Servlet Filter (Filter) (8), servletfilter

Servlet Filter (Filter) (8), servletfilter

1. servlet filter background

In the project, we will encounter such a requirement to filter the ip addresses of users accessing the server. Only the ip addresses in the list can access the service. To meet the requirement, whenever a client request is made, we will write the code for verifying the ip address. We need to do this for the servlet that can be accessed by the client. It is obvious that code redundancy is inconvenient to maintain. If the verification rules change, it is also very troublesome to modify.

To solve the above problems, the Filter technology came into being.

2. What is a servlet filter?

Servlet filters are defined in java servlet 2.3. It can check and modify the ServletRequest object and ServletResponse object that the servlet container passes to the servlet component.

3. Case studies

　　All servlet filters must implement the javax. servlet. Filter interface.

　NoteFilter

Package com. learn; import javax. servlet. *; import javax. servlet. http. httpServletRequest; import javax. servlet. http. httpServletResponse; import java. io. IOException; import java. io. printWriter;/*** Created by Administrator on login /09/29. */public class NoteFilter implements Filter {private FilterConfig config = null; private String ipTable = null; // ip address list @ Override public void init (FilterConfig filterCon Fig) throws ServletException {System. out. println ("note filter initial"); this. config = filterConfig; this. ipTable = config. getInitParameter ("ipTable") ;}@ Override public void doFilter (ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {System. out. println ("do filter starting"); // check the IP address if (! VeryfyIP (request, response) return; long befor = System. currentTimeMillis (); config. getServletContext (). log ("before call note Filter"); chain. doFilter (request, response); config. getServletContext (). log ("after call note Filter"); long after = System. currentTimeMillis (); String name = ""; if (request instanceof HttpServletRequest) {name = (HttpServletRequest) request ). getRequestURI ();} config. getServletContext (). log ("Note Filter: name:" + name + "time:" + (after-befor) + "ms") ;}@ Override public void destroy () {} private boolean veryfyIP (ServletRequest request, ServletResponse response) {String ip = request. getRemoteAddr (); System. out. println ("request ip:" + ip); System. out. println ("ipTable blacklist:" + ipTable); if (ip. indexOf (ipTable) =-1) {System. out. println ("Verification Failed"); response. setContentType ("text/html"); PrintWriter out = null; try {out = response. getWriter (); out. print ("
NoteServlet
Package com. learn; import javax. servlet. servletException; import javax. servlet. http. httpServlet; import javax. servlet. http. httpServletRequest; import javax. servlet. http. httpServletResponse; import java. io. IOException;/*** Created by Administrator on login /09/29. */public class NoteServlet extends HttpServlet {@ Override protected void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System. out. println ("filter passed ");}}
Web. xml configuration
<filter>        <filter-name>ip</filter-name>        <filter-class>com.learn.NoteFilter</filter-class>        <init-param>            <param-name>ipTable</param-name>            <param-value>127.0.0.1</param-value>        </init-param>    </filter>    <filter-mapping>        <filter-name>ip</filter-name>        <url-pattern>/note</url-pattern>    </filter-mapping>
<servlet>        <servlet-name>note</servlet-name>        <servlet-class>com.learn.NoteServlet</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>note</servlet-name>        <url-pattern>/note</url-pattern>    </servlet-mapping>
The result is as follows: