Java and Spring development

Introduction

This tutorial demonstrates how to develop a web service with Spring WS. It’s a contract first web service that uses JAXB for the binding. The focus area is how to configure and use Spring WS. Details about how to create an XSD schema and JAXB classes are explained in this tutorial.

I will also briefly show exception handling and validation support in relation to SOAP faults. But first some words about the contract first part.

Generate an XSD schema and JAXB classes

The sample XML request document that I will create an XSD schema from:

<accountBalanceRequest number="123456789" name="Bob" />

And the corresponding response document:

<accountBalanceResponse balance="100.50" number="1234567890" time="2009-05-30T09:30:10.5" />

After some tweaking, the XSD schema looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
	elementFormDefault="qualified"
	targetNamespace="http://www.redpill-linpro.com/account-balance-service"
	xmlns:a="http://www.redpill-linpro.com/account-balance-service">

	<xs:element name="accountBalanceRequest">
		<xs:complexType>
			<xs:attribute name="name" use="required" type="xs:string" />
			<xs:attribute name="number" use="required">
				<xs:simpleType>
					<xs:restriction base="xs:string">
						<xs:pattern value="\d{10}" />
					</xs:restriction>
				</xs:simpleType>
			</xs:attribute>
		</xs:complexType>
	</xs:element>

	<xs:element name="accountBalanceResponse">
		<xs:complexType>
			<xs:attribute name="balance" use="required" type="xs:decimal" />
			dateTime" />
		</xs:complexType>
	</xs:element>

</xs:schema>

After I have generated the JAXB classes, the source folder containing generated classes looks like this:

Now I have created the data contract part of the WSDL and generated the data binding classes used to parse the Java object to XML. Then its time to understand how Spring WS works.

The basics with Spring WS

You don’t need to create a WSDL file with Spring WS. The WSDL file is generated from one or more XSD schemas and some few Spring configuration beans. Spring WS solves the rest with naming patterns.

The request element must end with Request and the response element must end with Response. The same applies to Fault elements. The WSDL operation will be the element names except the Request/Response part. Here is the generated WSDL operation:

<wsdl:operation name="accountBalance">
 <wsdl:input message="tns:accountBalanceRequest" name="accountBalanceRequest">
 </wsdl:input>
 <wsdl:output message="tns:accountBalanceResponse" name="accountBalanceResponse">
 </wsdl:output>
</wsdl:operation>

The server code isn’t aware of the WSDL. This is a different approach than for example CXF that generates an interface your implementation must implement. The server implementation only has dependencies to the JAXB generated request and response classes. Spring WS finds the implementing method of a WSDL operation with annotations on the service class.

Server implementation

This tutorial contains one stub implementation. The implementation returns the same response every time except if the account number starts with 9. Then it throws a runtime exception. More about exception handling later. The implementation class must have the Spring @Endpoint annotation above the class name and the @PayloadRoot annotation above the method that will handle the web service request. The @PayloadRoot annotation must know the XSD schema namespace and the name of the request element specified in the XSD schema. See the highlighted lines in this stub implementation:

@Endpoint
public class AccountBalanceServiceStub {

	@PayloadRoot(namespace="http://www.redpill-linpro.com/account-balance-service",
			localPart="accountBalanceRequest")
	public AccountBalanceResponse findAccountBalance(
			AccountBalanceRequest accountBalanceRequest) {
		final AccountBalanceResponse response;

		if(isRequestValid(accountBalanceRequest)) {
			response = createDummyResponse();
		} else {
			throw new AccountNumberNotFoundException(
					"Account number " + accountBalanceRequest.getNumber() + " not valid.");
		}

		return response;
	}

	private AccountBalanceResponse createDummyResponse() {
		AccountBalanceResponse response = new ObjectFactory()
			.createAccountBalanceResponse();

		response.setBalance(BigDecimal.valueOf(100.50));
		response.setTime(XMLGregorianCalendarImpl.createDateTime(2010, 4, 4, 12, 0, 0));
		return response;
	}

	private boolean isRequestValid(final AccountBalanceRequest accountBalanceRequest) {
		final boolean valid;

		if(accountBalanceRequest.getNumber().startsWith("9")) {
			valid = false;
		} else {
			valid = true;
		}

		return valid;
	}
}

The @Endpoint annotation is a specialization of the @Component annotation. All beans marked with @Component can be found with a componet scan element in the Spring configuration.

