Axis2 Integration with the Spring Framework

This document is a guide on how to use Axis2 with the Spring Framework

For users of JSON and Spring Boot - or anyone interesed in a complete Spring Boot example that includes Spring Security - see the sample application in the JSON and Spring Boot User's Guide.

Update: Spring inside the AAR is no longer supported. See this commit: 

commit 9e392c0ae1f0abab3d4956fbf4c0818c9570021e
Author: Andreas Veithen <veithen@apache.org>
Date:   Sat May 6 22:21:10 2017 +0000

    AXIS2-3919: Remove the alternate class loading mechanism:
    - It degrades performance.
    - There is no test coverage for it.
    - With r1794157 in place, in most cases, no temporary files will be created and there is no need for a fallback mechanism.

Content

Introduction

Axis2 and Spring integration takes place when Spring supplies one of its pre-loaded beans to the Axis2 Message Receiver defined in the AAR services.xml. Axis2 typically uses reflection to instantiate the ServiceClass defined in the services.xml used by the Message Receiver. Alternatively, you can define a ServiceObjectSupplier that will supply the Object.

This guide describes how to use two separate ServiceObjectSupplier classes that are a part of the Axis2 standard distribution - one for use with a ServletContext, and one without. Configuring Axis2 with a ServletContext is simpler than without, and is recommended for most use cases. Without a ServletContext, ie, Spring inside the AAR, requires an extra Spring bean and is considered an advanced use case. Once configured, the Web service itself acts like any other Spring wired bean. These Spring beans can be loaded any way desired as Axis2 has no configuration file dependencies from Spring. Spring versions 1.2.6, 1.2.8 and 2.0 have been tested, but probably any version would work as only the core functionality is required.

This guide assumes some basic knowledge of Axis2. See the User's Guide for more information.

Programming Model

From an Axis2 standpoint, two hooks are needed to be placed into the AAR services.xml - the ServiceObjectSupplier that hooks Axis2 and Spring together, and the name of the Spring bean that Axis2 will use as the service. All Message Receivers are currently supported, as would be any Message Receiver that extends org.apache.axis2.receivers.AbstractMessageReceiver .

Simple Spring Config Example

For the purpose of this example, we'll configure Spring via a WAR file's web.xml. Let's add a context-param and a listener:

<listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<context-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>/WEB-INF/applicationContext.xml</param-value>
</context-param>

Next we will show two examples of Spring's /WEB-INF/applicationContext.xml referenced in the web.xml listener - one using a ServletContext, and one without.

With a ServletContext

This example (with a ServletContext) applicationContext.xml should be familiar to any Spring user:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">

<beans>
  <!-- Axis2 Web Service, but to Spring, its just another bean that has dependencies -->
  <bean id="springAwareService" class="spring.SpringAwareService">
    <property name="myBean" ref="myBean"/>
  </bean>

  <!-- just another bean / interface with a wired implementation, that's injected by Spring
          into the Web Service -->
   <bean id="myBean" class="spring.MyBeanImpl">
     <property name="val" value="Spring, emerge thyself" />
  </bean>
</beans>

If the service is running in a Servlet Container, i.e., Axis2 will be able to get a hold of the ServletContext, the services.xml for the example would be using SpringServletContextObjectSupplier such as:

 <service name="SpringAwareService">
    <description>
        simple spring example
    </description>
    <parameter name="ServiceObjectSupplier">org.apache.axis2.extensions.spring.receivers.SpringServletContextObjectSupplier</parameter>
    <parameter name="SpringBeanName">springAwareService</parameter>
    <operation name="getValue">
        <messageReceiver class="org.apache.axis2.receivers.RawXMLINOutMessageReceiver"/>
    </operation>
</service>

While the above example uses RawXMLINOutMessageReceiver as its messageReceiver class, all Message Receivers are currently supported, as would be any Message Receiver that extends org.apache.axis2.receivers.AbstractMessageReceiver .

Without a ServletContext

In case Axis2 can't get a ServletContext, (i.e., uses a different transport or is running Axis2 inside the AAR etc,) you have the option of defining a bean that takes advantage of Spring's internal abilities (ApplicationContextAware interface, specifically) to provide an Application Context to Axis2, with a bean ref 'applicationContext' :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">

<beans>
  <!-- Configure spring to give a hook to axis2 without a ServletContext -->
  <bean id="applicationContext" 
    class="org.apache.axis2.extensions.spring.receivers.ApplicationContextHolder" />

  <!-- Axis2 Web Service, but to Spring, its just another bean that has dependencies -->
  <bean id="springAwareService"
        class="spring.SpringAwareService">
    <property name="myBean" ref="myBean" />
  </bean>

  <!-- just another bean with a wired implementation, that's injected by Spring 
          into the Web Service -->
   <bean id="myBean"
        class="spring.MyBeanImpl">
     <property name="val" value="Spring, emerge thyself" />
  </bean>
</beans>

If the service is not running in a Servlet Container, i.e., Axis2 will not be able to get a hold of ServletContext or you prefer not to, the services.xml for the example will be using SpringAppContextAwareObjectSupplier such as:

 <service name="SpringAwareService">
    <description>
        simple spring example
    </description>
    <parameter name="ServiceObjectSupplier">org.apache.axis2.extensions.spring.receivers.SpringAppContextAwareObjectSupplier</parameter>
    <parameter name="SpringBeanName">springAwareService</parameter>
    <operation name="getValue">
        <messageReceiver class="org.apache.axis2.receivers.RawXMLINOutMessageReceiver"/>
    </operation>
</service>

While the above example uses RawXMLINOutMessageReceiver as its messageReceiver class, all Message Receivers are currently supported, as would be any Message Receiver that extends org.apache.axis2.receivers.AbstractMessageReceiver .

