J2EE Technologies: Web Services I

IBM Labs in Haifa

J2EE Technologies: Web Services I

Benny RochwergerResearch Staff Member

IBM Labs in Haifa

J2EE Technologies - Web Services I2 © 2003 IBM Corporation

Agenda

Web Services: What is it about

XML Primer

Simple Object Access Protocol – SOAP

Describing Web Services – WSDL

Discovering Web Services – UDDI

Web Services in the Marketplace

What is next

The Open Grid Services Architecture

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Web Services Overview

An platform and language independent architecture for program to

program communications

A Web Service is a software component that can be:

Described using a service description language

Published to a registry of services

Discovered using a standard mechanism (at runtime or design time)

Invoked through a declared API (usually over the network)

Composed with other services

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Web Services Overview (cont.)

A Web Service is an interface that describes a collection of operations

that are network accessible through standardized XML messaging

A Web Service is described using a standard, formal XML notion, called

service description, which covers message formats, transport protocols

and location

The interface hides the implementation details of the service

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The Service Oriented Architecture (SOA)

ServiceProvider

ServiceProvider

ServiceRegistry

ServiceRegistry

ServiceRequestor

ServiceRequestor

Publish

Bind

Find

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The Web Services Stack

ServicePublication/Discovery

ServicePublication/Discovery

ServiceDescription

ServiceDescription

XML MessagingXML Messaging

Transport NetworkTransport Network

UDDI

WSDL

SOAP

HTTP, SMTP, MQSeries, etc.

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Web Services Advantages

Big players, such as IBM, Sun and Microsoft, actively support it Reuses the big infrastructure already built for the Web and the HTTP

protocol SOAP as the de facto standard of doing RPC over the web

It has the potential to become a lingua franca that you can fall back on when all else fails

CORBA’s IIOP has not penetrated the internet as HTTP has If SOAP can run on HTTP or any other Internet Protocol, it is bound

to enter the domain the IIOP has not

Web Services are poised to do to program to program interactions, what

the Web did for program to user interactions

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The eXtensible Markup Language - XML

Generalized Markup Languages

Use tags to identify information

Surround information with start and end tags

<book>

<title>Crime and Punishment</title>

<author>

<FirstName>Fyodor</FirstName>

<LastName>Dostoevsky</LastName>

</author>

<Published>1866</Published>

</book>

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The XML Evolution

1986 - Standard Generalized Markup Language (SGML)

Meta-language

Do not defined a particular markup

Define how to formally specify markup languages

SGML application

Specific markup languages defined with the SGML meta-language

Very complex

Expensive software needed to process SGML

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The XML Evolution (cont.)

1992 - Hypertext Markup Language (HTML)

Successful instance of a SGML application

Tags to represent rich hypertext:

Text structuring: <H1>, <H2>, <P>, <BR>

Formatting: <B>, <I>

Linking and embedding: <A>, <IMG>

Data input: <FORM>, <INPUT>

Not extensible

Vendors added incompatible tags

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The XML Evolution (cont.)

2000 – eXtensible Markup Language (XML)

Simplify SGML

Control evolution of HTML

As SGML, it is a meta-language

Few optional features

Difficult to implement SGML features were dropped

De-facto standard for representing structured and semi-structured

information in a textual form

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Document-Centric vs. Data-Centric

Document-Centric XML

Semi-structured documents

Technical manuals, legal documents, product catalog

Typically consumed by humans

Data-Centric XML

Textual representation of highly structured information

Relational data, financial transactions, programming languages data

structures

Typically machine generated and consumed

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XML Instances

<?xml version=“1.0” encoding=“UTF-8” ?>

<PhoneBook>

<Contact>

<FirstName>John</FirstName>

<LastName>Doe</LastName>

<phone location=“home”>

04 987 6543

</phone>

<phone location=“work”>

04 876 5432

</phone>

</Contact>

</PhoneBook>

XML DeclarationRoot element

Element

Attribute

Text

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XML Namespaces

Avoid collisions in elements with common names by qualifying element names with unique identifiers

QName = Namespace identifier + element name Use URIs for identifiers (entirely for identification) To ease use of identifiers assign each URI a prefix

Defined through attributes, valid for all contained elements:

<Contact xmnls:myab=“http://my.company.com/addressbook”xmnls:bezeqab=“http://bezeq.co.il/addressbook”><myab:entry>

<myab:name>John Doe</myab:name></myab:entry><bezeqab:entry>

<bezeqab:FirstName>John</bezeqab:FirstName><bezeqab:LastName>Doe</bezeqab:LastName>

</bezeqab:entry></Contact>

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XML Schemas

Mechanism to specify:

the datatype of each element/attribute "this element shall hold an integer with the range 0 to 12,000"

the structure of instance documents "this element contains these elements, which contains these other elements,

etc"

