Whenever I try to use any EL (either $ or # syntax) in a taglib tag's
dynamic attribute in Tomcat 6.0.7, I get the following exception:
java.lang.NullPointerException
at
org.apache.jasper.compiler.Generator$GenerateVisitor.evaluateAttribute(Generator.java:2777)
at
org.apache.jasper.compiler.Generator$GenerateVisitor.generateSetters(Generator.java:2988)
at
org.apache.jasper.compiler.Generator$GenerateVisitor.generateCustomStart(Generator.java:2169)
at
org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1689)
at org.apache.jasper.compiler.Node$CustomTag.accept(Node.java:1507)
at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2336)
at org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2386)
at
org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1705)
at org.apache.jasper.compiler.Node$CustomTag.accept(Node.java:1507)
at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2336)
I traced into the source code of Tomcat 6.0.7 with a debugger and found
out the exception is caused by the code at the mentioned line 2777 of
Generator.java, which is trying to request a TagAttributeInfo from the
current attribute, but for a dynamic attribute the JspAttribute.tai
field is always null.
When I debug the evaluateAttribute method in question, I see that for
Node.JspAttribute attr, the "dynamic" field (attr.dynamic) is correctly
set to true and attr.getLocalName() returns the correct name of the
dynamic attribute. At line 2771 attr.isELInterpreterInput() returns
true, since attr.el != null. When I inspect attr.el, I see the EL
expresion is correctly parsed. Only, a few lines below that the code
fails with the NPE upon accessing the TagAttributeInfo object tai (which
is, as said always null for dynamic attributes).
--
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you must be good.
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