GH-2332 - Move to jSpecify for nullability verification.

Author: odrotbohm

.mvn/jvm.config

@@ -0,0 +1,10 @@
+--add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.model=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.processing=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED
+--add-exports jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED
+--add-opens jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED
+--add-opens jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED

pom.xml

@@ -72,6 +72,7 @@
 		<artifactory-maven-plugin.version>3.6.2</artifactory-maven-plugin.version>
 		<assertj.version>3.27.3</assertj.version>
 		<spring-asciidoctor-backends.version>0.0.7</spring-asciidoctor-backends.version>
+		<errorprone.version>2.36.0</errorprone.version>
 		<evo.version>1.3</evo.version>
 		<logback.version>1.5.18</logback.version>
 		<jacoco>0.8.12</jacoco>
@@ -81,6 +82,7 @@
 		<jsonpath.version>2.9.0</jsonpath.version>
 		<junit.version>5.12.2</junit.version>
 		<lombok.version>1.18.38</lombok.version>
+		<nullaway.version>0.12.7</nullaway.version>
 		<reactor-bom.version>2024.0.6</reactor-bom.version>
 		<slf4j.version>2.0.17</slf4j.version>
 		<spring.version>7.0.0-M5</spring.version>
@@ -149,6 +151,54 @@
 
 		</profile>
 
+		<profile>
+			<id>nullaway</id>
+			<build>
+				<plugins>
+					<plugin>
+						<groupId>org.apache.maven.plugins</groupId>
+						<artifactId>maven-compiler-plugin</artifactId>
+						<configuration>
+							<showWarnings>true</showWarnings>
+							
+						</configuration>
+						<executions>
+							<execution>
+								<id>default-compile</id>
+								<phase>none</phase>
+							</execution>
+							<execution>
+								<id>java-compile</id>
+								<phase>compile</phase>
+								<goals>
+									<goal>compile</goal>
+								</goals>
+								<configuration>
+									<annotationProcessorPaths>
+										<path>
+											<groupId>com.google.errorprone</groupId>
+											<artifactId>error_prone_core</artifactId>
+											<version>${errorprone.version}</version>
+										</path>
+										<path>
+											<groupId>com.uber.nullaway</groupId>
+											<artifactId>nullaway</artifactId>
+											<version>${nullaway.version}</version>
+										</path>
+									</annotationProcessorPaths>
+									<compilerArgs>
+										<arg>-XDcompilePolicy=simple</arg>
+										<arg>--should-stop=ifError=FLOW</arg>
+										<arg>-Xplugin:ErrorProne -XepDisableAllChecks -Xep:NullAway:ERROR -XepOpt:NullAway:OnlyNullMarked=true -XepOpt:NullAway:CustomContractAnnotations=org.springframework.lang.Contract</arg>
+									</compilerArgs>
+								</configuration>
+							</execution>
+						</executions>
+					</plugin>
+				</plugins>
+			</build>
+		</profile>
+
 		<profile>
 			<id>artifactory</id>
 			<properties>
@@ -469,6 +519,11 @@
 			<artifactId>kotlinx-coroutines-reactor</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+			<groupId>org.jspecify</groupId>
+			<artifactId>jspecify</artifactId>
+			<version>1.0.0</version>
+		</dependency>
 		<dependency>
 			<groupId>org.jetbrains.kotlin</groupId>
 			<artifactId>kotlin-test</artifactId>

src/main/java/org/springframework/hateoas/Affordance.java

@@ -19,8 +19,9 @@
 import java.util.Map;
 import java.util.Objects;
 
+import org.jspecify.annotations.Nullable;
 import org.springframework.http.MediaType;
-import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 
 /**
  * Hold the {@link AffordanceModel}s for all supported media types.
@@ -42,15 +43,32 @@ public Affordance(Map<MediaType, AffordanceModel> models) {
 	/**
 	 * Look up the {@link AffordanceModel} for the requested {@link MediaType}.
 	 *
-	 * @param mediaType
-	 * @return
+	 * @param mediaType must not be {@literal null}.
+	 * @return can be {@literal null}.
 	 */
 	@Nullable
 	@SuppressWarnings("unchecked")
 	public <T extends AffordanceModel> T getAffordanceModel(MediaType mediaType) {
 		return (T) this.models.get(mediaType);
 	}
 