Declarative mechanism for validating the contents of XML documents

A powerful alternative to older Document Type Definitions (DTDs)

XML based – reduces the need for yet another parser

Designed with namespaces in mind since the beginning

Extensive pre-defined simple types

Easy mechanism for creating new types

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<?xml version="1.0" encoding="UTF-8" ?><xsd:schema xmlns:xsd=http://www.w3.org/2001/XMLSchema>

<xsd:element name="BookStore"><xsd:complexType> <xsd:sequence> <xsd:element ref="Book" minOccurs="1" maxOccurs="unbounded" /> </xsd:sequence></xsd:complexType>

</xsd:element><xsd:element name="Book">

<xsd:complexType><xsd:sequence> <xsd:element name="Title" type="xsd:string" /> <xsd:element name="Author" type="xsd:string" /> <xsd:element name=“Published" type="xsd:date" /></xsd:sequence>

</xsd:complexType></xsd:element>

</xsd:schema>

XML Schema for a BookstoreDefine cardinality of elements

Create complex types out of a sequence of simple types

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XML Schema Builtin Datatypes

Numeric Data

Time Data

Textual Data

Binary Data

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Processing XML – Parsing Models

Pull parsing Application “pulls” from parser for next piece of information No standard API yet

Push parsing Parser “pushes” complete pieces of information read Application provides event-callback The Simple API for XML (SAX) is the de-facto standard

One-step parsing Read entire XML document and build an equivalent parsed tree The W3C Document Object Model (DOM) specification

Map XML objects to data structures used to build the parsed tree Very popular due to simplicity (compared with other methods) Not too efficient

Hybrid parsing Application thinks entire tree has been built (one-step parsing) Parser pulls data as needed (pull-parsing)

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Processing XML – SAX-based

import javax.xml.parsers.SAXParser;import javax.xml.parsers.SAXParserFactory;import org.xml.sax.Attributes;import org.xml.sax.SAXException;import org.xml.sax.helpers.DefaultHandler;

public class MySaxBasedApplication extends DefaultHandler {

public void processXML(InputStream XMLStream) { SAXParserFactory factory = SAXParserFactory.newInstance(); SAXParser parser = factory.newSAXParser(); parser.parse(XMLStream, this); }

public void startDocument() throws SAXException { // My code goes here . . . }

public void endDocument() throws SAXException { // My code goes here . . . }

Abstract class that defines all SAX callbackinterfaces

` Receive notification of end of a document

Receive notification of beginning of a document

Create the connection between our concrete handler and the SAX parser. Start parsing

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Processing XML – SAX-based (cont.)

public void startElement(String namespaceURI, String localName, String qualifiedName, Attributes attrs) throws SAXException { // My code goes here . . . }

public void endElement(String namespaceURI, String localName, String qualifiedName) throws SAXException { // My code goes here . . . }

public void characters(char buf[], int offset, int len) throws SAXException { // My code goes here . . . }

} // ENDOF: public class MySaxBasedApplication extends DefaultHandler

Receive notification of beginning of an element

Receive notification of end of an element

Receive notification of character data inside an element

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Processing XML – DOM-basedimport javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import org.w3c.dom.NodeList;import org.w3c.dom.Document;import org.w3c.dom.Element;

public class MyDomBasedApplication { public void processXML(InputStream XMLStream) { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.parser(XMLStream); // My code goes here . . . // use DOM interfaces to manipulate the tree: Element e = doc.getDocumentElement(); if (e.hasAttribute(“an-attribute”)) { // do something with Element e } }} // ENDOF: public class MyDomBasedApplication

Parse the entire XML document into a DOM tree

Then use the DOM interfaces to manipulate the tree

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Processing XML – DOM-based (cont.)

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XML Summary

XML Namespaces Key tool for resolving the problems of name recognition and collision Fundamental for mixing information from multiple schemas into a

single document XML Schema

De facto standard for describing document structure and XML data types for data-oriented XML applications

Java APIs for XML processing org.xml.sax

Push parsing, fast but hard to use org.w3c.dom

One-step parsing, easy to use but inefficient

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The Simple Object Access Protocol (SOAP)

XML-based protocol for messaging and RPC

Can works on top of existing transports

HTTP, SMTP, FTP, MQSeries

Use of XML schema for encoding typed values

Language independent

Generation of SOAP messages available in popular programming

language

C, Java, Perl

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A SOAP Message

Envelope Mandatory root element of SOAP messages Contains an optional header and the message body

Header Primary extensibility mechanism Usually handled by intermediaries Typical uses: authentication, authorization, transaction management,

tracing, etc. One or more header entries or headers Arbitrary XML mustUnderstand attribute

