Android 实现网络多线程APK文件下载
(转自：http://blog.csdn.net/mad1989/article/details/38421465)实现原理
(1)首先获得下载文件的长度，然后设置本地文件的长度。
(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。
如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如下图所示：
例如10M大小，使用3个线程来下载，
线程下载的数据长度 (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4M，第三个线程下载长度为2M
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=?
之前练习时的一个demo，不多说了，直接上代码吧，有关断点续传，需要使用数据库，不再加了，网上有很多成熟的项目可以直接用。
实例
MainApp： package com.amos.app;
2
3 import java.io.File;
4 import java.io.IOException;
5 import java.net.MalformedURLException;
6 import java.net.URL;
7 import java.net.URLConnection;
8 import com.amos.download.R;
9 import android.annotation.SuppressLint;
10 import android.app.Activity;
11 import android.os.Bundle;
12 import android.os.Environment;
13 import android.os.Handler;
14 import android.os.Message;
15 import android.util.Log;
16 import android.view.View;
17 import android.view.View.OnClickListener;
18 import android.widget.ProgressBar;
19 import android.widget.TextView;
20 import android.widget.Toast;
21
22 /**
23* @author yangxiaolong
24* @2014-5-6
25*/
26 public class MainApp extends Activity implements OnClickListener {
27
28 private static final String TAG = MainApp.class.getSimpleName();
29
30 /** 显示下载进度TextView */
31 private TextView mMessageView;
32 /** 显示下载进度ProgressBar */
33 private ProgressBar mProgressbar;
34
35 @Override
36 protected void onCreate(Bundle savedInstanceState) {
37 super.onCreate(savedInstanceState);
38 setContentView(R.layout.progress_activity);
39 findViewById(R.id.download_btn).setOnClickListener(this);
40 mMessageView = (TextView) findViewById(R.id.download_message);
41 mProgressbar = (ProgressBar) findViewById(R.id.download_progress);
42 }
43
44 @Override
45 public void onClick(View v) {
46 if (v.getId() == R.id.download_btn) {
47 doDownload();
48 }
49 }
50
51 /**
52 * 使用Handler更新UI界面信息
53 */
54 @SuppressLint("HandlerLeak")
55 Handler mHandler = new Handler() {
56 @Override
57 public void handleMessage(Message msg) {
58
59 mProgressbar.setProgress(msg.getData().getInt("size"));
60
61 float temp = (float) mProgressbar.getProgress()
62 / (float) mProgressbar.getMax();
63
64 int progress = (int) (temp * 100);
65 if (progress == 100) {
66 Toast.makeText(MainApp.this, "下载完成！", Toast.LENGTH_LONG).show();
67 }
68 mMessageView.setText("下载进度:" + progress + " %");
69
70 }
71 };
72
73 /**
74 * 下载准备工作，获取SD卡路径、开启线程
75 */
76 private void doDownload() {
77 // 获取SD卡路径
78 String path = Environment.getExternalStorageDirectory()
79 + "/amosdownload/";
80 File file = new File(path);
81 // 如果SD卡目录不存在创建
82 if (!file.exists()) {
83 file.mkdir();
84 }
85 // 设置progressBar初始化
86 mProgressbar.setProgress(0);
87
88 // 简单起见，我先把URL和文件名称写死，其实这些都可以通过HttpHeader获取到
89 String downloadUrl = "http://gdown.baidu.com/data/wisegame/91319a5a1dfae322/baidu_16785426.apk";
90 String fileName = "baidu_16785426.apk";
91 int threadNum = 5;
92 String filepath = path + fileName;
93 Log.d(TAG, "download filepath:" + filepath);
94 downloadTask task = new downloadTask(downloadUrl, threadNum, filepath);
95 task.start();
96 }
97
98 /**
99 * 多线程文件下载
100 *
101 * @author yangxiaolong
102 * @2014-8-7
103 */
104 class downloadTask extends Thread {
105 private String downloadUrl;// 下载链接地址
106 private int threadNum;// 开启的线程数
107 private String filePath;// 保存文件路径地址
108 private int blockSize;// 每一个线程的下载量
109
110 public downloadTask(String downloadUrl, int threadNum, String fileptah) {
111 this.downloadUrl = downloadUrl;
112 this.threadNum = threadNum;
113 this.filePath = fileptah;
114 }
115
116 @Override
117 public void run() {
118
119 FileDownloadThread[] threads = new FileDownloadThread;
120 try {
121 URL url = new URL(downloadUrl);
122 Log.d(TAG, "download file http path:" + downloadUrl);
123 URLConnection conn = url.openConnection();
124 // 读取下载文件总大小
125 int fileSize = conn.getContentLength();
126 if (fileSize <= 0) {
127 System.out.println("读取文件失败");
128 return;
129 }
130 // 设置ProgressBar最大的长度为文件Size
131 mProgressbar.setMax(fileSize);
132
133 // 计算每条线程下载的数据长度
134 blockSize = (fileSize % threadNum) == 0 ? fileSize / threadNum
135 : fileSize / threadNum + 1;
136
137 Log.d(TAG, "fileSize:" + fileSize + "blockSize:");
138
139 File file = new File(filePath);
140 for (int i = 0; i < threads.length; i++) {
141 // 启动线程，分别下载每个线程需要下载的部分
142 threads = new FileDownloadThread(url, file, blockSize,
143 (i + 1));
144 threads.setName("Thread:" + i);
145 threads.start();
146 }
147
148 boolean isfinished = false;
149 int downloadedAllSize = 0;
150 while (!isfinished) {
