Re: Handling null values

Hi, if you want to handle null values with FreeMarker you have to modify the
source code of tow methods:
    - freemarker.core.ComparisonExpression.isTrue(Environment env)
    - freemarker.core.DollarVariable.accept(Environment env)

code:

NEXT CODE WILL ALLOW YOU TO INTRODUCE EXPRESSIONS LIKE:
                        <#if my.variable != null>
                               ${my.variable}
                        </#if>
IT MEANS: IF my.variable EXISTS IN MODEL THEN CONTENT WILL BE PRINTED
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freemarker.core.ComparisonExpression
   boolean isTrue(Environment env) throws TemplateException {
    	TemplateModel ltm = null;
        TemplateModel rtm = null;
        try {
        	ltm = left.getAsTemplateModel(env);
        }
        catch (InvalidReferenceException exc) {
        	ltm = null;
        }
        try {
        	rtm = right.getAsTemplateModel(env);
        }
        catch (InvalidReferenceException exc) {
        	rtm = null;
        }
        
        if (env != null && env.isClassicCompatible()) {
            if (ltm == null) {
                ltm = TemplateScalarModel.EMPTY_STRING;
            }
            if (rtm == null) {
                rtm = TemplateScalarModel.EMPTY_STRING;
            }
        }
        
        int comp = 0;
        
        if (left.getSource().equals("null")) {
        	if (rtm != null)
        		comp = 1;
        }
        else if (right.getSource().equals("null")) {
        	if (ltm != null)
        		comp = 1;
        }
        else {
	        assertNonNull(ltm, left, env);
	        assertNonNull(rtm, right, env);
	        
	        if(ltm instanceof TemplateNumberModel && rtm instanceof
TemplateNumberModel) { 
	            Number first =
EvaluationUtil.getNumber((TemplateNumberModel)ltm, left, env);
	            Number second =
EvaluationUtil.getNumber((TemplateNumberModel)rtm, right, env);
	            ArithmeticEngine ae = 
	                env != null 
	                    ? env.getArithmeticEngine()
	                    : getTemplate().getArithmeticEngine();
	            comp = ae.compareNumbers(first, second);
	        }
	        else if(ltm instanceof TemplateDateModel && rtm instanceof
TemplateDateModel) {
	            TemplateDateModel ltdm = (TemplateDateModel)ltm;
	            TemplateDateModel rtdm = (TemplateDateModel)rtm;
	            int ltype = ltdm.getDateType();
	            int rtype = rtdm.getDateType();
	            if(ltype != rtype) {
	                throw new TemplateException(
	                    "Can not compare dates of different type. Left date is
of "
	                    + TemplateDateModel.TYPE_NAMES.get(ltype)
	                    + " type, right date is of " 
	                    + TemplateDateModel.TYPE_NAMES.get(rtype) + " type.", 
	                    env);
	            }
	            if(ltype == TemplateDateModel.UNKNOWN) {
	                throw new TemplateException(
	                    "Left date is of UNKNOWN type, and can not be
compared.", env);
	            }
	            if(rtype == TemplateDateModel.UNKNOWN) {
	                throw new TemplateException(
	                    "Right date is of UNKNOWN type, and can not be
compared.", env);
	            }
	            
	            Date first = EvaluationUtil.getDate(ltdm, left, env);
	            Date second = EvaluationUtil.getDate(rtdm, right, env);
	            comp = first.compareTo(second);
	        }
	        else if(ltm instanceof TemplateScalarModel && rtm instanceof
TemplateScalarModel) {
	            if(operation != EQUALS && operation != NOT_EQUALS) {
	                throw new TemplateException("Can not use operator " +
opString + " on string values.", env);
	            }
	            String first =
EvaluationUtil.getString((TemplateScalarModel)ltm, left, env);
	            String second =
EvaluationUtil.getString((TemplateScalarModel)rtm, right, env);
	            comp = env.getCollator().compare(first, second);
	        }
	        else if(ltm instanceof TemplateBooleanModel && rtm instanceof
TemplateBooleanModel) {
	            if(operation != EQUALS && operation != NOT_EQUALS) {
	                throw new TemplateException("Can not use operator " +
opString + " on boolean values.", env);
	            }
	            boolean first = ((TemplateBooleanModel)ltm).getAsBoolean();
	            boolean second = ((TemplateBooleanModel)rtm).getAsBoolean();
	            comp = (first ? 1 : 0) - (second ? 1 : 0);
	        }
	        // Here we handle compatibility issues
	        else if(env.isClassicCompatible()) {
	            String first = left.getStringValue(env);
	            String second = right.getStringValue(env);
	            comp = env.getCollator().compare(first, second);
	        }
	        else {
	            throw new TemplateException(
	                "The only legal comparisons are between two numbers, two
strings, or two dates.\n"
	                + "Left  hand operand is a " + ltm.getClass().getName() +
"\n"
	                + "Right hand operand is a " + rtm.getClass().getName() +
"\n"
	                , env);
	        }
        }
        
        switch (operation) {
            case EQUALS:
                return comp == 0;
            case NOT_EQUALS:
                return comp != 0;
            case LESS_THAN : 
                return comp < 0;
            case GREATER_THAN : 
                return comp > 0;
            case LESS_THAN_EQUALS :
                return comp <= 0;
            case GREATER_THAN_EQUALS :
                return comp >= 0;
            default :
                throw new TemplateException("unknown operation", env);
        }
    }
____________________________________________________________________



NEXT CODE WILL IGNORE UNDEFINED VARIABLES
IT MEANS THAT IF SOME VARIABLE IS NOT DEFINED IN MODEL FREE MARKER WILL
IGNORE IT
_______________________________________________________________________
freemarker.core.DollarVariable: 
	void accept(Environment env) throws TemplateException, IOException {
		String val = null;
		try {
			val = this.escapedExpression.getStringValue(env);
			if (val.trim().length() == 0) {
				val = getSource();
				System.out
						.println("\t[freemarker] Warning: variable not defined "
								+ getSource());
			}
		} catch (Exception exc) {
			val = getSource();
			System.out.println("\t[freemarker] Warning: variable not defined "
					+ getSource());
		}
		env.getOut().write(val);
	}

_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
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koevet wrote:
> 
> Hello, I have just started using Freemarker.
> 
> I have a basic problem. How do I set the template to handle null values of
> an int field of a pojo as String and display no values? 
> Currently my template looks like:
> 
> Event: "${event.eventSource!""}","${event.eventType!""}
> 
> eventType is a int field of a pojo. If the field is null, Freemarker
> displays 0 (default for int). I would like to change the behavior to
> display an empty String. And no, I can't change the type to Integer.
> 
> Thanks
> Luciano
> 

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