Transcript XML Web Services Practical Hints and Tips

XML Web Services
Hints and Tips
Bob Steemson
Product Architect
iSOFT plc
www.isoftplc.com
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Introduction
 Why use XML Web Services?
 Some thoughts on XML
 Building Web Service Code
 Summary
 Questions
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Why Use XML Web Services?
 Facilitates loose-coupling of applications
 Platform Independent
 Powerful XML tools available
 Standard Internet technology lowers costs
 Independent of proprietary platforms
 Independent of expensive third party software
 Open-source solutions available
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Some Thoughts on XML
 XML is not about text
 Understand and use namespaces
 Make use of XML Schemas
 Make use of XSLT
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XML is not about text
 Don’t build XML Strings “by hand”
 Use appropriate tools
– For example MXXMLWriter, XmlWriter, JDOM
– Will handle illegal characters and buffer data
– Will help ensure your XML is “well formed”
 Don’t “pretty print” XML strings unnecessarily
– Most XML will be passed from method to method or from
machine to machine
– View with tools like XML Spy or Internet Explorer
– If necessary, include an option in test tools
 Don’t keep parsing and serialising documents
– Once parsed, keep as a DOM as long as possible
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Understanding XML Namespaces
 Prevent element and attribute names from
different applications from clashing
 XML Namespaces associate element and attribute
names with a URI (URI or URN)
– The URI is a way of defining a globally unique string
– Two namespace URIs are equal if they are identical
character-by-character (case sensitive)
– There need not be a corresponding resource
 Namespace prefix is a local synonym for URI
– Avoids problems if URI contains illegal characters
– Two names with different prefixes are identical if
local names and URIs are the same
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Using XML Namespaces
 Always use namespaces for external XML
– Anything that may be seen outside this application
– Internal XML such as configurations may have no
namespace if you are certain it will not “escape”
 Avoid using the default namespace with no prefix
– Reserve “no prefix” to mean “no namespace”
– Can make writing XSLT more difficult
 Beware of domain name changes if using a URL
– Do not “hard code” the URL
– URL changes require coordination with partners
– Don’t forget Schema and XSL documents
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Make use of XML Schemas
 Create and publish a schema for each document
 Validate input XML before processing by default
– Allow validation to be turned off
 Have an option to validate output documents
– Use mainly for testing
– Turn this off by default – “Buyer beware”
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Make use of XSL Transformations
 XSLT is a powerful way of transforming XML
– Much more than a way of turning XML into HTML
 Can change or remove document namespaces
 Restructure elements or convert codes
 Simplify complex external schemas
– Can make serialisation & deserialisation simpler
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Building Web Services
 Designing Web Services
 Security requirements
 Think about testing
 Don’t leave namespaces at the default
 .NET Web Services Enhancements
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Designing Web Services
 Web Services should be “Coarse Grained”
– Think of complex transactions that involve multiple
co-operating objects, rather than object methods
– Try to have fewer methods and extend functionality
with options if necessary
 Try to make stabilise service signatures - WSDL
– Both ESI and the CHI Web Services have a single
method that includes a service type parameter
 Pass complex data as XML
– Consider passing XML as a DOM Element rather than
a string
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Web Services Security
 Keep security and other parameters separate
– Both may change – but probably not at the same time
 If possible, keep security credentials out of the
SOAP body
 Consider using WS-Security (see below)
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Web Services Testing
 Ensure that services can be tested in-house
 When writing a new service
– Write a simple interactive client for prototyping and
early development
– Create an automatic test client for long-term use
 When writing a client for an external service
–
–
–
–
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Provide a simple emulator for in-house testing
Allows progress while connections are set up
Allows future debugging in a closed environment
Update the emulator after external testing
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Web Services Tracing
 Use Web Services Tracing if all else fails
 Can be useful in sorting out namespace issues
 MS SOAP Toolkit (VB6) includes Trace Utility
 Apache SOAP includes TcpTunnelGui class
 .NET Web Services Enhancements classes have
built in trace facilities
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Use of Namespaces with SOAP
 Tools such as the MS SOAP Toolkit and .NET will
create WSDL files with default XML namespaces
 Always take the time to override these with
specific namespaces for your application
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.NET Web Services Enhancements
 Extension to standard .NET Web Services classes
– Download from MSDN (current version 1.0 SP1)
– Supports additional Web Services specifications that have
been developed by Microsoft, IBM and other partners
 WS-Security
– Supports security tokens for authentication
– Supports digital signing for message integrity
– Supports encryption for confidentiality
 WS-Routing
– Route of Web Services requests via intermediaries
 WS-Attachments
– Allows attachments to SOAP messages
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Summary
 XML Web Services provide a simple and reliable
way to connect applications
 Based on well-established technologies
 Cross-platform – but there are still grey areas
 Easier to design and deploy than many
alternatives such as DCOM or CORBA
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Questions
 Contact Details
[email protected]
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