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  array

private int total_filesize;//get length  , calculate down percentage

public DownUtil(String path,String targetFile,int ThreadNum){//outclass constructor
this.path = path;
this.targetFile = targetFile;
this.ThreadNum = ThreadNum;
threads = new DownThread[ThreadNum];//initial download object array
}

//main download method  create each downthread object
public 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 thread
for(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 thread
sumSize += threads[i].download_length;
}
return (sumSize*1.0)/total_filesize;
}

//Inner thread class
private 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 constructor
public DownThread(int startPos,int currentPartSize,RandomAccessFile currentPart){
this.startPos = startPos;
this.currentPartSize = currentPartSize;
this.currentPart = currentPart;
}

@Override
public 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  array

private int total_filesize;//get length  , calculate down percentage

public DownUtil(String path,String targetFile,int ThreadNum){//outclass constructor
this.path = path;
this.targetFile = targetFile;
this.ThreadNum = ThreadNum;
threads = new DownThread[ThreadNum];//initial download object array
}

//main download method  create each downthread object
public 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 thread
for(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 thread
sumSize += threads[i].download_length;
}
return (sumSize*1.0)/total_filesize;
}

//Inner thread class
private 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 constructor
public DownThread(int startPos,int currentPartSize,RandomAccessFile currentPart){
this.startPos = startPos;
this.currentPartSize = currentPartSize;
this.currentPart = currentPart;
}

@Override
public 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"
>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="下载资源的URL："
/>
<EditText
android: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"
/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="目标文件："
/>
<EditText
android: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"
/>
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="线程数："
/>

<NumberPicker
android:id="@+id/np_thread"
android:layout_width="match_parent"
android:layout_height="80dp"
android:focusable="true"
android:focusableInTouchMode="true" />

<Button
android: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 -->
<ProgressBar
android:id="@+id/bar"
android:layout_width="match_parent"
android:layout_height="20dp"
android:max="100"
style="?android:attr/progressBarStyleHorizontal"
/>
</LinearLayout>

***********************************************

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