[SPRING] Servlet

/**
A servlet is a small Java program that runs within a Web server. Servlets receive and respond to requests from Web clients, usually across HTTP, the HyperText Transfer Protocol.

To implement this interface, you can write a generic servlet that extends javax.servlet.GenericServlet or an HTTP servlet that extends javax.servlet.http.HttpServlet.

...
*/
public interface Servlet {

  /**
  Called by the servlet container to indicate 
  to a servlet that the servlet is being placed into service.
  */
  init(ServletConfig): void


  /**
  Called by the servlet container to allow the servlet to respond to a request. 
  This method is only called after the servlet's init() method has completed successfully.

  Servlets typically run inside multithreaded servlet containers that can handle multiple requests concurrently.
  Developers must be aware to synchronize access to any shared resources such as files, 
  network connections, and as well as the servlet's class and instance variables. 
  */
  service(ServletRequest, ServletResponse): void

  /**
  Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.

  This method is only called once all threads within the servlet's service method have exited or after a timeout period has passed.
  After the servlet container calls this method, it will not call the service method again on this servlet.
  */
  destroy(): void

  /**
  Returns information about the servlet, such as author, version, and copyright.
  */
  getServletInfo(): String

  /**
  Returns a ServletConfig object, which contains initialization and startup parameters for this servlet.
  */
  getServletConfig(): ServletConfig
}

/**
  A servlet configuration object used by a servlet container to pass information to a servlet during initialization.
  */
public interface ServletConfig {
  getServletName(): String

  getServletContext(): ServletContext

  getInitParameter(String): String

  getInitParameterNames(): Enumeration<String>
}

/**
Defines a generic, protocol-independent servlet.
*/
public abstract class GenericServlet implements Servlet, ServletConfig, java.io.Serializable {
  init(): void

  init(ServletConfig): void

  /**
  This method is declared abstract so subclasses, such as HttpServlet, must override it.
  */
  service(ServletRequest, ServletResponse): void (abstract)

  destroy(): void
  ...
}

/**
Provides an abstract class to be subclassed to create an HTTP servlet suitable for a Web site.
A subclass of HttpServlet must override at least one method, usually one of these:
- doGet, if the servlet supports HTTP GET requests
- doPost, for HTTP POST requests
- doPut, for HTTP PUT requests
- doDelete, for HTTP DELETE requests
- init and destroy, to manage resources that are held for the life of the servlet
- getServletInfo, which the servlet uses to provide information about itself

There's almost no reason to override the service method.
service handles standard HTTP requests by dispatching them to the handler methods for each HTTP request type (the doMethod methods listed above).
*/
public abstract class HttpServlet extends GenericServlet {
  ...

  doGet(HttpServletRequest, HttpServletResponse): void

  doPost(HttpServletRequest, HttpServletResponse): void

  doPut(HttpServletRequest, HttpServletResponse): void

  doDelete(HttpServletRequest, HttpServletResponse): void

  doHead(HttpServletRequest, HttpServletResponse): void

  doOptions(HttpServletRequest, HttpServletResponse): void

  doTrace(HttpServletRequest, HttpServletResponse): void

  /**
  Dispatches client requests to the protected service method. There's no need to override this method.

  1. 형변환 : Servlet -> HttpServlet
    - ServletRequest -> HttpServletRequest
    - ServletResponse -> HttpServletResponse
  2. service(HttpServletRequest, HttpServletResponse) 호출
  */
  service(ServletRequest, ServletResponse): void

  /**
  Receives standard HTTP requests from the public service method and dispatches them to the doMethod methods defined in this class.

  This method is an HTTP-specific version of the javax.servlet.Servlet.service method. 
  There's no need to override this method.

  1. HTTP 요청(GET, POST, ...)에 따라 doMethod() 호출
  */
  service(HttpServletRequest, HttpServletResponse): void (protected)
}