Today i found an exception while deploying my .war application to Tomcat web server for production usage, very weird because i never had this exception on my IDE before. This is the complete exception stacktrace,

Caused by: java.lang.IllegalArgumentException: Filter mapping specifies an unknown filter name FilterName
	at org.apache.catalina.core.StandardContext.addFilterMap(StandardContext.java:2506)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)

below is my web.xml content,

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="crm" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_4.xsd">
    <display-name>edw</display-name>
    <context-param>
        <param-name>edw</param-name>
        <param-value>edw</param-value>
    </context-param>
    
    <filter-mapping>
        <filter-name>FilterName</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
	
    <filter>
        <filter-name>FilterName</filter-name>
        <filter-class>com.edw.filter.FilterName</filter-class>
    </filter>
</web-app>

How to fix it is actually very simple, i only need to swap between and tag. Below is the correct web.xml.

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="crm" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_4.xsd">
    <display-name>edw</display-name>
    <context-param>
        <param-name>edw</param-name>
        <param-value>edw</param-value>
    </context-param>
    
    <filter>
        <filter-name>FilterName</filter-name>
        <filter-class>com.edw.filter.FilterName</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>FilterName</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

</web-app>

Weird eh :p