Java web services

Java
Web Services
Kumar Gaurav
k10gaurav@gmail.com

Agenda
1. Overview
2. Architecture
3. WSDL
4. SOAP
5. UDDI
6. An Example

Overview
General Definition
“Web services are software components that interact with one another
dynamically via standard Internet Technologies, making it possible to build
bridges between IT systems that otherwise would require extensive
development efforts”
-Gartner Group
Web services are
Complementary to existing technology
Building blocks (components) used to construct larger applications
Evolutionary technology: The latest in a long line of approaches for distributed
applications communication
Web services are NOT
A rip and replace technology
A solution to all the integration woes

Overview
Key Features
 Web services are self-contained.
On the client side, no additional software is required. A programming
language with XML and HTTP client support is enough to get you started.
On the server side, merely a Web server and a SOAP server are required.
 Web services are self-describing.
Neither the client nor the server knows or cares about anything besides the
format and content of request and response messages (loosely coupled
application integration).
 Web services can be published, located, and invoked across the Web.
This technology uses established lightweight Internet standards such as HTTP.
It leverages the existing infrastructure. Some additional standards that
are required to do so include SOAP, WSDL, and UDDI.
 Web services are language-independent and interoperable.
Client and server can be implemented in different environments. Existing
code does not have to be changed in order to be Web service enabled.
Cntd…

Overview
Key Features
 Web services are inherently open and standard-based.
XML and HTTP are the major technical foundation for Web services. A large part
of the Web service technology has been built using open-source projects.
Therefore, vendor independence and interoperability are realistic goals this
time.
 Web services build on proven mature technology
There are a lot of commonalities, as well as a few fundamental differences to
other distributed computing frameworks. For example, Web services are build
with SOA Architecture.
 Web services are loosely coupled
Traditionally, application design has depended on tight interconnections at both
ends. Web services require a simpler level of coordination that allows a more
flexible re-configuration for an integration of the services in question.
 Web services provide the ability to wrap existing applications
Already existing stand-alone applications can easily be integrated into the
service-oriented architecture by implementing a Web service as an interface.

Architecture
Characteristics of the Web service architecture
 Webservice that follows the service-oriented architecture employs a
loose coupling betweenthe participants. Such a loose coupling provides
greater flexibility:
 In this architecture, a client is not coupled to a server, but to a service.
Thus, the integration of the server to use takes place outside of the scope
of the client application programs.
 Functional components and their interfaces are separated. Therefore,
new interfaces can be plugged in more easily.
 Within complex applications, the control of business processes can be
isolated. A business rule engine can be incorporated to control the
workflow of a defined business process. Depending on the state of the
workflow, the engine calls the respective services.
 Bindings are specified using configuration files and can thus easily be
adapted to new needs.

Continue…
Concept of a service-oriented
 The service provider creates a Web service and possibly publishes its
interface and access information to the service registry.
 The service broker (also known as service registry) is responsible for making
the Web service interface and implementation access information
available to any potential service requestor.
 The service requestor locates entries in the broker registry using various find
operations and then binds to the service provider in order to invoke one of
its Web services.

Core Technologies
The following are the core technologies used for Web services.
 XML (eXtensible Markup Language)
The markup language that underlies most of the specifications used for Web
services. XML is a generic language that can be used to describe any kind of
content in a structured way, separated from its presentation to a specific device.
 SOAP (Simple Object Access Protocol)
SOAP similar to JDBC, is a network, transport, and programming language and
platform neutral protocol that allows a client to call a remote service. The message
format is XML.
 WSDL (Web services description language)
WSDL is an XML-based interface and implementation description language. The
service provider uses a WSDL document in order to specify the operations a Web
service provides, as well as the parameters and data types of these operations. A
WSDL document also contains the service access information.
 UDDI (universal description, discovery, and integration)
UDDI is both a client-side API and a SOAP-based server implementation that can be
used to store and retrieve information on service providers and Web services.

