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Implementing Web Services: A Comprehensive Guide

Learn about creating, publishing, locating, and invoking web services, implementing JAX-RPC services, and configuring clients and endpoints in Java.

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Implementing Web Services: A Comprehensive Guide

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  1. Web Services Broker UDDI based Registry Services Web Services requester Service delivery -SOAP Clients Web Services Provider Service container -SOAP Interfaces -WSDL Descriptions 3. Implementing Web Services General Approach 3.Stores service descriptions as binding templates&URL 2.Register/publish services 4.Locates services and its binding info 5.Invoke & obtain WSDL 6.Exchange data using SOAP RPC/Messaging A Web service can be created as a new application or from using an existing application by re-purposing them as services. 1.Create SOAP proxy interfaces and WSDL based service descriptions 1

  2. XML schema compiling Java class Java class Conforms to Instance Of marshalling unmarshalling <xml> <> </> </xml> Java Object Java Object XML document Web Services Support in J2EE Java Architecture for XML Binding (JAXB) provides Application developers with a way to generate programming objects based on XML definitions and vice versa, more specifically: -Marshalling: converting a Java object tree into an XML document. -Unmarshalling: converting an XML document into a Java object tree. -Validation: checking an XML document for conformance with a DTD. 2

  3. 3. Soap/http request 4. Soap/http response Application server -JAX-RPC runtime -JAX-RPC API -Service endpoint Client 2. Return information 1. Lookup service UDDI Sender Application Receiver Application JAXM API JAXM API JAXM Messaging Provider JAXM Messaging Provider SOAP message HTTP HTTP Java provides the Java API for XML Remote Procedure Calls (JAX-RPC) -Set of high-level Java APIs enabling XML-based Java applications to interoperate using RPC. -Used for synchronous communications Java provides the Java API for XML Messaging (JAXM) -Lightweight XML messaging API for application-to-application (A2A) integration and business-to- business (B2B) communication. -Support asynchronous communications 3

  4. JWSDP Environment J2SE Environment WSDL JAX-RPC Client Invocation Stubs/Dynamic Proxy/DII JAX-RPC Runtime JAX-RPC-based Service TIES JAX-RPC Runtime Request/Response Soap over HTTP JAX-RPC Application Architecture -A typical JAX-RPC application architecture model involves: • JAX-RPC Service: Java business component (e.g. servlet, bean). • JAX-RPC Service client: access exposed Web service. • Serialization/Deserialization:Java-to-XML and XML-to-Java mappings • JAX-RPC Runtime Environment: runtime mechanisms and execution environment for the Web services and service clients. 4

  5. JAX-RPC-based Service Implementation -JAX-RPC services can be implemented using Java classes ( RMI) or by using a WSDL document. Developing a JAX-RPC Service from Java Classes -The key steps include the following: • Define the Remote interface (Service Definition). • Implement the remote interface (Service Implementation). • Configure the Service. • Generate the Stubs and ties. • Package and deploy the service. Developing a JAX-RPC-based Service from a WSDL Document -This consists of developing a JAX-RPC-based service using a WSDL document exposed by an existing Web services environment. -The key steps include the following: • Create a service configuration referring to the WSDL. • Generate the client-side stubs and server-side ties. • Package and deploy the service. 5

  6. JAX-RPC Client Implementation • Can be implemented either as stub-based or dynamic proxy-based or dynamic invocation interface based. Stub-based Client -Uses the local stub classes generated (automatically) from the WSDL file. Dynamic Proxy-based Client -Enables the invocation of a target service endpoint dynamically at runtime, without requiring a local stub class. Dynamic Invocation Interface (DII) Client -Enables the client to discover and invoke target services dynamically at runtime. -The client uses a set of operations and parameters, and a search criterion to discover the target service. Hence a client can invoke a service and its methods without knowing in advance its data types. 6

  7. 4. Sample Implementation SOA for Sample Implementation <<participant>> StockClient <<request>> client: StockTrader <<participant>> StockBroker <<service>> broker: StockTrader <<interface>> StockTrader getStockQuote(index:int): double 7

  8. Web Service Implementation Service Definition import java.rmi.*; public interface StockTrader extends java.rmi.Remote { public double getStockQuote(int id) throws java.rmi.RemoteException; } Service Implementation import java.rmi.*; public class StockTraderImpl implements StockTrader { public double getStockQuote(int id) { return ((new Quote(id)).getValue()); } } 8

