Android实现简单断点续传和下载到本地功能

compile 'com.loopj.android:android-async-http:1.4.9'

 <uses-permission android:name="android.permission.INTERNET" </uses-permission 
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" </uses-permission 
 <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" </uses-permission 

<?xml version="1.0" encoding="utf-8"? 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/activity_main"
 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="com.lv.mama.test004.MainActivity" 


 <ProgressBar
  style="?android:attr/progressBarStyleHorizontal"
  android:layout_width="match_parent"
  android:layout_height="20dp"
  android:layout_marginTop="15dp"
  android:id="@+id/pb"
  android:layout_alignParentTop="true"
  android:layout_alignParentLeft="true"
  android:layout_alignParentStart="true"
  / 

 <TextView
  android:text="TextView"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_below="@+id/pb"
  android:layout_alignParentLeft="true"
  android:layout_alignParentStart="true"
  android:layout_marginLeft="20dp"
  android:layout_marginStart="20dp"
  android:layout_marginTop="13dp"
  android:id="@+id/tv_info" / 

 <Button
  android:text="暂停"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_marginTop="17dp"
  android:id="@+id/bt_pause"
  android:onClick="pause"
  android:layout_below="@+id/tv_info"
  android:layout_alignParentLeft="true"
  android:layout_alignParentStart="true"
  android:layout_marginLeft="11dp"
  android:layout_marginStart="11dp" / 

 <Button
  android:text="开始"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_marginRight="24dp"
  android:layout_marginEnd="24dp"
  android:id="@+id/bt_download"
  android:onClick="download"
  android:layout_alignBaseline="@+id/bt_pause"
  android:layout_alignBottom="@+id/bt_pause"
  android:layout_alignParentRight="true"
  android:layout_alignParentEnd="true" / 
</RelativeLayout 