Body One or more header body entries or bodies Arbitrary XML

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A SOAP Message - Example

<env:Envelope xmlns:env="http://www.w3.org/2002/06/soap-envelope">

<env:Header> <n:alertcontrol env:mustUnderstand="false“ xmlns:n="http://example.org/alertcontrol"> <n:priority>1</n:priority> <n:expires>2001-06-22T14:00:00-05:00</n:expires> </n:alertcontrol> </env:Header>

<env:Body> <m:alert xmlns:m="http://example.org/alert"> <m:msg>Pick up Mary at school at 2pm</m:msg> </m:alert> </env:Body>

</env:Envelope>

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Protocol packet

Service data

SOAP Envelope

Protocol packet

SOAP: XML Messaging

ApplicationApplication Web ServiceWeb Service

SOAP EngineSOAP Engine

Network ProtocolNetwork Protocol



Request

Response

Application data

SOAP Envelope

Service Requestor Service Provider

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SOAP over HTTP

POST /StockQuoteProj/servlet/rpcrouter HTTP/1.0Host: localhost:9081Content-Type: text/xml; charset=utf-8Content-Length: 469SOAPAction: ""

<?xml version='1.0' encoding='UTF-8'?>

<SOAP-ENV:Envelope xmlns:SOAPENV=“http://schemas.xmlsoap.org/soap/envelope/” xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:xsd="http://www.w3.org/2001/XMLSchema">

<SOAP-ENV:Body> <ns1:getQuote xmlns:ns1=“http://tempuri.org/StockQuoteService”> <symbol xsi:type="xsd:string">IBM</symbol> </ns1:getQuote> </SOAP-ENV:Body></SOAP-ENV:Envelope>

The SOAP envelope as the HTTP payload

The HTTP header

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SOAP over SMTP

From: [email protected]: [email protected]: Travel to LADate: Thu, 29 Nov 2001 13:20:00 ESTMessage-Id: <[email protected]>

<?xml version='1.0' ?><env:Envelope xmlns:env="http://www.w3.org/2001/12/soap-envelope"> <env:Body> <p:itinerary xmlns:p="http://travelcompany.example.org/reservation/travel"> <p:departure> <p:departing>New York</p:departing> <p:departureDate>2003-05-25</p:departureDate> <p:departureTime>late afternoon</p:departureTime> </p:departure> <p:return> <p:departing>Los Angeles</p:departing> <p:departureDate>2003-05-30</p:departureDate> <p:departureTime>mid morning</p:departureTime> </p:return> </p:itinerary></env:Body></env:Envelope>

The SOAP envelope as the SMTP payload

The SMTP header

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SOAP Intermediaries

Vertical extensibility

Capability of adding new pieces of information within a SOAP message

Horizontal extensibility

Targeting different parts of a SOAP message to different recipients

Achieved through intermediaries that process parts of SOAP messages as they travel from source to destination

Security

Scalability

Tracing

SOAP headers can be explicitly targeted at intermediaries SOAP-ENV:actor attribute

http://schemas.xmlsoap.org/soap/actor/next

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Protocol packet

Service data

SOAP Envelope

Protocol packet

SOAP Intermediaries

ApplicationApplication Web ServiceWeb Service





Application data

SOAP Envelope

Service Requestor Service Provider



SOAP Envelope



SOAP Envelope

Actor 1 Actor 2

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SOAP Intermediaries – Example <env:Envelope xmlns:env="http://www.w3.org/2001/12/soap-envelope"> <env:Header> <m:reservation xmlns:m="http://travelcompany.example.org/reservation" env:actor="http://www.w3.org/2001/12/soap-envelope/actor/next" env:mustUnderstand="true"> <m:reference>uuid:093a2da1-q345-739r-ba5d-pqff98fe8j7d</reference> </m:reservation> <n:passenger xmlns:n="http://mycompany.example.com/employees" env:actor="http://www.w3.org/2001/12/soap-envelope/actor/next" env:mustUnderstand="true"> <n:name>John Q. Public</n:name> </n:passenger> </env:Header> <env:Body> <p:itinerary xmlns:p="http://travelcompany.example.org/reservation/travel"> <p:departure> <p:departing>New York</p:departing><p:departureDate>2001-12-14</p:departureDate> </p:departure> <p:return> <p:departing>Los Angeles</p:departing><p:departureDate>2001-12-20</p:departureDate> </p:return> </p:itinerary></env:Body></env:Envelope>

The reservation system must keep an unique reference to the itinerary

The employees system must know who is traveling

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SOAP Error Handling

HTTP/1.0 500 Internal Server ErrorContent-Type: text/xml; charset=“utf-8”Content-Length: nnnn

<SOAP-ENV:Envelope xmlns:SOAP-ENV=“http://www.w3.org/2001/12/soap-envelope” SOAP-ENV:encodingStyle=“http://schemas.xmlsoap.org/soap/enconding/”>

