CodeGen Extensions

CodeGen extensions

Extension customization elements are used to extend or modify the actual code generation. CodeGen allows you to apply extensions either to a particular schema or to a set of schemas, so they fit into the customization document structure as child elements of a schema or schema-set element. Since they always apply to all the schemas associated with the parent schema or schema-set element, they must precede any other child elements. Here's a sample to show how this works, with the extension elements shown in bold:

<schema-set xmlns:xs="http://www.w3.org/2001/XMLSchema"
    type-substitutions="xs:integer xs:int xs:decimal xs:float">
  <name-converter strip-prefixes="OTA_"
      strip-suffixes="Type AttributeGroup Group Attributes"/>
  <class-decorator class="org.jibx.schema.codegen.extend.CollectionMethodsDecorator"/>
  <schema-set package="org.ota.air" names="OTA_Air*.xsd">
    <schema-type type-name="dateTime" java-class="org.joda.time.DateTime"
        format-name="DateTime.zoned"/>
    <schema-set generate-all="false" prefer-inline="true"
        names="OTA_AirCommonTypes.xsd OTA_AirPreferences.xsd"/>
    <schema name="OTA_AirAvailRS.xsd">
      <element path="element[@name=OTA_AirAvailRS]/**/element[@name=OriginDestinationOption]"
        ignore="true"/>
    </schema>
  </schema-set>
  <schema-set package="org.ota.hotel" names="OTA_Hotel*.xsd">
    <schema-set generate-all="false" prefer-inline="true"
        names="OTA_HotelCommonTypes.xsd OTA_HotelContentDescription.xsd
        OTA_HotelEvent.xsd OTA_HotelPreferences.xsd OTA_HotelReservation.xsd
        OTA_HotelRFP.xsd"/>
  </schema-set>
  ...

The name-converter (modifying the way names are generated) and class-decorator (adding collection helper methods to generated classes, in this case) elements are both children of the root schema-set element, so they apply to all code generation. The schema-type element (changing the Java type generated for a schema datatype) is a child of the nested schema-set, so it only applies to the code generation for schemas included in that set.

Extensible extensions

Some extension elements are designed to support selecting a particular implementation for an interface used during code generation. These extension elements normally have one required attribute, the 'class' attribute (though in the case of the name-converter extension, this attribute has a default value matching a built-in class). This attribute is used to supply the fully-qualified class name of your implementation class. Besides this required attribute, you can add other attributes which correspond to properties of your implementation class. These added attributes will be used to configure an instance of the class before it is used in code generation, so that you can customize general-purpose extension classes for each use.

CodeGen uses reflection to match any additional attributes to property or field names in your class (or in a superclass). First any hyphens in the attribute name are removed, with the character following any hyphen converted to uppercase. This modified name is then used to look for a method or field name, in three different forms.

Due to some legacy code handling, the preferred form of match is somewhat unusual - CodeGen looks for a method name starting with set followed by the attribute name (with the first letter of the name converted to uppercase) and ending with Text. The method may have either one or two parameters, with the first parameter a java.lang.String and the second (if defined) a org.jibx.runtime.IUnmarshallingContext. This form of match is intended for when the supplied attribute value needs to use some special conversion. If a match of this type is found, CodeGen calls the method to set the value, passing the attribute value text as the first parameter (and the unmarshalling context as the second parameter, if used).

If the preferred form of match described above is not found, CodeGen next looks for either a set method matching the attribute name (with the first letter of the attribute name converted to uppercase) with a single parameter, or a field name matching the attribute name with m_ prefix. The method parameter or field may be of any of the following types: boolean/java.lang.Boolean; double/java.lang.Double; float/java.lang.Float; int/java.lang.Integer; long/java.lang.Long; java.lang.String; or java.lang.String[]. CodeGen converts the supplied attribute value to the appropriate type (in the case of an array of String, by splitting at each embedded whitespace sequence and trimming all leading and trailing whitespace from each resulting value) and calls the method or sets the field value directly.

You can see the source code for the classes mentioned in the remainder of this section for examples of this correspondence between attribute names and method or field names.

