![]() ![]() Annotations can be read at runtime using reflection or during compile-time to generate additional code, making them incredibly versatile. They enable programmers to associate information with code elements, like classes, interfaces, methods, and fields, without impacting their behavior. ParameterDescriptor1.Java annotations are a powerful language feature that allows developers to add metadata to their code. ![]() ParameterDescriptor parameterDescriptor1 = new ParameterDescriptor() TODO parameterize parameter descriptors creates the method descriptor with parameter descriptors The generated class name will be the same as the annotated class name plus the string “BeanInfo”, as if we were generating a Bean information class: if (e.getKind() = ElementKind.CLASS) ", 1) The following example shows how to create a Java source file inside an Annotation Processor. This concern is critical if we want to write generators that honors -d and -s options in javac or directories defined in a Maven POM. By using the Filer we can be sure of using the right directories and that we are not losing valuable generated items in our file system. The (2) interface contract defines some methods for creating source files, class files or generic resources. The FilerĪs discussed in part 2, every processor have access to a processing environment that points to some interesting utilities. The Java Compiler will take care of validating the model (annotations should match the defined types). A processor will be able to read annotations found in source code – that is, extract the model – and do whatever we need to do with it – open a file, put contents on it. The central piece in this approach is the Annotation Processor. For example, create a remoting proxy or a data access object from an annotated bean. We can leverage this model to generate configuration files or to write new source files that are derived from one existing. Annotation Types will act as meta-models, while a set of Annotations in a given piece of code will act as a model. Generating source code with Annotation Processorsįrom what we have seen until now, Annotations are an excellent way for defining a meta-model and creating models. You can think of it as the schema or semantics of models. The meta-model, then, are the rules that we use to write our models. ![]() In this context, a model is no more than the abstraction that we use to represent our system, whatever level of detail we are using. When one level of abstraction is modeled, we can start to model the next one and the next, ending with a complete, deployable product. We model the software system that we intent to build at different levels of detail and with different approaches. One of the pillars of MDE is the construction of abstractions. Model and Meta-model in MDEīefore going into the details on how to generate source code using Annotation Processors, there is a couple of concepts that we would like to present, as we will be referring to them in the following slides: models and meta-models. Model-Drive Engineering is much more than generating source code, although we can think of it as a natural entry point to MDE methodologies.Īnnotation Processors is one of the many tools that we may use to generate source code. And doing it in an elegant and efficient way can be a cumbersome task!įortunately, in the last years Model-Driven Engineering (1) (MDE, sometimes referred also as Model-Driven Development or Model-Driven Architecture) has helped to evolve a practice that was more art than science – task for ninja coders – into a mature methodology strongly based on proven processes and tools. Code Generation using Annotation Processors in the Java language – part 3: Generating Source Code Now, in part 3, we are going to show how an Annotation Processor can be used to generate source code. In part 2 (read it here) we introduced Annotation Processors, how to build them and how to run them. In part 1 (read it here) we introduced what Annotations are in the Java language and some of their common uses. This post is the third and final part in my series about Code Generation using Annotation Processors in the Java language. ![]()
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