Enumerating @NamedQuery within @NamedQueries

David SalterMarch 24th, 2015Last Updated: March 24th, 2015

1 23 1 minute read

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

Reference:

Enumerating @NamedQuery within @NamedQueries from our JCG partner David Salter at the David Salter’s Blog blog.