多线程断点续传（代码，附有详细注解）

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import java.io.BufferedReader;

import java.io.File;

import java.io.FileInputStream;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

import android.os.Bundle;

import android.os.Environment;

import android.os.Handler;

import android.os.Message;

import android.app.Activity;

import android.view.View;

import android.widget.ProgressBar;

import android.widget.TextView;

public class MainActivity extends Activity {

String path = "http://169.254.88.88:8080/LiebaoFreeWiFi5.1.exe";
int threadCount = 3;
int finishedThread = 0;
//所有线程下载总进度
int downloadProgress = 0;
private ProgressBar pb;
private TextView tv;

Handler handler = new Handler(){
public void handleMessage(android.os.Message msg) {
tv.setText((long)pb.getProgress() * 100 / pb.getMax() + "%");
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

pb = (ProgressBar) findViewById(R.id.pb);
tv = (TextView) findViewById(R.id.tv);
}

public void click(View v){
Thread t = new Thread(){
@Override
public void run() {
//发送http请求，拿到目标文件长度
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(8000);
conn.setReadTimeout(8000);

if(conn.getResponseCode() == 200){
//获取长度
int length = conn.getContentLength();

//创建临时文件
File file = new File(Environment.getExternalStorageDirectory(), getNameFromPath(path));
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//设置临时文件大小与目标文件一致
raf.setLength(length);
raf.close();

//设置进度条的最大值
pb.setMax(length);

//计算每个线程下载区间
int size = length / threadCount;

for (int id = 0; id < threadCount; id++) {
//计算每个线程下载的开始位置和结束位置
int startIndex = id * size;
int endIndex = (id + 1) * size - 1;
if(id == threadCount - 1){
endIndex = length - 1;
}
System.out.println("线程" + id + "下载的区间：" + startIndex + " ~ " + endIndex);
new DownLoadThread(id, startIndex, endIndex).start();
}

}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
};
t.start();
}

public String getNameFromPath(String path){
int index = path.lastIndexOf("/");
return path.substring(index + 1);
}

class DownLoadThread extends Thread{

int threadId;
int startIndex;
int endIndex;

public DownLoadThread(int threadId, int startIndex, int endIndex) {
super();
this.threadId = threadId;
this.startIndex = startIndex;
this.endIndex = endIndex;
}

@Override
public void run() {
try {
File fileProgress = new File(Environment.getExternalStorageDirectory(), threadId + ".txt");
int lastProgress = 0;
if(fileProgress.exists()){
//读取进度临时文件中的内容
FileInputStream fis = new FileInputStream(fileProgress);
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
//得到上一次下载进度
lastProgress = Integer.parseInt(br.readLine());
//改变下载的开始位置，上一次下过的，这次就不请求了
startIndex += lastProgress;<
4000
br />fis.close();

//把上一次下载进度加到进度条进度中
downloadProgress += lastProgress;
//发送消息，让文本进度条改变
handler.sendEmptyMessage(1);
}

//发送http请求，请求要下载的数据
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(8000);
conn.setReadTimeout(8000);
//设置请求数据的区间
conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);

//请求部分数据，成功的响应码是206
if(conn.getResponseCode() == 206){
InputStream is = conn.getInputStream();

byte[] b = new byte[1024];
int len = 0;
//当前线程下载的总进度
int total = lastProgress;
File file = new File(Environment.getExternalStorageDirectory(), getNameFromPath(path));
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//设置写入的开始位置
raf.seek(startIndex);
while((len = is.read(b)) != -1){
raf.write(b, 0, len);
total += len;
System.out.println("线程" + threadId + "下载了：" + total);

//创建一个进度临时文件，保存下载进度
RandomAccessFile rafProgress = new RandomAccessFile(fileProgress, "rwd");
//每次下载1024个字节，就，就马上把1024写入进度临时文件
rafProgress.write((total + "").getBytes());
rafProgress.close();

//每次下载len个长度的字节，马上把len加到下载进度中，让进度条能反应这len个长度的下载进度
downloadProgress += len;
pb.setProgress(downloadProgress);

//发送消息，让文本进度条改变
handler.sendEmptyMessage(1);

}
raf.close();
System.out.println("线程" + threadId + "下载完毕------------------");

//3条线程全部下载完毕，才去删除进度临时文件
finishedThread++;

synchronized (path) {
if(finishedThread == threadCount){
for (int i = 0; i < threadCount; i++) {
File f = new File(Environment.getExternalStorageDirectory(), i + ".txt");
f.delete();
}
finishedThread = 0;
}
}
}

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

}

----------------------------------------Layout---------------------------------------------------

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<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin"

    tools:context=".MainActivity" 

    android:orientation="vertical"

    >

    <Button

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="下载" 

        android:onClick="click"

        />

    <ProgressBar 

        style="@android:style/Widget.ProgressBar.Horizontal"

        android:id="@+id/pb"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        />

    <TextView 

        android:id="@+id/tv"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="0%"

        android:layout_gravity="right"

        />

</LinearLayout>

下载地址：
http://download.csdn.net/detail/github_36186415/9637992