WSDL
WSDL architecture
 Web Services Description Language (WSDL) files
are written in Extensible Markup Language (XML).
 WSDL is one alternative to make service
interfaces and implementations available in the
UDDI registry.
 WSDL includes the workflow description (business
process execution language for Web services,
BPEL4WS)
 WSDL is the base for SOAP server deployment
and SOAP client generation.
A WSDL file contains the following parts:
Web service interface definition
 This is part contains the elements, as
well as the namespaces.
Web service implementation
 This part contains the definition of
the service and ports.
 The following is the structure of the
information in a WSDL file : A WSDL file
contains the following parts:

WSDL Architecture
 The following is the structure of the information in a WSDL file : A WSDL file
contains the following parts:
Port Type
Messages
Types
Bindings
Service
Ports
Operation Signatures
Parameter Definitions
Complex Type Definitions
Transport protocol and payload format
Service Definition Element
Supported Interface Bindings

Continue…
A WSDL file describes a Web service with the following elements:
 portType
 The description of the operations and associated messages. The
portType element defines abstract operations.
<portType name="EightBall">
<operation name="getAnswer">
<input message="ebs:IngetAnswerRequest"/>
<output message="ebs:OutgetAnswerResponse"/>
</operation>
</portType>
 message
 The description of input and output parameters and return values.
<message name="IngetAnswerRequest">
<part name="meth1_inType" type="ebs:questionType"/>
</message>
<message name="OutgetAnswerResponse">
<part name="meth1_outType" type="ebs:answerType"/>
</message>

WSDL
 types
 The schema for describing XML types used in the messages.
<types>
<xsd:schema targetNamespace="...">
<xsd:complexType name="questionType">
<xsd:element name="question" type="string"/> </xsd:complexType>
<xsd:complexType name="answerType">
...
</types>
 binding
 The bindings describe the protocol that is used to access a portType, as well as the data formats for
the messages that are defined by a particular portType element.
<binding name="EightBallBinding" type="ebs:EightBall"> <soap:binding style="rpc”
transport="schemas.xmlsoap.org/soap/http">
<operation name="ebs:getAnswer">
<soap:operation soapAction="urn:EightBall"/>
<input>
<soap:body
namespace="urn:EightBall" ... />
…

WSDL
The services and ports define the location of the Web service
 Service
 The service contains the Web service name and a list of ports.
 Ports
 The ports contain the location of the Web service and the
binding used for service access.
<service name="EightBall">
<port binding="ebs:EightBallBinding" name="EightBallPort">
<soap:address
location="localhost:8080/axis/EightBall"/>
</port>
</service>

SOAP
SOAP
 SOAP is a lightweight protocol intended for exchanging structured information
in a decentralized, distributed environment. SOAP uses XML technologies to
define an extensible messaging framework, which provides a message
construct that can be exchanged over a variety of underlying protocols. The
framework has been designed to be independent of any particular
programming model and other implementation specific semantics.
 It represents the main way of communication between the three key actors in
a service oriented architecture (SOA): service provider, service requestor and
service broker. The main goal of its design is to be simple and extensible. A
SOAP message is used to request a Web service.

SOAP
 SOAP can be used over any transport protocol such as TCP, HTTP, SMTP
 This protocol consists of three parts:
 An envelope that defines a framework for describing message content and
processing instructions.
 A set of encoding rules for expressing instances of application-defined data types.
 A convention for representing remote procedure calls and responses.
 SOAP is a protocol-independent transport and can be used in combination with a
variety of protocols. In Web services SOAP is used in combination with HTTP, HTTP
extension framework and Java Message Service (JMS).
 SOAP is also operating-system independent and not tied to any programming
language or component technology.
 As long as the client can issue XML messages, it does not matter what technology
is used to implement the client. Also, both server and client sides can reside on any
suitable platform.

SOAP
SOAP Schema:
The Envelope element is always the root element of a SOAP
message. The Envelope element contains an optional Header
element, followed by a mandatory Body element.
The Body element represents the message payload. The Body
element is a generic container in that it can contain any number of
elements from any namespace. This is ultimately where the data
goes that you're trying to send.
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Header>


</soap:Header>
<soap:Body>

</soap:Body>
</soap:Envelope>

SOAP
 SOAP Request
<soap:Body>
<x:TransferFunds xmlns:x="urn:examples-org:banking">
<from>01-4-2006</from>
<to>31-04-2006</to>
<amount>100.00</amount>
</x:TransferFunds>
</soap:Body>
</soap:Envelope>
 SOAP Response
<soap:Body>
<x:TransferFundsResponse xmlns:x="urn:examples-org:banking">
<balances>
<account>
<id>22-342439</id>
<balance>33.45</balance>
</account>
</balances>
</x:TransferFundsResponse>
</soap:Body>
</soap:Envelope>

