今天才知道，有2种方法：

1、适用于所有的servlet：只需修改conf目录下的server.xml即可自动匿名访问所有的servlet。

To let Tomcat run anonymous servlet classes that have not been defined in a web.xml file, you can enable the Tomcat "invoker" servlet by removing the comments around the servlet-mapping element in the web.xml file in the Tomcat conf directory:

  <!-- The mapping for the invoker servlet -->

<!--

  <servlet-mapping>

    <servlet-name>invoker</servlet-name>

    <url-pattern>/servlet/*</url-pattern>

  </servlet-mapping>

-->

When you edit web.xml in the Tomcat conf directory, the servlet is ready to go。

例如，after saving Ch09_06.java and building the project, start Tomcat with the Tomcat plug-in's buttons and navigate to http://localhost:8080/Ch09_06/servlet/org.eclipsebook.ch09.Ch09_06.

2、就是编辑每个项目中的web.xml文件：

lternatively, if you don't want to edit web.xml in the Tomcat conf directory to enable anonymous servlets, you can create a local web.xml for each project you create with the Tomcat plug-in.