第 3
5.ExecutorServie线程池
通过Executors的静态方法来创建，一般有三种：
1.单线程 ：Executors.newSingleThreadExecutor();
2.固定数量线程 ：Executors.newFixedThreadPool();
3.动态线程 ：Executors.newCachedThreadPool();
这里我们用固定5个线程来应用，使用方法是创建ExecutorService对象，然后执行submit(r)可以发起一个Runnable对象。用线程池来管理的好处是，可以保证系统稳定运行，适用与有大量线程，高工作量的情景下使用，假如要展示1000张图片如果创建1000个线程去加载，保证系统会死掉。用线程池就可以避免这个问题，可以用5个线程轮流执行，5个一组，执行完的线程不直接回收而是等待下次执行，这样对系统的开销就可以减小不少。
private void loadImagesByExecutors(final String url,final int id){
service.submit(new Runnable(){
@Override
public void run() {
// TODO Auto-generated method stub
Log.e("当前线程：", ""+Thread.currentThread().getName());
try {
final Drawable drawable = Drawable.createFromStream(new URL(url).openStream(), "image.gif");
mainHandler.post(new Runnable(){
@Override
public void run() {//这将在主线程运行
// TODO Auto-generated method stub
((ImageView)MainActivity.this.findViewById(id)).setImageDrawable(drawable);
}
});
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
}Log:
其实可能没有说清楚，第一种不算多线程。
1.loadImagesByHandler()是通过Handler.post()方法，构建两个Handler进行通信。
2.loadImagesByThread()，这个是直接new Thread()发起线程，在主线程的handler处理消息
3.loadImageByAsyncTask(),这个用的是异步任务，所有实现在它的内部结构里，可以在里头操作Ui.
4.loadImagesByExecutors()用的是线程池，使得线程可控，保证稳定运行。
其实常用的就是后三种，第二个用法灵活，简单，但不适宜大数量任务；第三个一般适用于单个任务，一次性任务；第四个一般用于大数量，高密度执行的使用情景，比如批量加载图片，批量下载文件等。
看一眼图吧：
全部源码：
1 package com.bvin.exec;
2
3 import java.io.IOException;
4 import java.net.MalformedURLException;
5 import java.net.URL;
6 import java.util.concurrent.ExecutorService;
7 import java.util.concurrent.Executors;
8
9 import android.app.Activity;
10 import android.graphics.drawable.Drawable;
11 import android.os.AsyncTask;
12 import android.os.Bundle;
13 import android.os.Handler;
14 import android.os.HandlerThread;
15 import android.os.Message;
16 import android.util.Log;
17 import android.view.View;
18 import android.widget.Button;
19 import android.widget.ImageView;
20
21 public class MainActivity extends Activity {
22 /** Called when the activity is first created. */
23
24 private Handler handler ;
25 private Button bt;
26 private Handler mainHandler = new Handler(){
27
28 @Override
29 public void handleMessage(Message msg) {
30 // TODO Auto-generated method stub
31 super.handleMessage(msg);
32 if(msg.what == 2012){
33 //只要在主线程就可以处理ui
34 ((ImageView)MainActivity.this.findViewById(msg.arg1)).setImageDrawable((Drawable)msg.obj);
35 }
36 }
37
38
39 };
40
41 private ExecutorService service = Executors.newFixedThreadPool(5);
42
43 @Override
44 public void onCreate(Bundle savedInstanceState) {
45 super.onCreate(savedInstanceState);
46 setContentView(R.layout.main);
47 initViews();
48 HandlerThread ht = new HandlerThread("down image thread");
49 ht.start();
50 handler = new Handler(ht.getLooper()){//如果有了looper那么这个handler就不可以处理ui了
51
52 @Override
53 public void handleMessage(Message msg) {
54 // TODO Auto-generated method stub
55 super.handleMessage(msg);
56
57
58 }
59
60 };
61
62 }
63
64 private void initViews(){
65
66 bt = (Button)findViewById(R.id.bt);
67 bt.setOnClickListener(new View.OnClickListener() {
68
69 @Override
70 public void onClick(View v) {
71 // TODO Auto-generated method stub
72 loadImagesByExecutors("http://news.baidu.com/z/resource/r/image/2012-11-23/23c1625aca99f02c50d8e510383a34e7.jpg",R.id.iv1);
73 loadImagesByExecutors("http://news.baidu.com/z/resource/r/image/2012-11-23/c4698d97ef6d10722c8e917733c7beb3.jpg",R.id.iv2);
74 loadImagesByExecutors("http://news.baidu.com/z/resource/r/image/2012-11-23/f332ffe433be2a3112be15f78bff5a40.jpg",R.id.iv3);
75 loadImagesByExecutors("http://news.baidu.com/z/resource/r/image/2012-11-23/6ff8a9c647a1e80bc602eeda48865d4c.jpg",R.id.iv4);
76 loadImagesByExecutors("http://news.baidu.com/z/resource/r/image/2012-11-23/f104d069f7443dca52a878d779392874.jpg",R.id.iv5);
77 }
78 });
79 }
80
81 private void loadImagesByHandler(final String url,final int id){//通过拥有looper的handler.post(runnable)，新建线程
