Introduction
If you're a Java developer using JPA, chances are that you've declared one or more @NamedQuery objects on your entities.
To declare a @NamedQuery on a class, the class must simply be annotated with the name of the query and its JPQL, such as:
@Entity
@NamedQuery(name = "findAllProjects",
query = "select p from Project p order by p.id")
public class Project
If however, we wish to declare multiple @NamedQuery annotations, we annotate the class with a @NamedQueries annotation which then contains a collection of @NamedQuery annotations as follows:
@Entity
@NamedQueries({
@NamedQuery(name = "findAllProjects",
query = "select p from Project p order by p.id"),
@NamedQuery(name = "findById",
query = "select p from Project p where p.id=:id")
})
public class Project
Enumerating the @NamedQuery annotations
Once you've created an entity with multiple @NamedQuery annotations, how can you check what annotations are present on the class?
Fortunately using reflection, its a fairly simple matter to enumerate the annotations on the class and find the details about them as shown in the following code.
NamedQueries annotation = Project.class.getAnnotation(
NamedQueries.class
);
for (Annotation annot : annotation.value()) {
System.out.println(annot.toString());
for (Method method : annot.annotationType().getDeclaredMethods()) {
if (method.getName().equalsIgnoreCase("name") ||
method.getName().equalsIgnoreCase("query")) {
try {
String result = method.getName() +
" : " +
method.invoke(annot, null).toString();
System.out.println(result);
} catch (IllegalAccessException | IllegalArgumentException
| InvocationTargetException e) {
// Oops - something has gone wrong.
break;
}
}
}
}
Running the above code produces the following output:
@javax.persistence.NamedQuery(lockMode=NONE, hints=[], name=findAllProjects, query=select p from Project p order by p.id)
name : findAllProjects
query : select p from Project p order by p.id
@javax.persistence.NamedQuery(lockMode=NONE, hints=[], name=findById, query=select p from Project p where p.id=:id)
name : findById
query : select p from Project p where p.id=:id
Credits
Photo by Xavier von Erlach on Unsplash
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