SOAP
 Fault Code
<soap:Body>
<soap:Fault>
<faultcode>soap:Server</faultcode>
<faultstring>Insufficient funds</faultstring> <detail>
<x:TransferError
xmlns:x="urn:examples-org:banking">
<sourceAccount>22- 342439</sourceAccount>
<transferAmount>
100.00</transferAmount>
<currentBalance>
89.23</currentBalance>
</x:TransferError>
</detail>
</soap:Fault>
</soap:Body>
</soap:Envelope>

UDDI
 The Universal Description, Discovery and Integration (UDDI)
define a way to publish and discover information about Web
services. The term “Web service” describes specific business
functionality exposed by a company, usually through an
Internet connection, for the purpose of providing a way for
another company or software program to use the service.
 Conceptually, the information provided in a UDDI business
registration consists of three components:
 white pages
 address, contact, and known identifiers;
 yellow pages
 industrial categorizations based on standard taxonomies;
 green pages
 the technical information about services that are exposed by
the business. Green pages include references to specifications
for Web services, as well as support for pointers to various file and
URL based discovery mechanisms if required.

Service Styles
Service Styles - RPC, Document, Wrapped, and Message
 RPC:
 RPC services are the default in Axis
 Axis will deserialize XML into Java objects which can be fed to your service, and will
serialize the returned Java object(s) from your service back into XML.
 Document
 Document services do not use any encoding (so in particular, you won't see multiref
object serialization or SOAP-style arrays on the wire) but DO still do XML<->Java
databinding
 Wrapped
 Wrapped services are just like document services, except that rather than binding
the entire SOAP body into one big structure, they "unwrap" it into individual
parameters
 Message
 Message services receive and return arbitrary XML in the SOAP Envelope without
any type mapping / data binding. If you want to work with the raw XML of the
incoming and outgoing SOAP Envelopes, write a message service
D:Program Files
j2sdk_nbnetbeans3.5to

Service Styles
 <schema targetNamespace="http://commerce.com/PO">
<complexType name="POType">
<sequence>
<element name="item" type="xsd:string"/>
<element name="quantity" type="xsd:int"/>
<element name="description" type="xsd:string"/>
</sequence>
</complexType>
<element name="PurchaseOrder" type="POType"/>
 document style service, this would map to a method like this:
 public void method(PurchaseOrder po)
In other words, the ENTIRE <PurchaseOrder> element would be handed to your method as a
single bean with three fields inside it. On the other hand,
• wrapped style service, it would map to a method like this:
 public void purchaseOrder(String item, int quantity, String description)
 Message Service
public Element [] method(Element [] bodies);
public SOAPBodyElement [] method (SOAPBodyElement [] bodies);
public Document method(Document body);
public void method(SOAPEnvelope req, SOAPEnvelope resp);

Service Styles
 Standard mappings from WSDL to Java

An Example
Axis Setup
 Axis software in the form of xml-axis-beta3-bin.zip can be downloaded from
http://archive.apache.org/dist/ws/axis/beta3
 Extract the folder from zip file to c:/xml-axis folder
 Set “%XML_AXIS% = c:/xml-axis” as environment variable
 Set classpath = %XML_AXIS%libaxis.jar; %XML_AXIS% libcommons-logging.jar;
%XML_AXIS%libjaxrpc.jar;c:xml-axisliblog4j-1.2.4.jar; %XML_AXIS%libtt-
bytecode.jar; %XML_AXIS%libwsdl4j.jar;%XML_AXIS%libxmlParserAPIs.jar;
%XML_AXIS%libsaaj.jar %JAVA_HOME%libtools.jar;
Apache Tomcat Setup
 Download Apache tomcat (jakarta-tomcat-4.1.31.exe) from
http://mirror.tomato.it/apache/jakarta/tomcat-4/v4.1.31/bin
 Set “CATALINA_HOME = C:Apache Tomcat 4.0” as environment variable
 Also set “path=%path%;CATALINA_HOMEbin”
 Add the following in server.xml (C:Apache Tomcat 4.0conf).
 <Context path="/axis" docBase="C:xml-axiswebappsaxis" debug="0"/>
 Start tomacat web server

An Example
A sample java Class
public class HelloWorld{
public String sayHello(String reader){
System.out.println("Service Called");
return "Hi " + reader + " How are you";
}
}
Steps to Expose as Web Service
 Write the following to a text file and name it as HelloWorldService.wsdd.
<?xml version="1.0" encoding="UTF-8"?>
<deployment xmlns=“http://xml.apache.org/axis/wsdd/” xmlns:java="http://xml.apache.org/axis/wsdd/providers/java">
<service name="HelloWorldService" provider="java:RPC">
<parameter name="allowedMethods" value=“sayHello"/>
<parameter name="className" value="HelloWorld"/>
</service>
</deployment>