82
83
84 handler.post(new Runnable(){//如果handler没有Looper那么它就不能构建新线程了
85
86 @Override
87 public void run() {
88 // TODO Auto-generated method stub
89 Log.e("当前线程：", ""+Thread.currentThread().getName());
90 Drawable drawable = null;
91 try {
92 drawable = Drawable.createFromStream(new URL(url).openStream(), "image.gif");
93 } catch (MalformedURLException e) {
94 // TODO Auto-generated catch block
95 e.printStackTrace();
96 } catch (IOException e) {
97 // TODO Auto-generated catch block
98 e.printStackTrace();
99 }
100 //SystemClock.sleep(2000);
101 //((ImageView)MainActivity.this.findViewById(id)).setImageDrawable(drawable);
102 Message msg = mainHandler.obtainMessage();
103 msg.what = 2012;
104 msg.arg1 = id;
105 msg.obj = drawable;
106 msg.sendToTarget();
107 }
108
109 });
110
111
112 }
113
114 private void loadImagesByThread(final String url,final int id){//通过Thread来new 出多个线程
115
116 new Thread(new Runnable(){
117
118 @Override
119 public void run() {
120 // TODO Auto-generated method stub
121 Log.e("当前线程：", ""+Thread.currentThread().getName());
122 Drawable drawable = null;
123 try {
124 drawable = Drawable.createFromStream(new URL(url).openStream(), "image.gif");
125 } catch (MalformedURLException e) {
126 // TODO Auto-generated catch block
127 e.printStackTrace();
128 } catch (IOException e) {
129 // TODO Auto-generated catch block
130 e.printStackTrace();
131 }
132 Message msg = mainHandler.obtainMessage();
133 msg.what = 2012;
134 msg.arg1 = id;
135 msg.obj = drawable;
136 msg.sendToTarget();
137
138 }
139
140 }).start();
141 }
142
143 private void loadImageByAsyncTask(final String url,final int id){//构建异步任务，这样就不用handler来处理消息了
144 DownloadTask task = new DownloadTask();
145 task.execute(""+id,url);//AsyncTask不可重复执行
146 }
147
148 private void loadImagesByExecutors(final String url,final int id){
149 service.submit(new Runnable(){
150
151 @Override
152 public void run() {
153 // TODO Auto-generated method stub
154 Log.e("当前线程：", ""+Thread.currentThread().getName());
155
156 try {
157 final Drawable drawable = Drawable.createFromStream(new URL(url).openStream(), "image.gif");
158 mainHandler.post(new Runnable(){
159
160 @Override
161 public void run() {//这将在主线程运行
162 // TODO Auto-generated method stub
163 ((ImageView)MainActivity.this.findViewById(id)).setImageDrawable(drawable);
164 }
165 });
166
167 } catch (MalformedURLException e) {
168 // TODO Auto-generated catch block
169 e.printStackTrace();
170 } catch (IOException e) {
171 // TODO Auto-generated catch block
172 e.printStackTrace();
173 }
174
175 }
176
177 });
178
179 }
180
181 class DownloadTask extends AsyncTask{
182
183 int id;
184 @Override
185 protected Drawable doInBackground(String... params) {//params保存url和控件id两个数据
186 // TODO Auto-generated method stub
187 Log.e("当前线程：", ""+Thread.currentThread().getName());
188 Drawable drawable = null;
189 this.id = Integer.parseInt(params[0]);
190 try {
191 drawable = Drawable.createFromStream(new URL(params[1]).openStream(), "image.gif");
192 } catch (MalformedURLException e) {
193 // TODO Auto-generated catch block
194 e.printStackTrace();
195 } catch (IOException e) {
196 // TODO Auto-generated catch block
197 e.printStackTrace();
198 }
199
200 return drawable;
201 }
202
203 @Override
204 protected void onPostExecute(Drawable result) {
205 // TODO Auto-generated method stub
206 super.onPostExecute(result);
207 ((ImageView)MainActivity.this.findViewById(id)).setImageDrawable(result);
208 }
209
210 @Override
211 protected void onPreExecute() {
212 // TODO Auto-generated method stub
213 super.onPreExecute();
214 }
215
216 @Override
217 protected void onProgressUpdate(Integer... values) {
218 // TODO Auto-generated method stub
219 super.onProgressUpdate(values);
220 }
221
222
223 }
224 }本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