  9. Configuring the Service -Service configuration requires creating a configuration file in an XML format that provides the following information: The name of the service. The name of the package containing the stubs and ties. The target namespace for the generated WSDL and its XML schema and class names of the remote interface and its implementation. -Sample configuration file: serviceconfig.xml <?xml version=“1.0” encoding=“UTF-8”?> <configuration xmlns=http://java.sun.com/xml/ns/jax-rpc/ri/config> <service name=“StockTrader” targetNamespace=http://www.binkadi.com/jws/wsdl typeNamespace=http://www.binkadi.com/jws/types packageName=“com.binkadi.jws.stock.jaxrpc”> <interface name=“jws.binkadi.jaxrpc.StockTrader” servantName=“jws.binkadi.jaxrpc.StockTraderImpl”/> </service> </configuration> 9

  10. JAX-RPC Client-Side APIs (javax.xml.rpc) -There are just a few key classes and interfaces that are needed to write Web service clients or service implementations: · Serviceinterface: A factory for stubs or dynamic invocation/proxy objects that are used to actually invoke methods · ServiceFactory class: A factory for Services · Callinterface: Used for dynamic invocation · Stub interface: Base interface for stubs 10

  11. Usage for Dynamic Invocation: • The client creates a ServiceFactory • From the ServiceFactory, the client instantiates a Service ServiceFactory sFactory = ServiceFactory.newInstance(); Service service = serviceFactory.createService(new Qname(qService)); - The Service is a factory object that creates the port. The port is a remote interface (java.rmi.Remote) into the Web service. - In the case of dynamic RPC, the Service object is used to create Call objects, which specify which method to call on the Web services port. Call call = service.createCall(target_port); call.setTargetEndpointAddress(target_endpoint); call.setOperationName(newQname(BODY_NAMESPACE_VALUE,”getStockPrice”)); 11

  12. Creating and running an RPC-style Web service client • Obtain the interface details of the Web service you want to invoke. · by getting a WSDL file that describes the Web service 2. Optionally generate Web service client invocation code (stubs). · This step is optional as there is usually a dynamic invocation API available where a stub is not required to invoke a Web service. 3. Write the client. · Static call: create or obtain a reference to a stub object and then call its Web service-exposed methods. · Dynamic call: create a call object and invoke a method on the web service (a stub is not required). 4. Run the client. · To run the client, your Web service runtime's client code will need to be in your classpath. 12

  13. Stub-based Client -Uses the local stub classes generated by the WSDL compiler. //import the Stub interface import javax.xml.rpc.Stub; public class StockClient { public static void main(String[] args) { try { //obtain the instance of Stub interface StockTrader_Stub stub = (StockTrader_Stub) (new StockTrader_Impl().getStockTraderPort()); //Configure the stub setting required properties stub._setProperty(javax.xml.rpc.Stub.ENDPOINT_ADDRESS_PROPERTY, http://www.binkadi.com/jws/jaxrpc/stocktrader); //Execute the remote method System.out.println(stub.getStockQuote(1233465)); } catch (Exception ex) { ex.printStackTrace(); } } } 13

  14. Dynamic Web service client 1. Import the needed classes: import javax.xml.namespace.QName; import javax.xml.rpc.Call; import javax.xml.rpc.Service; 2. Create a Service object: Service service = (Service) Class.forName("org.apache.axis.client.Service").newInstance(); 3. Use the Service to create the call object: Call call = (Call) service.createCall(); 4. Set the URL location of the Service: String endpoint ="http://localhost:6080/SimpleRPC/services/StockTrader"; call.setTargetEndpointAddress(endpoint); 5. Invoke the call object: Object [] arguments = new Object[0]; String stockId = (String) call.invoke(arguments); 14

  15. Example: import javax.xml.namespace.QName; import javax.xml.rpc.Call; import javax.xml.rpc.Service; public class StockClient { public static void main(String[] args) throws Exception{ String endpoint = "http://localhost:6080/SimpleRPC/services/StockTader"; String namespaceURI = "http://server.simplerpc.stock.lpc"; Service service = (Service) Class.forName("org.apache.axis.client.Service").newInstance(); Call call = (Call) service.createCall(); call.setTargetEndpointAddress(endpoint); call.setOperationName(new QName(namespaceURI,"getQuote")); Object [] arguments = new Object[0]; String quote = (String) call.invoke(arguments); System.out.println(“Stock quote: " + quote); } } 15

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