Controlling name handling

The name-converter extension element is used to control how XML names are converted to Java names. It can be used in two ways: To change the behavior of the default name converter class used by CodeGen (org.jibx.schema.codegen.extend.DefaultNameConverter), or to completely replace that default name converter class with your own implementation.

When used to change the behavior of the default name converter class used by CodeGen, the following attributes apply:

Default name converter customization attributes

When the name-converter element is used to replace the default name converter class with your own implementation, there's only one fixed attribute: The 'class' attribute. This attribute gives the fully-qualified name of your name converter implementation class, which must implement the org.jibx.schema.codegen.extend.NameConverter interface. You can use other attributes on the element to configure your name converter instance, as described above.

If you do take the approach of writing your own name converter implementation you'll probably want to refer to the default org.jibx.schema.codegen.extend.DefaultNameConverter implementation and either use it as the base for your own implementation or just subclass and override methods selectively.

Extending code generation

You can extend Java class generation to add special handling or features to the generated code, using class-decorator elements. Multiple class-decorator elements can be used, and by default the decorators are inherited by child schema-set and schema-set elements within the customizations. You can change this by using the inherit-decorators customization attribute.

The required 'class' attribute must give the fully-qualified class name of a class implementing the org.jibx.schema.codegen.extend.ClassDecorator interface. This interface defines methods called by CodeGen during the process of generating a Java class. The method parameters give your implementation code ways to hook into the code generation, which uses the Eclipse Abstract Syntax Tree (AST) model. You can then modify the AST in various ways to meet your needs.

Several decorators are provided with CodeGen, along with an abstract base class useful for writing your own decorators. These build-in decorators are described in the remainder of this section.

Base class for matching names

org.jibx.schema.codegen.extend.NameMatchDecoratorBase is a convenient base class to use if you want your decorator to apply only to some of the data model classes. Decorators based on this class support a 'match-name' attribute on the class-decorator customization. The value of this optional attribute is a name pattern, which can include one or more '*' wildcard match characters. Subclasses can call the base class matchName() method to check if a class name matches the pattern.

Adding collection methods

org.jibx.schema.codegen.extend.CollectionMethodsDecorator adds helper methods for collection values represented by java.util.List instances. The helper methods are int sizeXXX() to get the number of items in the list, void addXXX(type) to add an item to the list, type getXXX(int) to get an item by position, and void clearXXX() to remove all items from the list (where 'XXX' is the value name). No attributes are used with this decorator.

Changing the List implementation class

org.jibx.schema.codegen.extend.ListImplementationDecorator lets you set the implementation class to be used for instances of java.util.List in the data model. The required 'list-class' attribute must give the fully-qualified class name of the desired implementation class.

Extending a base class

org.jibx.schema.codegen.extend.ExtensionDecorator allows you to set a base class to be extended by your data model classes. This decorator class itself extends the abstract org.jibx.schema.codegen.extend.NameMatchDecoratorBase class described above, so you can use a 'match-name' attribute to control the data model classes which are modified by this decorator (matching on the simple class name, without package name). The 'base-class' attribute must give the desired base class name.

You can also use this decorator to customize the JiBX binding for data model classes to call user extension methods implemented by the base class. Use a 'pre-get-name' attribute to set a method to be called before marshalling the data class, a 'pre-set-name' attribute to set a method to be called before unmarshalling to the data class, and a 'post-set-name' attribute to set a method to be called after unmarshalling the data class.

Making data model classes serializable

org.jibx.schema.codegen.extend.SerializableDecorator is used to add the java.io.Serializable interface to generated data model classes. If a 'serial-version' attribute is used with this decorator it will also add a serialVersionUID value to each generated class, with the specified version (which must be a long integer value).

Schema datatypes

You can customize the code generation for schema built-in datatypes using the schema-type element. Besides determining the Java type to be used for a schema datatype, this also allows you to define the actual format used to convert instances of one into the other (see and <format> element for dicsussions of these conversions). The attributes used with the schema-type element are listed in the following table:

schema-type attributes