[SOLVED] Using HttpInvokerServiceExporter giving 500 error code

I am struggling for last two days to expose a service using HttpInvokerServiceExporter. The error says Did not receive successful HTTP response The complete stack trace is below for details. The code is checked in Git repo. Link is - Github link

org.springframework.remoting.RemoteAccessException: Could not access HTTP invoker remote service at [http://localhost:8080/spring-remoting/AccountService]; nested exception is java.io.IOException: Did not receive successful HTTP response: status code = 500, status message = [Internal Server Error]
org.springframework.remoting.httpinvoker.HttpInvokerClientInterceptor.convertHttpInvokerAccessException(HttpInvokerClientInterceptor.java:216)
org.springframework.remoting.httpinvoker.HttpInvokerClientInterceptor.invoke(HttpInvokerClientInterceptor.java:147)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
com.sun.proxy.$Proxy8.add(Unknown Source)
com.remoting.ClientInvoker.getCube(ClientInvoker.java:9)
org.apache.jsp.process_jsp._jspService(process_jsp.java:118)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

java.io.IOException: Did not receive successful HTTP response: status code = 500, status message = [Internal Server Error]
org.springframework.remoting.httpinvoker.SimpleHttpInvokerRequestExecutor.validateResponse(SimpleHttpInvokerRequestExecutor.java:185)
org.springframework.remoting.httpinvoker.SimpleHttpInvokerRequestExecutor.doExecuteRequest(SimpleHttpInvokerRequestExecutor.java:92)
org.springframework.remoting.httpinvoker.AbstractHttpInvokerRequestExecutor.executeRequest(AbstractHttpInvokerRequestExecutor.java:138)
org.springframework.remoting.httpinvoker.HttpInvokerClientInterceptor.executeRequest(HttpInvokerClientInterceptor.java:194)
org.springframework.remoting.httpinvoker.HttpInvokerClientInterceptor.executeRequest(HttpInvokerClientInterceptor.java:176)
org.springframework.remoting.httpinvoker.HttpInvokerClientInterceptor.invoke(HttpInvokerClientInterceptor.java:144)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
com.sun.proxy.$Proxy8.add(Unknown Source)
com.remoting.ClientInvoker.getCube(ClientInvoker.java:9)
org.apache.jsp.process_jsp._jspService(process_jsp.java:118)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

I have followed the documentation properly and have implemented all the steps. Below is the service interface:

package com.remoting;

public interface AccountService {
    public int add(int a, int b);
}

Then the service implementation

package com.remoting;
public class AccountServiceImpl implements AccountService {
    @Override
    public int add(int a, int b) {
        return a + b;
    }
}

Then the web.xml

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1">
    <display-name>spring-remoting</display-name>

<!-- The front controller of this Spring Web application, responsible for 
    handling all application requests -->
    <servlet>
        <servlet-name>accountExporter</servlet-name>
        <servlet-class>org.springframework.web.context.support.HttpRequestHandlerServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>accountExporter</servlet-name>
        <url-pattern>/AccountService</url-pattern>
    </servlet-mapping>
</web-app>

Then the application beans. The application beans are placed in applicationContext.xml and is inside the /WEB-INF/classes directory:

 <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.0.xsd">

<bean id="accountService" class="com.remoting.AccountServiceImpl"></bean>

<bean name="accountExporter"
    class="org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter">
    <property name="service" ref="accountService" />
    <property name="serviceInterface" value="com.remoting.AccountService" />
</bean>
<bean id="httpServer"
    class="org.springframework.remoting.httpinvoker.HttpInvokerProxyFactoryBean">
    <property name="serviceUrl" value="http://localhost:8080/spring-remoting/AccountService"></property>
    <property name="serviceInterface" value="com.remoting.AccountService"></property>
    </bean>

</beans>

Now to invoke the service I have two jsp files and a helper class to load the beans and invoke the function:

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Insert title here</title>
  </head>
  <body>
    <form action="process.jsp">
    Enter Number:<input type="text" name="number" /> <input type="submit"
        value="cube" />
    </form>
  </body>
</html>

process.jsp

<jsp:include page="index.jsp"></jsp:include>  
<hr/>  
<%@page import="com.remoting.ClientInvoker"%>  

<%  
  int number=Integer.parseInt(request.getParameter("number"));  
  out.print("sum of "+number+" is: "+ClientInvoker.sum(number));  
%>

Finally the ClientInvoker class

package com.remoting;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;  

public class ClientInvoker {  
    public static int sum(int number){  
        ApplicationContext context = new      ClassPathXmlApplicationContext("classpath:applicationContext.xml");  
        AccountService service = (AccountService)context.getBean("httpServer");  
        return service.add(4, 4);  
    }  
}

The applicationContext.xml is placed inside the /WEB-INF/classes directory.

Please let me know where I am going wrong.