Package org.springframework.data.util

Class NullableUtils

java.lang.Object
org.springframework.data.util.NullableUtils
public abstract class NullableUtils extends Object
Utility methods to introspect nullability rules declared in packages, classes and methods.

Nullability rules are declared using NonNullApi, Nullable, and JSR-305 javax.annotation.Nonnull annotations. By default (no annotation use), a package and its types are considered allowing null values in return values and method parameters. Nullability rules are expressed by annotating a package with a JSR-305 meta annotation such as Spring's NonNullApi. All types of the package inherit the package rule. Subpackages do not inherit nullability rules and must be annotated themself. 

 @org.springframework.lang.NonNullApi
 package com.example;
Nullable selectively permits null values for method return values or method parameters by annotating the method respectively the parameters: 
 public class ExampleClass {

        String shouldNotReturnNull(@Nullable String acceptsNull, String doesNotAcceptNull) {
                // …
        }

        @Nullable
        String nullableReturn(String parameter) {
                // …
        }
 }

javax.annotation.Nonnull is suitable for composition of meta-annotations and expresses via javax.annotation.Nonnull#when() in which cases non-nullability is applicable.

Since:
2.0
Author:
Mark Paluch
See Also:

  • Method Details

    • isNonNull

      public static boolean isNonNull(Method method, ElementType elementType)
      Determine whether ElementType in the scope of Method requires non-null values. Non-nullability rules are discovered from class and package annotations. Non-null is applied when javax.annotation.Nonnull is set to javax.annotation.meta.When#ALWAYS.
      Parameters:
      method - the method to inspect.
      elementType - the element type.
      Returns:
      false if ElementType allows null values by default. true if the methods return type is a primitive and false if the method is void.
      See Also:
      • isNonNull(Annotation, ElementType)

    • isNonNull

      public static boolean isNonNull(Class<?> type, ElementType elementType)
      Determine whether ElementType in the scope of type requires non-null values. Non-nullability rules are discovered from class and package annotations. Non-null is applied when javax.annotation.Nonnull is set to javax.annotation.meta.When#ALWAYS.
      Parameters:
      type - the class to inspect.
      elementType - the element type.
      Returns:
      false if ElementType allows null values. true the given type is a primitive.
      See Also:
      • isNonNull(Annotation, ElementType)

    • isNonNull

      @Contract("null, _ -> false") public static boolean isNonNull(@Nullable AnnotatedElement element, ElementType elementType)
      Determine whether ElementType in the scope of AnnotatedElement requires non-null values. This method determines default javax.annotation.Nonnull nullability rules from the annotated element
      Parameters:
      element - the scope of declaration, may be a Package, Class, or Method. Can be null.
      elementType - the element type.
      Returns:
      false if ElementType allows null values by default or if the given AnnotatedElement is null.

    • isExplicitNullable

      public static boolean isExplicitNullable(MethodParameter methodParameter)
      Determine whether a MethodParameter is explicitly annotated to be considered nullable. Nullability rules are discovered from method and parameter annotations. A MethodParameter is considered nullable when javax.annotation.Nonnull is set to one of javax.annotation.meta.When#UNKNOWN, javax.annotation.meta.When#NEVER, or javax.annotation.meta.When#MAYBE.
      Parameters:
      methodParameter - the method parameter to inspect.
      Returns:
      true if the parameter is nullable, false otherwise.