151 isfinished = true;
152 // 当前所有线程下载总量
153 downloadedAllSize = 0;
154 for (int i = 0; i < threads.length; i++) {
155 downloadedAllSize += threads.getDownloadLength();
156 if (!threads.isCompleted()) {
157 isfinished = false;
158 }
159 }
160 // 通知handler去更新视图组件
161 Message msg = new Message();
162 msg.getData().putInt("size", downloadedAllSize);
163 mHandler.sendMessage(msg);
164 // Log.d(TAG, "current downloadSize:" + downloadedAllSize);
165 Thread.sleep(1000);// 休息1秒后再读取下载进度
166 }
167 Log.d(TAG, " all of downloadSize:" + downloadedAllSize);
168
169 } catch (MalformedURLException e) {
170 e.printStackTrace();
171 } catch (IOException e) {
172 e.printStackTrace();
173 } catch (InterruptedException e) {
174 e.printStackTrace();
175 }
176
177 }
178 }
179
180 }FileDownloadThread:package com.amos.app;
2
3 import java.io.BufferedInputStream;
4 import java.io.File;
5 import java.io.IOException;
6 import java.io.RandomAccessFile;
7 import java.net.URL;
8 import java.net.URLConnection;
9 import android.util.Log;
10
11 /**
12* 文件下载类
13*
14* @author yangxiaolong
15* @2014-5-6
16*/
17 public class FileDownloadThread extends Thread {
18
19 private static final String TAG = FileDownloadThread.class.getSimpleName();
20
21 /** 当前下载是否完成 */
22 private boolean isCompleted = false;
23 /** 当前下载文件长度 */
24 private int downloadLength = 0;
25 /** 文件保存路径 */
26 private File file;
27 /** 文件下载路径 */
28 private URL downloadUrl;
29 /** 当前下载线程ID */
30 private int threadId;
31 /** 线程下载数据长度 */
32 private int blockSize;
33
34 /**
35 *
36 * @param url:文件下载地址
37 * @param file:文件保存路径
38 * @param blocksize:下载数据长度
39 * @param threadId:线程ID
40 */
41 public FileDownloadThread(URL downloadUrl, File file, int blocksize,
42 int threadId) {
43 this.downloadUrl = downloadUrl;
44 this.file = file;
45 this.threadId = threadId;
46 this.blockSize = blocksize;
47 }
48
49 @Override
50 public void run() {
51
52 BufferedInputStream bis = null;
53 RandomAccessFile raf = null;
54
55 try {
56 URLConnection conn = downloadUrl.openConnection();
57 conn.setAllowUserInteraction(true);
58
59 int startPos = blockSize * (threadId - 1);//开始位置
60 int endPos = blockSize * threadId - 1;//结束位置
61 //设置当前线程下载的起点、终点
62 conn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);
63 System.out.println(Thread.currentThread().getName() + "bytes="
64 + startPos + "-" + endPos);
65
66 byte[] buffer = new byte;
67 bis = new BufferedInputStream(conn.getInputStream());
68
69 raf = new RandomAccessFile(file, "rwd");
70 raf.seek(startPos);
71 int len;
72 while ((len = bis.read(buffer, 0, 1024)) != -1) {
73 raf.write(buffer, 0, len);
74 downloadLength += len;
75 }
76 isCompleted = true;
77 Log.d(TAG, "current thread task has finished,all size:"
78 + downloadLength);
79
80 } catch (IOException e) {
81 e.printStackTrace();
82 } finally {
83 if (bis != null) {
84 try {
85 bis.close();
86 } catch (IOException e) {
87 e.printStackTrace();
88 }
89 }
90 if (raf != null) {
91 try {
92 raf.close();
93 } catch (IOException e) {
94 e.printStackTrace();
95 }
96 }
97 }
98 }
99
100 /**
101 * 线程文件是否下载完毕
102 */
103 public boolean isCompleted() {
104 return isCompleted;
105 }
106
107 /**
108 * 线程下载文件长度
109 */
110 public int getDownloadLength() {
111 return downloadLength;
112 }
113
114 }补充:.xml文件：1 <?xml version="1.0" encoding="utf-8"?>
2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
3 android:layout_width="match_parent"
4 android:layout_height="match_parent"
5 android:background="@android:color/white"
6 android:orientation="vertical" >
7
8 <Button
9 android:id="@+id/download_btn"
10 android:layout_width="match_parent"
11 android:layout_height="60dp"
12 android:layout_gravity="center"
13 android:layout_marginLeft="10dp"
14 android:layout_marginRight="10dp"
15 android:layout_marginTop="50dp"
16 android:text="Download"
17 android:textSize="18sp" />
18
19 <ProgressBar
20 android:id="@+id/download_progress"
21 style="?android:attr/progressBarStyleHorizontal"
22 android:layout_width="fill_parent"
23 android:layout_height="wrap_content"
24 android:layout_marginLeft="10dip"
25 android:layout_marginRight="10dip"
26 android:layout_marginTop="20dp"
27 android:indeterminate="false"
28 android:max="100" />
29
30 <TextView
31 android:id="@+id/download_message"
32 android:layout_width="wrap_content"
33 android:layout_height="wrap_content"
34 android:layout_gravity="center"
35 android:layout_marginTop="10dp"
36 android:maxLines="1"
37 android:text="50%"
38 android:textSize="18dip" />
39
40 </LinearLayout>效果图：
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