Transcript Java XML Binding

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, and Web Application Development
– Web Services, Part I: SOAP
– A general familiarity with XML simple and complex
schema types.
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 and consume a generated
WSDL2Java client proxy .
Web Services with Apache CXF
Java XML Binding
Modeling Web Service Messages with JAXB
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 a large
family of technologies, strategies, and libraries:
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DOM
StAX
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 spaces:
• DOM (Document Object Model)
– Entire document model is held in memory as nodes in a
document tree.
• Streaming
– An event-based API for operating on each piece of the XML document
individually and in sequence. Often used to stream XML for building DOM
trees or construct XML Object bindings.
• XML-to-Object Binding
– XML types and elements are bound to Java types and fields.
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 XML streaming event-based (StAX) 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 generate JAXB annotated
classes from an existing XML Schema.
• The Schemagen tool (also included in the JDK) can generate an
XML schema from JAXB annotated classes.
JAXB and Web Services
As a data modeling API, JAXB is particularly useful
to web services, because:
• 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 data objects and back
again.
• Fits into an RPC-style of service method invocation with POJO
parameters and results.
* 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 handles the marshalling and unmarshalling
of serviced XML, it can be helpful to know how CXF does
it.
• A web service developer occasionally needs to
experiment with how JAXB annotations affect the
parsing and rendering of XML.
• A web service developer often needs to debug issues
that arise from data being marshalled or unmarshalled
incorrectly.
• The JAXB Marshalling/Unmarshalling APIs can be used
to apply additional validation or to generate a schema.
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 document into instances of
// those classes.
MyClass obj = (MyClass)
jaxb.createUnmarshaller().unmarshall(xml)
The Unmarshaller can accept XML input as a character
stream, a file, a DOM node, or several other input types.
JAXB: Marshalling
Marshalling objects into XML is just as easy:
// Create a JAXB context for your Java data classes
JAXBContext jaxb = JAXBContext.newInstance(myClasses);
// Marshall your Java object hierarchy into an XML document.
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 is a registry of all the classes that can be bound to
XML types.
• It is a factory for Marshaller and Unmarshaller instances.
• It can be supplied listeners and a Schema for additional
validation.
• It can be used to generate an XML Schema from your
JAXB annotated classes.
JAXB: Non-annotated Class Demo
• <Prepared demo with non-annotated
marshalling>
JAXB: Annotations
Although JAXB can bind almost any Java 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 Java
XML data binding. Here are just a few:
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@XmlRootElement
@XmlElement
@XmlAttribute
@XmlElementWrapper
• @XmlElementRef
• @XmlElementRefs
• @XmlTransient
These and more can be found in the following package:
• javax.xml.bind.annotation
• <insert link to docs or tutorial>
JAXB: Annotated Class Demo
• <Prepared demo with annotated marshalling>
JAXB: Rules and Conventions
Some general rules about JAXB annotations:
• Concrete classes must have a public default no-arg constructor.
• Properties that reference interfaces must be annotated with one
or more @XmlElementRef annotations that identify the possible
concrete types.
• Annotations may be placed on the fields or on the setters but not
on both.
• By convention, annotating fields is preferable for simple POJOs.
• Properties not bound to XML values must be annotated with
@XmlTransient.
Apache CXF: SOAP: Lab 1
Lab 1: JAXB Data Binding
http://tech.lds.org/wiki/Web_Services_with_Apache_CXF_-_Part_2
Web Services with Apache CXF
WSDL to Java
Consuming 3rd Party Web Services
WSDL 2 Java
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 stubs to access the web service.
• Using a WSDL-to-Java tool to automatically
generate the necessary web service stubs from a
published WSDL.
WSDL to Java: Code Generation
• What is generated?
• How do use what is generated?
– Service client
– Endpoint interface
– JAXB annotated model classes
WSDL to Java: Code Generation
IDE Demo
WSDL 2 Java: Code Generation
WSDL to Java
CXF provides the wsdl2java tool to consume thirdparty SOAP services:
• wsdl2Java
WSDL to Java: Lab 2
Lab 2: Using WSDL to Java
http://tech.lds.org/wiki/Web_Services_with_Apache_CXF_-_Part_2
WSDL to Java: Spring Integration
• When the generated stubs aren’t enough.
– Need to apply security (WSS4J/Spring Security)
– Need to apply addition in/out interceptors
• <Spring integration of generated endpoint in
Spring>
WSDL to Java: Spring Integration
Demo
Using an endpoint interface generated by WSDL to
Java in a Spring integration test.
Conclusion
• The standard Java APIs can be used to model
your data for use by web services.
• The JDK, CXF, and the Java Stack provide code
generation and configuration utilities to make it
easier to consume third-party web services.
• For more information about JAXB and CXF, please
visit the links on the following page.
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