[jira] [Resolved] (HADOOP-13191) FileSystem#listStatus should not return null

["John Zhuge (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-13191?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

John Zhuge resolved HADOOP-13191.
---------------------------------
    Resolution: Duplicate

Thanks [~boky01], it is a dup of HADOOP-7352.

One idea is to add {{@NotNull}} to {{FileSystem#listStatus}}:
{code}
  @NotNull
  public abstract FileStatus[] listStatus(Path f) throws IOException;
{code}

Then run IntelliJ - Analyze - "Run Inspection by Name ..." - "@NotNull/@Nullible problems" (multiple times if necessary) in order to:
* Propagate {{@NotNull}} to subclasses' {{listStatus}} method
* Detect any implementation of {{listStatus}} that may return {{null}}

> FileSystem#listStatus should not return null
> --------------------------------------------
>
>                 Key: HADOOP-13191
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13191
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: fs
>    Affects Versions: 2.6.0
>            Reporter: John Zhuge
>            Assignee: John Zhuge
>            Priority: Minor
>
> This came out of discussion in HADOOP-12718. The {{FileSystem#listStatus}} contract does not indicate {{null}} is a valid return and some callers do not test {{null}} before use:
> AbstractContractGetFileStatusTest#testListStatusEmptyDirectory:
> {code}
>     assertEquals("ls on an empty directory not of length 0", 0,
>         fs.listStatus(subfolder).length);
> {code}
> ChecksumFileSystem#copyToLocalFile:
> {code}
>       FileStatus[] srcs = listStatus(src);
>       for (FileStatus srcFile : srcs) {
> {code}
> SimpleCopyLIsting#getFileStatus:
> {code}
>       FileStatus[] fileStatuses = fileSystem.listStatus(path);
>       if (excludeList != null && excludeList.size() > 0) {
>         ArrayList<FileStatus> fileStatusList = new ArrayList<>();
>         for(FileStatus status : fileStatuses) {
> {code}
> IMHO, there is no good reason for {{listStatus}} to return {{null}}. It should return empty list instead.
> To enforce the contract that null is an invalid return, update javadoc and consider Intellij IDEA's @Nullable and @NotNull annotations.
> So far, I am only aware of the following functions that can return null:
> * RawLocalFileSystem#listStatus



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