+	/**
+	 * Look up the {@link AffordanceModel} for the requested {@link MediaType}.
+	 *
+	 * @param mediaType must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 * @since 3.0
+	 */
+	@SuppressWarnings("unchecked")
+	public <T extends AffordanceModel> T getRequiredAffordanceModel(MediaType mediaType) {
+
+		var result = getAffordanceModel(mediaType);
+
+		Assert.notNull(result, () -> "No affordance model found for %s!".formatted(mediaType));
+
+		return (T) result;
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see java.lang.Iterable#iterator()

src/main/java/org/springframework/hateoas/AffordanceModel.java

@@ -24,10 +24,10 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import org.jspecify.annotations.Nullable;
 import org.springframework.core.ResolvableType;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
-import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
 /**

src/main/java/org/springframework/hateoas/CollectionModel.java

@@ -22,11 +22,11 @@
 import java.util.Iterator;
 import java.util.Objects;
 
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.core.ResolvableType;
 import org.springframework.core.ResolvableTypeProvider;
-import org.springframework.lang.NonNull;
-import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 
@@ -44,7 +44,7 @@ public class CollectionModel<T> extends RepresentationModel<CollectionModel<T>>
 
 	private final Collection<T> content;
 	private final @Nullable ResolvableType fallbackType;
-	private ResolvableType fullType;
+	private @Nullable ResolvableType fullType;
 
 	/**
 	 * Creates an empty {@link CollectionModel} instance.

src/main/java/org/springframework/hateoas/EntityModel.java

@@ -21,9 +21,10 @@
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.Objects;
 
-import org.springframework.lang.NonNull;
-import org.springframework.lang.Nullable;
+import org.jspecify.annotations.NonNull;
+import org.jspecify.annotations.Nullable;
 import org.springframework.util.Assert;
 
 import com.fasterxml.jackson.annotation.JsonAnyGetter;
@@ -50,7 +51,7 @@
  */
 public class EntityModel<T> extends RepresentationModel<EntityModel<T>> {
 
-	private T content;
+	private @Nullable T content;
 
 	/**
 	 * Creates an empty {@link EntityModel}.
@@ -118,19 +119,17 @@ public static <T> EntityModel<T> of(T content, Iterable<Link> links) {
 	 *
 	 * @return the content
 	 */
-	@Nullable
 	@JsonUnwrapped
 	@JsonSerialize(using = MapSuppressingUnwrappingSerializer.class)
 	public T getContent() {
-		return content;
+		return Objects.requireNonNull(content);
 	}
 
 	// Hacks to allow deserialization into an EntityModel<Map<String, Object>>
 
-	@Nullable
 	@JsonAnyGetter
 	@SuppressWarnings("unchecked")
-	private Map<String, Object> getMapContent() {
+	private @Nullable Map<String, Object> getMapContent() {
 		return Map.class.isInstance(content) ? (Map<String, Object>) content : null;
 	}
 

src/main/java/org/springframework/hateoas/InputType.java

@@ -22,8 +22,6 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;
 
-import org.springframework.hateoas.mediatype.html.HtmlInputType;
-
 /**
  * Annotation to declare a dedicated input type for a property of an representation model. Input types are usually
  * derived from the property's type or JSR-303 validation annotations. Use this annotation to override the type.

src/main/java/org/springframework/hateoas/Link.java

@@ -23,7 +23,7 @@
 import java.util.Map;
 import java.util.Objects;
 
-import org.springframework.lang.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.springframework.util.Assert;
 
 import com.fasterxml.jackson.annotation.JsonIgnore;
@@ -184,7 +184,10 @@ public static Link of(UriTemplate template, LinkRelation relation) {
 	 * Empty constructor required by the marshaling framework.
 	 */
 	protected Link() {
+
 		this.affordances = new ArrayList<>();
+		this.rel = LinkRelation.of("__synthetic__");
+		this.href = "__synthetic__";
 	}
 
 	/**

src/main/java/org/springframework/hateoas/Links.java

@@ -28,7 +28,7 @@
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
-import org.springframework.lang.Nullable;
+import org.jspecify.annotations.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 

src/main/java/org/springframework/hateoas/NonComposite.java

@@ -21,8 +21,6 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;
 
-import org.springframework.web.bind.annotation.RequestParam;
-
 /**
  * Annotation to be used in combination with {@link RequestParam} to indicate that collection based values are supposed
  * to be rendered as non-composite values, i.e. like {@code param=value1,value2,value3} rather than