如果值为空，则保留 FreeMarker 标记

Question

So I'm currently trying to figure out if there is anyway to preserve the freemarker markup if the data model provided doesn't contain that value. I know about ${VALUE!"DEFAULTVALUE"} , but that does not work with FreeMarker markup.

Essentially, what I'm trying to do is something along the lines of:

${TEST}${1}${2}

If the data model is set up as the following:

Map root = new HashMap();
root.put("1","ONE");
root.put("2","TWO");

When this is applied to the Template object, a null error is thrown because test is undefined. What I'm trying to get happen is if TEST is undefined, the template should still be processed into the following:

${TEST}ONETWO

Is there any way to do this using features in the FreeMarker library? I can do this with pattern matching, but there must be an easier way.

Thanks.

Answer 1

Try using ?has_content for TEST , maybe that will help. But I am not sure, if that suits to your requirements.

Answer 2

The FreeMarker library allows you to write a custom exception handler.

Unfortunately FreeMarker doesn't give the exact token that fails but you can work it out from the error message.

        cfg.setTemplateExceptionHandler(new TemplateExceptionHandler() {
        @Override
        public void handleTemplateException(TemplateException te, Environment e, Writer writer) throws TemplateException {
            try {
                String errorString = te.getFTLInstructionStack();
                int startIndex = errorString.indexOf('$');

                if (startIndex != -1) {
                    int endIndex = errorString.indexOf('}', startIndex);
                    if (endIndex != -1) {
                        writer.write(errorString.substring(startIndex, endIndex + 1));
                    }
                    else {
                        throw te;
                    }
                }
                else {
                    throw te;
                }
            }
            catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    });