android下多线程下载,断点续传,及暂停按钮

package cn.itcast.mutiledownload;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class DemoActivity extends Activity implements OnClickListener {

private ProgressBar pb;
private Button bt;
private TextView tv;
private EditText et;
boolean flag = true;
boolean stopflag = false;
private Handler handler = new Handler() {

@Override
public void handleMessage(Message msg) {
//初始值为0; pb.setMax(len);
//里面的进度条的变化
pb.setProgress(total);
//文件的总长度.
int max = pb.getMax();
//变化的total大于=max.为保险起见.
if (total >= (max - 1)) {
total = max;
flag = false;
}
//total是变化的.
int result = total * 100 / max;
//
tv.setText("当前进度 :" + result + "%");

super.handleMessage(msg);
}
};
//定义全局变量total.
int total = 0;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
pb = (ProgressBar) this.findViewById(R.id.pb);
bt = (Button) this.findViewById(R.id.bt);
tv = (TextView) this.findViewById(R.id.tv_process);
et = (EditText) this.findViewById(R.id.et);
bt.setOnClickListener(this);

}

@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.bt:
// 创建一个子线程 定期的更新ui

//初始状态,里面的按钮的内容是开始下载,当点击按钮的时候,文本设
//开始下载.就不执行return方法.
if("开始下载".equals(bt.getText().toString())){
bt.setText("暂停");
stopflag = false;
}
else {
//就return暂停了.若果stopflag为真的话,就执行return方法.
bt.setText("开始下载");
stopflag = true;
}
//在onclick按钮点击的时候开始的第一件事,子线程更新ui.
new Thread() {
@Override
public void run() {
super.run();
//flag初始值为true.
while (flag) {
try {
sleep(1000);
// 如果total > = 文件长度
//每隔一秒发送消息.
Message msg = new Message();
//msg不带东西.
handler.sendMessage(msg);
} catch (InterruptedException e) {
e.printStackTrace();
}

}
}
}.start();

// 开始执行下载的操作
String path = et.getText().toString().trim();
if ("".equals(path)) {
Toast.makeText(this, "路径不能为空", 1).show();
return;
}
// 在onclick按钮点击的时候开始的第二件事,开启另外3个子线程.下载.
try {
//在线程里面穿件连接
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setRequestProperty("User-Agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
int code = conn.getResponseCode();
if (code == 200) {
int len = conn.getContentLength();
RandomAccessFile file = new RandomAccessFile(
"/mnt/sdcard/" + getFilenName(path), "rwd");
// 1.设置本地文件大小跟服务器的文件大小一致
file.setLength(len);
// 主线程中,设置进度条的最大值
pb.setMax(len);

// 2 .假设开启3 个线程
int threadnumber = 3;
int blocksize = len / threadnumber;
/**
* 线程1 0~ blocksize 线程2 1*bolocksize ~ 2*blocksize 线程3
* 2*blocksize ~ 文件末尾
*/
for (int i = 0; i < threadnumber; i++) {
int startposition = i * blocksize;
int endpositon = (i + 1) * blocksize;
if (i == (threadnumber - 1)) {
// 最后一个线程
endpositon = len;
}
//开启3个线程.
DownLoadTask task = new DownLoadTask(i, path,
startposition, endpositon);
task.start();
}

}
} catch (Exception e) {
Toast.makeText(this, "下载出现异常", 0).show();
e.printStackTrace();
}

break;
}

}

class DownLoadTask extends Thread {

int threadid;
String filepath;
int startposition;
int endpositon;

public DownLoadTask(int threadid, String filepath, int startposition,
int endpositon) {
this.threadid = threadid;
this.filepath = filepath;
this.startposition = startposition;
this.endpositon = endpositon;

}

@Override
public void run() {
try {
// 创建一个文件对象 ,记录当前某个文件的下载位置
File postionfile = new File("/mnt/sdcard/" + threadid + ".txt");
URL url = new URL(filepath);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
System.out.println("线程" + threadid + "正在下载 " + "开始位置 : "
+ startposition + "结束位置 " + endpositon);
//如果postionfile存在的话,就证明以前有下载的一部分文件.
if (postionfile.exists()) {
//从文件中读取下载的地址.
FileInputStream fis = new FileInputStream(postionfile);
//流转化为byte.
byte[] result = StreamTool.getBytes(fis);
//转化为str.
String str = new String(result);
if (!"".equals(str)) {
//转化为int.
int newstartposition = Integer.parseInt(str);
//为了保险起见.
if (newstartposition > startposition) {
//从以前的地址开始下载.
startposition = newstartposition;
}
}
}

// "Range", "bytes=2097152-4194303")
//
conn.setRequestProperty("Range", "bytes=" + startposition + "-"
+ endpositon);
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
//下载文件最好设置user-Agent.
conn.setRequestProperty("User-Agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
InputStream is = conn.getInputStream();
RandomAccessFile file = new RandomAccessFile("/mnt/sdcard/"
+ getFilenName(filepath), "rwd");
// 设置 数据从文件哪个位置开始写
file.seek(startposition);
byte[] buffer = new byte[1024];
int len = 0;
// currentPostion代表当前读到的服务器数据的位置 ,
// 同时这个值写出去的,也就是已经存储的文件的位置
//while循环就是表示下载.
int currentPostion = startposition;

//len=is.read(buffer).len是变化的,所以total += len;是连续的.
while ((len = is.read(buffer)) != -1) {
//暂停 stopflag为false.
if (stopflag) {
return;
}
file.write(buffer, 0, len);

synchronized (DemoActivity.this) {
//total=total+len;
//DemoActivity.this是锁.同步当前的activity.
total += len;

}
//这里目的是做断点下载的.防止手机停电,电脑死机.下次没有保存数据.
//currentPostion =currentPostion+ len;
//每一次写的时候,当前的位置就增减len.
currentPostion += len;
// 需要把currentPostion 信息给持久化到存储设备
String position = currentPostion + "";

FileOutputStream fos = new FileOutputStream(postionfile);
//将位置写到文件里面.
//将文件的position写入postionfile.
fos.write(position.getBytes());
fos.flush();
fos.close();
}

file.close();
System.out.println("线程" + threadid + "下载完毕");
// 当线程下载完毕后 把文件删除掉
if (postionfile.exists()) {
postionfile.delete();
}

} catch (Exception e) {
e.printStackTrace();
}

super.run();
}

}

public String getFilenName(String path) {
int start = path.lastIndexOf("/") + 1;
return path.substring(start, path.length());
}
}

<pre class="java" name="code">package cn.itcast.mutiledownload;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;

public class StreamTool {
/**
* 把一个inputstream里面的内容转化成一个byte[]
*/

public static byte[] getBytes(InputStream is) throws Exception{
ByteArrayOutputStream bos = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int len = 0;
while((len = is.read(buffer))!=-1){
bos.write(buffer, 0, len);
}
is.close();
bos.flush();
byte[] result = bos.toByteArray();
System.out.println(new String(result));
return  result;
}
}