Android多线程下载和断点续传

具体思路：文件总长度/线程个数=得到每个线程下载文件的大小

每一个线程位置的计算

开始位置：(线程Id-1)*每一块的大小

结束位置：(线程Id*每块的大小)-1
用到一个文件随机访问类RandomAccessFile

package com.example.mutildownloader2;

import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

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

public class MainActivity extends Activity {
protected static final int DOWN_LOAD_ERROR = 1;
protected static final int SERVER_ERROR = 2;
public static final int DOWN_LAOD_FINSIH = 3;
public static final int UPDATE_TEXT = 4;
private EditText et_path;
private ProgressBar pb; //下载的进度条.
public static int threadCount = 3;
public static int runningThread = 3 ;

public int currentProcess = 0; //当前进度.

private TextView tv_process;

private Handler handler = new Handler(){
public void handleMessage(android.os.Message msg) {
switch (msg.what) {
case DOWN_LOAD_ERROR:
Toast.makeText(getApplicationContext(), "下载失败", 0).show();
break;
case SERVER_ERROR:
Toast.makeText(getApplicationContext(), "服务器 错误,下载失败", 0).show();
break;
case DOWN_LAOD_FINSIH:
Toast.makeText(getApplicationContext(), "文件下载完毕", 0).show();
break;
case UPDATE_TEXT:
tv_process.setText("当前进度:"+pb.getProgress()*100/pb.getMax());
break;
}

};
};

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
et_path = (EditText) this.findViewById(R.id.et_path);
pb = (ProgressBar) findViewById(R.id.pb);
tv_process = (TextView) findViewById(R.id.tv_process);
}

public void downLoad(View view) {
final String path = et_path.getText().toString().trim();
if (TextUtils.isEmpty(path)) {
Toast.makeText(this, "下载路径错误", 0).show();
return;
}
currentProcess = 0;
new Thread() {
public void run() {
try {
//String path = "http://192.168.1.100:8080/360.exe";
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
conn.setConnectTimeout(5000);
conn.setRequestMethod("GET");
int code = conn.getResponseCode();
if (code == 200) {
// 服务器返回的数据的长度 实际上就是文件的长度
int length = conn.getContentLength();
pb.setMax(length);//设置进度条的最大值.
System.out.println("文件总长度:" + length);
// 在客户端本地 创建出来一个大小跟服务器端文件一样大小的临时文件
RandomAccessFile raf = new RandomAccessFile("/sdcard/setup.exe",
"rwd");
// 指定创建的这个文件的长度
raf.setLength(length);
raf.close();

// 假设是3个线程去下载资源.
// 平均每一个线程下载的文件的大小.
int blockSize = length / threadCount;
for (int threadId = 1; threadId <= threadCount; threadId++) {
// 第一个线程下载的开始位置
int startIndex = (threadId - 1) * blockSize;
int endIndex = threadId * blockSize - 1;
if (threadId == threadCount) {// 最后一个线程 下载的长度 要稍微长一点
endIndex = length;
}
System.out.println("线程:" + threadId + "下载:---"
+ startIndex + "--->" + endIndex);
new DownloadThread(path, threadId, startIndex, endIndex)
.start();
}

} else {
System.out.println("服务器错误.");
Message msg = new Message();
msg.what = SERVER_ERROR;
handler.sendMessage(msg);
}
} catch (Exception e) {
e.printStackTrace();
Message msg = new Message();
msg.what = DOWN_LOAD_ERROR;
handler.sendMessage(msg);

}

};
}.start();

}

/**
* 下载文件的子线程 每一个线程 下载对应位置的文件
*
* @author Administrator
*
*/
public  class DownloadThread extends Thread {
private int threadId;
private int startIndex;
private int endIndex;
private String path;

/**
* @param path
*            下载文件在服务器上的路径
* @param threadId
*            线程id
* @param startIndex
*            线程下载的开始位置
* @param endIndex
*            线程下载的结束位置.
*/
public DownloadThread(String path, int threadId, int startIndex,
int endIndex) {
this.threadId = threadId;
this.startIndex = startIndex;
this.endIndex = endIndex;
this.path = path;
}

