Android 多线程断点下载

package com.itheima.mutiledownloader;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.renderscript.Program.TextureType;
import android.text.TextUtils;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.ProgressBar;
import android.widget.Toast;

public class MainActivity extends Activity {
protected static final int DOWNLOAD_ERROR = 1;
private static final int THREAD_DOWNLOAD_ERROR = 2;
public static final int DONWLOAD_FINISH = 3;
private EditText et_path;
private EditText et_number;
private LinearLayout ll_pb;
private String path;
private static int threadCount = 4;
private static int blockSize = 0;
private static int livingThread = 0;

private List<ProgressBar> pbs;

private Handler handler = new Handler() {
public void handleMessage(android.os.Message msg) {
switch (msg.what) {
case DOWNLOAD_ERROR:
Toast.makeText(getApplicationContext(), "初始化下载失败", 1).show();
break;
case THREAD_DOWNLOAD_ERROR:
String str = (String) msg.obj;
Toast.makeText(getApplicationContext(), str, 1).show();
break;
case DONWLOAD_FINISH:
Toast.makeText(getApplicationContext(), "下载完毕", 1).show();
findViewById(R.id.bt).setEnabled(true);
break;
}
};
};

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
et_path = (EditText) findViewById(R.id.et_path);
et_number = (EditText) findViewById(R.id.et_number);
ll_pb = (LinearLayout) findViewById(R.id.ll_pb);

}

public void click(View view) {
path = et_path.getText().toString().trim();
String strNumber = et_number.getText().toString().trim();
if (TextUtils.isEmpty(path) || TextUtils.isEmpty(strNumber)) {
Toast.makeText(this, "请输入参数", 0).show();
return;
} else {
// 下载的线程的个数
threadCount = Integer.parseInt(strNumber);
pbs = new ArrayList<ProgressBar>();
ll_pb.removeAllViews();
for (int i = 0; i < threadCount; i++) {
ProgressBar pb = (ProgressBar) View.inflate(
getApplicationContext(), R.layout.pb_item, null);
pb.setPadding(5, 5, 5, 5);
ll_pb.addView(pb, LayoutParams.MATCH_PARENT, 12);
//在集合里面添加进度条的引用.
pbs.add(pb);
}
findViewById(R.id.bt).setEnabled(false);
new Thread() {
public void run() {
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
// 服务器文件的长度
int length = conn.getContentLength();
// 本地创建一个大小跟服务器一样的文件
RandomAccessFile raf = new RandomAccessFile(Environment
.getExternalStorageDirectory()
.getAbsolutePath()
+ "/" + getFileName(path), "rw");
raf.setLength(length);
System.out.println("文件的总长度:" + length);
// 计算每个线程下载的位置.
blockSize = length / threadCount;
System.out.println("每一个块的平均长度:" + blockSize);
livingThread = threadCount;
for (int i = 1; i <= threadCount; i++) {
int startIndex = (i - 1) * blockSize;
int endIndex = i * blockSize - 1;
if (i == threadCount) {
endIndex = length;
}
//设置进度条的总进度
pbs.get(i-1).setMax(endIndex-startIndex);
new Thread(
new DownLoadTask(i, startIndex, endIndex))
.start();
}
} catch (Exception e) {
e.printStackTrace();
Message msg = Message.obtain();
msg.what = DOWNLOAD_ERROR;
handler.sendMessage(msg);
}
};
}.start();

}
}

/**
* 获取下载的文件的名称
*
* @param path
* @return
*/
private static String getFileName(String path) {
int start = path.lastIndexOf("/") + 1;
return path.substring(start);
}

private class DownLoadTask implements Runnable {

private int id;
private int startIndex;
private int endIndex;

public DownLoadTask(int id, int startIndex, int endIndex) {
this.id = id;
this.startIndex = startIndex;
this.endIndex = endIndex;
}

@Override
public void run() {
try {
int downloadCount =  0 ;
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url
.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
// 在每次下载之前,检查是否存在已经下载大小的记录文件.
File f = new File(Environment.getExternalStorageDirectory()
.getAbsolutePath()
+ "/"
+ getFileName(path)
+ id
+ ".txt");
if (f.exists() && f.length() > 0) {
FileInputStream fis = new FileInputStream(f);
BufferedReader br = new BufferedReader(
new InputStreamReader(fis));
// 已经下载的大小.
downloadCount = Integer.parseInt(br.readLine());
startIndex += downloadCount;
br.close();
fis.close();
}
conn.setRequestProperty("Range", "bytes=" + startIndex + "-"
+ endIndex);
System.out.println("线程id:" + id + " 下载的位置:" + startIndex
+ "~~~" + endIndex);
RandomAccessFile raf = new RandomAccessFile(Environment
.getExternalStorageDirectory().getAbsolutePath()
+ "/"
+ getFileName(path), "rwd");
InputStream is = conn.getInputStream();
// 指定线程下载存放文件的开始位置.
raf.seek(startIndex);
int len = 0;
byte[] buffer = new byte[4096];
int total = 0;// 记录当前线程下载的大小.
while ((len = is.read(buffer)) != -1) {
File file = new File(Environment
.getExternalStorageDirectory().getAbsolutePath()
+ "/" + getFileName(path) + id + ".txt");
RandomAccessFile positionRaf = new RandomAccessFile(file,
"rwd");
raf.write(buffer, 0, len);
total += len;
positionRaf.write(String.valueOf(total).getBytes());
positionRaf.close();
pbs.get(id-1).setProgress(total+downloadCount);
}
raf.close();
is.close();
System.out.println("线程:" + id + "下载完毕...");
} catch (Exception e) {
e.printStackTrace();
Message msg = Message.obtain();
msg.what = THREAD_DOWNLOAD_ERROR;
msg.obj = "线程:" + id + "下载失败.";
handler.sendMessage(msg);
} finally {
synchronized (MainActivity.this) {
livingThread--;
if (livingThread <= 0) {
System.out.println("全部下载完毕...");
Message msg = Message.obtain();
msg.what = DONWLOAD_FINISH;
handler.sendMessage(msg);
for (int i = 1; i <= threadCount; i++) {
File f = new File(Environment
.getExternalStorageDirectory()
.getAbsolutePath()
+ "/" + getFileName(path) + i + ".txt");
System.out.println(f.delete());
}
}
}

}
}
}
}