attached with class, interface, methods or fields to indicate some additional information which. Since compiler warnings are to be issued in the sample module, showWarnings must be set to true, and in the log module, the compiler must be run with -proc:none, as described above (compilerArgs). Java Annotation is a tag that represents the metadata i.e. The Validated annotation is a class-level annotation that we can use to tell Spring to validate parameters that are passed into a method of the annotated class. Here, it is important to remember that the maven-compiler-plugin must be configured in both modules. The annotation Validated defined at class-level annotation is necessary to trigger method validation for a specific bean to begin with. Our example with Maven can be viewed at the following URL. This separation must take place so that Maven can compile the annotation processor independently and before its use. In order to use annotation processors with Maven, for example, the build must be divided into separate modules. Note: found at .sample.HelloĪnnotation processors can also be used with standard build tools and IDEs. The compiler should now call the annotation processor and we should see the following line on the console: com/cloudogu/blog/annotationprocessor/sample/*.java Now, we can compile our test class and thus test our annotation processor: This is important, as the compiler already finds our registry (the file saved under META-INF/services), but our processor is not yet compiled. The parameter -proc:none deactivates all of the annotation processors. proc:none com/cloudogu/blog/annotationprocessor/log/*.java First, we compile the annotation and the processor: RELEASE_8 ) public class LogProcessor extends AbstractProcessor Īfter creating the example class, we can compile and test our annotation processor. To do so, we must first create our annotation ( ".log.Log" ) ( SourceVersion. Our example annotation processor is supposed to issue a notification when a certain annotation is found. A simple annotation processorĪnnotation processors must implement the interface in most cases it is recommended to extend the class, as it contains useful auxiliary methods. Then, we will see how our simple annotation processor can be used with a build tool, such as Maven. To begin with, we will only use this annotation processor with the help of the Java compiler. In the first section of this article, we will create a simple annotation processor that issues a log message during compilation. At this point, the annotation processor can perform its task and determine whether additional processors should be called for the annotation found. If the compiler finds an annotation, it checks whether a processor has been registered for it. This can include single, multiple, or all annotations. In this context, the annotation processor is able to determine which annotations it wishes to be notified of. ĭuring the build, annotation processors are called by the compiler (javac) when one of the configured annotations has been found. The code used in this article can be viewed at. Now we’re going to see how to take advantage of them by using Java’s Reflection API.This is the introduction part of a blogpost series, in which we will take a look at the basic functionality of annotation processors using a small example. So far we’ve seen how to create custom annotations, and how to use them to decorate the Person class. Moreover, we want the initNames() method to be called before serialization.īy setting the key parameter of the annotation to “personAge,” we are indicating that we’ll use this name as the identifier for the field in the JSON output.įor the sake of demonstration, we made initNames() private, so we can’t initialize our object by calling it manually, and our constructors aren’t using it either. In addition, the output should contain only the firstName, lastName, and age fields of that object. This.lastName = (0, 1).toUpperCase()īy using our custom annotations, we’re indicating that we can serialize a Person object to a JSON string. Class Person String String = "personAge")
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