Plexus – How auto-configuration works

The contents of this document are a work in progress

Plexus Auto Configuration

Auto configuration is ...

If you are familiar with libraries like xstream you will feel at home. If not, it's simple enough anyway.

The best way to understand how the plexus ComponentConfigurator functions is by example. Assuming that the auto-configuration mechanism is applied to class:

com.MyComponent

class com.MyComponent implements com.SomeInterface
{
   private String propertyA;

   private int propertyB;

   ...
}

with a plexus configuration like so:

<component>
  <role>com.SomeInterface</role>
  <implementation>com.MyComponent</implementation>
    <configuration>
        <propertyA>foo</propertyA>
        <propertyB>1</propertyA>
    </configuration>
</component>

The actions the plexus ComponentConfigurator would perform on the instance of component would be something like this:

com.SomeInterface component = new com.MyComponent();

component.propertyA = "foo";

component.propertyB = 1;

Types Supported by Autoconfiguration

Basic

java.lang.Boolean & boolean
java.lang.Byte & byte
java.lang.Character & char
java.lang.Double & double
java.lang.Float & float
java.lang.Integer & int
java.lang.Long & long
java.lang.Short & short
java.lang.StringBuffer
java.lang.String
java.util.Date (todo: document supported patterns)
java.math.BigDecimal
java.math.BigInteger

Composite types (Object properties)

Object with properties

Component implementation:

class com.MyComponent
{
   private Person person;

   ...
}

class com.Person
{
   private String firstname;

   private String lastname;

   ...
}

Component configuration :

<configuration>
   <person>
       <firstname>Baltzar<firstname>
       <lastname>Gabka</lastname>
   </person>
</configuration>

Actions taken by Component Configurator:

Person person = new Person();

person.firstname = "Baltazar";
person.lastname = "Gabka";

component.person = person;

Collections
TODO: Collections example.

java.lang.Properties

Component implementation:

class com.MyComponent
{
   private Properties propertiesA;
   ...
}

Component configuration :

<configuration>
   <propertiesA>
      <property>
          <name>key1</name>
          <value>value1</value>
      </property>
      <property>
          <name>key2</name>
          <value>value2</value>
      </property>
   </propertiesA>
</configuration>

Actions taken by Component Configurator:

com.MyComponent component;

Properties properties = new Properties();

properties.put( "key1", "name1" )

properties.put( "key2", "name2" )

setFieldValue( component, "propertiesA", properties );

component.propertiesA = properties;

Advanced mapping

<foos elements="java.lang.String"/>
    <id>ala</id>
    <id>ala</id>
    <id>ala</id>
</foos>

or possibly (pending implementation)

<foos elements="com.MyBean" implementation="java.util.LinkedList"/>
    <bean>
        <id>foo</id>
    </bean>
    <bean>
        </id>ala</id>
    </bean>
</foos>