Hi list,
I'm using xalan-j 2.4.0 on Java 1.4.2 to execute some XPath expressions.
I wish to use some custom functions in these expressions, so I have
created the appropriate org.apache.xpath.functions.Function class:
my.pack.FuncDictionary
My code is inspired by xalan, and compiles and instanciates fine.
The code I am using to execute the XPath expression is the following:
<code>
1: XPathContext xpathSupport = new XPathContext();
2: PrefixResolverDefault prefixResolver = new PrefixResolverDefault(
(contextNode.getNodeType() == Node.DOCUMENT_NODE)
? ((Document) contextNode).getDocumentElement() : contextNode);
//Install hook functions
3: FunctionTable.installFunction("dictionary", new FuncDictionary());
4: Class c = Class.forName(new FuncDictionary().getClass().getName());
5: System.out.println(c);
// Create the XPath object.
6: XPath xpath = new XPath(expr, null, prefixResolver, XPath.SELECT,
null);
// Execute the XPath, and have it return the result
7: int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);
8: return xpath.execute(xpathSupport, ctxtNode, prefixResolver).str();
</code>
It is called with: expr == "dictionary('a','b','a','c')"
Symptoms are as follow:
All works well until the new XPath() call on line 6, where a
ClassNotFoundException occurs, wrapped by a TransformerException.
Traceback:
javax.xml.transform.TransformerException:
java.lang.ClassNotFoundException: my/pack/FuncDictionary
at
org.apache.xpath.compiler.FuncLoader.getFunction(FuncLoader.java:154)
at
org.apache.xpath.compiler.FunctionTable.getFunction(FunctionTable.java:2
84)
at
org.apache.xpath.compiler.Compiler.compileFunction(Compiler.java:1055)
at org.apache.xpath.compiler.Compiler.compile(Compiler.java:208)
at org.apache.xpath.compiler.Compiler.compile(Compiler.java:156)
at org.apache.xpath.XPath.<init>(XPath.java:209)
at
my.pack.CustomPDFBuilderHook.processXPath(CustomPDFBuilderHook.java:155)
at
my.pack.CustomPDFBuilderHook.main(CustomPDFBuilderHook.java:184)
Caused by: java.lang.ClassNotFoundException: my/pack/FuncDictionary
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:141)
at
org.apache.xpath.compiler.FuncLoader.getFunction(FuncLoader.java:146)
at
org.apache.xpath.compiler.FunctionTable.getFunction(FunctionTable.java:2
84)
at
org.apache.xpath.compiler.Compiler.compileFunction(Compiler.java:1055)
at org.apache.xpath.compiler.Compiler.compile(Compiler.java:208)
at org.apache.xpath.compiler.Compiler.compile(Compiler.java:156)
at org.apache.xpath.XPath.<init>(XPath.java:209)
at
my.pack.CustomPDFBuilderHook.processXPath(CustomPDFBuilderHook.java:155)
at
my.pack.CustomPDFBuilderHook.main(CustomPDFBuilderHook.java:184)
Apparently, xalan-j cannot re-instantiate my FuncDictionary from the
class name.
What I figured out from the source & debugging:
FunctionTable.installFunction("dictionary", new FuncDictionary())
assigns an id to this function, and stores a FunctionLoader for
"my.pack.FuncDictionary" for this id. It also registers the Id with
"dictionary" in Keywords.m_functions
When the XPath expression is lexed, "dictionary('a','b','a','c')"
transforms to a function call to that id (37 as happens)
Then the expression is compiled, and the compiler retrieves the
FuncLoader for id 37, and tries to create the function.
The function is created with Class.forName(m_funcName), followed by
newInstance()
The Class.forName() is where the exception occurs, and it is called with
"my.pack.FuncDictionary"
It seems that the ClassLoader for the class FuncLoader is null when this
is called.
In my research I have managed to create a more minimal example:
FunctionTable.getFunction(FunctionTable.FUNC_CURRENT);
//OK
int i = FunctionTable.installFunction("test", new FuncCurrent());
//i = 37
FunctionTable.getFunction(i);
//OK
int j = FunctionTable.installFunction("dictionary", new
FuncDictionary());
//j = 38
FunctionTable.getFunction(j);
//exception!
Is there something I'm missing, is this a known bug with a work-around?
Please ask for any clarification you might need.
TIA,
Jonathan Winterflood
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