Tomcat JNDI返回null而不是bean

Question

I am trying to use GlobalNamingResources to create a global bean that will be used by 2 different webapps (on the same tomcat of course).

My problem is that I get a NullPointerException when I try to set new data to the class I got from the JNDI.

I followed the following link, and I am still not sure what I did wrong: http://tomcat.apache.org/tomcat-7.0-doc/config/globalresources.html

This is the line that crashes my servlet:

single.setText("TEXT");

this is my test servlet:

     @WebServlet("/JNDIServlet")
     public class JNDIServlet extends HttpServlet {

     /**
      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         try {

              Thread.sleep(4000);
              Context initCtx = new InitialContext();
              Context envCtx = (Context) initCtx.lookup("java:comp/env");
              SingletonClass single = (SingletonClass) envCtx.lookup("TestMe");
              single.setText("TEXT");
              initCtx.rebind("TestMe", single);
              response.getWriter().println(envCtx.lookup("TestMe").toString());
         } catch (NamingException e) {
              e.printStackTrace();
         } catch (InterruptedException e) {
        e.printStackTrace();
         }
     }

my "SingletonClass" is just a pojo:

package com.jndi.test;

public class SingletonClass {

    private String text;

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

    public SingletonClass() {
    }

}

this is my web.xml file:

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
  <display-name>JNDIServletTest</display-name>

  <resource-ref>
<res-ref-name>TestMe</res-ref-name>
<res-type>com.jndi.test.SingletonClass</res-type>
<res-auth>Container</res-auth>
  </resource-ref>
</web-app>

and finally, the relevant part from my server.xml file from the tomcat:

<GlobalNamingResources>

    <Resource name="TestMe" auth="Container"
                    type="com.jndi.test.SingletonClass"
                    factory="org.apache.naming.factory.BeanFactory"/>

<!-- Editable user database that can also be used by
     UserDatabaseRealm to authenticate users
-->
<Resource auth="Container" description="User database that can be updated and saved" factory="org.apache.catalina.users.MemoryUserDatabaseFactory" name="UserDatabase" pathname="conf/tomcat-users.xml" type="org.apache.catalina.UserDatabase"/>
</GlobalNamingResources>

also, I have added the needed Resource link in the context.xml in my tomcat:

<ResourceLink name="TestMe" global="TestMe" type="com.jndi.test.SingletonClass"/>

Can anyone please provide me some insight about what I did wrong?

Thanks a lot :)

Answer 1

[SOLVED]

Part 1:
In ResourceLink of webapp's context.xml , use a different name from that used for global name defined for Resource in server.xml

Part 2:
Remove duplicate implementation JARs/classes of the resource bean from-webapp's-lib and keep the ones placed in tomcat lib.

Part 2 Explained:
In my case, i had created a factory in a separate package and packaged it as a JAR. I was using the JAR in both webapp's lib and tomcat lib.
This resulted in a ClassCastException (caused as the Resource was created with tomcat's version class - and then the application tried to cast it to the class from it's own lib [if interested, read a little more about ClassLoaders in tomcat, which will make things a lot clearer]).

Reference: JNDI ClassCastException