Switch to JSpecify annotations

This commit updates the whole Spring Framework codebase to use JSpecify
annotations instead of Spring null-safety annotations with JSR 305
semantics.

JSpecify provides signficant enhancements such as properly defined
specifications, a canonical dependency with no split-package issue,
better tooling, better Kotlin integration and the capability to specify
generic type, array and varargs element null-safety. Generic type
null-safety is not defined by this commit yet and will be specified
later.

A key difference is that Spring null-safety annotations, following
JSR 305 semantics, apply to fields, parameters and return values,
while JSpecify annotations apply to type usages. That's why this
commit moves nullability annotations closer to the type for fields
and return values.

See gh-28797

spring-beans/src/test/java/org/springframework/beans/AbstractPropertyAccessorTests.java

@@ -34,6 +34,7 @@ import java.util.SortedSet;
 import java.util.TreeMap;
 import java.util.TreeSet;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.annotation.Autowire;
@@ -49,7 +50,6 @@ import org.springframework.core.convert.ConversionFailedException;
 import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.core.convert.support.GenericConversionService;
-import org.springframework.lang.Nullable;
 import org.springframework.util.StringUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;

spring-beans/src/test/java/org/springframework/beans/BeanUtilsTests.java

@@ -33,6 +33,7 @@ import java.util.List;
 import java.util.Locale;
 import java.util.UUID;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
@@ -46,7 +47,6 @@ import org.springframework.cglib.proxy.Enhancer;
 import org.springframework.cglib.proxy.MethodInterceptor;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceEditor;
-import org.springframework.lang.Nullable;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
@@ -868,13 +868,11 @@ class BeanUtilsTests {
 			this.value = value;
 		}
 
-		@Nullable
-		public Integer getCounter() {
+		public @Nullable Integer getCounter() {
 			return counter;
 		}
 
-		@Nullable
-		public Boolean isFlag() {
+		public @Nullable Boolean isFlag() {
 			return flag;
 		}
 

spring-beans/src/test/java/org/springframework/beans/factory/DefaultListableBeanFactoryTests.java

@@ -39,6 +39,7 @@ import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
 import jakarta.annotation.Priority;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.BeansException;
@@ -87,7 +88,6 @@ import org.springframework.core.convert.support.GenericConversionService;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.UrlResource;
 import org.springframework.core.testfixture.io.SerializationTestUtils;
-import org.springframework.lang.Nullable;
 import org.springframework.util.StringValueResolver;
 
 import static org.assertj.core.api.Assertions.assertThat;

spring-beans/src/test/java/org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessorTests.java

@@ -40,6 +40,7 @@ import java.util.concurrent.Callable;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
@@ -73,7 +74,6 @@ import org.springframework.core.ResolvableType;
 import org.springframework.core.annotation.AnnotationAwareOrderComparator;
 import org.springframework.core.annotation.Order;
 import org.springframework.core.testfixture.io.SerializationTestUtils;
-import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.ReflectionUtils;
@@ -4294,8 +4294,7 @@ class AutowiredAnnotationBeanPostProcessorTests {
 
 	static class MixedNullableInjectionBean {
 
-		@Nullable
-		public Integer nullableBean;
+		public @Nullable Integer nullableBean;
 
 		public String nonNullBean;
 
@@ -4309,8 +4308,7 @@ class AutowiredAnnotationBeanPostProcessorTests {
 
 	static class MixedOptionalInjectionBean {
 
-		@Nullable
-		public Integer nullableBean;
+		public @Nullable Integer nullableBean;
 
 		public String nonNullBean;
 

spring-beans/src/test/java/org/springframework/beans/factory/aot/BeanDefinitionMethodGeneratorFactoryTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.beans.factory.aot;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
@@ -24,7 +25,6 @@ import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.beans.factory.support.RegisteredBean;
 import org.springframework.core.Ordered;
 import org.springframework.core.test.io.support.MockSpringFactoriesLoader;
-import org.springframework.lang.Nullable;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
@@ -205,8 +205,7 @@ class BeanDefinitionMethodGeneratorFactoryTests {
 
 		private final int order;
 
-		@Nullable
-		private RegisteredBean registeredBean;
+		private @Nullable RegisteredBean registeredBean;
 
 		MockBeanRegistrationExcludeFilter(boolean excluded, int order) {
 			this.excluded = excluded;

spring-beans/src/test/java/org/springframework/beans/factory/aot/BeanDefinitionPropertiesCodeGeneratorTests.java

