How to skip the setting of 'filter' and 'locker' attribute if custom DirectoryScanner is used in Spring Integration 4.2.0 with XML Config

Question

With Spring Integration 4.2.0, it mentioned that 'filter' and 'locker' must be present if custom Scanner is being used (https://jira.spring.io/browse/INT-3619).

I don't know how to set this with XML config if I simply override the listEligibleFiles() method and use the default filters provided by DefaultDirectoryScanner.

e.g.

// using the default filters
public class MyDirectoryScanner extends DefaultDirectoryScanner {
    @Override
    protected File[] listEligibleFiles(File directory) throws IllegalArgumentException {
        return super.listEligibleFiles(directory);
    }
}

<bean id="myCustomScanner"
      class="com.company.MyDirectoryScanner" />

<int-file:inbound-channel-adapter directory="my_directory"
                                  prevent-duplicates="true"
                                  scanner="myCustomScanner"
                                  channel="myChannel">
    <int:poller fixed-rate="10"
                time-unit="SECONDS" max-messages-per-poll="5" />
</int-file:inbound-channel-adapter>

Answer 1

It's not clear what you mean; that JIRA was to fix a bug where those properties were incorrectly overridden.

When injecting a custom scanner, you need to set those properties on your scanner rather than via the namespace.

Answer 2

use the default filters provided by DefaultDirectoryScanner.

The DefaultDirectoryScanner has the code:

public DefaultDirectoryScanner() {
    final List<FileListFilter<File>> defaultFilters = new ArrayList<FileListFilter<File>>(2);
    defaultFilters.add(new IgnoreHiddenFileListFilter());
    defaultFilters.add(new AcceptOnceFileListFilter<File>());
    this.filter = new CompositeFileListFilter<File>(defaultFilters);
}

So, if you would like do not use AcceptOnceFileListFilter (or any other default) you should follow with the recommendation from the Docs and use setFilter() of the DirectoryScanner contract. For this purpose there is FileListFilterFactoryBean with the setPreventDuplicates() to be set to false.

And yes, remove, please, prevent-duplicates="true" from your configuration, because it is prohibited, when scanner is in use:

Assert.state(!(this.scannerExplicitlySet && (this.filter != null || this.locker != null)),
            "The 'filter' and 'locker' options must be present on the provided external 'scanner': "
                    + this.scanner);

The filter can be set to null on the DefaultDirectoryScanner by the way...

I'm converting the JIRA to Documentation just to be more clear on the matter.