public boolean start()

in core/src/main/java/org/apache/struts2/components/IteratorComponent.java [253:331]
59 lines of code
22 McCabe index (conditional complexity)

    public boolean start(Writer writer) {
        //Create an iterator status if the status attribute was set.
        if (statusAttr != null) {
            statusState = new IteratorStatus.StatusState();
            status = new IteratorStatus(statusState);
        }

        if (beginStr != null)
            begin = (Integer) findValue(beginStr,  Integer.class);

        if (endStr != null)
            end = (Integer) findValue(endStr,  Integer.class);

        if (stepStr != null)
            step = (Integer) findValue(stepStr,  Integer.class);

        ValueStack stack = getStack();

        if (value == null && begin == null && end == null) {
            value = "top";
        }
        Object iteratorTarget = findValue(value);
        iterator = MakeIterator.convert(iteratorTarget);

        if (begin != null) {
            //default step to 1
            if (step == null)
                step = 1;

            if (iterator == null) {
                //classic for loop from 'begin' to 'end'
                iterator = new CounterIterator(begin, end, step, null);
            } else {
                //only arrays and lists are supported
                if (iteratorTarget.getClass().isArray()) {
                    Object[] values = (Object[]) iteratorTarget;
                    if (end == null)
                        end = step > 0 ? values.length - 1 : 0;
                    iterator = new CounterIterator(begin, end, step, Arrays.asList(values));
                } else if (iteratorTarget instanceof List values) {
                    if (end == null)
                        end = step > 0 ? values.size() - 1 : 0;
                    iterator = new CounterIterator(begin, end, step, values);
                } else {
                    //so the iterator is not based on an array or a list
                    LOG.error("Incorrect use of the iterator tag. When 'begin' is set, 'value' must be" +
                            " an Array or a List, or not set at all. 'begin', 'end' and 'step' will be ignored");
                }
            }
        }

        // get the first
        if ((iterator != null) && iterator.hasNext()) {
            Object currentValue = iterator.next();
            stack.push(currentValue);

            if (currentValue != null) {
                threadAllowlist.allowClassHierarchy(currentValue.getClass());
            }

            String var = getVar();

            if ((var != null)) {
                putInContext(currentValue);
            }

            // Status object
            if (statusAttr != null) {
                statusState.setLast(!iterator.hasNext());
                oldStatus = stack.getContext().get(statusAttr);
                stack.getContext().put(statusAttr, status);
            }

            return true;
        } else {
            super.end(writer, "");
            return false;
        }
    }