Spring Beans and Dependency Injection - Part 5

Using the Spring Beans.

We will create ShopServlet and CheckoutServlet so we can play with the Spring Beans we just created from a browser.

First, let us create a utility class to load the Spring Beans.

In your /src/org/confucius folder, create a class SpringUtils.java, like this:

 package org.confucius;  
   
 import org.springframework.context.ApplicationContext;  
 import org.springframework.context.support.ClassPathXmlApplicationContext;  
   
 public class SpringUtils {  
      private static ApplicationContext springContext = null;  
        
      public static ApplicationContext getSpringContext() {  
           if (springContext == null){  
                springContext = new ClassPathXmlApplicationContext("spring-beans.xml");  
           }  
             
           return springContext;  
      }  
        
 }  

This method loads the Spring Context exactly once, from the spring-beans.xml file.

Now, in your /src/org/confucius, create a Class ShopServlet.java, like this:

 package org.confucius;  
   
 import java.io.IOException;  
   
 import javax.servlet.ServletException;  
 import javax.servlet.http.HttpServlet;  
 import javax.servlet.http.HttpServletRequest;  
 import javax.servlet.http.HttpServletResponse;  
   
 public class ShopServlet extends HttpServlet {  
        
      public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
           Shop shop = (Shop) SpringUtils.getSpringContext().getBean("shop");  
           Cart cart = shop.getCart();  
             
           int numItems = cart.getNumItems();  
           cart.setNumItems(numItems+1);  
             
           response.getWriter().write("Number of items in shopping cart = " + cart.getNumItems());  
             
      }  
             
 }  
   

This Servlet gets the shop bean and increments the items in its cart.

Now in your /src/org/confucius, create a class CheckoutServlet.java, like this:

 package org.confucius;  
   
 import java.io.IOException;  
   
 import javax.servlet.ServletException;  
 import javax.servlet.http.HttpServlet;  
 import javax.servlet.http.HttpServletRequest;  
 import javax.servlet.http.HttpServletResponse;  
   
 public class CheckoutServlet extends HttpServlet {  
        
      public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
           Checkout checkout = (Checkout) SpringUtils.getSpringContext().getBean("checkout");  
           Cart cart = checkout.getCart();  
             
           response.getWriter().write("Number of items in checkout cart = " + cart.getNumItems());  
             
      }  
             
 }  
   

This Servlet get the checkout bean and prints the number of items in its cart.


Update your web.xml to use these Servlets, like this:

 <web-app>   
  <servlet>  
   <servlet-name>shop</servlet-name>  
   <servlet-class>org.confucius.ShopServlet</servlet-class>  
  </servlet>  
    
  <servlet>  
   <servlet-name>checkout</servlet-name>  
   <servlet-class>org.confucius.CheckoutServlet</servlet-class>  
  </servlet>  
    
  <servlet-mapping>  
     <servlet-name>shop</servlet-name>  
     <url-pattern>/shop</url-pattern>  
  </servlet-mapping>  
    
  <servlet-mapping>  
     <servlet-name>checkout</servlet-name>  
     <url-pattern>/checkout</url-pattern>  
  </servlet-mapping>  
    
 </web-app>