利用监听者模式实现后台多文件下载的监听

来源：互联网发布：交英语的软件编辑：程序博客网时间：2024/04/28 22:20

项目聊天功能中，需要监听图片的下载进度。类型于QQ的聊天图片查看。 当退出查看界面时， 下载进程仍在后台运行，再次进入查看界面，如何监听到图片的下载进度呢。 如图

这里写图片描述

/** * 下载文件 * * @param url * @param outputStream     输出流 * @param onUpdateListener 下载进度监听 * @return */public boolean downLoadFile(String url, OutputStream outputStream, OnUpdateListener onUpdateListener) {    if (StringUtils.isStrEmpty(url)) {        return false;    }    if (onUpdateListener != null) {        downloadObserver.put(url, onUpdateListener);    }    HttpGet get = new HttpGet(url);    // Header headerRange = new BasicHeader("connection", "close");    // get.addHeader(headerRange);    get.addHeader("connection", "close");    InputStream in = null;    try {        HttpResponse response = getDownloadClient(url).execute(get);        if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {            HttpEntity he = response.getEntity();            if (onUpdateListener != null) {                onUpdateListener.onTotal(he.getContentLength());            }            in = he.getContent();            byte[] buffer = new byte[1024];            int len = 0;            long total = 0;            while ((len = in.read(buffer)) != -1) {                outputStream.write(buffer, 0, len);                if (onUpdateListener != null) {                    onUpdateListener.onProcess(total);                }            }            return true;        }    } catch (Exception e) {        e.printStackTrace();    } finally {        try {            if (in != null)                in.close();        } catch (IOException e) {            e.printStackTrace();        }    }    return false;}

这是原来的下载代码，这里的监听只能在第一次进放查看页面时生效。那么如何在重新进入时仍然能监听到下载的进度呢。这里借鉴到监听者模式的思想。使用一个集合来管理监听者对象

private Map<String, OnUpdateListener> downloadObserver = new HashMap<String, OnUpdateListener>();

提供添加监听的方法，一个url对应一public void addObserver(String url, OnUpdateListener onUpdateListener) {
if (onUpdateListener != null) {
downloadObserver.put(url, onUpdateListener);
onUpdateListener.onTotal(-1);
}
}的 Listener动态获取

/** * 下载文件 * * @param url * @param outputStream     输出流 * @param onUpdateListener 下载进度监听 * @return */public boolean downLoadFile(String url, OutputStream outputStream, OnUpdateListener onUpdateListener) {    if (StringUtils.isStrEmpty(url)) {        return false;    }    if (onUpdateListener != null) {        downloadObserver.put(url, onUpdateListener);    }    HttpGet get = new HttpGet(url);    // Header headerRange = new BasicHeader("connection", "close");    // get.addHeader(headerRange);    get.addHeader("connection", "close");    InputStream in = null;    try {        HttpResponse response = getDownloadClient(url).execute(get);        if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {            HttpEntity he = response.getEntity();            if (downloadObserver.get(url) != null) {                downloadObserver.get(url).onTotal(he.getContentLength());            }            in = he.getContent();            byte[] buffer = new byte[1024];            int len = 0;            long total = 0;            while ((len = in.read(buffer)) != -1) {                outputStream.write(buffer, 0, len);                if (downloadObserver.get(url) != null) {                    total += len;                    downloadObserver.get(url).onProcess(total);                }            }            return true;        }    } catch (Exception e) {        e.printStackTrace();    } finally {        try {            if (in != null)                in.close();        } catch (IOException e) {            e.printStackTrace();        }    }    return false;}

这样，在任意地方都可以监听到子线程的下载进度。

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