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-tx/src/test/java/org/springframework/transaction/annotation/TransactionBeanRegistrationAotProcessorTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.transaction.annotation;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.aot.generate.GenerationContext;
@@ -26,7 +27,6 @@ import org.springframework.beans.factory.aot.BeanRegistrationAotContribution;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.beans.factory.support.RegisteredBean;
 import org.springframework.beans.factory.support.RootBeanDefinition;
-import org.springframework.lang.Nullable;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.mock;
@@ -96,8 +96,7 @@ class TransactionBeanRegistrationAotProcessorTests {
 		}
 	}
 
-	@Nullable
-	private BeanRegistrationAotContribution createContribution(Class<?> beanClass) {
+	private @Nullable BeanRegistrationAotContribution createContribution(Class<?> beanClass) {
 		DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
 		beanFactory.registerBeanDefinition(beanClass.getName(), new RootBeanDefinition(beanClass));
 		return this.processor.processAheadOfTime(RegisteredBean.of(beanFactory, beanClass.getName()));

spring-tx/src/test/java/org/springframework/transaction/event/CapturingSynchronizationCallback.java

@@ -16,8 +16,9 @@
 
 package org.springframework.transaction.event;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationEvent;
-import org.springframework.lang.Nullable;
 
 /**
  * @author Juergen Hoeller
@@ -25,14 +26,11 @@ import org.springframework.lang.Nullable;
  */
 class CapturingSynchronizationCallback implements TransactionalApplicationListener.SynchronizationCallback {
 
-	@Nullable
-	ApplicationEvent preEvent;
+	@Nullable ApplicationEvent preEvent;
 
-	@Nullable
-	ApplicationEvent postEvent;
+	@Nullable ApplicationEvent postEvent;
 
-	@Nullable
-	Throwable ex;
+	@Nullable Throwable ex;
 
 	@Override
 	public void preProcessEvent(ApplicationEvent event) {

spring-tx/src/test/java/org/springframework/transaction/interceptor/BeanFactoryTransactionTests.java

@@ -23,6 +23,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.aopalliance.intercept.MethodInterceptor;
 import org.aopalliance.intercept.MethodInvocation;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -36,7 +37,6 @@ import org.springframework.beans.testfixture.beans.DerivedTestBean;
 import org.springframework.beans.testfixture.beans.ITestBean;
 import org.springframework.beans.testfixture.beans.TestBean;
 import org.springframework.core.io.ClassPathResource;
-import org.springframework.lang.Nullable;
 import org.springframework.transaction.PlatformTransactionManager;
 import org.springframework.transaction.TransactionDefinition;
 import org.springframework.transaction.TransactionException;

spring-tx/src/test/java/org/springframework/transaction/interceptor/PlatformTransactionManagerFacade.java

@@ -16,7 +16,8 @@
 
 package org.springframework.transaction.interceptor;
 
-import org.springframework.lang.Nullable;
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.transaction.PlatformTransactionManager;
 import org.springframework.transaction.TransactionDefinition;
 import org.springframework.transaction.TransactionStatus;

spring-tx/src/test/java/org/springframework/transaction/interceptor/TransactionInterceptorTests.java

@@ -19,13 +19,13 @@ package org.springframework.transaction.interceptor;
 import java.io.Serializable;
 import java.util.Properties;
 
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.core.testfixture.io.SerializationTestUtils;
-import org.springframework.lang.Nullable;
 import org.springframework.transaction.PlatformTransactionManager;
 import org.springframework.transaction.TransactionDefinition;
 import org.springframework.transaction.TransactionException;

spring-tx/src/test/java/org/springframework/transaction/reactive/ReactiveTestTransactionManager.java

@@ -18,9 +18,9 @@ package org.springframework.transaction.reactive;
 
 import java.util.function.Function;
 
+import org.jspecify.annotations.Nullable;
 import reactor.core.publisher.Mono;
 
-import org.springframework.lang.Nullable;
 import org.springframework.transaction.CannotCreateTransactionException;
 import org.springframework.transaction.ReactiveTransactionManager;
 import org.springframework.transaction.TransactionDefinition;
@@ -40,11 +40,9 @@ class ReactiveTestTransactionManager extends AbstractReactiveTransactionManager
 
 	private final boolean canCreateTransaction;
 
-	@Nullable
-	private Function<String, RuntimeException> forceFailOnCommit;
+	private @Nullable Function<String, RuntimeException> forceFailOnCommit;
 
-	@Nullable
-	private Function<String, RuntimeException> forceFailOnRollback;
+	private @Nullable Function<String, RuntimeException> forceFailOnRollback;
 
 	protected boolean begin = false;