<context:component-scan base-package="com.redpill.linpro" />

Another alternative for those that prefer to define their Spring beans explicitly:

<bean class="com.redpill.linpro.transport.account.ws.AccountBalanceServiceStub" />

Spring WS needs an implementation of the EndpointMapping interface like this:

<bean class="org.springframework.ws.server.endpoint.mapping
	.PayloadRootAnnotationMethodEndpointMapping" />

Since the stub implementation uses JAXB classes as input parameter and return type, the Spring configuration must also include these two beans for parsing XML:

<oxm:jaxb2-marshaller id="marshaller"
	contextPath="com.redpill.linpro.ws.account.balance.service" />

<bean class="org.springframework.ws.server.endpoint.adapter
	.GenericMarshallingMethodEndpointAdapter">

	<constructor-arg ref="marshaller" />
</bean>

Exception handling and SoapFault

If something unexpected occurs on the server, it’s best practice with modern programming languages to throw exceptions. The SOAP specification supports SOAP faults and with a framework like Spring WS, these SOAP faults are converted into runtime exceptions of type SoapFaultException. An example of an SOAP fault captured with an TCP/IP monitor:

<SOAP-ENV:Body>
	<SOAP-ENV:Fault>
		<faultcode>SOAP-ENV:Client</faultcode>
		<faultstring xml:lang="en">Account number 9998765432 not valid.
	</SOAP-ENV:Fault>
</SOAP-ENV:Body>

The SOAP fault above is the result of throwing an AccountNotFoundException.

It’s several ways to configure Spring WS to convert an exception into a SOAP fault element, but I will only demonstrate how to do it with annotations. If you’re interested, see the reference documentation for more information about the mapping alternative.

The @SoapFault annotation below helps the exception resolver to convert the exception to a SoapFault. Ant the FaultCode enum will be mapped to a fault-code element.

@SoapFault(faultCode = FaultCode.CLIENT)
public class AccountNumberNotFoundException extends RuntimeException {

	public AccountNumberNotFoundException(String message) {
		super(message);
	}
}

The exception resolver bean that converts all the exceptions marked with @SoapFault annotation:

<bean class="org.springframework.ws.soap.server.endpoint
	.SoapFaultAnnotationExceptionResolver" />

A good web service client framework should convert a SOAP fault element to an exception and throw it to the client as a runtime exception. Below is a stacktrace printed from a caught SoapFaultClientException on the client-side:

org.springframework.ws.soap.client.SoapFaultClientException: Account number 9998765432 not valid.
	at org.springframework.ws.soap.client.core.SoapFaultMessageResolver.resolveFault(SoapFaultMessageResolver.java:37)
	at org.springframework.ws.client.core.WebServiceTemplate.handleFault(WebServiceTemplate.java:738)
	at org.springframework.ws.client.core.WebServiceTemplate.doSendAndReceive(WebServiceTemplate.java:564)
	at org.springframework.ws.client.core.WebServiceTemplate.sendAndReceive(WebServiceTemplate.java:502)
	at org.springframework.ws.client.core.WebServiceTemplate.marshalSendAndReceive(WebServiceTemplate.java:351)
       ....

The SOAP specification supports five fault-codes and it’s easy to configure in the @SoapFault annotation.

Validating

To enable validating, you have to add a PayloadValidatingInterceptor and reference to that interceptor from the interceptor list in the PayloadRootAnnotationMethodEndpointMapping.

<bean
	class="org.springframework.ws.server.endpoint.mapping.PayloadRootAnnotationMethodEndpointMapping">
	<property name="interceptors">
		<list>
			<ref local="validatingInterceptor" />
		</list>
	</property>
</bean>

<bean
	class="org.springframework.ws.soap.server.endpoint.SoapFaultAnnotationExceptionResolver" />

<bean id="validatingInterceptor"
	class="org.springframework.ws.soap.server.endpoint.interceptor.PayloadValidatingInterceptor">
	<property name="schema" value="/WEB-INF/schemas/account-balance-service.xsd" />
	<property name="validateRequest" value="true" />
	<property name="validateResponse" value="true" />
</bean>

If you’re not specifying the validate parameters above, only the request will be validated by default.

An example of a SOAP fault returned from the server with a request containing an account number with more than ten digits:

<SOAP-ENV:Fault>
	<faultcode>SOAP-ENV:Client</faultcode>
	<faultstring xml:lang="en">Validation error</faultstring>
	<detail>
		ValidationError xmlns:spring-ws="http://springframework.org/spring-ws">
                        cvc-pattern-valid:
			Value '0987654321000000000000000000000000000' is not facet-valid with
			respect to pattern '\d{10}' for type
			'#AnonType_numberaccountBalanceRequest'.
			</spring-ws:ValidationError>
		<spring-ws:ValidationError xmlns:spring-ws="http://springframework.org/spring-ws">
                        cvc-attribute.3:
			The value '0987654321000000000000000000000000000' of attribute 'number' on
			element 'ns2:accountBalanceRequest' is not valid with respect to
			its type, 'null'.</spring-ws:ValidationError>
	</detail>
</SOAP-ENV:Fault>

As you can see, validating doesn’t require any code changes. It’s just to add an interceptor in the configuration. The same can be done in other areas like security.

