웹 개발을 하다보면
http request 를 받아서 bussiness logic 이 실행 되기 전에
뭔가 선 작업 처리를 해 주어야 하는 경우가 있다.
예를 들어 http header 값을 보고 access 를 reject 시킨다던가
parameter 의 encoding 을 UTF-8 로 바꿔준다던가...
(실제로 filter 의 실용예 중 거의 대부분이 후자인 UTF-8 encoding 이다)
실제 servlet filter 예제를 만들어서 아래와 같이 올리니 참고 하길 바란다.
1. 웹 프로젝트 구조 (eclipse 의 dynamic web project 구조)
2. 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_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>HelloServlet</display-name>
<servlet>
<servlet-name>helloservlet</servlet-name>
<servlet-class>com.test.HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>helloservlet</servlet-name>
<url-pattern>/HelloServlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<!-- filter definition -->
<filter>
<filter-name>TestFilter</filter-name>
<filter-class>com.test.TestFilter</filter-class>
<init-param>
<param-name>param1</param-name>
<param-value>param1-value</param-value>
</init-param>
</filter>
<!-- filter url mapping -->
<filter-mapping>
<filter-name>TestFilter</filter-name>
<url-pattern>/HelloServlet</url-pattern>
</filter-mapping>
</web-app>
3. HelloServlet.java
package com.test;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class HelloServlet
*/
@WebServlet("/HelloServlet")
public class HelloServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public HelloServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
System.out.println("Hello Servlet . GET");
System.out.println("get enter");
PrintWriter writer = response.getWriter();
writer.println("<html><body>");
writer.println("get enter");
writer.println("</body></html>");
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
System.out.println("Hello Servlet . POST");
System.out.println("post enter");
PrintWriter writer = response.getWriter();
writer.println("<html><body>");
writer.println("post enter");
writer.println("</body></html>");
}
}
4. TestFilter.java
package com.test;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class TestFilter implements Filter{
private String param1;
@Override
public void destroy() {
// TODO Auto-generated method stub
System.out.println("destroy method running");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
// TODO Auto-generated method stub
System.out.println("before servlet running");
System.out.println("param1==="+param1);
//init parameter using
chain.doFilter(request, response);
System.out.println("after servlet running");
}
@Override
public void init(FilterConfig config) throws ServletException {
// TODO Auto-generated method stub
param1 = config.getInitParameter("param1");
}
}
5. 이렇게 하고 http://localhost:8080/FilterTest/HelloServlet 을 브라우저에서 호출 하면
System.out 으로 console 에 찍힌 로그는 아래와 같다.
console 결과 :
before servlet running
param1===param1-value
Hello Servlet . GET
get enter
after servlet running
소스를 천천히 읽어보면 내용을 이해하실 겁니다.
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