Presentation on theme: "Web Services with Apache CXF Part 2: JAXB and WSDL to Java Robert Thornton."— Presentation transcript:
Web Services with Apache CXF Part 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 Binding Modeling Web Service Messages with JAXB
Introduction In all software applications and data management systems, languages are necessary to describe the data and perform instructions. A single language is rarely adequate in real-world applications, certainly not in the enterprise. Usually at least two languages are necessary: A language to describe the data for storage or transfer. A language to perform manipulations on that data.
XML XML is a language for describing data: – Platform agnostic. – Strongly typed (though use of XML Schema) – Useful for long or short-term data storage. – Useful for data transfer between vastly different architectures. – Particularly useful to describe the operations and messages passed to and from web services.
Java Java is a language for performing instructions: – Strongly typed. – Object-oriented. – Machine and operating system independent (through its JVM). – Exceptionally useful for implementing software that performs services. – Available on servers, desktops, mobile devices, cards, nearly everywhere.
Java and XML Bringing them together: How do we instruct Java to read, process, and write XML? How do we keep the Java XML processing simple and clean? How do we make it maintainable long term? These are questions that many technologies have attempted to address.
Java and XML: Choices, choices…. As Java has matured, several strategies and APIs have developed around Java XML processing: 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. XML-to-Object Binding – XML types and elements are bound to Java types and fields. In practice, most solutions use some combination of these. Web services typically use XML-to-Object binding.
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 CXF handles the marshalling and unmarshalling of serviced XML, but 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); // Unmarshall the XML document to instances of those classes. Foo obj = (Foo) jaxb.createUnmarshaller().unmarshall(xml); The Unmarshaller can accept XML input as a character stream, a file, a DOM node, or several other input types. Can be supplied listeners and a schema for validation. Note that the Unmarshaller is not guaranteed to be thread-safe.
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. It can be supplied listeners and a Schema for validation. Note that the Marshaller is not guaranteed to be thread-safe.
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 used to generate an XML Schema from your JAXB annotated classes. Because the JAXBContext is immutable, it is safe for use as a singleton by multiple threads.
JAXB: Non-annotated Class Demo Demo XML Output without JAXB Annotations
JAXB: Annotations Annotations control many aspects of XML marshalling: annotation is required for classes that represent an XML document root element. All other annotations are optional in most cases, but useful nonetheless: Other annotations 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, and so forth. annotation can tell JAXB to ignore certain fields during marshalling.
JAXB: Common Annotations JAXB defines many annotations to customize Java XML data binding. Here are just These and more can be found in the following package: javax.xml.bind.annotation For usage information see the JAXB API Documentation.JAXB API Documentation
JAXB: Non-annotated Class Demo Demo XML Output with JAXB Annotations
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 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
Web Services with Apache CXF WSDL to Java Consuming 3 rd Party Web Services
WSDL 2 Java Third-party SOAP web services are typically consumed in one of two ways: Using a client JAR prepared by the service provider. – Contains the necessary Java classes and stubs for accessing the web service. Using a WSDL-to-Java tool. – Automatically generates the necessary Java classes and stubs from a published web service descriptor, or WSDL. – Note that the WSDL is not the same as the service endpoint. An endpoint is where the web service accepts SOAP requests A WSDL may be queried from the endpoint (e.g. by appending ?wsdl to the enpoint URL.
WSDL to Java: Code Generation What is generated by a WSDL to Java tool? A service client. – Will extend javax.xml.ws.Service and/or be annotated with One or more service endpoint interfaces. – Will have annotation Model classes bound to any complex XML types used by the service. – Will have with JAXB annotations. An object factory is also generated to facilitate the creation generated stubs.
WSDL to Java: Code Generation Demos A Generated Web Service Client A Generated Endpoint Interface Generated JAXB Model Classes
WSDL 2 Java: Code Generation Client code generation is cool, but … When do you use it?
WSDL to Java: Code Generation Option #1: One-time generation Run command-line tools and copy to project. – wsimport (JDK) – wsdl2java (CXF) IDE Web Service Client Wizards When to use? Need to customize what is generated Want to avoid dependence on build tools
WSDL to Java: Code Generation Option #2: Build-time generation Using Maven Plugins: – org.codehaus.mojo:jaxws-maven-plugin Uses the JDK wsimport tool – org.apache.cxf:cxf-codegen-plugin Uses the CXF wsdl2java tool When to use? Need to stay up-to-date with a changing WSDL. Don’t need to tweak generated code Don’t want to own or manage the generated source code.
WSDL to Java: Code Generation Due to its integration with CXF, the Java Stack recommends the CXF wsdl2java tool if there is a need to generate web-service clients at build-time. org.apache.cxf cxf-codegen-plugin...
WSDL to Java: Spring Integration Managing the generated endpoint with Spring: When the generated stubs aren’t enough. – Need to apply security (WSS4J/Spring Security) – Need to apply additional in/out interceptors Stack namespace handler: – To simplify common security and configuration needs – CXF namespace handler: – For more advanced client configuration.
WSDL to Java: Spring Configuration Attributes to service-class – The bean name of the service endpoint interface. endpoint – The published endpoint service address. user, password, password-type – For user authentication. Both plain text and digest passwords are supported. wam-authenticator, wam-cookie-resolver-ref – Provides authentication through WAM ssl-trust-server – Specifies whether the server’s SSL cert should be automatically trusted.
WSDL to Java: Spring Configuration Example Usage:
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: Java 6 API Documentation JDK 6 Programmer Guides Java Stack Documentation