【移动应用开发技术】怎么在Android中利用线程池控制并发数

【移动应用开发技术】怎么在Android中利用线程池控制并发数

这篇文章给大家介绍怎么在Android中利用线程池控制并发数，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。Android是一种基于Linux内核的自由及开放源代码的操作系统，主要使用于移动设备，如智能手机和平板电脑，由美国Google公司和开放手机联盟领导及开发。主要实现步奏：1、定义一个DownUtil类，下载工作基本在此类完成，在构造器中初始化UI线程的Handler。用于子线程和UI线程传递下载进度值。2、所有的下载任务都保存在LinkedList。在init（）方法中开启一个后台线程，不断地从LinkedList中取任务交给线程池中的空闲线程执行。3、每当addTask方法添加一个任务，就向mPoolThreadHandler发送条消息，就从任务队列中取出一个任务交给线程池执行。这里使用了使用了Semaphore信号量，也就是说只有当一个任务执行完成之后，release（）一个信号量，才能从LinkedList中取出一个任务再去执行，否则acquire（）方法会一直阻塞线程，直到上一个任务完成。public

class

DownUtil

{

//定义下载资源的路径

private

String

path;

//指定下载文件的保存位置

private

String

targetFile;

//定义下载文件的总大小

private

int

fileSize;

//线程池

private

ExecutorService

mThreadPool;

//线程数量

private

static

final

int

DEFAULT_THREAD_COUNT

=

5;

//任务队列

private

LinkedList<Runnable>

mTasks;

//后台轮询线程

private

Thread

mPoolThread;

//后台线程的handler

private

Handler

mPoolThreadHandler;

//UI线程的Handler

private

Handler

mUIThreadHandler;

//信号量

private

Semaphore

semaphore;

private

Semaphore

mHandlerSemaphore

=

new

Semaphore(0);

//下载线程数量

private

int

threadNum;

public

DownUtil(String

path

,

String

targetFile

,

int

threadNum

,

final

ProgressBar

bar)

{

this.path

=

path;

this.targetFile

=

targetFile;

this.threadNum

=

threadNum;

init();

mUIThreadHandler

=

new

Handler()

{

int

sumSize

=

0;

@Override

public

void

handleMessage(Message

msg)

{

if

(msg.what

==

0x123)

{

int

size

=

msg.getData().getInt("upper");

sumSize

+=

size;

Log.d("sumSize"

,

sumSize

+

"");

bar.setProgress((int)

(sumSize

*

1.0

/

fileSize

*

100));

}

}

};

}

private

void

init()

{

mPoolThread

=

new

Thread()

{

public

void

run()

{

Looper.prepare();

mPoolThreadHandler

=

new

Handler()

{

public

void

handleMessage(Message

msg)

{

if

(msg.what

==

0x111)

{

mThreadPool.execute(getTask());

try

{

semaphore.acquire();

}

catch

(InterruptedException

e)

{

e.printStackTrace();

}

}

}

};

mHandlerSemaphore.release();

Looper.loop();

}

};

mPoolThread.start();

mThreadPool

=

Executors.newFixedThreadPool(DEFAULT_THREAD_COUNT);

mTasks

=

new

LinkedList<>();

semaphore

=

new

Semaphore(DEFAULT_THREAD_COUNT);

}

public

void

downLoad()

{

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");

//得到文件的大小

fileSize

=

conn.getContentLength();

conn.disconnect();

int

currentPartSize

=

fileSize

/

threadNum

+

1;

RandomAccessFile

file

=

new

RandomAccessFile(targetFile

,

"rw");

file.setLength(fileSize);

file.close();

for

(int

i

=

0

;

i

<

threadNum

;

i++)

{

//计算每条线程下载的开始位置

int

startPos

=

i

*

currentPartSize;

//每条线程使用一个RandomAccessFile进行下载

RandomAccessFile

currentPart

=

new

RandomAccessFile(targetFile

,

"rw");

//定位该线程的下载位置

currentPart.seek(startPos);

//将任务添加到任务队列中

addTask(new

DownThread(startPos

,

currentPartSize

,

currentPart));

}

}

catch

(IOException

e)

{

e.printStackTrace();

}

}

private

Runnable

getTask()

{

if

(!mTasks.isEmpty())

{

return

mTasks.removeFirst();

}

return

null;

}

private

synchronized

void

addTask(Runnable

task)

{

mTasks.add(task);

try

{

if

(mPoolThreadHandler

==

null)

{

mHandlerSemaphore.acquire();

}

}

catch

(InterruptedException

e)

{

e.printStackTrace();

}

mPoolThreadHandler.sendEmptyMessage(0x111);

}

private

class

DownThread

implements

Runnable

{

//当前线程的下载位置

private

int

startPos;

//定义当前线程负责下载的文件大小

private

int

currentPartSize;

//当前线程需要下载的文件块

private

RandomAccessFile

currentPart;

//定义该线程已经下载的字节数

private

int

length;

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();

//跳过startPos个字节

skipFully(inStream

,

this.startPos);

byte[]

buffer

=

new

byte[1024];

int

hasRead

=

0;

while

(length

<

currentPartSize

&&

(hasRead

=

inStream.read(buffer))

>

0)

{

currentPart.write(buffer

,

0

,

hasRead);

//累计该线程下载的总大小

length

+=

hasRead;

}

Log.d("length"

,

length

+

"");

//创建消息

Message

msg

=

new

Message();

msg.what

=

0x123;

Bundle

bundle

=

new

Bundle();

bundle.putInt("upper"

,

length);

msg.setData(bundle);

//向UI线程发送消息

mUIThreadHandler.sendMessage(msg);

semaphore.release();

currentPart.close();

inStream.close();

}

catch

(Exception

e)

{

e.printStackTrace();

}

}

}

public

static

void

skipFully(InputStream

in

,

long

bytes)

throws

IOException

{

long

remaining

=

bytes;

long

len

=

0;

while

(remaining

>

0)

{

len

=

in.skip(remaining);

remaining

-=

len;

}

}

}以下是MainActivity的代码：public

class

MainActivity

extends

Activity

{

EditText

url;

EditText

target;

Button

downBn;

ProgressBar

bar;

DownUtil

downUtil;

private

String

savePath;

@Override

protected

void

onCreate(Bundle

savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

//获取界面中的四个界面控件

url

=

(EditText)

findViewById(R.id.address);

target

=

(EditText)

findViewById(R.id.target);

try

{

File

sdCardDir

=

Environment.getExternalStorageDirectory();

savePath

=

sdCardDir.getCanonicalPath()

+

"/d.chm";

}

catch

(Exception

e)

{

e.printStackTrace();

}

target.setText(savePath);

downBn

=

(Button)

findViewById(R.id.down);

bar

=

(ProgressBar)

findViewById(R.id.bar);

downBn.setOnClickListener(new

View.OnClickListener()

{

@Override

public

void

onClick(View

view)

{

downUtil

=

new

DownUtil(url.getText().toString()

,

target.getText().toString()

,

7

,

bar);

new

Thread()

{

@Override

public

void

run()

{

try

{

downUtil.downLoad();

}

catch

(Exception

e)

{

e.printStackTrace();

}

}

}.start();

}

});

}

}页面布局比较简单这里一并贴出：<LinearLayout

xmlns:android="/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical">

<TextView

android:layout_width="match_parent"

android:layout_height="wrap_content