@Nullable all the way: null-safety at field level

This commits extends nullability declarations to the field level, formalizing the interaction between methods and their underlying fields and therefore avoiding any nullability mismatch.

Issue: SPR-15720

spring-oxm/src/main/java/org/springframework/oxm/castor/CastorMarshaller.java

@@ -60,6 +60,7 @@ import org.springframework.oxm.ValidationFailureException;
 import org.springframework.oxm.XmlMappingException;
 import org.springframework.oxm.support.AbstractMarshaller;
 import org.springframework.oxm.support.SaxResourceUtils;
+import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.xml.DomUtils;
 import org.springframework.util.xml.StaxUtils;
@@ -94,12 +95,15 @@ public class CastorMarshaller extends AbstractMarshaller implements Initializing
 	public static final String DEFAULT_ENCODING = "UTF-8";
 
 
+	@Nullable
 	private Resource[] mappingLocations;
 
 	private String encoding = DEFAULT_ENCODING;
 
+	@Nullable
 	private Class<?>[] targetClasses;
 
+	@Nullable
 	private String[] targetPackages;
 
 	private boolean validating = false;
@@ -112,10 +116,13 @@ public class CastorMarshaller extends AbstractMarshaller implements Initializing
 
 	private boolean marshalExtendedType = true;
 
+	@Nullable
 	private String rootElement;
 
+	@Nullable
 	private String noNamespaceSchemaLocation;
 
+	@Nullable
 	private String schemaLocation;
 
 	private boolean useXSITypeAtRoot = false;
@@ -126,32 +133,44 @@ public class CastorMarshaller extends AbstractMarshaller implements Initializing
 
 	private boolean ignoreExtraElements = false;
 
+	@Nullable
 	private Object rootObject;
 
 	private boolean reuseObjects = false;
 
 	private boolean clearCollections = false;
 
+	@Nullable
 	private Map<String, String> castorProperties;
 
+	@Nullable
 	private Map<String, String> doctypes;
 
+	@Nullable
 	private Map<String, String> processingInstructions;
 
+	@Nullable
 	private Map<String, String> namespaceMappings;
 
+	@Nullable
 	private Map<String, String> namespaceToPackageMapping;
 
+	@Nullable
 	private EntityResolver entityResolver;
 
+	@Nullable
 	private XMLClassDescriptorResolver classDescriptorResolver;
 
+	@Nullable
 	private IDResolver idResolver;
 
+	@Nullable
 	private ObjectFactory objectFactory;
 
+	@Nullable
 	private ClassLoader beanClassLoader;
 
+	@Nullable
 	private XMLContext xmlContext;
 
 
@@ -456,8 +475,9 @@ public class CastorMarshaller extends AbstractMarshaller implements Initializing
 	 * @see XMLContext#addMapping(org.exolab.castor.mapping.Mapping)
 	 * @see XMLContext#addClass(Class)
 	 */
-	protected XMLContext createXMLContext(Resource[] mappingLocations, Class<?>[] targetClasses,
-			String[] targetPackages) throws MappingException, ResolverException, IOException {
+	protected XMLContext createXMLContext(@Nullable Resource[] mappingLocations,
+			@Nullable Class<?>[] targetClasses, @Nullable String[] targetPackages)
+			throws MappingException, ResolverException, IOException {
 
 		XMLContext context = new XMLContext();
 		if (!ObjectUtils.isEmpty(mappingLocations)) {
@@ -520,7 +540,8 @@ public class CastorMarshaller extends AbstractMarshaller implements Initializing
 	protected void marshalSaxHandlers(Object graph, ContentHandler contentHandler, @Nullable LexicalHandler lexicalHandler)
 			throws XmlMappingException {
 
-		Marshaller marshaller = xmlContext.createMarshaller();
+		Assert.state(this.xmlContext != null, "CastorMarshaller not initialized");
+		Marshaller marshaller = this.xmlContext.createMarshaller();
 		marshaller.setContentHandler(contentHandler);
 		doMarshal(graph, marshaller);
 	}
@@ -532,7 +553,8 @@ public class CastorMarshaller extends AbstractMarshaller implements Initializing
 
