How to get annotations of a member variable

Question

I want to know a class s some member variable s annotations   I use BeanInfo beanInfo   Introspector getBeanInfo User class  to introspect a class   and use BeanInfo getPropertyDescriptors     to find specific property   and use Class type   propertyDescriptor getPropertyType   to get the property s Class    But I don t know how to get the annotations added to the member variable    I tried type getAnnotations     and type getDeclaredAnnotations     but both return the Class s annotations   not what I want   For example    class User       Id   private Long id      Column name  ADDRESS ID     private Address address        getters   setters     Entity  Table name    Address    Cache usage   CacheConcurrencyStrategy NONSTRICT READ WRITE  class Address              I want to get the address s annotation    Column   not class Address s annotations   Entity    Table     Cache    How to achieve it   Thanks

User · Answer

You can get annotations on the getter method:

propertyDescriptor.getReadMethod().getDeclaredAnnotations();

Getting the annotations of a private field seems like a bad idea... what if the property isn't even backed by a field, or is backed by a field with a different name? Even ignoring those cases, you're breaking abstraction by looking at private stuff.

User · Answer

Everybody describes issue with getting annotations  but the problem is in definition of your annotation  You should to add to your annotation definition a  Retention RetentionPolicy RUNTIME     Retention RetentionPolicy RUNTIME   Target ElementType FIELD  public  interface MyAnnotation      int id

User · Answer

You have to use reflection to get all the member fields of User class  iterate through them and find their annotations  something like this   public void getAnnotations Class clazz       for Field field   clazz getDeclaredFields             Class type   field getType            String name   field getName            field getDeclaredAnnotations      do something to these

User · Answer

Or you could try this  try       BeanInfo bi   Introspector getBeanInfo User getClass         PropertyDescriptor   properties   bi getPropertyDescriptors        for PropertyDescriptor property   properties              One way         for Annotation annotation   property getAnnotations                 if annotation instanceof Column                    String string   annotation name                                      Other way         Annotation annotation   property getAnnotation Column class           String string   annotation name           catch  IntrospectonException ie        ie printStackTrace        Hope this will help

User · Answer

If you need know if a annotation specific is present  You can do so       Field   fieldList   obj getClass   getDeclaredFields             boolean isAnnotationNotNull  isAnnotationSize  isAnnotationNotEmpty           for  Field field   fieldList                   Return the boolean value             isAnnotationNotNull   field isAnnotationPresent NotNull class               isAnnotationSize   field isAnnotationPresent Size class               isAnnotationNotEmpty   field isAnnotationPresent NotEmpty class                And so on for the other annotations     I hope help someone

User · Answer

My way  import org slf4j Logger  import org slf4j LoggerFactory   import java beans BeanInfo  import java beans Introspector  import java beans PropertyDescriptor   public class ReadAnnotation       private static final Logger LOGGER   LoggerFactory getLogger ReadAnnotation class        public static boolean hasIgnoreAnnotation String fieldName  Class entity  throws NoSuchFieldException           return entity getDeclaredField fieldName  isAnnotationPresent IgnoreAnnotation class              public static boolean isSkip PropertyDescriptor propertyDescriptor  Class entity            boolean isIgnoreField          try               isIgnoreField   hasIgnoreAnnotation propertyDescriptor getName    entity             catch  NoSuchFieldException e                LOGGER error  Can not check IgnoreAnnotation   e               isIgnoreField   true                    return isIgnoreField             public void testIsSkip   throws Exception           Class lt TestClass gt  entity   TestClass class          BeanInfo beanInfo   Introspector getBeanInfo entity            for  PropertyDescriptor propertyDescriptor   beanInfo getPropertyDescriptors                  System out printf  Field  s  has annotation  b   propertyDescriptor getName     isSkip propertyDescriptor  entity

User · Answer

for Field field   cls getDeclaredFields       Class type   field getType      String name   field getName      Annotation   annotations   field getDeclaredAnnotations        See also  http   docs oracle com javase tutorial reflect class classMembers html

User · Answer

package be fery annotation   import javax persistence Column  import javax persistence Entity  import javax persistence Id  import javax persistence PrePersist    Entity public class User        Id     private Long id        Column name    ADDRESS ID       private Address address        PrePersist     public void doStuff               And a testing class       package be fery annotation   import java lang annotation Annotation  import java lang reflect Field  import java lang reflect Method   public class AnnotationIntrospector        public AnnotationIntrospector             super               public Annotation   findClassAnnotation Class lt   gt  clazz            return clazz getAnnotations               public Annotation   findMethodAnnotation Class lt   gt  clazz  String methodName             Annotation   annotations   null          try               Class lt   gt    params   null              Method method   clazz getDeclaredMethod methodName  params               if  method    null                    annotations   method getAnnotations                            catch  SecurityException e                e printStackTrace              catch  NoSuchMethodException e                e printStackTrace                      return annotations             public Annotation   findFieldAnnotation Class lt   gt  clazz  String fieldName            Annotation   annotations   null          try               Field field   clazz getDeclaredField fieldName               if  field    null                    annotations   field getAnnotations                            catch  SecurityException e                e printStackTrace              catch  NoSuchFieldException e                e printStackTrace                      return annotations                         param args             public static void main String   args            AnnotationIntrospector ai   new AnnotationIntrospector            Annotation   annotations          Class lt User gt  userClass   User class          String methodDoStuff    doStuff           String fieldId    id           String fieldAddress    address               Find class annotations         annotations   ai findClassAnnotation be fery annotation User class           System out println  Annotation on class      userClass getName                        are             showAnnotations annotations               Find method annotations         annotations   ai findMethodAnnotation User class  methodDoStuff           System out println  Annotation on method      methodDoStuff      are             showAnnotations annotations               Find field annotations         annotations   ai findFieldAnnotation User class  fieldId           System out println  Annotation on field      fieldId      are             showAnnotations annotations            annotations   ai findFieldAnnotation User class  fieldAddress           System out println  Annotation on field      fieldAddress      are             showAnnotations annotations               public static void showAnnotations Annotation   ann            if  ann    null              return          for  Annotation a   ann                System out println a toString                          Hope it helps      -

[java] How to get annotations of a member variable?

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