequestProperty("Charset", "UTF-8");//**UTF-8***in android platform conn.setRequestProperty("Connection", "Keep-Alive");//total_filesize = conn.getContentLength();conn.disconnect();RandomAccessFile file = new RandomAccessFile(targetFile,"rw");file.setLength(total_filesize);file.close();int currentPartSize = total_filesize/ThreadNum + 1;int startPos = 0;//create each download threadfor(int i = 0;i<ThreadNum;i++){startPos = i*currentPartSize;//***RandomAccessFile currentPart = new RandomAccessFile(targetFile,"rw");currentPart.seek(startPos);threads[i] = new DownThread(startPos,currentPartSize,currentPart);//threads[i].start();//}}public double getCompleteRate(){int sumSize = 0;for(int i = 0;i<ThreadNum;i++){//calculate the already download amount of each threadsumSize += threads[i].download_length;}return (sumSize*1.0)/total_filesize;}//Inner thread classprivate class DownThread extends Thread{//private int startPos;private int currentPartSize;private RandomAccessFile currentPart;public int download_length = 0;//calculate percentage in outer class method//inner class constructorpublic DownThread(int startPos,int currentPartSize,RandomAccessFile currentPart){this.startPos = startPos;this.currentPartSize = currentPartSize;this.currentPart = currentPart;}@Overridepublic void run(){try{URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection)url.openConnection();//conn.setConnectTimeout(5 * 1000);conn.setRequestMethod("GET");conn.setRequestProperty("Accept","image/gif, image/jpeg, image/pjpeg, image/pjpeg, "+ "application/x-shockwave-flash, application/xaml+xml, "+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "+ "application/x-ms-application, application/vnd.ms-excel, "+ "application/vnd.ms-powerpoint, application/msword, */*");conn.setRequestProperty("Accept-Language", "zh-CN");conn.setRequestProperty("Charset", "UTF-8");conn.setRequestProperty("Connection", "Keep-Alive");//InputStream inStream = conn.getInputStream();inStream.skip(startPos);//byte []buffer = new byte[1024];int hasRead = 0;////while((download_length<=currentPartSize)&&(hasRead = inStream.read(buffer))!=-1){while((download_length<currentPartSize)&&(hasRead = inStream.read(buffer))!=-1){currentPart.write(buffer, 0, hasRead);//download_length += hasRead;}currentPart.close();inStream.close();}catch(Exception e){e.printStackTrace();}}}}

activity_multi_thread_down.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:orientation="vertical"android:layout_width="match_parent"android:layout_height="match_parent"><TextViewandroid:layout_width="match_parent" android:layout_height="wrap_content"android:text="下载资源的URL："/><EditTextandroid:id="@+id/url"  android:layout_width="match_parent" android:layout_height="wrap_content"android:text="http://zhangmenshiting.baidu.com/data2/music/108215782/14385500158400128.mp3?xcode=403698f0ca4477d527224dddfa01e691cc816ddc4bb4461a"/><TextViewandroid:layout_width="match_parent" android:layout_height="wrap_content"android:text="目标文件："/><EditTextandroid:id="@+id/target"  android:layout_width="match_parent" android:layout_height="wrap_content"android:text="/mnt/sdcard/时间都去哪儿了.mp3"/><TextViewandroid:layout_width="match_parent" android:layout_height="wrap_content"android:text="线程数："/><NumberPickerandroid:id="@+id/np_thread"android:layout_width="match_parent"android:layout_height="80dp"android:focusable="true"android:focusableInTouchMode="true" /><Buttonandroid:id="@+id/down"  android:layout_width="wrap_content" android:layout_height="wrap_content"android:layout_gravity="center"android:text="下载"/><!-- 定义一个水平进度条,用于显示下载进度 --><ProgressBarandroid:id="@+id/bar" android:layout_width="match_parent" android:layout_height="20dp"android:max="100"style="?android:attr/progressBarStyleHorizontal"/></LinearLayout>

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注释：

1.核心代码：

首先创建一个文件指针file指向将要写的文件，设置该文件的大小，然后关闭该文件指针。

接着在创建不同线程的for()循环中让不同线程的new currentPart文件指针指向该文件的不同部分；让不同线程写该文件的不同部分。

2.核心Java  IO API支持：

（1）

public class RandomAccessFile

extends Object

implements DataOutput, DataInput, Closeable

此类的实例支持对随机访问文件的读取和写入。随机访问文件的行为类似存储在文件系统中的一个大型 byte 数组。存在指向该隐含数组的光标或索引，称为文件指针；输入操作从文件指针开始读取字节，并随着对字节的读取而前移此文件指针。如果随机访问文件以读取/写入模式创建，则输出操作也可用；输出操作从文件指针开始写入字节，并随着对字节的写入而前移此文件指针。写入隐含数组的当前末尾之后的输出操作导致该数组扩展。该文件指针可以通过getFilePointer 方法读取，并通过seek 方法设置。

构造方法：

RandomAccessFile(String name,String mode)
创建从中读取和向其中写入（可选）的随机访问文件流，该文件具有指定名称。

方法摘要

void seek(long pos) 
设置到此文件开头测量到的文件指针偏移量，在该位置发生下一个读取或写入操作。

void write(byte[] b, int off, int len) 
将 len 个字节从指定 byte 数组写入到此文件，并从偏移量 off 处开始。

void setLength(long newLength) 
设置此文件的长度。

（2）

java.io 
类 InputStream
long skip(long n) 
跳过和丢弃此输入流中数据的 n 个字节。

3. 计算每条线程需要下载的数据长度的原理及影响的详细分析:

 * 1 如果资源大小模于线程数时结果为0,那么表示每条线程需要下载的大小恰好将原大小等分

 * 2 当然更多的情况是有余数的(即不能整除).那么此时该怎么办呢?每条线程该下载的长度是多少呢?

 *   我们可以这么做:

（1）原大小/除以线程的条数

 （2） 在1的基础上+1

  这样就表示每条线程要下载的大小长度

4.需要添加的相关权限

<!-- 在SD卡中创建与删除文件权限-->

    <uses-permissionandroid:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>

    <!--向SD卡写入数据权限 -->

    <uses-permissionandroid:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

    <!--授权访问网络 -->

    <uses-permissionandroid:name="android.permission.INTERNET"/>

5.注意：

线程中不能处理UI操作  比如toast 

要处理UI操作都只能通知Handler  更新用户UI界面