Collect variables from a template

[Holger Willebrandt]

Hello everybody,

i would like to parse a velocity template and collect information about
all variables that are used within it.
Therefore, i use the Parser class in the following way:
//here a reader for the template and a collector for the variables
//will be supplied
public static void findVariables(Reader reader, List collector)
                throws ParseException {
        VelocityCharStream cstream = new VelocityCharStream(reader, 0, 0);
        Parser parser = new Parser(cstream);
        findVariables(parser.process(), collector); //call method below
}

//this method will recursively collect the variables and store them
//in the collector.
public static void findVariables(Node startNode, List collector) {
        if (startNode.getClass().equals(ASTReference.class)) {
                if (!collector.contains(startNode.literal())) {
                        collector.add(startNode.literal());
                }
        }
        for (int i = 0; i < startNode.jjtGetNumChildren(); i++) {
                findVariables(startNode.jjtGetChild(i), collector);
        }
}

The code is working as long as the template does not contain a #foreach 
statement.
Whenever i try to parse velocity code with a #foreach, i get the following 
error:

java.lang.NullPointerException
        at org.apache.velocity.runtime.parser.Parser.Directive(Parser.java:628)
        at org.apache.velocity.runtime.parser.Parser.Statement(Parser.java:319)
        at org.apache.velocity.runtime.parser.Parser.process(Parser.java:258)

Looking into velocity's source code, revealed that the Parser is missing a 
RuntimeServices instance, resp. a template name.

It would be nice to have a way of collecting all variables and validating the 
synatx (a ParseException would indicate a syntax error) at once.

Any kind of help or advice is welcome.

Thanks, Holger



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