之前开发的一个和第三方合作的apk，在之前公司的 Android 5.1 系统的手表上运行正常，今天在公司新开发的 Android 7.1系统的手表上运行的时候，使用 DownloadManager 下载之后，查询下载状态的时候，报了异常
java.lang.SecurityException: COLUMN_LOCAL_FILENAME is deprecated; use ContentResolver.openFileDescriptor() insteadAI 代码解读
异常详细信息如下：
03-17 15:59:43.288 31487-31487/com.netease.xtc.cloudmusic E/CloudMusicDownloadService: DownloadChangeObserver.onChange() throwable = java.lang.SecurityException: COLUMN_LOCAL_FILENAME is deprecated; use ContentResolver.openFileDescriptor() instead
at android.app.DownloadManager$CursorTranslator.getString(DownloadManager.java:1545)
at com.netease.xtc.cloudmusic.services.download.CloudMusicDownloadService.queryDownloadStatus(CloudMusicDownloadService.java:634)
at com.netease.xtc.cloudmusic.services.download.CloudMusicDownloadService.access$900(CloudMusicDownloadService.java:55)
at com.netease.xtc.cloudmusic.services.download.CloudMusicDownloadService$DownloadChangeObserver$3.call(CloudMusicDownloadService.java:590)
at com.netease.xtc.cloudmusic.services.download.CloudMusicDownloadService$DownloadChangeObserver$3.call(CloudMusicDownloadService.java:587)
at rx.Observable.unsafeSubscribe(Observable.java:8666)
at rx.internal.operators.OperatorSubscribeOn$1.call(OperatorSubscribeOn.java:94)
at rx.internal.schedulers.CachedThreadScheduler$EventLoopWorker$1.call(CachedThreadScheduler.java:220)
at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:428)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:272)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1133)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:607)
at java.lang.Thread.run(Thread.java:761)
AI 代码解读
跳转到报错的地方，如下图所示： 
在运行下面两行代码的时候报错了。
int fileNameIdx = c.getColumnIndex(DownloadManager.COLUMN_LOCAL_FILENAME);
String fileName = c.getString(fileNameIdx);
AI 代码解读
而且 DownloadManager.COLUMN_LOCAL_FILENAME 已经是被废弃的常量了，点击查看源代码如下所示：
/**
* Path to the downloaded file on disk.
* <p>
* Note that apps may not have filesystem permissions to directly access
* this path. Instead of trying to open this path directly, apps should use
* {@link ContentResolver#openFileDescriptor(Uri, String)} to gain access.
*
* @deprecated apps should transition to using
* {@link ContentResolver#openFileDescriptor(Uri, String)}
* instead.
*/
@Deprecated
public final static String COLUMN_LOCAL_FILENAME = "local_filename";
AI 代码解读
Android 在 Android 7.0 或更高版本开发的应用在尝试访问DownloadManager.COLUMN_LOCAL_FILENAME 时会触发java.lang.SecurityException。
Android官方建议我们使用 ContentResolver#openFileDescriptor(Uri, String)来获取文件相关信息。源代码如下所示：
/**
* Open a raw file descriptor to access data under a URI. This
* is like {@link #openAssetFileDescriptor(Uri, String)}, but uses the
* underlying {@link ContentProvider#openFile}
* ContentProvider.openFile()} method, so will <em>not</em> work with
* providers that return sub-sections of files. If at all possible,
* you should use {@link #openAssetFileDescriptor(Uri, String)}. You
* will receive a FileNotFoundException exception if the provider returns a
* sub-section of a file.
*
* <h5>Accepts the following URI schemes:</h5>
* <ul>
* <li>content ({@link #SCHEME_CONTENT})</li>
* <li>file ({@link #SCHEME_FILE})</li>
* </ul>
*
* <p>See {@link #openAssetFileDescriptor(Uri, String)} for more information
* on these schemes.
* <p>
* If opening with the exclusive "r" or "w" modes, the returned
* ParcelFileDescriptor could be a pipe or socket pair to enable streaming
* of data. Opening with the "rw" mode implies a file on disk that supports
* seeking. If possible, always use an exclusive mode to give the underlying
* {@link ContentProvider} the most flexibility.
* <p>
* If you are writing a file, and need to communicate an error to the
* provider, use {@link ParcelFileDescriptor#closeWithError(String)}.
*
* @param uri The desired URI to open.
* @param mode The file mode to use, as per {@link ContentProvider#openFile
* ContentProvider.openFile}.
* @return Returns a new ParcelFileDescriptor pointing to the file. You
* own this descriptor and are responsible for closing it when done.
* @throws FileNotFoundException Throws FileNotFoundException if no
* file exists under the URI or the mode is invalid.
* @see #openAssetFileDescriptor(Uri, String)
*/
public final @Nullable ParcelFileDescriptor openFileDescriptor(@NonNull Uri uri,
@NonNull String mode) throws FileNotFoundException {
return openFileDescriptor(uri, mode, null);
}
AI 代码解读
查看Android 官方文档，关于Android 7.0 的权限管理更改，如下图所示：
参考链接为：
https://developer.android.google.cn/about/versions/nougat/android-7.0-changes.html#sharing-files
因此为了解决这个异常，我们有以下两个方法解决。
方法一、使用 ContentResolver#openFileDescriptor(Uri, String)来替代访问由 DownloadManager 公开的文件。
方法二、使用DownloadManager.COLUMN_LOCAL_URI查出文件Uri，然后使用Uri new一个File，再获取File的相关信息，如下所示：
int fileUriIdx = c.getColumnIndex(DownloadManager.COLUMN_LOCAL_URI);
String fileUri = c.getString(fileUriIdx);
String fileName = null;
if (Build.VERSION.SDK_INT > Build.VERSION_CODES.M) {
if (fileUri != null) {
fileName = Uri.parse(fileUri).getPath();
}
} else {
//Android 7.0以上的方式：请求获取写入权限，这一步报错
//过时的方式：DownloadManager.COLUMN_LOCAL_FILENAME
int fileNameIdx = c.getColumnIndex(DownloadManager.COLUMN_LOCAL_FILENAME);
fileName = c.getString(fileNameIdx);
}
AI 代码解读
运行之后，不会报错，并且能够获取到正常的文件名。
参考链接
1. https://developer.android.google.cn/about/versions/nougat/android-7.0-changes.html#sharing-files
2. http://www.cnblogs.com/dazhao/p/6547811.html
3. http://www.jianshu.com/p/56b9fb319310
作者：欧阳鹏 欢迎转载，与人分享是进步的源泉！
转载请保留原文地址： http://blog.csdn.net/ouyang_peng/article/details/62891782
