How to check if a variable exists in a FreeMarker template

Question

I have a Freemarker template which contains a bunch of placeholders for which values are supplied when the template is processed  I want to conditionally include part of the template if the userName variable is supplied  something like     if exists userName    Hi   userName   How are you     if exists    However  the FreeMarker manual seems to indicate that if exists is deprecated  but I can t find another way to achieve this  Of course  I could simple providing an additional boolean variable isUserName and use that like this     if isUserName    Hi   userName   How are you     if    But if there s a way of checking whether userName exists then I can avoid adding this extra variable

User · Answer

I think a lot of people are wanting to be able to check to see if their variable is not empty as well as if it exists. I think that checking for existence and emptiness is a good idea in a lot of cases, and makes your template more robust and less prone to silly errors. In other words, if you check to make sure your variable is not null AND not empty before using it, then your template becomes more flexible, because you can throw either a null variable or an empty string into it, and it will work the same in either case.

<#if p?? && p?has_content>1</#if>

Let's say you want to make sure that p is more than just whitespace. Then you could trim it before checking to see if it has_content.

<#if p?? && p?trim?has_content>1</#if>

UPDATE

Please ignore my suggestion -- has_content is all that is needed, as it does a null check along with the empty check. Doing p?? && p?has_content is equivalent to p?has_content, so you may as well just use has_content.

User · Answer

To check if the value exists     if userName       Hi   userName   How are you     if    Or with the standard freemarker syntax    lt  if userName   gt     Hi   userName   How are you   lt   if gt    To check if the value exists and is not empty    lt  if userName has content gt      Hi   userName   How are you   lt   if gt

User · Answer

Also I think if exists was used like   Hi   userName if exists   How are you    which will not break if userName is null  the result if null would be   Hi   How are you    if exists is now deprecated and has been replaced with the default operator   as in  Hi   userName    How are you    the default operator also supports a default value  such as   Hi   userName  John Doe    How are you

User · Answer

To check if the value exists     if userName       Hi   userName   How are you     if    Or with the standard freemarker syntax    lt  if userName   gt     Hi   userName   How are you   lt   if gt    To check if the value exists and is not empty    lt  if userName has content gt      Hi   userName   How are you   lt   if gt

User · Answer

To check if the value exists     if userName       Hi   userName   How are you     if    Or with the standard freemarker syntax    lt  if userName   gt     Hi   userName   How are you   lt   if gt    To check if the value exists and is not empty    lt  if userName has content gt      Hi   userName   How are you   lt   if gt

User · Answer

This one seems to be a better fit    lt  if userName has content gt      do something  lt   if gt    http   freemarker sourceforge net docs ref builtins expert html

User · Answer

Also I think if exists was used like   Hi   userName if exists   How are you    which will not break if userName is null  the result if null would be   Hi   How are you    if exists is now deprecated and has been replaced with the default operator   as in  Hi   userName    How are you    the default operator also supports a default value  such as   Hi   userName  John Doe    How are you

User · Answer

For versions previous to FreeMarker 2 3 7   You can not use    to handle missing values  the old syntax is    lt  if userName exists gt     Hi   userName   How are you   lt   if gt

User · Answer

For versions previous to FreeMarker 2 3 7   You can not use    to handle missing values  the old syntax is    lt  if userName exists gt     Hi   userName   How are you   lt   if gt

User · Answer

Also I think if exists was used like   Hi   userName if exists   How are you    which will not break if userName is null  the result if null would be   Hi   How are you    if exists is now deprecated and has been replaced with the default operator   as in  Hi   userName    How are you    the default operator also supports a default value  such as   Hi   userName  John Doe    How are you

User · Answer

This one seems to be a better fit    lt  if userName has content gt      do something  lt   if gt    http   freemarker sourceforge net docs ref builtins expert html

User · Answer

Also I think if exists was used like   Hi   userName if exists   How are you    which will not break if userName is null  the result if null would be   Hi   How are you    if exists is now deprecated and has been replaced with the default operator   as in  Hi   userName    How are you    the default operator also supports a default value  such as   Hi   userName  John Doe    How are you

User · Answer

I think a lot of people are wanting to be able to check to see if their variable is not empty as well as if it exists. I think that checking for existence and emptiness is a good idea in a lot of cases, and makes your template more robust and less prone to silly errors. In other words, if you check to make sure your variable is not null AND not empty before using it, then your template becomes more flexible, because you can throw either a null variable or an empty string into it, and it will work the same in either case.

<#if p?? && p?has_content>1</#if>

Let's say you want to make sure that p is more than just whitespace. Then you could trim it before checking to see if it has_content.

<#if p?? && p?trim?has_content>1</#if>

UPDATE

Please ignore my suggestion -- has_content is all that is needed, as it does a null check along with the empty check. Doing p?? && p?has_content is equivalent to p?has_content, so you may as well just use has_content.

User · Answer

To check if the value exists     if userName       Hi   userName   How are you     if    Or with the standard freemarker syntax    lt  if userName   gt     Hi   userName   How are you   lt   if gt    To check if the value exists and is not empty    lt  if userName has content gt      Hi   userName   How are you   lt   if gt

[java] How to check if a variable exists in a FreeMarker template?

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