Android 实现断点续传
断点续传：
断点续传指的是在下载或上传时，将下载或上传任务（一个文件或一个压缩包）人为的划分为几个部分，每一个部分采用一个线程进行上传或下载，如果碰到网络故障，可以从已经上传或下载的部分开始继续上传下载以后未上传下载的部分，而没有必要从头开始上传下载。用途可以节省时间，提高速度。测试服务器是否支持断点续传的方法：
浏览器测试：
看看某个请求的响应头信息里面是否包含：Accept-Ranges bytes
比如请求hao123，相应头信息里面包含：
Accept-Ranges bytes
Cache-Control max-age=0
Content-Encoding gzip
Content-Length 59107
Content-Type text/html;charset=UTF-8
Date Fri, 03 Jan 2014 02:40:27 GMT
Etag "1946829081"
Expires Fri, 03 Jan 2014 02:40:27 GMT
LFY cq01.13
Last-Modified Fri, 03 Jan 2014 02:40:00 GMT
SFY cq01.14
Server BWS/1.0
Set-Cookie hz=0; path=/; domain=www.hao123.com
Vary Accept-Encoding表明支持断点续传
curl测试：
curl –-range 100-200 http://192.168.9.155/johnny/testzip.zip > download_1看下载文件的大小是否是100字节。
如果服务器支持断点续传，那么在请求头信息里面加上属性就可以了：
RANGE: bytes=1000-
这一行就是告诉服务器这个文件从1000字节开始传，前面就不要传了。
Java代码实现：
DownLoaderTask.javapackage com.johnny.testdownloadbreakpoint;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.DialogInterface.OnCancelListener;
import android.content.DialogInterface.OnClickListener;
import android.os.AsyncTask;
import android.util.Log;
public class DownLoaderTask extends AsyncTask {
private final String TAG = "DownLoaderTask";
private URL mUrl;
private File mFile;
private ProgressDialog mDialog;
private int mProgress = 0;
private ProgressReportingOutputStream mOutputStream;
private Context mContext;
public DownLoaderTask(String url,String out,Context context){
super();
if(context!=null){
mDialog = new ProgressDialog(context);
mContext = context;
}
else{
mDialog = null;
}
try {
mUrl = new URL(url);
String fileName = new File(mUrl.getFile()).getName();
mFile = new File(out, fileName);
Log.d(TAG, "out="+out+", name="+fileName+",mUrl.getFile()="+mUrl.getFile());
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
//super.onPreExecute();
if(mDialog!=null){
mDialog.setTitle("Downloading...");
mDialog.setMessage(mFile.getName());
mDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mDialog.setOnCancelListener(new OnCancelListener() {
@Override
public void onCancel(DialogInterface dialog) {
// TODO Auto-generated method stub
cancel(true);
}
});
mDialog.show();
}
}
@Override
protected Long doInBackground(Void... params) {
// TODO Auto-generated method stub
if(!checkURL()){
Log.e(TAG, "url can not access.....");
return 0l;
}
return download();
}
@Override
protected void onProgressUpdate(Integer... values) {
// TODO Auto-generated method stub
//super.onProgressUpdate(values);
if(mDialog==null)
return;
if(values.length>1){
int contentLength = values[1];
if(contentLength==-1){
mDialog.setIndeterminate(true);
}
else{
mDialog.setMax(contentLength);
}
}
else{
mDialog.setProgress(values[0].intValue());
}
}
@Override
protected void onPostExecute(Long result) {
// TODO Auto-generated method stub
//super.onPostExecute(result);
if(mDialog!=null&&mDialog.isShowing()){
mDialog.dismiss();
}
if(isCancelled())
return;
}
private long download(){
URLConnection connection = null;
int bytesCopied = 0;
try {
connection = mUrl.openConnection();
int length = connection.getContentLength();
if(mFile.exists()&&length == mFile.length()){
Log.d(TAG, "file "+mFile.getName()+" already exits!!");
return 0l;
}
else if(mFile.exists()&&length > mFile.length()){
Log.d(TAG, "Downdoad from breakpoint : size is = "+mFile.length()+", total is "+length);
publishProgress(0,length);
mProgress=(int) mFile.length();
URLConnection connection1=mUrl.openConnection();
connection1.setRequestProperty("RANGE", "bytes="+ mFile.length() +"-");
bytesCopied=copyFromBreakPoint(connection1.getInputStream(),mFile);
if(bytesCopied!=length&&length!=-1){
Log.d(TAG, "Download incomplete bytesCopied="+mFile.length()+", length"+length);
}
}
else if(!mFile.exists()){
mOutputStream = new ProgressReportingOutputStream(mFile);
publishProgress(0,length);
bytesCopied =copy(connection.getInputStream(),mOutputStream);
if(bytesCopied!=length&&length!=-1){
Log.d(TAG, "Download incomplete bytesCopied="+bytesCopied+", length"+length);
}
mOutputStream.close();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return bytesCopied;
}
private int copy(InputStream input, OutputStream output){
byte[] buffer = new byte[1024*8];
BufferedInputStream in = new BufferedInputStream(input, 1024*8);
BufferedOutputStream out = new BufferedOutputStream(output, 1024*8);
int count =0,n=0;
try {
while((n=in.read(buffer, 0, 1024*8))!=-1){
out.write(buffer, 0, n);
count+=n;
if(isCancelled()){
Log.e(TAG, "stop downloading .....");
//out.flush();
//out.close();
//in.close();
break;
}
}
out.flush();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
try {
out.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return count;
}
private int copyFromBreakPoint(InputStream input, File output){
byte[] buffer = new byte[1024*8];
int count =0,n=0;
try {
RandomAccessFile fos = new RandomAccessFile(output, "rw");
fos.seek(output.length());
while(true){
n=input.read(buffer);
if(n<=0){
break;
}
fos.write(buffer, 0, n);
mProgress += n;
publishProgress(mProgress);
}
input.close();
fos.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return 0;
}
private boolean checkURL(){
boolean ret = false;
try {
HttpURLConnection conn = (HttpURLConnection) mUrl.openConnection();
if(conn.getResponseCode()==200)
ret=true;
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return ret;
}
private final class ProgressReportingOutputStream extends FileOutputStream{
public ProgressReportingOutputStream(File file)
throws FileNotFoundException {
super(file);
// TODO Auto-generated constructor stub
}
@Override
public void write(byte[] buffer, int byteOffset, int byteCount)
throws IOException {
// TODO Auto-generated method stub
super.write(buffer, byteOffset, byteCount);
mProgress += byteCount;
publishProgress(mProgress);
}
}
} MainActivity.java
package com.johnny.testdownloadbreakpoint;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
doDownLoadWork();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
private void doDownLoadWork(){
DownLoaderTask task = new DownLoaderTask("http://192.168.9.155/johnny/H264+MP3.flv", "/storage/emulated/legacy/", this);
//DownLoaderTask task = new DownLoaderTask("http://192.168.9.155/johnny/test.h264", getCacheDir().getAbsolutePath()+"/", this);
task.execute();
}
}