Reading a global variable from tomcat with JNDI. Example not working

Question

Hi you can help me to make this example work?
Context initCtx = new InitialContext();
Context envCtx = (Context)initCtx.lookup("java:comp/env");
Object o = envCtx.lookup("testvariable");
<GlobalNamingResources>
<Environment name="testvariable" type="java.lang.Boolean" value="false"/>
Nice greetings Christian

Answer 1

I found out that in addition to having the JNDI lookup code, you have to
- have the environment variable declared in the app server configuration
- have a resource-env-ref entry in your webapp module
- have the application container bind your named variable with the global variable
I am using tomcat 5.5, and have done the following. with success.
the following example uses the default sample environment variable in the tomcat server.xml
in tomcat server.xml:
<GlobalNamingResources>
<Environment
name="simpleValue"
type="java.lang.Integer"
value="30"/>
</GlobalNamingResources>
in my application's web.xml:
<resource-env-ref>
<description>Test read resource environment variable</description>
<resource-env-ref-name>simpleValue</resource-env-ref-name>
<resource-env-ref-type>java.lang.Integer</resource-env-ref-type>
</resource-env-ref>
in my META-INF/context.xml (or otherwise, in tomcat's context deployment configuration)
<ResourceLink name="simpleValue" global="simpleValue"
type="java.lang.Integer"/>
Note: in theory, the named resource by your web app could be different from the global environment variable, but here they are the same 'simpleValue'
This is the really important step, that with out it, nothing works.,
the context.xml is known to work with tomcat when it exists in META-INF/context.xml inside the .war file (i use war files to deploy, but you should be able to create META-INF/context in an unpacked webapp directory too, and tomcat will find it.,
I can not say what it is like for other app servers, but this mapping step is the critical point that i discovered after A LOT of hair pulling.
then, make use of it, i created a jndiTest.jsp:
<%@ page import="javax.naming.Context" %>
<%@ page import="javax.naming.InitialContext" %>
<%@ page import="javax.naming.NamingException" %>
<%
try {
Context initCtx = new InitialContext();
Context ctx = (Context) initCtx.lookup("java:/comp/env");
Object o = ctx.lookup("simpleValue");
%>
<%=o%><br>
<%
catch (NamingException ex) {
System.err.println(ex);
%>
since my server.xml defines the value for 'simpleValue' to be 30, this page displays 30