Tomcat4.1.24 以后为了安全问题 servelet 要在web.xml 中设置，
下面是Example中的例子:

<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app>

<display-name>Tomcat Examples</display-name>
<description>
Tomcat Example servlets and JSP pages.
</description>

<!-- Define servlet-mapped and path-mapped example filters -->
<filter>
<filter-name>Servlet Mapped Filter</filter-name>
<filter-class>filters.ExampleFilter</filter-class>
<init-param>
<param-name>attribute</param-name>
<param-value>filters.ExampleFilter.SERVLET_MAPPED</param-value>
</init-param>
</filter>
<filter>
<filter-name>Path Mapped Filter</filter-name>
<filter-class>filters.ExampleFilter</filter-class>
<init-param>
<param-name>attribute</param-name>
<param-value>filters.ExampleFilter.PATH_MAPPED</param-value>
</init-param>
</filter>
<filter>
<filter-name>Request Dumper Filter</filter-name>
<filter-class>filters.RequestDumperFilter</filter-class>
</filter>

<!-- Example filter to set character encoding on each request -->
<filter>
<filter-name>Set Character Encoding</filter-name>
<filter-class>filters.SetCharacterEncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>gb2312</param-value>
</init-param>
</filter>

<filter>
<filter-name>Compression Filter</filter-name>
<filter-class>compressionFilters.CompressionFilter</filter-class>

<init-param>
<param-name>compressionThreshold</param-name>
<param-value>10</param-value>
</init-param>
<init-param>
<param-name>debug</param-name>
<param-value>0</param-value>
</init-param>
</filter>

<!-- Define filter mappings for the defined filters -->
<filter-mapping>
<filter-name>Servlet Mapped Filter</filter-name>
<servlet-name>invoker</servlet-name>
</filter-mapping>
<filter-mapping>
<filter-name>Path Mapped Filter</filter-name>
<url-pattern>/servlet/*</url-pattern>
</filter-mapping>

<!-- Example filter mapping to apply the "Set Character Encoding" filter
to *all* requests processed by this web application -->
<!--
<filter-mapping>
<filter-name>Set Character Encoding</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
-->

<!--
<filter-mapping>
<filter-name>Compression Filter</filter-name>
<url-pattern>/CompressionTest</url-pattern>
</filter-mapping>
-->

<!--
<filter-mapping>
<filter-name>Request Dumper Filter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
-->

<!-- Define example application events listeners -->
<listener>
<listener-class>listeners.ContextListener</listener-class>
</listener>
<listener>
<listener-class>listeners.SessionListener</listener-class>
</listener>

<!-- Define servlets that are included in the example application -->

<servlet>
<servlet-name>SendMailServlet</servlet-name>
<servlet-class>SendMailServlet</servlet-class>
</servlet>

<servlet>
<servlet-name>
snoop
</servlet-name>
<servlet-class>
SnoopServlet
</servlet-class>
<!--
<init-param>
<param-name>foo</param-name>
<param-value>bar</param-value>
</init-param>
-->
<run-as>
<description>Security role for anonymous access</description>
<role-name>tomcat</role-name>
</run-as>
</servlet>

<servlet>
<servlet-name>
servletToJsp
</servlet-name>
<servlet-class>
servletToJsp
</servlet-class>
</servlet>
<servlet>
<servlet-name>
CompressionFilterTestServlet
</servlet-name>
<servlet-class>
compressionFilters.CompressionFilterTestServlet
</servlet-class>

</servlet>

<servlet-mapping>
<servlet-name>invoker</servlet-name>
<url-pattern>/servlet/*</url-pattern>
</servlet-mapping>

<servlet-mapping>
<servlet-name>
CompressionFilterTestServlet
</servlet-name>
<url-pattern>
/CompressionTest
</url-pattern>
</servlet-mapping>

<servlet-mapping>
<servlet-name>SendMailServlet</servlet-name>
<url-pattern>/SendMailServlet</url-pattern>
</servlet-mapping>

<servlet-mapping>
<servlet-name>
snoop
</servlet-name>
<url-pattern>
/snoop
</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>
servletToJsp
</servlet-name>
<url-pattern>
/servletToJsp
</url-pattern>
</servlet-mapping>

