org.springframework.data.util

Class NullableUtils

java.lang.Object

org.springframework.data.util.NullableUtils

public final class NullableUtils
extends Object

Utility methods to introspect nullability rules declared in packages, classes and methods.

Nullability rules are declared using NonNullApi and Nullable and JSR-305 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) {
                // …
        }
 }
 

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

Since:

2.0

Author:

Mark Paluch

See Also:

NonNullApi, Nullable, Nonnull

Method Summary

Modifier and Type	Method and Description
static boolean	isExplicitNullable(MethodParameter methodParameter) Determine whether a MethodParameter is explicitly annotated to be considered nullable.
static boolean	isNonNull(AnnotatedElement element, ElementType elementType) Determine whether ElementType in the scope of AnnotatedElement requires non-null values.
static boolean	isNonNull(Class<?> type, ElementType elementType) Determine whether ElementType in the scope of type requires non-null values.
static boolean	isNonNull(Method method, ElementType elementType) Determine whether ElementType in the scope of Method requires non-null values.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

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 Nonnull is set to When.ALWAYS.

Parameters:

type - the class to inspect.

elementType - the element type.

Returns:

true if ElementType allows null values by default.

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 Nonnull is set to When.ALWAYS.

Parameters:

type - the class to inspect.

elementType - the element type.

Returns:

true if ElementType allows null values by default.

See Also:

isNonNull(Annotation, ElementType)

isNonNull

public static boolean isNonNull(AnnotatedElement element,
                                ElementType elementType)

Determine whether ElementType in the scope of AnnotatedElement requires non-null values. This method determines default nullability rules from the annotated element

Parameters:

element - the scope of declaration, may be a Package, Class, or Method.

elementType - the element type.

Returns:

true if ElementType allows null values by default.

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 Nonnull is set to one of When.UNKNOWN, When.NEVER, or When.MAYBE.

Parameters:

methodParameter - the method parameter to inspect.

Returns:

true if the parameter is nullable, false otherwise.