Servlet advanced

filter The interception process ：

Filter Three methods in the interface ：
init Method ： After the filter object is created , Execute initialization method .
doFilter Method ： In this method, interception and release are implemented .
destroy Method ： After the filter is destroyed , perform .
Implement the program ：
package cn.itcast.chapter08.filter;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class MyServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
response.getWriter().print(“hello Filter”);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

establish MyFilter Of Filter class , Intercept access servlet resources , If you want to release , perform doFilter Method ：
package cn.itcast.chapter08.filter;
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;

/**

• Servlet Filter implementation class MyFilter
  */
  public class MyFilter implements Filter {

  /**

  • @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
    */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
    throws IOException, ServletException {
    // Allow access to target resources
    chain.doFilter(request, response);
    System.out.println(“ Output content , Represents the interception response ”);
    }

  /**

  • @see Filter#init(FilterConfig)
    */
    public void init(FilterConfig fConfig) throws ServletException {
    // TODO Auto-generated method stub
    }

}
stay web.xml In the document servlet To configure ：

MyFilter
/MyServlet

filter mapping ：
Use wildcards “*” Intercept all user requests ： There are three forms of configuration ：
Full catalog match ： such as /MyServlet
Directory matching ： such as /,/aa/ On behalf of intercepting aa All requests in the directory
Extension matching ： such as .do,.action, Wrong writing ：/*.do
Different ways to intercept requests ：
REQUEST： When the user visits the page directly ,web The container will call the filter
INCLUDE： If the target resource passes RequestDispatcher Of include() Method access , Then the filter will be called . besides , The filter will not be called .
FORWARD： If the target resource passes RequestDispatcher Of forward() Method access , Then the filter will be called . besides , The filter will not be called .
ERROR： If the target resource is called through the declarative exception handling mechanism , Then the filter will be called

filter chain ：
Create two filters MyFilter01 and MyFilter02：
MyFilter01：
packagecn.itcast.chapter08.filter;

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;

/**

• Servlet Filter implementation class MyFilter01
  */
  public class MyFilter01 implements Filter {

  /**

  • @see Filter#destroy()
    */
    public void destroy() {
    // TODO Auto-generated method stub
    }

  /**

  • @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
    */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
    throws IOException, ServletException {
    response.getWriter().print(“hello MyFilter01-------before
    ”);
    chain.doFilter(request, response);
    response.getWriter().print(“hello MyFilter01-------after
    ”);
    }

  /**

  • @see Filter#init(FilterConfig)
    */
    public void init(FilterConfig fConfig) throws ServletException {
    // TODO Auto-generated method stub
    }

}
MyFilter02：
package itcast.chapter08.filter;

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;

/**

• Servlet Filter implementation class MyFilter02
  */
  public class MyFilter02 implements Filter {

  /**

  • @see Filter#destroy()
    */
    public void destroy() {
    // TODO Auto-generated method stub
    }

  /**

  • @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
    */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
    throws IOException, ServletException {
    response.getWriter().print(“hello MyFilter02-----------before
    ”);
    chain.doFilter(request, response);
    response.getWriter().print(“hello MyFilter02-----------after
    ”);
    }

  /**

  • @see Filter#init(FilterConfig)
    */
    public void init(FilterConfig fConfig) throws ServletException {
    // TODO Auto-generated method stub
    }

}

FilterConfig Interface ：