Using NotNull Annotation in method argument

Question

I just started using the  NotNull annotation with Java 8 and getting some unexpected results   I have a method like this   public List lt Found gt  findStuff  NotNull List lt Searching gt  searchingList            code here         I wrote a JUnit test passing in the null value for the argument searchingList  I was expecting some type of error to happen but it went through as though the annotation was not there  Is this expected behavior  From what I understood  this was to allow you to skip writing the boilerplate null check code   An explanation of what exactly  NotNull is supposed to do would be greatly appreciated

User · Answer

If you are using Spring  you can force validation by annotating the class with  Validated   import org springframework validation annotation Validated    More info available here  Javax validation  NotNull annotation usage

User · Answer

As mentioned above  NotNull does nothing on its own  A good way of using  NotNull would be using it with Objects requireNonNull   public class Foo       private final Bar bar       public Foo  NotNull Bar bar            this bar   Objects requireNonNull bar   bar must not be null

User · Answer

To test your method validation in a test  you have to wrap it a proxy in the  Before method     Before public void setUp         this classAutowiredWithFindStuffMethod   MethodValidationProxyFactory createProxy this classAutowiredWithFindStuffMethod       With MethodValidationProxyFactory as    import org springframework context support StaticApplicationContext  import org springframework validation beanvalidation MethodValidationPostProcessor   public class MethodValidationProxyFactory    private static final StaticApplicationContext ctx   new StaticApplicationContext     static       MethodValidationPostProcessor processor   new MethodValidationPostProcessor        processor afterPropertiesSet       init advisor     ctx getBeanFactory                addBeanPostProcessor processor       SuppressWarnings  unchecked   public static  lt T gt  T createProxy T instance         return  T  ctx getAutowireCapableBeanFactory                applyBeanPostProcessorsAfterInitialization instance  instance getClass                        getName            And then  add your test      Test public void findingNullStuff      assertThatExceptionOfType ConstraintViolationException class  isThrownBy    - gt  this classAutowiredWithFindStuffMethod findStuff null

User · Answer

I do this to create my own validation annotation and validator   ValidCardType java annotation to put on methods fields    Constraint validatedBy    CardTypeValidator class    Documented  Target    ElementType ANNOTATION TYPE  ElementType METHOD  ElementType FIELD     Retention RetentionPolicy RUNTIME  public  interface ValidCardType       String message   default  Incorrect card type  should be among    MasterCard       Visa         Class lt   gt    groups   default         Class lt   extends Payload gt    payload   default         And  the validator to trigger the check  CardTypeValidator java   public class CardTypeValidator implements ConstraintValidator lt ValidCardType  String gt        private static final String   ALL CARD TYPES     MasterCard    Visa          Override     public void initialize ValidCardType status              public boolean isValid String value  ConstraintValidatorContext context            return  Arrays asList ALL CARD TYPES  contains value              You can do something very similar to check  NotNull

User · Answer

SO  NotNull just is a tag   If you want to validate it  then you must use something like hibernate validator jsr 303  ValidatorFactory validatorFactory   Validation buildDefaultValidatorFactory    Validator validator   validatorFactory getValidator     Set lt ConstraintViolation lt List lt Searching gt  gt  violations   validator validate searchingList

User · Answer

To make  NotNull active you need Lombok   https   projectlombok org features NonNull  import lombok NonNull    Follow  Which  NotNull Java annotation should I use

User · Answer

Nullable and  NotNull do nothing on their own  They are supposed to act as Documentation tools   The  Nullable Annotation reminds you about the necessity to introduce an NPE check when    Calling methods that can return null  Dereferencing variables  fields  local variables  parameters  that can be null    The  NotNull Annotation is  actually  an explicit contract declaring the following    A method should not return null  A variable  like fields  local variables  and parameters  cannot should not  hold null value     For example  instead of writing           param aX should not be null     public void setX final Object aX            some code     You can use   public void setX  NotNull final Object aX            some code     Additionally   NotNull is often checked by ConstraintValidators  eg  in spring and hibernate     The  NotNull annotation doesn t do any validation on its own because the annotation definition does not provide any ConstraintValidator type reference   For more info see     Bean validation NotNull java Constraint java ConstraintValidator java

[java] Using NotNull Annotation in method argument

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