@Override
public void run() {
try {

// 检查是否存在 记录下载长度的文件 ,如果存在读取这个文件的数据.
File tempFile = new File("/sdcard/"+threadId + ".txt");
if (tempFile.exists() && tempFile.length() > 0) {
FileInputStream fis = new FileInputStream(tempFile);
byte[] temp = new byte[1024];
int leng = fis.read(temp);
String downloadLen = new String(temp, 0, leng);
int downloadlenInt = Integer.parseInt(downloadLen);

int alreadyDownlodint = downloadlenInt - startIndex ;
currentProcess+=alreadyDownlodint; //计算上次断点 已经下载的文件的长度.

startIndex = downloadlenInt;//修改下载的真实的开始位置.
fis.close();
}
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
conn.setRequestMethod("GET");
// 重要: 请求服务器下载部分的文件 指定文件的位置.
conn.setRequestProperty("Range", "bytes=" + startIndex + "-"
+ endIndex);
System.out.println("线程真实下载:" + threadId + "下载:---" + startIndex
+ "--->" + endIndex);
conn.setConnectTimeout(5000);
int code = conn.getResponseCode(); // 从服务器请求全部资源 200 ok
// 如果从服务器请求部分资源 206 ok
if (code == 206) {
InputStream is = conn.getInputStream();// 已经设置了 请求的位置
RandomAccessFile raf = new RandomAccessFile("/sdcard/setup.exe",
"rwd");
// 随机写文件的时候 从哪个位置开始写
raf.seek(startIndex);// 定位文件
int len = 0;
byte[] buffer = new byte[1024];
int total = 0;// 已经下载的数据长度
while ((len = is.read(buffer)) != -1) {
RandomAccessFile file = new RandomAccessFile("/sdcard/"+threadId
+ ".txt", "rwd");// 作用: 记录当前线程下载的数据长度
raf.write(buffer, 0, len);
total += len;
//System.out.println("线程:" + threadId + "total:" + total);
file.write(( total+startIndex+"").getBytes());//记录的是 下载位置.
file.close();

//更新进度条
synchronized (MainActivity.this) {
currentProcess+=len;//获取所有线程下载的总进度.
pb.setProgress(currentProcess);//更改界面上progressbar 进度条的进度
//特殊情况 progressbar progressdialog 进度条对话框 可以直接在子线程里面更新ui  内部代码 特殊处理
Message msg = Message.obtain();//复用旧的消息 避免创建新的消息
msg.what = UPDATE_TEXT;
handler.sendMessage(msg);
}

}
is.close();
raf.close();
System.out.println("线程:" + threadId + "下载完毕了...");
} else {
System.out.println("线程:" + threadId + "下载失败...");
}
//如何去判断应用程序已经下载完毕.
} catch (Exception e) {
e.printStackTrace();
}finally{
threadFinish();
}

}

private synchronized void threadFinish() {
runningThread --;
if(runningThread==0){//所有的线程 已经执行完毕了.
for(int i= 1;i<=3;i++){
File file = new File("/sdcard/"+i+".txt");
file.delete();
}
System.out.println("文件下载完毕 ,删除所有的下载记录.");
Message msg = new Message();
msg.what = DOWN_LAOD_FINSIH;
handler.sendMessage(msg);
}
}
}
}

给出布局文件

<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="m
4000
atch_parent"
android:orientation="vertical"
tools:context=".MainActivity" >

<EditText
android:id="@+id/et_path"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="请输入下载的路径" >
</EditText>

<ProgressBar
android:id="@+id/pb"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />

<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="downLoad"
android:text="下载" />

<TextView
android:id="@+id/tv_process"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="下载进度" />

</LinearLayout>

还要添加两条权限
    <uses-permission android:name="android.permission.INTERNET"/>网络权限

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>存储卡权限