 	@Override
 	protected void marshalWriter(Object graph, Writer writer) throws XmlMappingException, IOException {
-		Marshaller marshaller = xmlContext.createMarshaller();
+		Assert.state(this.xmlContext != null, "CastorMarshaller not initialized");
+		Marshaller marshaller = this.xmlContext.createMarshaller();
 		marshaller.setWriter(writer);
 		doMarshal(graph, marshaller);
 	}
@@ -641,6 +663,7 @@ public class CastorMarshaller extends AbstractMarshaller implements Initializing
 	}
 
 	private Unmarshaller createUnmarshaller() {
+		Assert.state(this.xmlContext != null, "CastorMarshaller not initialized");
 		Unmarshaller unmarshaller = this.xmlContext.createUnmarshaller();
 		customizeUnmarshaller(unmarshaller);
 		return unmarshaller;

spring-oxm/src/main/java/org/springframework/oxm/jaxb/ClassPathJaxb2TypeScanner.java

@@ -33,6 +33,7 @@ import org.springframework.core.type.classreading.MetadataReader;
 import org.springframework.core.type.classreading.MetadataReaderFactory;
 import org.springframework.core.type.filter.AnnotationTypeFilter;
 import org.springframework.core.type.filter.TypeFilter;
+import org.springframework.lang.Nullable;
 import org.springframework.oxm.UncategorizedMappingException;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -64,7 +65,7 @@ class ClassPathJaxb2TypeScanner {
 	private final String[] packagesToScan;
 
 
-	public ClassPathJaxb2TypeScanner(ClassLoader classLoader, String... packagesToScan) {
+	public ClassPathJaxb2TypeScanner(@Nullable ClassLoader classLoader, String... packagesToScan) {
 		Assert.notEmpty(packagesToScan, "'packagesToScan' must not be empty");
 		this.resourcePatternResolver = new PathMatchingResourcePatternResolver(classLoader);
 		this.packagesToScan = packagesToScan;

spring-oxm/src/main/java/org/springframework/oxm/jaxb/Jaxb2Marshaller.java

@@ -131,30 +131,42 @@ public class Jaxb2Marshaller implements MimeMarshaller, MimeUnmarshaller, Generi
 	/** Logger available to subclasses */
 	protected final Log logger = LogFactory.getLog(getClass());
 
+	@Nullable
 	private String contextPath;
 
+	@Nullable
 	private Class<?>[] classesToBeBound;
 
+	@Nullable
 	private String[] packagesToScan;
 
+	@Nullable
 	private Map<String, ?> jaxbContextProperties;
 
+	@Nullable
 	private Map<String, ?> marshallerProperties;
 
+	@Nullable
 	private Map<String, ?> unmarshallerProperties;
 
+	@Nullable
 	private Marshaller.Listener marshallerListener;
 
+	@Nullable
 	private Unmarshaller.Listener unmarshallerListener;
 
+	@Nullable
 	private ValidationEventHandler validationEventHandler;
 
+	@Nullable
 	private XmlAdapter<?, ?>[] adapters;
 
+	@Nullable
 	private Resource[] schemaResources;
 
 	private String schemaLanguage = XMLConstants.W3C_XML_SCHEMA_NS_URI;
 
+	@Nullable
 	private LSResourceResolver schemaResourceResolver;
 
 	private boolean lazyInit = false;
@@ -165,14 +177,18 @@ public class Jaxb2Marshaller implements MimeMarshaller, MimeUnmarshaller, Generi
 
 	private boolean checkForXmlRootElement = true;
 
+	@Nullable
 	private Class<?> mappedClass;
 
+	@Nullable
 	private ClassLoader beanClassLoader;
 
 	private final Object jaxbContextMonitor = new Object();
 
+	@Nullable
 	private volatile JAXBContext jaxbContext;
 
+	@Nullable
 	private Schema schema;
 
