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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 21822] - Placing a Valve inside a Context gives Null Pointer Exception...
Date Wed, 23 Jul 2003 11:55:28 GMT
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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=21822

Placing a Valve inside a Context gives Null Pointer Exception...





------- Additional Comments From banil@novell.com  2003-07-23 11:55 -------
Analysis of the problem:
In ValveBase::createObjectName line 292, host is expected to have a non-null 
value. This will happen only if parent has been set for the current Context 
that has a Valve definition.

This call can be traced back to org.apache.catalina.core.ContainerBase.addValve
(ContainerBase.java:1306), which can be further traced back to 
org.apache.commons.digester.SetNextRule.end(SetNextRule.java:256).

If we look at ContextRuleSet::addRuleInstances, (line 248) statement:
digester.addObjectCreate(prefix + "Context/Valve",
                                 null, // MUST be specified in the element
                                 "className");
is setting the corresponding Rule whose later execution (*end*) leads to NPE.

Another statement in same method (line 164):
            digester.addSetNext(prefix + "Context",
                                "addChild",
                                "org.apache.catalina.Container");
is responsible for correctly setting the parent-child relationship between Host 
and the current Context. But before the *end* of this Rule can be called, the 
*end* of the previous Rule gets called leading to NPE.

Hence, if we decide to retain the statement (line 291) 
Host host = (Host) container.getParent(); 
in ValveBase::createObjectName, then we should make sure that this call would 
return a non-null Host reference.

One of the ways to achieve this is the following modification:
--------------------------------------------------------------------
--- Tomcat5.0.4\jakarta-tomcat-
catalina\catalina\src\share\org\apache\catalina\startup\SetDocBaseRule.java
	Mon Jul 14 20:54:26 2003
+++ Modified\Tomcat5.0.4\jakarta-tomcat-
catalina\catalina\src\share\org\apache\catalina\startup\SetDocBaseRule.java
	Wed Jul 23 17:13:10 2003
@@ -127,6 +127,8 @@
         }
         String appBase = host.getAppBase();
 
+        child.setParent(host);
+
         if (!(host instanceof StandardHost)) {
             return;
         }
---------------------------------------------------------------------

An additional call to child.setParent(host) in *begin* will make sure that 
later call to getParent() returns a non-null Host reference.

Of course, there could be other ways to fix this problem.

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