[Spring] 21 - Spring Web Services

• Introduction to Web Services
• Why use or build a web service?
• Best practices for implementing a web service
• Quick start using Spring Web Services
• Endpoint mappings
• Object-XML marshalling
• Client access
• WSDL?

---

---

Web Services enable Loose Coupling

"Loosely coupled systems are considered useful when either the source or the destination computer systems are subject to frequent changes" ~ Wikipedia (July 2007)

Loose coupling increases tolerance ...
changes should not cause incompatibility

---

---

Web Services enable Interoperability

• XML is the lingua franca in the world of interoperability
• XML is understood by all major platforms
• SAX, StAX or DOM in Java
• System.XML or .NET XML Parser in .NET
• REXML or XmlSimple in Ruby
• Peral-XML or XML::Simple in Perl

* Notes:
Web services - the functions provided by other third party provider.
i.e. the specific functions which vendor provides in order to give your programs used,m usually via a URL.

Web Services - no need to code and maintain by yourself, just call others function to use.

---

---

Best practices for implementing your web services
(i.e. You acts as a google map, a service provider)

• Remember: 

• web services != SOAP (Simple Object Access Protocol)
• web services != RPC (Remote Procedure Call)

• Design contract independently from service interface
• Refrain (經常重複) from using stubs (存根) and skeletons
• Don't use validation for incoming requests
• Use XPath

 

---

---

Spring MVC vs Spring Web Services

---

---

Define a schema

---

---

Bootstrap the application tier

---

---

Architecture of our application exposed using a web service

---

---

Endpoint mappings (i.e. HandlerMapping)

• Spring Web Services provides several strategies for mapping requests to endpoints
• Message Payload
• SOAPAction Header
• XPath
• Annotations

---

---

Object-XML Marshalling

---

---

Marshaller Implementations

• All popular OXM technologies are supported:
• JAXB (1 and 2)
• Castor
• JiBX
• XmlBeans
• XStream

---

---

Object-XML Marshalling

---

---

Configuring a Castor Marshaller

---

---

Spring Web Services on the Client

• WebService Template
• Simplifies web service access
• Works directly with the XML payload
• Extracts body of a SOAP message
• Also works with POX (Plain Old XML)
• Can use marshallers /unmarshallers
• Provides convenience methods for sending and receiving web service messages
• Provides callbacks for more sophisticated usage