This is an FYI to announce some initial, long-overdue support in javadoc
for documenting system properties (JDK-5076751).
Currently, system properties are just documented using ad-hoc narrative
text, which is fine if you know where to look for any given property.
JDK 12 introduces a new inline javadoc tag, {@systemProperty
/property-name/} which can be used to "declare" the name of a system
property. You can use this tag as a drop-in replacement for the
plain-text property name; it will have no overt effect on the narrative
text, but it will cause the property name to be put into the search
index and the A-Z index. Thus, property names will become searchable, to
allow users to easily find the definition of any such system property.
Adding support into javadoc is only part of the story. Now that the
support is in javadoc, we want to update the API documentation, so that
the documentation is updated for all Java SE and JDK system properties.
Where should the tag be used? The tag should be used in the text of the
defining instance of the property. This is where the characteristics of
the system property are described, which may include information like:
"what is the property for", "how and when is it set", "can it be
modified", and so on. For example, it could be used in the docs for
System.getProperties [1] or Networking Properties [2] In general, it
should -not- be used in situations that merely refer to the system
property by name. For example, the docs for Path.toAbsolutePath [3]
make a reference to the system property user.dir, but that is not a
definition of the property.
Going forward, in future releases, we expect to explore some
enhancements to this feature. Here are some of the ideas that have been
suggested:
* Create a "summary page" that lists all the system properties. This
would be somewhat similar to the current top-level "Constant Values"
page.
* Add information regarding the "scope" of the definition: is it
defined by the Java SE specification, or JDK, or JavaFX, etc. This
information could be used to organize the content on the summary page.
* Update @see and {@link} to be able to refer to system properties.
* Allow a short description to be included in the {@systemProperty}
tag. This text could be included in the search index, the A-Z index,
and the summary page.
-- Jon
[1]:
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/System.html#getProperties()
[2]:
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/doc-files/net-properties.html
[3]:
https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/file/Path.html#toAbsolutePath()
