Robert Thornton

Web Services with Apache CXFPart 2: JAXB and WSDL to Java

Robert Thornton

Notes

• This is a training, NOT a presentation• Please ask questions• This is being recorded• https://tech.lds.org/wiki/Java_Stack_Training• Prerequisites– Maven– Spring– Web Application Development– Web Services, Part I: SOAP

Objectives

At the end of this presentation, the participant will be able to:• Understand the role of JAXB as a web service data binding

solution.• Model data entities using JAXB annotations.• Understand the purpose and usage of the CXF WSDL2Java tool.• Be able to use WSDL2Java to generate a client proxy in a stand-

alone Java application.• Be able to configure Spring to manage a generated WSDL2Java

client proxy .• Be able to use JAXB as the data binding solution in a Java Stack

application.

Java and XML

The Marriage of XML and Java:• XML is a data markup language.– Used for long or short-term data storage.– Useful for data transfer between vastly different architectures.– Particularly useful for web service architectures.

• Java is an object-oriented programming language.– Unmarshalls (reads) data from existing XML into Java data

objects.– Performs manipulations on Java objects via services.– Marshalls (writes) Java objects into a new XML representation.

Java and XML: Choices, choices….

The marriage of Java and XML has produced many child technogies, strategies, and libraries:

• DOM• SAX• JAXP• DOM4J• JAXB

• XML Beans• JDOM• XStream• and many more….

Java and XML: Overview

Most Java-XML strategies fall into three camps:• DOM (Document Object Model)

– Used to represent the entire document model in memory as hierarchical nodes in the document tree.

• XML-to-Object Binding– Used to represent XML types and elements as Java types and objects and vice-

versa.

• SAX (Simple API for XML)– An event-based API for operating on each piece of the XML document individually

and in sequence. Most often used to parse DOM trees or construct XML Object bindings.

In practice, most solutions use some combination of these.

JAXB: A Data Binding Solution

The JAXB API is the standard solution provided by the JDK for Java XML data binding:• Java classes are bound to XML types, elements, and

attributes through Java annotations.• A SAX event-based parser is used to parse XML

documents and construct Java objects as well as to write Java objects back to XML.

• The XJC tool (included in the JDK) can convert an existing XML schema into Java classes or create an XML schema from annotated Java classes.

JAXB and Web Services

As a data modeling API, JAXB is particularly useful to web services:• XML is the most common form of data transport.• Annotated Java classes can be made to represent XML

schema types.• JAXB APIs can unmarshall XML into Java objects and

back again.* Note that the CXF web service framework automatically handles the marshalling and unmarshalling of XML data to and from JAXB annotated Java classes.

JAXB: Marshalling and Unmarshalling

Although CXF typically handles the marshalling and unmarshalling for you, it can be helpful to know how to do it “manually”. For example:• It allows you to experiment with how JAXB

annotations affect the parsing and rendering of XML.

• It helps you debug issues that arise from data being marshalled or unmarshalled incorrectly.

JAXB: Unmarshalling

JAXB makes unmarshalling from XML easy:

// Just create a JAXB context for your Java data classesJAXBContext jaxb = JAXBContext.newInstance(myClasses);

// Then unmarshall the XML into instances of those classes.MyClass obj = jaxb.createUnmarshaller().unmarshall(xml)

The Unmarshaller can accept XML input as a character stream, a file, a DOM node, or a number of other input types.

JAXB: Marshalling

Marshalling back into XML from Java object is just as easy:

// Create a JAXB context for your Java data classesJAXBContext jaxb = JAXBContext.newInstance(myClasses);

// Marshall the Java objects their XML representation.jaxb.createMarshaller().marshall(myObject, output);

The Marshaller can serialize the XML to a character stream, a file, a DOM node, or several other output types.

JAXB: The Context

Instances of the JAXBContext class effectively represent an “in-memory” schema of your data:• It’s a registry of all the classes that can be bound

to XML types.• It’s a factory for Marshaller and Unmarshaller

instances.• It can be supplied listeners and a Schema object

for additional or custom validation.

JAXB: Annotations

Although JAXB can bind almost any data object with little or no annotations, annotations are typically desirable, for example:• They can tell JAXB whether to unmarshal a field into an

attribute or an element.• They can inform JAXB of ID fields, element order, and

other schema constraints.• They can be used to identify or customize schema types,

element names, attribute names, element wrapping, etc.

JAXB: Common Annotations

JAXB defines many annotations to customize the Java-XML data binding. Here are just a few:• @XmlRootElement• @XmlType• @XmlElement• @XmlAttribute

• @XmlID• @XmlElementRef• @XmlElementWrapper• @XmlTransient

These and more can be found in the following package:• javax.xml.bind.annotation

Some general rules about JAXB annotations:• JAXB cannot bind Java interfaces to XML types.• Your class can reference an interface on a field if

you annotate it with an @XmlElementRef that identifies the concrete type.

• Apply JAXB annotations to either abstract or concrete types.

• Annotations on Java class properties must be placed on the fields or the setters but not both.

Apache CXF: SOAP: Lab 1

Lab 1: JAXB Data Bindinghttp://tech.lds.org/wiki/Web_Services_with_Apache_CXF_-_Part_2

Consuming 3rd Party Web Services

Third-party SOAP web services are typically consumed in one of the following ways:• Using a client JAR that contains the necessary

Java classes and service proxies to access the web service.

• Using a WSDL-to-Java tool to automatically generate a web service proxy from a published WSDL.

WSDL to Java

CXF provides the wsdl2java tool to consume third-party SOAP services:• wsdl2Java

Apache CXF: SOAP: Lab 2

Lab 2: Using WSDL 2 Javahttp://tech.lds.org/wiki/Web_Services_with_Apache_CXF_-_Part_2

Apache CXF: SOAP: Lab 3

Lab 3: WSDL 2 Java in the Java Stackhttp://tech.lds.org/wiki/Web_Services_with_Apache_CXF_-_Part_2

Resources

On the web:• http://cxf.apache.org• http://www.w3.org/TR/soap/• http://en.wikipedia.org/wiki/Cxf• http://en.wikipedia.org/wiki/SOAP• http://ajaxonomy.com/2008/xml/web-services-part-1-soap-vs-res

tIn Print:• Developing Web Services with Apache CXF and Axis 2, Kent Kai Iok

Tong, TipTech Development, 2005-2010. ISBN: 978-0-557-25432-3