@@ -29,6 +29,7 @@ import java.util.function.Supplier;
 import javax.lang.model.element.Modifier;
 
 import org.assertj.core.api.InstanceOfAssertFactories;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.reactivestreams.Publisher;
@@ -58,7 +59,6 @@ import org.springframework.core.test.tools.TestCompiler;
 import org.springframework.javapoet.CodeBlock;
 import org.springframework.javapoet.MethodSpec;
 import org.springframework.javapoet.ParameterizedTypeName;
-import org.springframework.lang.Nullable;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -706,15 +706,13 @@ class BeanDefinitionPropertiesCodeGeneratorTests {
 			this.name = name;
 		}
 
-		@Nullable
 		@Override
-		public String getObject() {
+		public @Nullable String getObject() {
 			return getPrefix() + " " + getName();
 		}
 
-		@Nullable
 		@Override
-		public Class<?> getObjectType() {
+		public @Nullable Class<?> getObjectType() {
 			return String.class;
 		}
 

spring-beans/src/test/java/org/springframework/beans/factory/aot/DefaultBeanRegistrationCodeFragmentsTests.java

@@ -21,6 +21,7 @@ import java.lang.reflect.Executable;
 import java.lang.reflect.Method;
 import java.util.function.UnaryOperator;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.aot.generate.GenerationContext;
@@ -44,7 +45,6 @@ import org.springframework.beans.testfixture.beans.factory.aot.SimpleBeanFactory
 import org.springframework.core.ResolvableType;
 import org.springframework.javapoet.ClassName;
 import org.springframework.javapoet.CodeBlock;
-import org.springframework.lang.Nullable;
 import org.springframework.util.ReflectionUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;

spring-beans/src/test/java/org/springframework/beans/factory/support/CglibSubclassingInstantiationStrategyTests.java

@@ -22,10 +22,9 @@ import java.util.regex.Pattern;
 import java.util.stream.Stream;
 
 import org.assertj.core.api.ThrowableAssert.ThrowingCallable;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
-import org.springframework.lang.Nullable;
-
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
 
@@ -147,8 +146,7 @@ class CglibSubclassingInstantiationStrategyTests {
 
 	static class MyReplacer implements MethodReplacer {
 
-		@Nullable
-		Object returnValue;
+		@Nullable Object returnValue;
 
 		void reset() {
 			this.returnValue = null;

spring-beans/src/test/java/org/springframework/beans/factory/support/ConstructorResolverAotTests.java

@@ -22,6 +22,7 @@ import java.util.List;
 import java.util.Locale;
 import java.util.concurrent.Executor;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.factory.FactoryBean;
@@ -32,7 +33,6 @@ import org.springframework.beans.testfixture.beans.factory.generator.factory.Num
 import org.springframework.beans.testfixture.beans.factory.generator.factory.SampleFactory;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.annotation.MergedAnnotations.SearchStrategy;
-import org.springframework.lang.Nullable;
 import org.springframework.util.ReflectionUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;

spring-beans/src/test/java/org/springframework/beans/factory/xml/ResourceEntityResolverTests.java

@@ -16,13 +16,13 @@
 
 package org.springframework.beans.factory.xml;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.xml.sax.InputSource;
 
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
-import org.springframework.lang.Nullable;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
@@ -94,8 +94,7 @@ class ResourceEntityResolverTests {
 
 		private final boolean shouldThrow;
 
-		@Nullable
-		private final InputSource returnValue;
+		private final @Nullable InputSource returnValue;
 
 		boolean fallbackInvoked = false;
 
@@ -112,8 +111,7 @@ class ResourceEntityResolverTests {
 		}
 
 		@Override
-		@Nullable
-		protected InputSource resolveSchemaEntity(String publicId, String systemId) {
+		protected @Nullable InputSource resolveSchemaEntity(String publicId, String systemId) {
 			this.fallbackInvoked = true;
 			if (this.shouldThrow) {
 				throw new ResolutionRejectedException();

spring-beans/src/test/java/org/springframework/beans/support/PagedListHolderTests.java

@@ -19,10 +19,10 @@ package org.springframework.beans.support;
 import java.util.ArrayList;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.beans.testfixture.beans.TestBean;
-import org.springframework.lang.Nullable;
 
 import static org.assertj.core.api.Assertions.assertThat;