WSDL specific configuration

Spring WS generates the WSDL document on runtime. Since the generating is based on naming patterns as described in the basic chapter earlier in this tutorial, all you need to specify is the schema, the name of the port type and the URI. You can specify a full URI, but since the dispatcher servlet already knows the application’s URI, it’s sufficient to only add the relative URI.

The WSDL definition Spring bean used in this tutorial:

<bean name="accountBalanceServiceDefinition"
	class="org.springframework.ws.wsdl.wsdl11.DefaultWsdl11Definition">
	<property name="schema">
		<bean class="org.springframework.xml.xsd.SimpleXsdSchema">
			<property name="xsd"
				value="/WEB-INF/schemas/account-balance-service.xsd" />
		</bean>
	</property>
	<property name="portTypeName" value="AccountBalanceService" />
	<property name="locationUri" value="/account-balance-service" />
</bean>

The WSDL file this bean generates is available if you click on the link below:

<wsdl:definitions
	targetNamespace="http://www.redpill-linpro.com/account-balance-service">

	<wsdl:types>
		<xs:schema elementFormDefault="qualified"
			targetNamespace="http://www.redpill-linpro.com/account-balance-service">

			<xs:element name="accountBalanceRequest">
				<xs:complexType>
					<xs:attribute name="name" type="xs:string" use="required" />
					<xs:attribute name="number" use="required">
						<xs:simpleType>
							<xs:restriction base="xs:string">
								<xs:pattern value="\d{10}" />
							</xs:restriction>
						</xs:simpleType>
					</xs:attribute>
				</xs:complexType>
			</xs:element>

			<xs:element name="accountBalanceResponse">
				<xs:complexType>
					<xs:attribute name="balance" type="xs:decimal" use="required" />
					<xs:attribute name="time" type="xs:dateTime" use="required" />
				</xs:complexType>
			</xs:element>
		</xs:schema>
	</wsdl:types>

	<wsdl:message name="accountBalanceRequest">
		<wsdl:part element="tns:accountBalanceRequest" name="accountBalanceRequest">
		</wsdl:part>
	</wsdl:message>

	<wsdl:message name="accountBalanceResponse">
		<wsdl:part element="tns:accountBalanceResponse" name="accountBalanceResponse">
		</wsdl:part>
	</wsdl:message>

	portType name="AccountBalanceService">
		<wsdl:operation name="accountBalance">
			<wsdl:input message="tns:accountBalanceRequest" name="accountBalanceRequest">
			</wsdl:input>
			<wsdl:output message="tns:accountBalanceResponse" name="accountBalanceResponse">
			</wsdl:output>
		</wsdl:operation>
	</wsdl:portType>

	AccountBalanceServiceSoap11" type="tns:AccountBalanceService">
		<soap:binding style="document"
			transport="http://schemas.xmlsoap.org/soap/http" />

		<wsdl:operation name="accountBalance">
			soapAction="" />
			<wsdl:input name="accountBalanceRequest">
				<soap:body use="literal" />
			</wsdl:input>
			<wsdl:output name="accountBalanceResponse">
				<soap:body use="literal" />
			</wsdl:output>
		</wsdl:operation>
	</wsdl:binding>

	<wsdl:service name="AccountBalanceServiceService">
		<wsdl:port binding="tns:AccountBalanceServiceSoap11" name="AccountBalanceServiceSoap11">
			<soap:address location="/account-balance-service" />
		</wsdl:port>
	</wsdl:service>
</wsdl:definitions>

The URL to the WSDL file can be found with this pattern: URL to the servlet + DefaultWsdl11Definition bean name + .wsdl. In my case it’s available here: http://localhost:8081/ws-demo/account-balance-service/accountBalanceServiceDefinition.wsdl

Servlet configuration

The web.xml file must configure the Spring WS servlet to be of type MessageDispatcherServlet.

<servlet-name>account-balance-service</servlet-name>
	<servlet-class>org.springframework.ws.transport.http.MessageDispatcherServlet</servlet-class>
	<init-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>/WEB-INF/spring/account-balance-service-ws-config.xml</param-value>
	</init-param>
</servlet>

This servlet has its own Spring context with all the web service logic.