<SOAP-ENV:Body> <SOAP-ENV:Fault>

<faultcode>Client.AuthenticationFailure</faultcode><faultstring>Failed to authenticate client</faultstring><faultactor>where-the-problem-occurred</faultactor>

</SOAP-ENV:Fault> </SOAP-ENV:Body></SOAP-ENV:Envelope>

Transport Protocol Error indicationThe mandatory faultcode element: - VersionMismatch - MustUnderstand - Client - Server

Human readable message identifying cause of the problemWhere in the message path the error ocurred

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SOAP Data Encoding

How to encode complex data types that do not have a direct representation in

XML Schema

Arrays, arbitrary data structures

Explicitly specify encoding rules of the message or parts of it

The encodingStyle attribute

SOAP defined encoding rulesSOAP-ENV:encodingStyle=http://schemas.xmlsoap.org/soap/encoding

No default encoding, i.e., this attribute is mandatory at least for the SOAP-ENV:Envelope element

Data encoding rules

Well defined mapping between abstract data models (ADM) and XML

syntax

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SOAP Data Encoding (cont.)

Simple types

Map to XML Schema built-in types

Compound types

Composed of several parts, each with an associated type

Parts are distinguished by an accesor Name or relative position of a part

Structs Compound types whose parts are distinguished only by their name

Arrays Compound types whose parts are distinguished only by their ordinal

position

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SOAP Data Encoding - Arrays

<element name=“arrayOfNumbers”> <complexType base=“SOAP-ENC:Array> <element name=“number” type=“xsd:int” maxOcurrs=“unbounded”/> </complexType></element>

<arrayOfNumbers SOAP-ENC:arrayType=“xsd:int[2]”> <number>11</number> <number>22</number></arrayOfNumbers>

<SOAP-ENC:Array SOAP-ENC:arrayType=“xsd:int[2]”> <SOAP-ENC:int>11</SOAP-ENC:int> <SOAP-ENC:int>22</SOAP-ENC:int></SOAP-ENC:Array>

Array encoding without schemaEncoding using the schemaSchema for an array of integers

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SOAP Data Encoding – Structured Data

Does the XML format on the wire matters ? No Use automatic “data to XML and back” encoding systems

SerializerSerializer

DeserializerDeserializerApp

licat

ion

Dat

aA

pplic

atio

n D

ata

XM

LX

ML

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codegen

SOAP Data Encoding – Structured Data

Does the XML format on the wire matters ? Yes Automatic generated XML might not be good enough

Delegate XML processing to application Build and register custom serializers/deserializers

Manually Use of schema compilers

SerializerSerializer

DeserializerDeserializerApp

licat

ion

Dat

aA

pplic

atio

n D

ata

XM

LX

ML

SchemaSchema Schema CompilerSchema Compiler

codegen

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Messaging versus RPC

Messaging Focus is data, which can be in any

conceivable format APIs

sendMessage(), getMessage(), registerMessageCallback()

In the WS contextCarry XML dataCould be one-way or request-

responseAsynchronous

Remote Procedure Call Focus is logic APIs:

Call(target, operation, params[]) In the WS context

Direct, synchronous, request-response invocationsPass data structures

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SOAP RPC

<?xml version='1.0' encoding='UTF-8'?>

<SOAP-ENV:Envelope xmlns:SOAPENV=“http://schemas.xmlsoap.org/soap/envelope/” xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">

<SOAP-ENV:Body> <ns1:getQuote xmlns:ns1=“http://tempuri.org/StockQuoteService”>

<symbol xsi:type="xsd:string">IBM</symbol> </ns1:getQuote> </SOAP-ENV:Body></SOAP-ENV:Envelope>

Operation Parameter

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SOAP Messaging

<env:Envelope xmlns:env="http://www.w3.org/2001/12/soap-envelope"> <env:Body> <p:itinerary xmlns:p="http://travelcompany.example.org/reservation/travel"> <p:departure> <p:departing>New York</p:departing> <p:departureDate>2003-05-25</p:departureDate> <p:departureTime>late afternoon</p:departureTime> </p:departure> <p:return> <p:departing>Los Angeles</p:departing> <p:departureDate>2003-05-30</p:departureDate> <p:departureTime>mid morning</p:departureTime> </p:return> </p:itinerary></env:Body></env:Envelope>

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SOAP Summary

The flexible SOAP envelope

Vertical extensibility using SOAP headers

SOAP intermediaries

Horizontal extensibility

Encoding data using SOAP

SOAP for messaging and RPC applications

SOAP over multiple network protocols

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Agenda

Web Services: What is it about

XML Primer

Simple Object Access Protocol – SOAP

Describing Web Services – WSDL

Discovering Web Services – UDDI

Web Services in the Marketplace

What is next

The Open Grid Services Architecture

IBM Labs in Haifa

J2EE Technologies: Web Services I

Benny RochwergerResearch Staff Member

Documents

J2EE Technologies: Web Services I