Transcript Introduction to Web Services - Department of Computer Engineering

Web Services
Kanda Runapongsa
([email protected])
Dept. of Computer Engineering
Khon Kaen University
Overview
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Introduction to Web Services
Web Services Standards
Java Support for Web Services
Apache Axis
Installing Apache Axis
 Invoking a service
 Deploying a service
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Web Services -- Basics
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Expose services to other processes
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Internet or intranet
Black boxes
Component-like, reusable
 Do not know how the service is
implemented
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Based on open standards
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HTTP, XML, and SOAP
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Web Services -- Basics
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Interconnect
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Applications
Different clients
Many devices
Distribution and integration of application
logic
Web Services are loosely coupled
Enable the programmable Web
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Not just purely interactive Web
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Web Services -- Basics
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What is a ‘Web Service’?
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‘Web’ accessible
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Service architecture
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Usually implies accessible via HTTP
Request/response
XML data transfer
Many serious Web services in use for
years
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Custom XML formats specific for each service
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Web Services -- Examples
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A Stock quote service
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The request asks for the current price of a
specified stock
The response gives the stock price
A service that maps out an efficient route
for the delivery of goods
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A business sends a request containing the
delivery destinations
The response returns the most cost-effective
delivery route
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Web Services -- Examples
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Web services and consumers of Web
services are typically businesses,
making Web services predominantly
business-to-business (B2B)
transactions
An enterprise can be the provider of
Web services and also the consumer
of other Web services
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Web Services Interaction
Diagram
UDDI
Registry
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Request WSDL location
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Download WSDL
Send SOAP messages
With XML documents
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WSDL
Web
Services
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Web Services Infrastructure
Language and platform
independent infrastructure for
 loosely-coupled, interoperable
 App2app communication over the
Internet
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Web Services Infrastructure
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Language and platform independent
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Separation of specification and
implementation
Loosely coupled
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Message based, synchronous and
asynchronous interactions
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Web Services Infrastructure
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Over the Internet
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No centralized control, use of
established protocols, security
considerations
Inter-operable
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Standards based
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Early (Internet) Technologies
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SMTP/MINE: Protocols of Email
FTP, NNTP
HTTP/HTTPs, HTML
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The protocols behind the Internet’s
popularity
Most of these facilitated application
to human interaction over the
Internet/intranet
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Early (Intranet) Technologies
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Distributed object model
Components: packaging and
interoperability
 Remoting: remote method invocation
 COM/DCOM from Microsoft, CORBA,
 Java RMI and EJBs
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What’s Wrong with That?
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Limited COM support on nonWindows platforms
COBRA: Server object implementation
not portable
Most of these facilitated app2app
within a trusted intranet and without
much consideration to interoperability
across different implementations
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App2App Interaction – the Web
Services Way
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Transport protocol
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HTTP/HTTPS
Data encoding
SOAP (Simple Object Access Protocol)
 XML Schema
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Interface Description
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WSDL (Web Services Description
Language)
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The Web Services Way (Cont)
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Service Description and Discovery
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UDDI (Universal Description, Discovery
and Integration)
Security
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WS-Security, XML-Signature, XMLEncryption
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What is SOAP?
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Simple Object Access Protocol
It defines a standard packaging format
for transmitting XML data between
applications on a network
 Usually request-response structure
 Transport normally HTTP, but can be
anything (SMTP, etc.)
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A SOAP Message
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A SOAP message is just an XML
document
The message might be sent from one
application to another to synchronize
contact information on two different
systems
SOAP takes advantages of XML
namespaces and XML schemas
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SOAP Message Structure
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SOAP Envelope:
Top-level wrapper
SOAP Header
(Optional):
Extension information
SOAP Body:
Application data
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Envelope is wrapper
for content, but no
useful information
Optional header can
contain control
information
Body contains actual
data in XML encoding
Attachments can hold
other types of data
(binary, etc.)
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A SOAP Message Example
<?xml version=“1.0” encoding=“UTF8”?>
<soap:Envelope
xmlns:soap=“http://schemas.xmlsoap
.org/soap/envelope/”>
xmlns:addr=“http://www.abc.com/jw
sbook/bookQuote”>
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A Soap Message Example
<soap:Body>
<addr:address>
<addr:name>Amazon.com</addr:
name>
<addr:zip>90952</addr:zip>
</addr:address>
</soap:Body>
</soap:Envelope>
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WSDL
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Web Services Description Language
A standard for describing the
structure of the XML data exchanged
between two systems using SOAP
When you create a new Web service,
you can also create a WSDL
document that describes about the
type of data we are exchanging
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WSDL 1.1 Document Structure
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Type
s
Messages
A WSDL document
describes
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Port Types
Bindings
Services
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What the service
can do
Where it resides
How to invoke it
WSDL descriptions
can be made
available from an
UDDI registry
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Why Do We Need UDDI?
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Universal Description, Discovery, and
Integration
We still need a guidance to find the
WSDL documents
UDDI can help others find our Web
services easily and use them to
communicate with our Web services
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What is UDDI?
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UDDI defines a standard set of Web
service operations that are used to
store and look up information about
other Web service applications
UDDI defines a standard SOAP-based
interface for a Web services registry
A UDDI is often referred to as a
“Yellow Pages” for Web services
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Java APIs for XML
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Java API for XML Processing (JAXP) –
Process XML documents using various
parsers
Java API for XML-based RPC (JAXRPC) – sends SOAP method calls
Java API for XML Registries (JAXR) –
provides a standard way to access
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Apache Axis
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Apache Axis is a toolkit to create and
consume Web Services for the Java
platform which can be downloaded from
http://ws.apache.org/axis/index.html
Axis 1.1 supports numerous Java
technologies
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SAAJ (SOAP with Attachments API for XML)
JAX-RPC (Java API for XML based Remote
Procedure Call)
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Apache Axis
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A simple stand-alone server
A server which plugs into servlet
engines such as Tomcat
Extensive support for the Web
Service Description Language (WSDL)
Emitter tooling that generates Java
classes from WSDL
A tool for monitoring TCP/IP packets
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Apache Axis – Web Service
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Create an object that has methods and
publish it on the Internet
You can access your Web service just like
if it was a local object through a protocol
called SOAP
All the operations of a Web service are
expressed through a WSDL
The WSDL file is used to access and call
operations on Web services
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Concepts: SOAP & AXIS
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Apache Axis is an Open Source SOAP
server and client
SOAP is a mechanism for interapplication communication between
systems written in arbitrary
languages, across the Internet
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Concepts: SOAP & AXIS
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SOAP usually exchanges messages over
HTTP
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The client POSTs a SOAP request
The client then receives either
An HTTP success code and a SOAP response
Or an HTTP error code
Open Source means that you get the
source, but there is no formal support
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Concepts: SOAP & AXIS
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SOAP messages are XML messages
These messages exchange structured
information between SOAP systems
Messages consist of one or more
SOAP elements inside an envelope,
Headers, and the SOAP Body
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Concepts: SOAP & AXIS
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Axis handles the magic of converting
Java objects to SOAP data when it
sends it over the wire or receive
results
SOAP Faults are sent by the server
when something goes wrong; Axis
converts these to Java exceptions
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Concepts: SOAP & AXIS
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Axis implements the JAX-RPC API,
one of the standard ways to program
Java services
Axis is compiled in the JAR file
axis.jar; it implements the JAX-RPC
API declared in the JAR files
jaxrpc.jar and saaj.jar
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References
Web Services with JAX-RPC and Axis
http://pankaj-k.net/axis4tag/
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