Modularity And Oddballs

Oddjob's extension points.

In this section we take a look at the many options for making our classes available to Oddjob. We'll learn how to tell Oddjob to use nice short element names like <copy> and we'll learn how to write an Oddball which is an Oddjob plugin.

• The Class System
• The Descriptor Factory
• Dynamic Design
• Per Oddjob Modularity
• Oddballs

The Class System

In the first instance Oddjob finds its classes...

• On the path given by the -classpath option.
• In any .jar in the lib directory.
• In any .jar in the opt/lib directory.
• In the opt/classes directory.

We can prove this by copying an example class:

$ mkdir opt/classes/org
$ mkdir opt/classes/org/oddjob
$ mkdir opt/classes/org/oddjob/devguide
$ cp examples/classes/org/oddjob/devguide/HelloWorldJob.class opt/classes/org/oddjob/devguide
$ java -jar run-oddjob.jar -f examples/devguide/hello1.xml
Hello World!

The Descriptor Factory

How can we use our own XML elements instead of boring old <bean> elements? Provide an implementation of an ArooaDescriptorFactory.

When Oddjob starts it has one of these factory things that scans the classpath for any number of META-INF/arooa.xml XML files which it expects to be able to parse to create another factory. It joins all these little factories together and creates a big factory (For those that like design patterns this is of course the classic Composite Pattern).

There's an example of one of these XML files in the examples directory called helloperson-arooa.xml. It's for our HelloPersonJob example from the previous section and it looks like this.

<arooa:descriptor xmlns:arooa="http://rgordon.co.uk/oddjob/arooa">
    <components>
        <arooa:bean-def element="hello" className="org.oddjob.devguide.HelloPersonJob"/>
    </components>
    <values>
        <arooa:bean-def element="person" className="org.oddjob.devguide.Person"/>
    </values>
</arooa:descriptor>

If we copy the descriptor:

$ cp examples/devguide/helloperson-arooa.xml examples/classes/META-INF/arooa.xml

We can modify our original configuration to become:

<oddjob>
    <job>
        <hello formal="true">
            <person>
                <person title="Mr" firstname="John" surname="Smith"/>
            </person>
        </hello>
    </job>
</oddjob>

And run it:

$ java -jar run-oddjob.jar -cp examples/classes -f examples/devguide/helloperson2.xml
Hello Mr Smith.

Dynamic Design

Once a component has been given an element to class mapping, Oddjob Designer will automatically create a form for it:

And for person too:

Ok, not pretty - but it can make a pleasant change from XML.

Per Oddjob Modularity

A nested Oddjob job within Oddjob can also be configured with it's own class loader and descriptor factory.

<oddjob id="this">
    <job>
        <oddjob file="${this.dir}/helloperson2.xml">
            <descriptorFactory>
                <import file="${this.dir}/helloperson-arooa.xml"/>
            </descriptorFactory>
            <classLoader>
                <url-class-loader>
                    <files>
                        <file file="${this.dir}/../classes"/>
                    </files>
                </url-class-loader>
            </classLoader>
        </oddjob>
    </job>
</oddjob>

This does the same as the above. No classpath required.

$ java -jar run-oddjob.jar -f examples/devguide/helloperson-main.xml
Hello Mr Smith.

The difference is that a new class loader is created and used to load the HelloPersonJob class.

Oddballs

Oddballs are Oddjob's plugin architecture.

Oddballs extends the above features of Oddjob modularity by defining a recognised directory structure for deploying a set of job classes and their dependent libraries.

An Oddball is any directory in Oddjob's oddballs directory. Oddballs find their classes...

• In any .jar in the lib directory.
• In the classes directory.

(Familiar to those who know Servlets. But there's no web.xml, instead...)

When the Oddball loads it scans this classpath for any number of META-INF/arooa.xml XML file from which it creates it's ArooaDescriptorFactory.

Oddjob comes pre-installed with some Oddballs for Ant tasks, mail, FTP, an HSQL database server, and an optional Oddball, oj-spring which is in the /opt/oddballs directory. To install an Oddball simply move this to Oddjob's oddballs directory.

$ mv opt/oddballs/oj-spring oddballs

To un-install it, simply move it out of the oddballs directory.