newbie question MVC Step by step errors

[mcgyver5]

I am working throught the MVC step by step exercise and I've encountered a null pointer exception when I try to reference
getProdMan.getProducts() in the SpringTestController class (step 19). the List "products" never seems to be instantiated anywhere. My questions are:
does spring "magically" create and populate this list from the data I put in the xml file? and if so where does it do that and where am I going wrong?

Thanks!

[robh]

Can you post your configuration and an example of the problem in code please.

Thanks

Rob

[mcgyver5]

robh,

sorry to take so long to respond, I have been away.
my configuration is as follows
Tomcat 4.1 on Win2k

my problem is that the List "products" never gets instantiated or populated and so I get a null pointer exception when trying to access it in the handleRequest method of the controller.

When I put code in to instantiate and populate products, the problem goes away, but I get the impression this is supposed to be done automatically somehow and this is what I do not understand.

The Controller:

public class SpringTestController implements Controller {
    protected final Log logger = LogFactory.getLog(getClass());
    private ProductManager prodMan= new ProductManager();

    public ProductManager getProdMan() {
        return prodMan;
    }

    public void setProdMan(ProductManager prodMan) {

        this.prodMan = prodMan;
    }

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        String now = (new java.util.Date()).toString();       
        Map myModel = new HashMap();
        myModel.put("now",now);
        // the nullPointer exception happens on this line:
        myModel.put("products",this.getProdMan().getProducts());
        return new ModelAndView("hello","model",myModel);
    }
}

The Product:

public class Product implements Serializable {

    private String description;
    private Double price;

    public Double getPrice() {
        
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    public void setDescription(String s){
        description = s;
    }
    public String getDescription(){
        return description;
    }
}

Here is productManager:

public class ProductManager implements Serializable{

    private ArrayList products;

    public ArrayList getProducts() {

        return products;
    }

    public void setProducts(ArrayList products) {
        this.products = products;
    }
}

here is the SpringTest-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http&#58;//www.springframework.org/dtd/spring-beans.dtd">

<!--
- Application context definition for "springapp" DispatcherServlet.
  -->

<beans>
    <bean id="SpringTestController" class="SpringTestController"/>

    <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="mappings">
            <props>
                <prop key="/hello.htm">SpringTestController</prop>
            </props>
        </property>
    </bean>

    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="viewClass">
            <value>org.springframework.web.servlet.view.JstlView</value>

        </property>
        <property name="prefix"><value>/WEB-INF/jsp/</value></property>
        <property name="suffix"><value>.jsp</value></property>
    </bean>

    <bean id="prodMan" class="ProductManager">
        <property name="products">
            <list>
                <ref bean="product1"/>
                <ref bean="product2"/>
                <ref bean="product3"/>
            </list>
        </property>
    </bean>

    <bean id="product1" class="Product">
        <property name="description">
            <value>Lamp</value>
        </property>
    </bean>

    <bean id="product2" class="Product">
        <property name="description">
            <value>Battery</value>
        </property>
    </bean>

    <bean id="product3" class="Product">
        <property name="description">
            <value>Valve</value>
        </property>
    </bean>

    <bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource">
        <property name="basename">
            <value>messages</value>
        </property>
    </bean>

</beans>

and, just in case, web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC '-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN' 'http&#58;//java.sun.com/dtd/web-app_2_3.dtd'>

<web-app>
    <servlet>
        <servlet-name>SpringTest</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>SpringTest</servlet-name>
        <url-pattern>*.htm</url-pattern>
    </servlet-mapping>

    <welcome-file-list>
        <welcome-file>
      index.jsp
        </welcome-file>
    </welcome-file-list>
</web-app>

[keller]

Looks like you forgot to inject your Product Manager into your controller. This is why you are gettting an NPE.

Replace this:

<bean id="SpringTestController" class="SpringTestController"/>

With this:

<bean id="SpringTestController" class="SpringTestController">
  <property name="prodMan"><ref bean="prodMan"/></property>
</bean>

And you should be good to go.


Keller

[mcgyver5]

Fabulous! It is working now. I must have checked that 6 times and I still messed it up when copying.