4.3 The controller
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## 4.3 The controller

The Spring’s MVC style of web application development is used in which the central type is the `Controller` class.

### Import the web project

The GreenPages application is divided into OSGi bundles that are represented as Eclipse projects. In this step import the `greenpages.web` project.

Starting with no projects, import the web project by right-clicking in the Package Explorer view and selecting the Import… menu item. In the dialog that opens, choose General → Existing Projects into Workspace and select Next. In the following dialog set the root directory to the value of `$GREENPAGES_HOME/start/greenpages.web` and press Finish.

(Initially this project may have compiler errors; this is to be expected particularly if the Maven repository hasn’t yet been created.) When this project is imported go to the next step.

### The controller class

In the `src/main/java` source folder of the `greenpages.web` project the package `greenpages.web` should contain the controller class named `GreenPagesController`. Create this by right-clicking on the `greenpages.web` package in the `src/main/java` source folder and selecting New → Class. (If Class is not offered on the New menu the Java perspective may not be being used, in which case look for the Class option under Other… in the Java section.)

Name the new class `GreenPagesController` and press Finish.

The code should be edited to look like this:

    @Controller
    public class GreenPagesController {
    	…
        @RequestMapping("/home.htm")
        public void home() {
        }
        …

The annotations `Controller` and `RequestMapping` are from Spring Framework and are imported by adding the lines:

    import org.springframework.stereotype.Controller;
    import org.springframework.web.bind.annotation.RequestMapping;

STS will offer (as a Quick Fix) to insert imports for these Spring Framework annotations the first time they are used. (Java 1.6 supports annotations, and the Spring Framework libraries are accessible by linking to the correct Web Server runtime environment or generating the correct dependencies for the Maven plug-in.)

### Enabling component scanning

Spring will detect the `@Controller` annotation and create a bean of controller type, provided that it scans the classpath for these. Spring’s component scanning is enabled by inserting a `context` tag in one of the Spring bean definition files.

Open the `WEB-INF/greenpages-servlet.xml` file in the `src/main/webapp` folder and ensure the following lines are present:

    	<!-- enable classpath scanning -->
    	<context:component-scan base-package="greenpages.web" />

Experiment by adding and removing this line, saving the file after each change. (Easily done by commenting it—use the Toggle Comment shortcut in STS.) Look in the Spring Explorer view for a bean named `greenPagesController` dynamically created by the `component-scan` tag.

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