= Property Overriding
:index-group: OpenEJB Standalone Server
:jbake-date: 2018-12-05
:jbake-type: page
:jbake-status: published

OpenEJB consists of several components (containers,
resource adapters, security services, etc.) all of which are pluggable
and have their own unique set of configurable properties. These
components are required to specify their default property values in
their service-jar.xml file. This means that at a minimum you as a user
only need to specify what you'd like to be different. You specify the
property name and the new value and the default value will be
overwritten before the component is created.

We call this overriding and there are several ways to do it.

= The openejb.xml

The default openejb.xml file has most of the useful properties for each
component explicitly listed with default values for documentation
purposes. It is safe to delete them and be assured that no behavior will
change if a smaller config file is desired.

Overriding can also be done via the command line or plain Java system
properties. See link:system-properties.html[System Properties] for
details.

== What properties are available?

To know what properties can be overridden the './bin/openejb properties'
command is very useful: see link:properties-tool.html[Properties Tool]

Its function is to connect to a running server and print a canonical
list of all properties OpenEJB can see via the various means of
configuration. When sending requests for help to the users list or jira,
it is highly encouraged to send the output of this tool with your
message.

== Not configurable via openejb.xml

The only thing not yet configurable via this file are ServerServices due
to OpenEJB's embeddable nature and resulting long-standing tradition of
keeping the container system separate from the server layer. This may
change someday, but until then ServerServices are configurable via
conf/.properties files such as conf/ejbd.properties to configure the
main protocol that services EJB client requests.

The format those properties files is greatly adapted from the xinet.d
style of configuration and even shares similar functionality and
properties such as host-based authorization (HBA) via the 'only_from'
property.

== Restoring openejb.xml to the defaults

To restore this file to its original default state, you can simply
delete it or rename it and OpenEJB will see it's missing and unpack
another openejb.xml into the conf/ directory when it starts.

This is not only handy for recovering from a non-functional config, but
also for upgrading as OpenEJB will not overwrite your existing
configuration file should you choose to unpack a new distro over the
top of an old one -- this style of upgrade is safe provided you move
your old lib/ directory first.
