Servlet & JSP day6 - Event 모델, Attribute(속성)

 

Event 모델

☞ Event : 컴포넌트에 가해진 동작, 변화

1. 컴포넌트에서 Event가 발생하는 것을 감시하는 Container

2. 발생한 Event를 처리하는 동작을 가진 객체(Listener Class)

  - Event Handler : 발생한 Event 처리 동작(메소드)

  - Event Source :  Event가 발생한 컴포넌트

ex) 버튼을 클릭하면 안녕이라고 출력한다.

Event Source : 버튼

Event : 클릭

Event Handler : 안녕을 출력하는 동작

 

 

 

MyServletContextListener.java

 

package servlet.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class MyServletContextListener implements ServletContextListener{
 //Web Application이 시작시 Web Container에 의해 호출됨
 public void contextInitialized(ServletContextEvent sce){
  System.out.println("--------------------------------");
  System.out.println("MyServletContextListener.contextInitialized실행");
  System.out.println("--------------------------------");
 }
 //Web Application이 종료될때 Web container에 의해 호출됨
 public void contextDestroyed(ServletContextEvent sce){
  System.out.println("--------------------------------");
  System.out.println("MyServletContextListener.contextDestroyed 실행");
  System.out.println("--------------------------------");
 }

}

 

DriverLoadingListener.java

package servlet.listener; 

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class DriverLoadingListener implements ServletContextListener {
 public DriverLoadingListener() { }
 public void contextInitialized(ServletContextEvent sce) {
  // DriverLoading
  // ServletContext 조회
  ServletContext ctx = sce.getServletContext();
  String driverClass = ctx.getInitParameter("driver class");
  System.out.println("driverClass : " + driverClass);

  try {
   Class.forName(driverClass);
   System.out.println("------------driverLoading 성공----------------");
  } catch (ClassNotFoundException e) {
   e.printStackTrace();
  }
 }
 public void contextDestroyed(ServletContextEvent arg0) { }
}

 

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
<listener>
   <listener-class>servlet.listener.MyServletContextListener</listener-class>
  </listener>
  <listener>
   <listener-class>servlet.listener.DriverLoadingListener</listener-class>
  </listener>
  <context-param>
   <param-name>driver class</param-name>
   <param-value>oracle.jdbc.driver.OracleDriver</param-value>
  </context-param>
</web-app>

 

Attribute(속성)

☞ Attribute란?

- Web Application 구성 컴포넌트들(Servlet, JSP, Listener)에 공유하는 객체

 

☞ Scope

- Attribute들을 공유하기 위한 공유 장소의 영역(저장 장소)

- 공유 범위에 따라 3가지 영역이 있다.

1. request scope : HttpServletRequest 이용

- 요청 ~ 응답까지 공유

 

    

 

2. session scope : HttpSession 이용

- 한명의 클라이언트(웹브라우저)가 로그인 ~ 로그아웃까지 공유

 

 

3. application scope : SevletContext 이용

- Application 시작 ~ 종료까지 공유

 

 

☞ 관련 메소드

- Attribute는 key-value 쌍으로 관리된다.

- setAttribute(String key, Object value) : 공유영역에 Attribute 저장

- getAttribute(String key, Object value) : 저장된 Attribute 조회

- getAttributeNames() : Enumeration : Attribute들에 연결된 name들 조회

 

 

GetAttributeServlet.java

package servlet.attribute;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class SetAttributeServlet extends HttpServlet {

 private static final long serialVersionUID = 1L;

 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  doPost(request, response);
 }

 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  //Application Scope에 greeting -안녕하세요 설정
  //Application Scope - SevletContext
  //Attribute : 안녕하세요 - String
  ServletContext ctx = getServletContext();
  ctx.setAttribute("greeting", "안녕하세요");
  ctx.setAttribute("name", "홍길동");
  ctx.setAttribute("age", 30); // 30: Integer
  PrintWriter out = response.getWriter();
  out.println("<html><body>");
  out.println("<a href='/myweb/get_attribute'>Get Attribute</a>");
  out.println("</body></html>");
 }

}

 

SetAttributeServlet.java

package servlet.attribute;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class GetAttributeServlet extends HttpServlet {
 private static final long serialVersionUID = 1L;
 
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  doPost(request, response);
 }
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  //Application Scope에 설정된(binding) Attribute를 조회하여 출력
  ServletContext  ctx = getServletContext();
  
  //lookup
  String name = (String)ctx.getAttribute("name");
  String greeting = (String)ctx.getAttribute("greeting");
  Integer age = (Integer)ctx.getAttribute("age");
  response.setContentType("text/html;charset=utf-8");
  PrintWriter out = response.getWriter();
  out.println("<html><body>");
  out.println("인사말 : " + greeting +"<br>");
  out.println("이름 : " + name + "<br>");
  out.println("나이 : " + age + "<br>");
  out.println("</body></html>");
 }

}
 

 

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">

<servlet>
    <description></description>
    <display-name>SetAttributeServlet</display-name>
    <servlet-name>SetAttributeServlet</servlet-name>
    <servlet-class>servlet.attribute.SetAttributeServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>SetAttributeServlet</servlet-name>
    <url-pattern>/set_attribute</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>GetAttributeServlet</display-name>
    <servlet-name>GetAttributeServlet</servlet-name>
    <servlet-class>servlet.attribute.GetAttributeServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>GetAttributeServlet</servlet-name>
    <url-pattern>/get_attribute</url-pattern>
  </servlet-mapping>
</web-app>

 

SetAttributeServlet을 통해 name, greeting, age의 값을 미리 지정해주고 그 값을 getServletContext()를 통해서 같은 Web Application 내에 존재하는 LifecycleServlet을 통해 name, greeting, age의 value를 조회 할 수 있다.

 

SetAttributeServlet에서 설정한 name, greeting, age 값을 LifecycleServlet.java에서 조회

package servlet.lifecycle;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LifecycleServlet extends HttpServlet{
 public LifecycleServlet() {
  System.out.println("LifecycleServlet 객체생성");
 }
 //init() : 객체 생성 직후
 public void init() {
  System.out.println("LifecycleServlet.init() 메소드 실행");
 }
 //destroy() : 객체 소멸 직전
 public void destroy() {
  System.out.println("LifecycleServlet.destroy() 메소드 실행");
 }
 //service() -> doGet(): 클라이언트 요청이 들어올 때 마다 호출
 public void doGet(HttpServletRequest request, HttpServletResponse response) {
  ServletContext ctx = getServletContext();
  String name = (String)ctx.getAttribute("name");
  String greeting = (String)ctx.getAttribute("greeting");
  Integer age = (Integer)ctx.getAttribute("age"); 
  System.out.println(name + " , " + greeting + " , " + age);
 }
}