Revise concurrent JAXBContext creation towards computeIfAbsent

Closes spring-projectsgh-23879

Author: jhoeller

spring-web/src/main/java/org/springframework/http/codec/xml/Jaxb2XmlDecoder.java

@@ -221,7 +221,7 @@ private Object unmarshal(List<XMLEvent> events, Class<?> outputClass) {
 		}
 	}
 
-	private Unmarshaller initUnmarshaller(Class<?> outputClass) throws JAXBException {
+	private Unmarshaller initUnmarshaller(Class<?> outputClass) throws CodecException, JAXBException {
 		Unmarshaller unmarshaller = this.jaxbContexts.createUnmarshaller(outputClass);
 		return this.unmarshallerProcessor.apply(unmarshaller);
 	}

spring-web/src/main/java/org/springframework/http/codec/xml/Jaxb2XmlEncoder.java

@@ -140,7 +140,7 @@ public DataBuffer encodeValue(Object value, DataBufferFactory bufferFactory,
 		}
 	}
 
-	private Marshaller initMarshaller(Class<?> clazz) throws JAXBException {
+	private Marshaller initMarshaller(Class<?> clazz) throws CodecException, JAXBException {
 		Marshaller marshaller = this.jaxbContexts.createMarshaller(clazz);
 		marshaller.setProperty(Marshaller.JAXB_ENCODING, StandardCharsets.UTF_8.name());
 		marshaller = this.marshallerProcessor.apply(marshaller);

spring-web/src/main/java/org/springframework/http/codec/xml/JaxbContextContainer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,37 +24,40 @@
 import javax.xml.bind.Marshaller;
 import javax.xml.bind.Unmarshaller;
 
-import org.springframework.util.Assert;
+import org.springframework.core.codec.CodecException;
 
 /**
  * Holder for {@link JAXBContext} instances.
  *
  * @author Arjen Poutsma
+ * @author Juergen Hoeller
  * @since 5.0
  */
 final class JaxbContextContainer {
 
 	private final ConcurrentMap<Class<?>, JAXBContext> jaxbContexts = new ConcurrentHashMap<>(64);
 
 
-	public Marshaller createMarshaller(Class<?> clazz) throws JAXBException {
+	public Marshaller createMarshaller(Class<?> clazz) throws CodecException, JAXBException {
 		JAXBContext jaxbContext = getJaxbContext(clazz);
 		return jaxbContext.createMarshaller();
 	}
 
-	public Unmarshaller createUnmarshaller(Class<?> clazz) throws JAXBException {
+	public Unmarshaller createUnmarshaller(Class<?> clazz) throws CodecException, JAXBException {
 		JAXBContext jaxbContext = getJaxbContext(clazz);
 		return jaxbContext.createUnmarshaller();
 	}
 
-	private JAXBContext getJaxbContext(Class<?> clazz) throws JAXBException {
-		Assert.notNull(clazz, "Class must not be null");
-		JAXBContext jaxbContext = this.jaxbContexts.get(clazz);
-		if (jaxbContext == null) {
-			jaxbContext = JAXBContext.newInstance(clazz);
-			this.jaxbContexts.putIfAbsent(clazz, jaxbContext);
-		}
-		return jaxbContext;
+	private JAXBContext getJaxbContext(Class<?> clazz) throws CodecException {
+		return this.jaxbContexts.computeIfAbsent(clazz, key -> {
+			try {
+				return JAXBContext.newInstance(clazz);
+			}
+			catch (JAXBException ex) {
+				throw new CodecException(
+						"Could not create JAXBContext for class [" + clazz + "]: " + ex.getMessage(), ex);
+			}
+		});
 	}
 
 }

spring-web/src/main/java/org/springframework/http/converter/xml/AbstractJaxb2HttpMessageConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,7 +25,6 @@
 import javax.xml.bind.Unmarshaller;
 
 import org.springframework.http.converter.HttpMessageConversionException;
-import org.springframework.util.Assert;
 
 /**
  * Abstract base class for {@link org.springframework.http.converter.HttpMessageConverter HttpMessageConverters}
@@ -106,19 +105,15 @@ protected void customizeUnmarshaller(Unmarshaller unmarshaller) {
 	 * @throws HttpMessageConversionException in case of JAXB errors
 	 */
 	protected final JAXBContext getJaxbContext(Class<?> clazz) {
-		Assert.notNull(clazz, "Class must not be null");
-		JAXBContext jaxbContext = this.jaxbContexts.get(clazz);
-		if (jaxbContext == null) {
+		return this.jaxbContexts.computeIfAbsent(clazz, key -> {
 			try {
-				jaxbContext = JAXBContext.newInstance(clazz);
-				this.jaxbContexts.putIfAbsent(clazz, jaxbContext);
+				return JAXBContext.newInstance(clazz);
 			}
 			catch (JAXBException ex) {
 				throw new HttpMessageConversionException(
-						"Could not instantiate JAXBContext for class [" + clazz + "]: " + ex.getMessage(), ex);
+						"Could not create JAXBContext for class [" + clazz + "]: " + ex.getMessage(), ex);
 			}
-		}
-		return jaxbContext;
+		});
 	}
 
 }