The Spring MVC lifecycle describes the sequence of events that occur during the processing of an HTTP request and response in a Spring MVC application. The lifecycle is divided into several stages, each of which is responsible for performing a specific task. Here is a brief overview of the Spring MVC lifecycle stages:
- Request processing
- Handler mapping
- Handler execution
- View Resolution
- View Rendering
- Response finalization
Let’s take a closer look at each stage in the Spring MVC lifecycle and see what happens in each stage with an example:
Request processing
This stage begins when the Spring DispatcherServlet receives a request. The DispatcherServlet is the entry point for all requests in a Spring MVC application. Once the request is received, the DispatcherServlet creates a new request and response object and passes them to the next stage.
Handler mapping
In this stage, the DispatcherServlet maps the incoming request to the appropriate handler. The HandlerMapping interface is responsible for mapping requests to handlers. The handler mapping process is done based on the information provided by the handler mapping configuration. This configuration is usually defined in the Spring configuration file.
Handler execution
Once the handler is identified, the DispatcherServlet executes the handler’s logic. The handler can be a simple Java class or a controller that implements the Controller interface. During the handler execution, the handler processes the request, performs business logic, and prepares the model data that will be used by the view.
View Resolution
After the handler completes its execution, the DispatcherServlet needs to resolve the view that will be used to render the response. The ViewResolver interface is responsible for resolving the view. The view resolver takes the view name returned by the handler and resolves it to an actual view object.
View Rendering
In this stage, the resolved view object is used to render the response. The view object can be a JSP file, a FreeMarker template, or any other view technology. The view renders the model data that was prepared by the handler.
Response finalization
After the view is rendered, the DispatcherServlet finalizes the response and sends it back to the client. The response finalization includes setting the response headers, content type, and sending the response to the client.
Sure, here’s a code example of the Spring MVC lifecycle:
@Controller
@RequestMapping("/example")
public class ExampleController {
@RequestMapping("/method")
public ModelAndView exampleMethod() {
ModelAndView modelAndView = new ModelAndView("exampleView");
modelAndView.addObject("message", "Hello World");
return modelAndView;
}
@PostConstruct
public void postConstruct() {
System.out.println("ExampleController bean created.");
}
@PreDestroy
public void preDestroy() {
System.out.println("ExampleController bean destroyed.");
}
}In this example, we have a controller called ExampleController with a request mapping /example. It also has a method with request mapping /method that returns a ModelAndView object containing a message.
The @PostConstruct and @PreDestroy annotations are used to specify methods that should be executed after the bean has been constructed and before it is destroyed, respectively. In this case, postConstruct() will be executed after the ExampleController bean has been created, and preDestroy() will be executed before it is destroyed.
During the lifecycle of the ExampleController bean, Spring will perform several steps:
- Instantiation: Spring will create a new instance of the ExampleController bean.
- Dependency Injection: Spring will inject any dependencies required by the bean. In this case, there are no dependencies to inject.
- Initialization: Spring will call the postConstruct() method to perform any necessary initialization.
- Usage: The ExampleController bean will be used to handle requests that match its request mappings.
- Destruction: When the application context is shut down, Spring will call the preDestroy() method to perform any necessary cleanup.
By using the @PostConstruct and @PreDestroy annotations, we can ensure that certain code is executed at specific points in the bean’s lifecycle. This can be useful for performing initialization or cleanup tasks, or for logging messages to help with debugging.