netbeans.apache.org/src/content/wiki/DevFaqDotShadowFiles.adoc

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= What are `{asterisk}.shadow` files?
:jbake-type: wikidev
:jbake-tags: wiki, devfaq, needsreview
:jbake-status: published
:keywords: Apache NetBeans wiki DevFaqDotShadowFiles
:description: Apache NetBeans wiki DevFaqDotShadowFiles
:toc: left
:toc-title:
:syntax: true
:wikidevsection: _configuration_how_modules_install_things
:position: 9


`{asterisk}.shadow` files are mainly used in the xref:DevFaqSystemFilesystem.adoc[system filesystem]
for configuration data.
They are the functional equivalent of Unix symbolic links -
a `{asterisk}.shadow` file is a pointer to another file whose
behavior in every respect except its path and file name is the same as the original.

`{asterisk}.shadow` files are commonly used where only a single instance of an object is needed,
but it must be registered in multiple folders.
For example, a general `Action` is declared in the `Actions/` folder of the
system filesystem.
But the action also needs to appear in menus and toolbars, possibly other places.
So, rather than create multiple instances of an action, one xref:DevFaqInstanceDataObject.adoc[`{asterisk}.instance` file]
is created in the xref:DevFaqModulesLayerFile.adoc[module's layer file], in the `Actions/` folder.
Then `{asterisk}.shadow` files are created in all of the other places the `{asterisk}.instance` file would be needed,
pointing to the original file.

Declaring a .shadow file in the system filesystem looks like this:

[source,xml]
----

<folder name="A">
  <file name="com-foo-mymodule-MyClass.instance"/>
</folder>
<folder name="B">
  <file name="Shadow1.shadow">
    <attr name="originalFile" stringvalue="A/com-foo-mymodule- MyClass.instance"/>
  </file>
</folder>
<folder name="C">
  <file name="anotherShadow.shadow">
    <attr name="originalFile" stringvalue="A/com-foo-mymodule-MyClass.instance"/>
  </file>
</folder>
----

Shadow files can also point to real files on disk.
For example, the Favorites tab in the NetBeans IDE
uses shadow files to link to real directories on disk.

== Creating Shadow Files Programmatically

If you need to create `.shadow` files programmatically, use link:https://bits.netbeans.org/dev/javadoc/org-openide-loaders/org/openide/loaders/DataShadow.html#create(org.openide.loaders.DataFolder,%20java.lang.String,%20org.openide.loaders.DataObject[`DataShadow.create()`] -- do not write `FileObject`s and try to set attributes on them.  In an XML layer, a `DataShadow`'s original file is pointed to by a file attribute.  On disk, that is accomplished via the _file's content_ instead.  To reliably create `DataShadow`s, let the infrastructure do it for you - do not make assumptions about how the original file is pointed to.
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== Apache Migration Information

The content in this page was kindly donated by Oracle Corp. to the
Apache Software Foundation.

This page was exported from link:http://wiki.netbeans.org/DevFaqDotShadowFiles[http://wiki.netbeans.org/DevFaqDotShadowFiles] , 
that was last modified by NetBeans user Jglick 
on 2010-06-14T21:42:08Z.


*NOTE:* This document was automatically converted to the AsciiDoc format on 2018-02-07, and needs to be reviewed.
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