FilterConfig Interface
We will get the configuration information detail from the web.xml file by using FilterConfig object which is created by the web container.
Methods of FilterConfig interface
There are following 4 methods in the FilterConfig interface.
- public void init(FilterConfigconfig): init() method is invoked only once it is used to initialize the filter.
- public String getInitParameter(String parameterName): Returns the parameter value for the specified parameter name.
- publicjava.util.EnumerationgetInitParameterNames(): Returns an enumeration containing all the parameter names.
- publicServletContextgetServletContext(): Returns the ServletContext object.
Example of FilterConfig
In this example, if you change the param-value to no, request will be forwarded to the servlet otherwise filter will create the response with the message: this page is underprocessing. Let's see the simple example of FilterConfig.
Required Files:
- index.html
- MyFilter1.java
- WelcomeServlet.java
- web.xml
index.html
<html> <body> <a href="Myservlet">click</a> </body> </html>
MyFilter1.java
import java.io.IOException; import java.io.PrintWriter; import javax.servlet.*; public class MyFilter1 implements Filter{ FilterConfig config; public void init(FilterConfig config) throws ServletException { this.config=config; } public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { PrintWriter out=resp.getWriter(); String s1=config.getInitParameter("processing"); if(s1.equals("yes")){ out.print("This page is under processing"); } else{ chain.doFilter(req, resp);//sends request to next resource } } public void destroy() {} }
WelcomeServlet.java
import java.io.IOException; import java.io.PrintWriter; impor javax.servlet.ServletException; import javax.servlet.http.*; public class WelcomeServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.print("welcome to JavaRace"); } }
web.xml
<web-app> <servlet> <servlet-name>WelcomeServlet</servlet-name> <servlet-class>WelcomeServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>WelcomeServlet</servlet-name> <url-pattern>/WelcomeServlet</url-pattern> </servlet-mapping> <filter> <filter-name>f1</filter-name> <filter-class>MyFilter</filter-class> <init-param> <param-name>processing</param-name> <param-value>no</param-value> </init-param> </filter> <filter-mapping> <filter-name>f1</filter-name> <url-pattern>/WelcomeServlet</url-pattern> </filter-mapping> </web-app>
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