Download Developing Web Services with Apache CXF and Axis 2

Web Services with Apache CXF
Part 2: JAXB and WSDL to Java
Robert Thornton
Notes
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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 standalone 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:
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DOM
SAX
JAXP
DOM4J
JAXB
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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 viceversa.
• 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 classes
JAXBContext 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 classes
JAXBContext 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:
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@XmlRootElement
@XmlType
@XmlElement
@XmlAttribute
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@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 Binding
http://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 thirdparty SOAP services:
• wsdl2Java
Apache CXF: SOAP: Lab 2
Lab 2: Using WSDL 2 Java
http://tech.lds.org/wiki/Web_Services_with_Apache_CXF_-_Part_2
Apache CXF: SOAP: Lab 3
Lab 3: WSDL 2 Java in the Java Stack
http://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-vsrest
In Print:
• Developing Web Services with Apache CXF and Axis 2, Kent Kai Iok
Tong, TipTech Development, 2005-2010. ISBN: 978-0-557-25432-3