An Example
 Use the above wsdl file to expose as web service with the following command.
 java -classpath "%classpath%;C:jarsaxis.jar;C:jarsjaxrpc.jar;C:jarscommons-
logging-1.0.3.jar;C:jarscommons-discovery-0.2.jar;C:jarsjndi.jar;C:jarssaaj.jar;."
org.apache.axis.client.AdminClient -h localhost -p 8080 -s
WebservicesTest/servlet/AxisServlet "C:HelloWorldService.wsdd“
 Test the exposed web service
 http://localhost:8080/WebservicesTest/servlet/AxisServlet
 Click on “wsdl” to view wsdl file in browser.
 Use the following command to generate wsdl file for the exposed service
 Java org.apache.axis.wsdl.Java2WSDL HelloWorld -l
http://localhost:8080/WebservicesTest/services/HelloWorldService
 Copy the wsdl file to %XML_AXIS% root
 Use the following command to generate the stubs for given wsdl file
 java org.apache.axis.wsdl.WSDL2Java C:xml-axisHelloWorldService.wsdl
 For the generated stubs write a java class to access the web service.

An Example
Java code to access the web service via stubs
import java.rmi.RemoteException;
import javax.xml.rpc.ServiceException;
public class HelloWorldStubClient {
public static void main(String[] args) {
try{
//Fetch HelloWorldService object from Service Locator generated
HelloWorldService hWorldService = new HelloWorldServiceLocator();
//Fetch actual service hosted from the service.
HelloWorld hWorld = hWorldService.getHelloWorldService();
//call the Service method
System.out.println(hWorld.sayHello("Harish"));
}catch(ServiceException sExc){
sExc.printStackTrace();
}catch(RemoteException rExc){
rExc.printStackTrace();
}
}
}

An Example
 java org.apache.axis.utils.tcpmon

Documentation
 The JAX-WS 2.0 specification demands that the exception annotated with @WebFault must
have two constructors and one method:
 WrapperException(String message, FaultBean faultInfo)
WrapperException(String message, FaultBean faultInfo, Throwable cause)
FaultBean getFaultInfo()
The WrapperException is replaced by the name of the exception, and FaultBean is replaced by
the class name that implements the fault bean. The fault bean is a Java bean that contains the
information of the fault and is used by the Web service client to know the cause for the fault.
 Sample
 @javax.xml.ws.WebFault(name="AddNumbersException",
    targetNamespace="http://server.fromjava/jaxws")
public class AddNumbersException_Exception extends Exception {
    private fromjava.client.AddNumbersException faultInfo;
    public AddNumbersException_Exception(String message, AddNumbersException faultInfo) {
        super(message);
        this.faultInfo = faultInfo;
    }
    public AddNumbersException_Exception(String message, AddNumbersException faultInfo,
                                         Throwable cause) {
        super(message, cause);
        this.faultInfo = faultInfo;
    }
    public AddNumbersException getFaultInfo() {
        return faultInfo;
    }
}

Documentation
HandlerChain
Example:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<javaee:handler-chains xmlns:javaee=http://java.sun.com/xml/ns/javaee xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<javaee:handler-chain>
<javaee:handler-chain-name>Service Framework Handlers</javaee:handler-chain-name>
<javaee:handler>
<javaee:handler-name>LoggingHandler</javaee:handler-name>
<javaee:handler-class>com.test.handlers.LoggingHandler
</javaee:handler-class>
</javaee:handler>
<javaee:handler>
<javaee:handler-name>ThrottlingHandler</javaee:handler-name>
<javaee:handler-class>com.test.handlers.ThrottlingHandler
</javaee:handler-class>
</javaee:handler>
</javaee:handler-chain>
</javaee:handler-chains>

Documentation
HandlerChain
Example:
Handler Interface
public class LoggingHandler implements
SOAPHandler<SOAPMessageContext>
public boolean handleFault(SOAPMessageContext context)
public boolean handleMessage(SOAPMessageContext context)
public Set<QName> getHeaders()

Documentation
 URLs
 http://today.java.net/pub/a/today/2006/09/19/asynchronous-jax-
ws-web-services.html
 http://java.sun.com/webservices/docs/2.0/tutorial/doc/
 http://ws.apache.org/axis/java/user-guide.html#Introduction

Java web services

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