Transforming models into text using JET transformations and exemplars

You can create template-based model-to-text transformations that enable you to define a transformation based on one or more exemplar projects. Exemplar projects are established solutions to common development problems. The Eclipse Modeling Framework Technology (EMFT) Java™ Emitter Templates (JET) transformations that you create can be invoked directly by users, consumed by other Java code, or combined with other model-to-text transformations to generate more complex transformations. You can create JET transformations that use templates to automate repetitive activities to provide more consistent solutions.

Exemplar projects are Eclipse projects that are examples of the application files and folders that you want a model-to-text transformation to generate. You can define a transformation input schema that describes the variable elements of the exemplar and then associate code generation actions with these schema elements. The files that the transformation creates use JET templates that are based on the exemplar artifacts. You complete the JET transformation authoring process by modifying these templates to include content that is derived from the transformation input.

When you run a JET transformation, it generates a solution similar to the exemplar artifacts, but the solution is customized to meet the requirements that are specified in the transformation input. You can implement JET transformations to automate the generation of the following types of applications:

Deployment scripts that migrate applications from development environments to test and production environments
Infrastructure code, for example, entity and session beans, session facades, and data transfer objects for EJB applications that are based on best practices
Java code that implements model-to-model transformations

By automating the generation of these types of applications, you can reduce the number of errors in the application, produce application code more quickly, and ensure adherence to project or organizational standards.

A JET newsgroup is available from the Eclipse Web site. You can subscribe to the newsgroup by following the link to the Eclipse Web site in the Related Information section below, and searching for the eclipse.modeling.m2t newsgroup. See the Related Information section for links to additional JET content.

Creating and configuring JET transformations
When you create a Java Emitter Template (JET) transformation project, you can also configure the properties of the transformation, specify JET tag library information, and define the scope of the exemplar project by adding or deleting exemplar artifacts from the JET transformation project.
Defining input schemas and output actions for JET transformations
The input schema for a Java Emitter Template (JET) transformation describes the input that a transformation expects. When you create a JET transformation project, the New Project wizard creates an input schema with a root element. You can also import an existing input schema into an existing JET project. Existing schemas are Eclipse Modeling Framework core (Ecore) files with the name input.schema in the root of a JET project. Using a valid transformation input schema ensures that the input to the transformation is structurally correct, and enables transformation users to create input with fewer syntax or semantic errors.
Generating JET templates
When you finish creating and refining the transformation input schema and output actions, you must run the Update Project command to generate the JET templates that the input model defines. When you run the Update Project command, the JET transformation updates the main.jet file to match the input schema elements and the transformation output hierarchy. The JET transformation also creates the JET templates that were seeded from the exemplar files, and creates the schema.xsd file, which represents the transformation input schema.
Editing JET templates
You can edit the JET templates that are generated after you run the Update Project command. You might edit JET templates to add iterative or conditional content, or to replace text in the template with references to attributes or elements in the input model.
Protecting changes to generated JET transformation code
To prevent changes to the main.jet template from being overwritten when you modify the main.jet template directly, you must modify or remove the <%--@generated--%> comment that corresponds to the change that you want to protect.
Displaying Java classes that the JET compiler generates
To view the Java classes that the JET compiler generates from the JET templates, you must change the filter settings for the Project Explorer view or Package Explorer view.
Creating transformation input files from XML Schema Definitions
An XML Schema Definition (XSD) is generated when you run the Update Project command. You can use the XML Schema Definition to create XML input files for a JET transformation. Creating XML input files using the XML Schema Definition ensures that your XML input files conform to the transformation input schema.
Creating launch configurations for JET transformations
You can create launch configurations for the input files to test JET transformations. Creating launch configurations enables you to store configuration information, which eliminates the need to supply configuration information each time that you run a JET transformation.
Managing JET launch configurations
You can manage your JET launch configurations from multiple perspectives, including the Java perspective. Launch configurations enable you to preserve arguments that you specify when you run a JET transformation.
Overriding JET templates in other JET transformations
You can specify that a JET transformation override the templates of another JET transformation. This functionality enables you to customize the behavior of an existing JET transformation by replacing only specific templates.

Related information

Model-to-text JET transformation FAQ

Eclipse newsgroups

Article on developerWorks: Introduction to the transformation authoring feature