In an environment without a ServletContext, one way you could load the applicationContext.xml file is in a place that will be run once. Upon start-up, execute the following:

import org.springframework.context.support.ClassPathXmlApplicationContext;

 public void createSpringAppCtx(ClassLoader cl)
            throws Exception {

    ClassPathXmlApplicationContext ctx = new
      ClassPathXmlApplicationContext(new String[] {Constants.MY_PATH +
      "spring/applicationContext.xml"}, false);
           ctx.setClassLoader(cl);
           ctx.refresh();
}

Putting It All Together

From here, it's just standard Axis2 coding. Only now the service has Spring wiring capabilities. The implementation is the same whether using either SpringServletContextObjectSupplier or SpringAppContextAwareObjectSupplier. The service is as follows:

package spring;

import org.apache.axiom.om.OMAbstractFactory;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMFactory;
import org.apache.axiom.om.OMNamespace;
import org.apache.axiom.om.OMText;

public class SpringAwareService {

    private MyBean myBean = null;

    //spring 'injects' this implementation
    public void setMyBean(MyBean myBean) {
            this.myBean = myBean;
    }

    // The web service
    public OMElement getValue(OMElement ignore) {
            OMFactory factory=
                OMAbstractFactory.getOMFactory();
            OMNamespace payloadNs= factory.createOMNamespace(
                "http://springExample.org/example1", "example1");
            OMElement payload =
                factory.createOMElement("string", payloadNs);
            OMText response = factory.createOMText(this.myBean.emerge());
            payload.addChild(response);
            return payload;
    }
}

For those who are new to Spring, one of the ideas is that you program an Interface, as the implementation is pluggable. This idea is referenced in the Spring config file above. Below is the interface:

package spring;

/** Interface for Spring aware Bean */
public interface MyBean {
         String emerge();
}

Here's the implementation:

/** Spring wired implementation */
public class MyBeanImpl implements MyBean {

    String str = null;
    // spring 'injects' this value
    public void setVal(String s) {
        str = s;
    }
    // web service gets this value
    public String emerge() {
        return str;
    }
}

Lastly here's the client - not really necessary for the example, other than for completeness:

package client;

import java.io.StringWriter;

import javax.xml.stream.XMLOutputFactory;

import org.apache.axiom.om.OMAbstractFactory;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMFactory;
import org.apache.axiom.om.OMNamespace;
import org.apache.axis2.addressing.EndpointReference;
import org.apache.axis2.client.Options;
import org.apache.axis2.client.ServiceClient;

public class TestClient {
    private static EndpointReference targetEPR =
        new EndpointReference(
               "http://localhost:8080/axis2/services/SpringAwareService");

    /**
     * Simple axis2 client.
     *
     * @param args Main
     */
    public static void main(String[] args) {
        try {
            OMFactory factory = OMAbstractFactory.getOMFactory();
            OMNamespace omNs = factory.createOMNamespace(
                        "http://springExample.org/example1", "example1");

            OMElement method = factory.createOMElement("getValue", omNs);
            OMElement value = factory.createOMElement("Text", omNs);
            value.addChild(factory.createOMText(value, "Some String "));
            method.addChild(value);

            ServiceClient serviceClient = new ServiceClient();

            Options options = new Options();
            serviceClient.setOptions(options);
            options.setTo(targetEPR);

            //Blocking invocation
            OMElement result = serviceClient.sendReceive(method);

            StringWriter writer = new StringWriter();
            result.serialize(XMLOutputFactory.newInstance()
                    .createXMLStreamWriter(writer));
            writer.flush();

            System.out.println("Response: " + writer.toString());
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

The examples above assume that both the spring framework .jar and the axis2-spring-*.jar are under WEB-INF/lib. In such a case, the classes shown in this tutorial need to be placed in a JAR under WEB-INF/lib. In this example the JAR layout is:

./mySpring.jar
./META-INF
./META-INF/MANIFEST.MF
./spring
./spring/MyBean.class
./spring/MyBeanImpl.class
./spring/SpringAwareService.class

Since all the user classes are in mySpring.jar in this example, the AAR merely contains the services.xml file:

./springExample.aar
./META-INF
./META-INF/MANIFEST.MF
./META-INF/services.xml

To run this example, make sure you have the axis2-spring*.jar that comes from the axis2-std-*-bin distro in the server side WEB-INF/lib, as well as the appropriate Spring jar - most will use the full spring.jar, but the minimum requirements are spring-core, spring-beans, spring-context, and spring-web. When running the client, you should see this output:

Response: <example1:string xmlns:example1="http://springExample.org/example1" 
  xmlns:tns="http://ws.apache.org/axis2">Spring, emerge thyself</example1:string>