andriod 断点下载

来源：互联网发布：勇士队球员得分数据编辑：程序博客网时间：2024/04/29 02:55

以前没有用过断点下载，觉着这个东西非常高深，经高人指点后，觉着并没有那么难。ps:项目用的是高人封装的httputils，但是没有封装断点下载。

原理如下：
startProgress ：断点的位置
①：在请求的head中添加 .addHeader(“RANGE”, “bytes=” + startProgress + “-“)
②：RandomAccessFile 的feek（startProgress ）跳转到断点位置
RandomAccessFile randomAccessFile;
if(randomAccessFile==null){
randomAccessFile = new RandomAccessFile(file,”rw”);
}
randomAccessFile.seek(startPosition);
⑤：用RandomAccessFile 写入文件

具体实现：（自定义httputils下载的callback）

public  abstract class MyFileCallBack extends Callback<File> {    /**     * 目标文件存储的文件夹路径     */    private String destFileDir;    /**     * 目标文件存储的文件名     */    private String destFileName;    private long startPosition;    private  RandomAccessFile randomAccessFile;    public MyFileCallBack(String destFileDir, String destFileName,long startPosition)    {        this.destFileDir = destFileDir;        this.destFileName = destFileName;        this.startPosition=startPosition;    }    @Override    public File parseNetworkResponse(Response response, int id) throws Exception    {        return saveFile(response,id);    }    public File saveFile(Response response,final int id) throws IOException    {        InputStream is = null;        byte[] buf = new byte[2048];        // int len = 0;        // FileOutputStream fos = null;        try        {            is = response.body().byteStream();            final long total = response.body().contentLength();            long sum = 0;            File dir = new File(destFileDir);            if (!dir.exists())            {                dir.mkdirs();            }            File file = new File(dir, destFileName);            if(randomAccessFile==null){                randomAccessFile = new RandomAccessFile(file,"rw");            }            randomAccessFile.seek(startPosition);            int len;            while ((len = is.read(buf)) != -1)            {                sum += len;                randomAccessFile.write(buf, 0, len);                final long finalSum = sum;                OkHttpUtils.getInstance().getDelivery().execute(new Runnable()                {                    @Override                    public void run()                    {                        inProgress(finalSum * 1.0f / total,total,id);                    }                });            }            return file;        } finally        {            try            {                response.body().close();                if (is != null) is.close();                if( randomAccessFile!=null){                    randomAccessFile.close();                }            } catch (IOException e)            {            }        }    }}

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