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Step 2 : to write FirstFilter Step 3 : to configure web.xml Step 4 : Visit the page Step 5 : init() method Step 6 : Filter Startup failed
Filter Like a sentry post , The user's request needs to go through Filter
And there can be multiple filters
Develop a simple FirstFilter, Used to print user access ip Address and page visited
HttpServletRequest request = (HttpServletRequest) req; doFilter() Method req The type of the parameter is ServletRequest, Need to convert to HttpServletRequest Types make it easy to call certain methods ( reference resources request Common methods ) String ip = request.getRemoteAddr(); Get the name of the incoming user ip address String url = request.getRequestURL().toString(); Get the page address visited by the user System.out.printf("%s %s Visited %s%n", date, ip, url); Print it out on the console chain.doFilter(request, response); filter Release , Indicates to continue running the next filter , Or finally visit some servlet,jsp,html wait
package filter; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class FirstFilter implements Filter { @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; String ip = request.getRemoteAddr(); String url = request.getRequestURL().toString(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date d = new Date(); String date = sdf.format(d); System.out.printf("%s %s Visited %s%n", date, ip, url); chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { } }
stay web.xml In filter Configuration of , and servlet The configuration is very similar
<url-pattern>/*</url-pattern>
Indicates that all accesses will be filtered If configured as
<url-pattern>*.jsp</url-pattern>
It means only filtering jsp
<filter> <filter-name>FirstFilter</filter-name> <filter-class>filter.FirstFilter</filter-class> </filter> <filter-mapping> <filter-name>FirstFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
<filter> <filter-name>FirstFilter</filter-name> <filter-class>filter.FirstFilter</filter-class> </filter> <filter-mapping> <filter-name>FirstFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
Restart tomcat, Access information of all users , Can be printed out
With Servlet Need to configure
Self starting Will follow tomcat Start and execute init() The method is different .
Filter certain Will follow tomcat The start-up is self starting .
package filter; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class FirstFilter implements Filter { @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; String ip = request.getRemoteAddr(); String url = request.getRequestURL().toString(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date d = new Date(); String date = sdf.format(d); System.out.printf("%s %s Visited %s%n", date, ip, url); chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { System.out.println("First Filter init()"); } }
Filter yes web Application is a very important link , If Filter Startup failed , Or there is a compilation error ,
Not only this Filter out of commission ,
whole web The application will fail to start , The user cannot access the page
At startup tomcat In the process , You will also see such words ：
serious : Context [] startup failed due to previous errors
This is often used to prompt Filter Startup failed
package filter; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class FirstFilter implements Filter { @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; String ip = request.getRemoteAddr(); String url = request.getRequestURL().toString(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date d = new Date(); String date = sdf.format(d); System.out.printf("%s %s Visited %s%n", date, ip, url); chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { System.out.println(" Deliberately causing an anomaly "); Object o = null; o.toString(); } }
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Q & A area
2021-01-03
add Filter The client cannot jump after
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2020-07-18
about ip address
1 One answer
Ah Ju Jump to the problem location Answer time ：2020-08-28
Check whether the virtual machine is used or the computer has multiple network cards
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2020-07-01
The files are normal , but tomcat Cannot display automatically after startup FirstFilter.java In file doFilter（） Method content
2020-06-26
Why print twice init？
2020-06-19
Yes Filter Then , Start tomcat Always reporting errors
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