<taglib>
<taglib-uri>
http://jakarta.apache.org/tomcat/debug-taglib
</taglib-uri>
<taglib-location>
/WEB-INF/jsp/debug-taglib.tld
</taglib-location>
</taglib>

<taglib>
<taglib-uri>
http://jakarta.apache.org/tomcat/examples-taglib
</taglib-uri>
<taglib-location>
/WEB-INF/jsp/example-taglib.tld
</taglib-location>
</taglib>

<resource-ref>
<res-ref-name>mail/Session</res-ref-name>
<res-type>javax.mail.Session</res-type>
<res-auth>Container</res-auth>
</resource-ref>

<security-constraint>
<display-name>Example Security Constraint</display-name>
<web-resource-collection>
<web-resource-name>Protected Area</web-resource-name>
<!-- Define the context-relative URL(s) to be protected -->
<url-pattern>/jsp/security/protected/*</url-pattern>
<!-- If you list http methods, only those methods are protected -->
<http-method>DELETE</http-method>
<http-method>GET</http-method>
<http-method>POST</http-method>
<http-method>PUT</http-method>
</web-resource-collection>
<auth-constraint>
<!-- Anyone with one of the listed roles may access this area -->
<role-name>tomcat</role-name>
<role-name>role1</role-name>
</auth-constraint>
</security-constraint>

<!-- Default login configuration uses form-based authentication -->
<login-config>
<auth-method>FORM</auth-method>
<realm-name>Example Form-Based Authentication Area</realm-name>
<form-login-config>
<form-login-page>/jsp/security/protected/login.jsp</form-login-page>
<form-error-page>/jsp/security/protected/error.jsp</form-error-page>
</form-login-config>
</login-config>

<!-- Security roles referenced by this web application -->
<security-role>
<role-name>role1</role-name>
</security-role>
<security-role>
<role-name>tomcat</role-name>
</security-role>

<!-- Environment entry examples -->
<!--env-entry>
<env-entry-description>
The maximum number of tax exemptions allowed to be set.
</env-entry-description>
<env-entry-name>maxExemptions</env-entry-name>
<env-entry-value>15</env-entry-value>
<env-entry-type>java.lang.Integer</env-entry-type>
</env-entry-->
<env-entry>
<env-entry-name>minExemptions</env-entry-name>
<env-entry-value>1</env-entry-value>
<env-entry-type>java.lang.Integer</env-entry-type>
</env-entry>
<env-entry>
<env-entry-name>foo/name1</env-entry-name>
<env-entry-value>value1</env-entry-value>
<env-entry-type>java.lang.String</env-entry-type>
</env-entry>
<env-entry>
<env-entry-name>foo/bar/name2</env-entry-name>
<env-entry-value>true</env-entry-value>
<env-entry-type>java.lang.Boolean</env-entry-type>
</env-entry>
<env-entry>
<env-entry-name>name3</env-entry-name>
<env-entry-value>1</env-entry-value>
<env-entry-type>java.lang.Integer</env-entry-type>
</env-entry>
<env-entry>
<env-entry-name>foo/name4</env-entry-name>
<env-entry-value>10</env-entry-value>
<env-entry-type>java.lang.Integer</env-entry-type>
</env-entry>

<!-- EJB Reference -->
<ejb-ref>
<description>Example EJB Reference</description>
<ejb-ref-name>ejb/Account</ejb-ref-name>
<ejb-ref-type>Entity</ejb-ref-type>
<home>com.mycompany.mypackage.AccountHome</home>
<remote>com.mycompany.mypackage.Account</remote>
</ejb-ref>

<!-- Local EJB Reference -->
<ejb-local-ref>
<description>Example Local EJB Reference</description>
<ejb-ref-name>ejb/ProcessOrder</ejb-ref-name>
<ejb-ref-type>Session</ejb-ref-type>
<local-home>com.mycompany.mypackage.ProcessOrderHome</local-home>
<local>com.mycompany.mypackage.ProcessOrder</local>
</ejb-local-ref>

</web-app>