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, 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 stand-

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

WSDL2Java client proxy .

Web Services with Apache CXF

Java XML BindingModeling 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:

• DOM• StAX• JAXP• DOM4J• JAXB

• 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 UnmarshallingAlthough 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 classesJAXBContext 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 classesJAXBContext 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:• @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 Bindinghttp://tech.lds.org/wiki/Web_Services_with_Apache_CXF_-_Part_2

Web Services with Apache CXF

WSDL to JavaConsuming 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 third-party SOAP services:• wsdl2Java

WSDL to Java: Lab 2

Lab 2: Using WSDL to Javahttp://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

DemoUsing 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-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