It’s a good practice to separate the servlet specific Spring configuration from the business and integration logic. Since this tutorial only contains a stub implementation, this application doesn’t have any business layer. With a normal application, the web.xml file should also contain these two elements:

<pre><context-param>
	<param-name>contextConfigLocation</param-name>
	classpath:config.xml
</context-param>

<listener>
	<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

The config.xml file in this tutorial is just a dummy file with none Spring beans. If you have many separate Spring configuration files, then you can add them all in the param-value element separated with a comma.

Finally, you have to add mapping elements before the dispatcher servlet will work as expected.

<servlet-mapping>
	<servlet-name>account-balance-service</servlet-name>
	<url-pattern>/account-balance-service/*</url-pattern>
</servlet-mapping>

<mime-mapping>
	<extension>wsdl</extension>
	<mime-type>text/xml</mime-type>
</mime-mapping>

<mime-mapping>
	<extension>xsd</extension>
	<mime-type>text/xml</mime-type>
</mime-mapping>

Click on the show source link below if you want to see the whole web.xml file.

<?xml version="1.0" encoding="ISO-8859-1"?>
xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
	version="2.4">

	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>classpath:config.xml</param-value>
	</context-param>

	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>

	<servlet>
		<servlet-name>account-balance-service</servlet-name>
		<servlet-class>org.springframework.ws.transport.http.MessageDispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>/WEB-INF/spring/account-balance-service-ws-config.xml</param-value>
		</init-param>
	</servlet>

	<servlet-mapping>
		<servlet-name>account-balance-service</servlet-name>
		<url-pattern>/account-balance-service/*</url-pattern>
	</servlet-mapping>

	<mime-mapping>
		<extension>wsdl</extension>
		<mime-type>text/xml</mime-type>
	</mime-mapping>

	<mime-mapping>
		<extension>xsd</extension>
		<mime-type>text/xml</mime-type>
	</mime-mapping>

</web-app>

The important beans in the Spring servlet configuration file is already described earlier in this tutorial, but the link below shows all the beans.

<?xml version="1.0" encoding="UTF-8"?>
xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:oxm="http://www.springframework.org/schema/oxm"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/oxm
	http://www.springframework.org/schema/oxm/spring-oxm-3.0.xsd
		http://www.springframework.org/schema/beans
		http://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/context
		http://www.springframework.org/schema/context/spring-context-3.0.xsd">

	<oxm:jaxb2-marshaller id="marshaller"
		contextPath="com.redpill.linpro.ws.account.balance.service" />

	<bean class="org.springframework.ws.server.endpoint.adapter.GenericMarshallingMethodEndpointAdapter">
		<constructor-arg ref="marshaller" />
	</bean>

	<bean
		class="org.springframework.ws.server.endpoint.mapping
		.PayloadRootAnnotationMethodEndpointMapping">
		<property name="interceptors">
			<list>
				<ref local="validatingInterceptor" />
			</list>
		</property>
	</bean>

	<bean class="org.springframework.ws.soap.server.endpoint.SoapFaultAnnotationExceptionResolver" />

	<bean id="validatingInterceptor"
		class="org.springframework.ws.soap.server.endpoint.interceptor.PayloadValidatingInterceptor">
		<property name="schema" value="/WEB-INF/schemas/account-balance-service.xsd" />
		<property name="validateRequest" value="true" />
		<property name="validateResponse" value="true" />
	</bean>

	<bean name="accountBalanceServiceDefinition"
		class="org.springframework.ws.wsdl.wsdl11.DefaultWsdl11Definition">
		<property name="schema">
			<bean class="org.springframework.xml.xsd.SimpleXsdSchema">
				<property name="xsd"
					value="/WEB-INF/schemas/account-balance-service.xsd" />
			</bean>
		</property>
		<property name="portTypeName" value="AccountBalanceService" />
		<property name="locationUri" value="/account-balance-service" />
	</bean>

	<context:component-scan base-package="com.redpill.linpro" />

</beans>

Summary

Spring WS is a lightweight web service alternative that takes care of the WSDL for you. It’s the easiest framework I have tried and should be a good framework in most situations. If you like to generate the service interfaces in addition to the transfer objects, you should consider CXF that’s another great alternative, else give this one a chance.

I have never been a huge fan of WSDL files and an alternative that handles all the plumbing for me is very nice. That enables faster development without loosing control over the data being exhanged with the client.

The code used in this article was developed in my work time at Redpill Linpro. It can be downloaded here