 	private boolean supportDtd = false;
@@ -202,6 +218,7 @@ public class Jaxb2Marshaller implements MimeMarshaller, MimeUnmarshaller, Generi
 	/**
 	 * Return the JAXB context path.
 	 */
+	@Nullable
 	public String getContextPath() {
 		return this.contextPath;
 	}
@@ -219,6 +236,7 @@ public class Jaxb2Marshaller implements MimeMarshaller, MimeUnmarshaller, Generi
 	/**
 	 * Return the list of Java classes to be recognized by a newly created JAXBContext.
 	 */
+	@Nullable
 	public Class<?>[] getClassesToBeBound() {
 		return this.classesToBeBound;
 	}
@@ -237,6 +255,7 @@ public class Jaxb2Marshaller implements MimeMarshaller, MimeUnmarshaller, Generi
 	/**
 	 * Return the packages to search for JAXB2 annotations.
 	 */
+	@Nullable
 	public String[] getPackagesToScan() {
 		return this.packagesToScan;
 	}
@@ -464,27 +483,33 @@ public class Jaxb2Marshaller implements MimeMarshaller, MimeUnmarshaller, Generi
 	 * Return the JAXBContext used by this marshaller, lazily building it if necessary.
 	 */
 	public JAXBContext getJaxbContext() {
-		if (this.jaxbContext != null) {
-			return this.jaxbContext;
+		JAXBContext context = this.jaxbContext;
+		if (context != null) {
+			return context;
 		}
 		synchronized (this.jaxbContextMonitor) {
-			if (this.jaxbContext == null) {
+			context = this.jaxbContext;
+			if (context == null) {
 				try {
 					if (StringUtils.hasLength(this.contextPath)) {
-						this.jaxbContext = createJaxbContextFromContextPath();
+						context = createJaxbContextFromContextPath();
 					}
 					else if (!ObjectUtils.isEmpty(this.classesToBeBound)) {
-						this.jaxbContext = createJaxbContextFromClasses();
+						context = createJaxbContextFromClasses(this.classesToBeBound);
 					}
 					else if (!ObjectUtils.isEmpty(this.packagesToScan)) {
-						this.jaxbContext = createJaxbContextFromPackages();
+						context = createJaxbContextFromPackages(this.packagesToScan);
 					}
+					else {
+						context = JAXBContext.newInstance();
+					}
+					this.jaxbContext = context;
 				}
 				catch (JAXBException ex) {
 					throw convertJaxbException(ex);
 				}
 			}
-			return this.jaxbContext;
+			return context;
 		}
 	}
 
@@ -512,25 +537,25 @@ public class Jaxb2Marshaller implements MimeMarshaller, MimeUnmarshaller, Generi
 		}
 	}
 
-	private JAXBContext createJaxbContextFromClasses() throws JAXBException {
+	private JAXBContext createJaxbContextFromClasses(Class<?>... classesToBeBound) throws JAXBException {
 		if (logger.isInfoEnabled()) {
 			logger.info("Creating JAXBContext with classes to be bound [" +
-					StringUtils.arrayToCommaDelimitedString(this.classesToBeBound) + "]");
+					StringUtils.arrayToCommaDelimitedString(classesToBeBound) + "]");
 		}
 		if (this.jaxbContextProperties != null) {
-			return JAXBContext.newInstance(this.classesToBeBound, this.jaxbContextProperties);
+			return JAXBContext.newInstance(classesToBeBound, this.jaxbContextProperties);
 		}
 		else {
-			return JAXBContext.newInstance(this.classesToBeBound);
+			return JAXBContext.newInstance(classesToBeBound);
 		}
 	}
 
-	private JAXBContext createJaxbContextFromPackages() throws JAXBException {
+	private JAXBContext createJaxbContextFromPackages(String... packagesToScan) throws JAXBException {
 		if (logger.isInfoEnabled()) {
 			logger.info("Creating JAXBContext by scanning packages [" +
-					StringUtils.arrayToCommaDelimitedString(this.packagesToScan) + "]");
+					StringUtils.arrayToCommaDelimitedString(packagesToScan) + "]");
 		}
-		ClassPathJaxb2TypeScanner scanner = new ClassPathJaxb2TypeScanner(this.beanClassLoader, this.packagesToScan);
+		ClassPathJaxb2TypeScanner scanner = new ClassPathJaxb2TypeScanner(this.beanClassLoader, packagesToScan);
 		Class<?>[] jaxb2Classes = scanner.scanPackages();
 		if (logger.isDebugEnabled()) {
 			logger.debug("Found JAXB2 classes: [" + StringUtils.arrayToCommaDelimitedString(jaxb2Classes) + "]");

spring-oxm/src/main/java/org/springframework/oxm/jibx/JibxMarshaller.java

@@ -87,26 +87,35 @@ public class JibxMarshaller extends AbstractMarshaller implements InitializingBe
 	private static final String DEFAULT_BINDING_NAME = "binding";
 
 
+	@Nullable
 	private Class<?> targetClass;
 
+	@Nullable
 	private String targetPackage;
 
+	@Nullable
 	private String bindingName;
 
 	private int indent = -1;
 
 	private String encoding = "UTF-8";
 