public class MainActivity extends AppCompatActivity {
protected static final String TAG = "OtherActivity";
//下载线程的数量
private final static int threadsize = 3;
protected static final int SET_MAX = 0;
public static final int UPDATE_VIEW = 1;
private ProgressBar pb;
private Button bt_download;
private Button bt_pause;
private TextView tv_info;
//显示进度和更新进度
private Handler mHandler = new Handler() {
public void handleMessage(android.os.Message msg) {
switch (msg.what) {
case SET_MAX://设置进度条的最大值
int filelength = msg.arg1;
pb.setMax(filelength);
break;
case UPDATE_VIEW://更新进度条 和 下载的比率
int len = msg.arg1;//新下载的长度
pb.setProgress(pb.getProgress() + len);//设置进度条的刻度
int max = pb.getMax();//获取进度的最大值
int progress = pb.getProgress();//获取已经下载的数据量
// 下载：30 总：100
int result = (progress * 100) / max;
tv_info.setText("下载:" + result + "%");
break;
default:
break;
}
}
;
};
String uri = "http://c.hiphotos.baidu.com/image/pic/item/b90e7bec54e736d1e51217c292504fc2d46269f3.jpg";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//找到控件
pb = (ProgressBar) findViewById(R.id.pb);
tv_info = (TextView) findViewById(R.id.tv_info);
bt_download = (Button) findViewById(R.id.bt_download);
bt_pause = (Button) findViewById(R.id.bt_pause);
//数据的回显
//确定下载的文件
String name = getFileName(uri);
File file = new File(Environment.getExternalStorageDirectory(), name);
if (file.exists()) {//文件存在回显
//获取文件的大小
int filelength = (int) file.length();
pb.setMax(filelength);
try {
//统计原来所有的下载量
int count = 0;
//读取下载记录文件
for (int threadid = 0; threadid < threadsize; threadid++) {
//获取原来指定线程的下载记录
int existDownloadLength = readDownloadInfo(threadid);
count = count + existDownloadLength;
}
//设置进度条的刻度
pb.setProgress(count);
//计算比率
int result = (count * 100) / filelength;
tv_info.setText("下载:" + result + "%");
} catch (Exception e) {
e.printStackTrace();
}
}
}
//暂停
private boolean flag = false;//是否在下载
public void pause(View v){
flag = false;
bt_download.setEnabled(true);
bt_pause.setEnabled(false);
}
//下载
public void download(View v){
flag = true; //是在下载
bt_download.setEnabled(false);//一点击变成不可点击
bt_pause.setEnabled(true);//一点击变成可点击
new Thread(){//子线程
public void run() {
try {
//获取服务器上文件的大小
HttpClient client = new DefaultHttpClient();
HttpHead request = new HttpHead(uri);
HttpResponse response = client.execute(request);
//response 只有响应头 没有响应体
if(response.getStatusLine().getStatusCode() == 200){
Header[] headers = response.getHeaders("Content-Length");
String value = headers[0].getValue();
//文件大小
int filelength = Integer.parseInt(value);
Log.i(TAG, "filelength:"+filelength);
//设置进度条的最大值
Message msg_setmax = Message.obtain(mHandler, SET_MAX, filelength, 0);
msg_setmax.sendToTarget();
//处理下载记录文件
for(int threadid=0;threadid<threadsize;threadid++){
//对应的下载记录文件
File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
//判断文件是否存在
if(!file.exists()){
//创建文件
file.createNewFile();
}
}
//在sdcard创建和服务器大小一样的文件
String name = getFileName(uri);
File file = new File(Environment.getExternalStorageDirectory(),name);
//随机访问文件
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//设置文件的大小
raf.setLength(filelength);
//关闭
raf.close();
//计算每条线程的下载量
int block = (filelength%threadsize == 0)?(filelength/threadsize):(filelength/threadsize+1);
//开启三条线程执行下载
for(int threadid=0;threadid<threadsize;threadid++){
new DownloadThread(threadid, uri, file, block).start();
}
}
} catch (Exception e) {
e.printStackTrace();
}
};
}.start();
}
//线程下载类
private class DownloadThread extends Thread {
private int threadid;//线程的id
private String uri;//下载的地址
private File file;//下载文件
private int block;//下载的块
private int start;
private int end;
public DownloadThread(int threadid, String uri, File file, int block) {
super();
this.threadid = threadid;
this.uri = uri;
this.file = file;
this.block = block;
//计算下载的开始位置和结束位置
start = threadid * block;
end = (threadid + 1) * block - 1;
try {
//读取该条线程原来的下载记录
int existDownloadLength = readDownloadInfo(threadid);
//修改下载的开始位置 从新下载
start = start + existDownloadLength;
} catch (Exception e) {
e.printStackTrace();
}
}
//下载 状态码：200是普通的下载  206是分段下载  Range:范围
@Override
public void run() {
super.run();
try {
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//跳转到起始位置
raf.seek(start);
//分段下载
HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet(uri);
request.addHeader("Range", "bytes:"+start+"-"+end);//添加请求头
HttpResponse response = client.execute(request);
if(response.getStatusLine().getStatusCode() == 200){
InputStream inputStream = response.getEntity().getContent();
//把流写入到文件
byte[] buffer = new byte[1024];
int len = 0;
while((len = inputStream.read(buffer)) != -1){
//如果暂停下载 点击暂停 false 就直接return 点击下载true接着下载
if(!flag){
return;//标准线程结束
}
//写数据
raf.write(buffer, 0, len);
//读取原来下载的数据量 这里读取是为了更新下载记录
int existDownloadLength = readDownloadInfo(threadid);//原来下载的数据量
//计算最新的下载
int newDownloadLength = existDownloadLength + len;
//更新下载记录 从新记录最新下载位置
updateDownloadInfo(threadid, newDownloadLength);
//更新进度条的显示 下载的百分比
Message update_msg = Message.obtain(mHandler, UPDATE_VIEW, len, 0);
update_msg.sendToTarget();
//模拟 看到进度条动的效果
SystemClock.sleep(50);
}
inputStream.close();
raf.close();
Log.i(TAG, "第"+threadid+"条线程下载完成");
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
/**
* 读取指定线程的下载数据量
* @param threadid 线程的id
* @return
* @throws Exception
*/
public int readDownloadInfo(int threadid) throws Exception{
//下载记录文件
File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
BufferedReader br = new BufferedReader(new FileReader(file));
//读取一行数据
String content = br.readLine();
int downlength = 0;
//如果该文件第一次创建去执行读取操作 文件里面的内容是 null
if(!TextUtils.isEmpty(content)){
downlength = Integer.parseInt(content);
}
//关闭流
br.close();
return downlength;
}
/**
* 更新下载记录
* @param threadid
* @param newDownloadLength
*/
public void updateDownloadInfo(int threadid,int newDownloadLength) throws Exception{
//下载记录文件
File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
FileWriter fw = new FileWriter(file);
fw.write(newDownloadLength+"");
fw.close();
}
/**
* 获取文件的名称
* @param uri
* @return
*/
private String getFileName(String uri){
return uri.substring(uri.lastIndexOf("/")+1);
}
}