findAncestorWithClass() Problem

[Mohit G Gupta]

I am unable to understand how

findAncestorWithClass(JspTag from,java.lang.Class klass)

functions.


could somebody provide an example that explains the working of findAncestorWithClass ?

[Piyush Joshi]

Its a static method in SimpleTagSupport class.

You must have read the JavaDocs for this method.

For understanding how it works, here is the source code from Tomcat implementation:

public static final JspTag findAncestorWithClass(
        JspTag from, Class<?> klass) 
    {
        boolean isInterface = false;

        if (from == null || klass == null
                || (!JspTag.class.isAssignableFrom(klass)
                    && !(isInterface = klass.isInterface()))) {
            return null;
        }

        for (;;) {
            JspTag parent = null;
            if( from instanceof SimpleTag ) {
                parent = ((SimpleTag)from).getParent();
            }
            else if( from instanceof Tag ) {
                parent = ((Tag)from).getParent();
            }
            if (parent == null) {
                return null;
            }

            if (parent instanceof TagAdapter) {
                parent = ((TagAdapter) parent).getAdaptee();
            }

            if ((isInterface && klass.isInstance(parent))
                    || klass.isAssignableFrom(parent.getClass())) {
                return parent;
            }

            from = parent;
        }
    } 

Read the code above, its pretty straightforward to see how it has been implemented (see the for loop above).

I think now you can write an example yourself. Isn't it?