In my last entry, I modified my Maven project so it can be deployed to Google App Engine. This time, I’m going to work on my actual application so I can finally have something to show to other people.
Right now, my Spring web application works fine on Google App Engine. Let me go over the code that I have so far. I first made a bean called Manufacturer:
package com.jenanderic.domain;
public class Manufacturer {
private int id;
private String name;
private String address;
// Constructors
// Getters and Setters
}
Next, I made an implementation class of a service interface for the bean that I just made:
package com.jenanderic.service;
// Imports
public class ManufacturerServiceImpl implements ManufacturerService {
@Autowired
private List<Manufacturer> manufacturers;
// Getters and Setters
}
I made it autowired so Spring will do the injection for me. I then made the controller to handle the requests:
package com.jenanderic.web;
// Imports
@Controller
@RequestMapping("/manufacturer")
public class ManufacturerController {
private ManufacturerService manufacturerService;
@Autowired
public void setManufacturerService(ManufacturerService manufacturerService) {
this.manufacturerService = manufacturerService;
}
@RequestMapping(method = RequestMethod.GET)
public String getManufacturerList(Model model) {
model.addAttribute("manufacturers", manufacturerService.getAllManufacturers());
return "manufacturer_list";
}
}
Then, I made the template page since the controller returns a page called manufacturer_list.jsp:
<%@ include file="/WEB-INF/jsp/include.jsp" %>
<html>
<head>
<title><spring:message code="manufacturer.title" /></title>
</head>
<body>
<h2><spring:message code="manufacturer.heading" /></h2>
<c:forEach items="${manufacturers}" var="manufacturer">
<p><c:out value="${manufacturer.id}"/> -
<c:out value="${manufacturer.name}"/> - <c:out value="${manufacturer.address}"/></p>
</c:forEach>
</body>
</html>
Now that everything’s almost done, it’s time to make an actual bean to inject into the controller. I placed it in the Application’s context:
<?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:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<bean id="manufacturerService" class="com.jenanderic.service.ManufacturerServiceImpl">
<property name="manufacturers">
<list>
<ref local="manufacturer1" />
<ref local="manufacturer2" />
<ref local="manufacturer3" />
</list>
</property>
</bean>
<bean id="manufacturer1" class="com.jenanderic.domain.Manufacturer">
<property name="id" value="1" />
<property name="name" value="Manufacturer #1" />
<property name="address" value="Address1" />
</bean>
<bean id="manufacturer2" class="com.jenanderic.domain.Manufacturer">
<property name="id" value="2" />
<property name="name" value="Manufacturer #2" />
<property name="address" value="Address2" />
</bean>
<bean id="manufacturer3" class="com.jenanderic.domain.Manufacturer">
<property name="id" value="3" />
<property name="name" value="Manufacturer #3" />
<property name="address" value="Address3" />
</bean>
</beans>
Since I have it autowired, I don’t need to explicitly inject it into the controller. Pretty cool, right?
Anyway, if I build and run the web app in GAE’s development server, it will run smoothly with no problems, so I’m sure that my web app runs 100% fine at this point.
Of course, I need to add persistence in the application since web apps are mostly about persistence. This is where it gets complicated. Even though I have plenty of experience working with database-driven applications, Google App Engine makes it seem otherwise.
Google App Engine works in a manner very different from traditional platforms. The most noticeable is the way it handles persistence; it doesn’t support relational databases. Google App Engine uses a non-relational database called the datastore. At the moment, I don’t have a full grasp of the pros and cons of not being able to use a relational database, but I’m pretty sure it has a great impact with the way you will build your application. Working with a non-relational database means that you have to manually maintain indexes with hand-written code. Aside from that, you have to manually write code for merging the results of multiple queries. Bummer.
Terence hacks 