+	@Nullable
 	private Boolean standalone;
 
+	@Nullable
 	private String docTypeRootElementName;
 
+	@Nullable
 	private String docTypeSystemId;
 
+	@Nullable
 	private String docTypePublicId;
 
+	@Nullable
 	private String docTypeInternalSubset;
 
+	@Nullable
 	private IBindingFactory bindingFactory;
 
 	private final TransformerFactory transformerFactory = TransformerFactory.newInstance();
@@ -241,6 +250,7 @@ public class JibxMarshaller extends AbstractMarshaller implements InitializingBe
 		if (this.targetClass != null) {
 			return (this.targetClass == clazz);
 		}
+		Assert.state(this.bindingFactory != null, "JibxMarshaller not initialized");
 		String[] mappedClasses = this.bindingFactory.getMappedClasses();
 		String className = clazz.getName();
 		for (String mappedClass : mappedClasses) {
@@ -443,6 +453,7 @@ public class JibxMarshaller extends AbstractMarshaller implements InitializingBe
 	 * @throws JiBXException in case of errors
 	 */
 	protected IMarshallingContext createMarshallingContext() throws JiBXException {
+		Assert.state(this.bindingFactory != null, "JibxMarshaller not initialized");
 		IMarshallingContext marshallingContext = this.bindingFactory.createMarshallingContext();
 		marshallingContext.setIndent(this.indent);
 		return marshallingContext;
@@ -454,6 +465,7 @@ public class JibxMarshaller extends AbstractMarshaller implements InitializingBe
 	 * @throws JiBXException in case of errors
 	 */
 	protected IUnmarshallingContext createUnmarshallingContext() throws JiBXException {
+		Assert.state(this.bindingFactory != null, "JibxMarshaller not initialized");
 		return this.bindingFactory.createUnmarshallingContext();
 	}
 

spring-oxm/src/main/java/org/springframework/oxm/support/AbstractMarshaller.java

@@ -77,6 +77,7 @@ public abstract class AbstractMarshaller implements Marshaller, Unmarshaller {
 
 	private boolean processExternalEntities = false;
 
+	@Nullable
 	private DocumentBuilderFactory documentBuilderFactory;
 
 	private final Object documentBuilderFactoryMonitor = new Object();

spring-oxm/src/main/java/org/springframework/oxm/xstream/XStreamMarshaller.java

@@ -122,40 +122,56 @@ public class XStreamMarshaller extends AbstractMarshaller implements BeanClassLo
 	public static final String DEFAULT_ENCODING = "UTF-8";
 
 
+	@Nullable
 	private ReflectionProvider reflectionProvider;
 
+	@Nullable
 	private HierarchicalStreamDriver streamDriver;
 
+	@Nullable
 	private HierarchicalStreamDriver defaultDriver;
 
+	@Nullable
 	private Mapper mapper;
 
+	@Nullable
 	private Class<? extends MapperWrapper>[] mapperWrappers;
 
 	private ConverterLookup converterLookup = new DefaultConverterLookup();
 
 	private ConverterRegistry converterRegistry = (ConverterRegistry) this.converterLookup;
 
+	@Nullable
 	private ConverterMatcher[] converters;
 
+	@Nullable
 	private MarshallingStrategy marshallingStrategy;
 
+	@Nullable
 	private Integer mode;
 
+	@Nullable
 	private Map<String, ?> aliases;
 
+	@Nullable
 	private Map<String, ?> aliasesByType;
 
+	@Nullable
 	private Map<String, String> fieldAliases;
 
+	@Nullable
 	private Class<?>[] useAttributeForTypes;
 
+	@Nullable
 	private Map<?, ?> useAttributeFor;
 
+	@Nullable
 	private Map<Class<?>, String> implicitCollections;
 
+	@Nullable
 	private Map<Class<?>, String> omittedFields;
 
+	@Nullable
 	private Class<?>[] annotatedClasses;
 
 	private boolean autodetectAnnotations;
@@ -164,10 +180,12 @@ public class XStreamMarshaller extends AbstractMarshaller implements BeanClassLo
 
 	private NameCoder nameCoder = new XmlFriendlyNameCoder();
 
+	@Nullable
 	private Class<?>[] supportedClasses;
 
 	private ClassLoader beanClassLoader = new CompositeClassLoader();
 
+	@Nullable
 	private XStream xstream;