[stringtemplate-interest] joining attributes with a separator when some are optional

[Henno Vermeulen]

Hello,

What would be the simplest syntax with StringTemplate to join multiple attributes with a separator without getting too many separators when an attribute is empty/absent/null? This is a use case I encounter very often! I normally solve it in Java using a utility method "joinNonBlank(separator, String... strings)" which only concats the non-blank Strings with the given separator.

For example when formatting a person's name or address and certain attributes (e.g. surname prefix, country of address) are optional.

A complete address could be formatted as "<address>\n<zipCode> <city>\n<country>". However, I don't want the separating "\n" in case the country is absent and I don't want the space between zipCode and city if either of them are absent. Similarly a person's name may be formatted as "<firstName> <surNamePrefix> <surName>", but I don't want a separating space in case a field is empty/absent/null.

Below you can find a failing unit test (because of extra spaces) where I would like the personTemplate changed so that it satisfies the test. (Will the solution make a difference if the attributes are part of a Person object as in "<person.firstName> < person.surNamePrefix> < person.surName>"?)

Thank you,
Henno Vermeulen
Huize Molenaar

     @Test
     public void firstNamePrefixSurNameJoinedNonEmpty() {
         // TODO how do we join multiple attributes with a separator?
         String personTemplate = "<firstName> <surNamePrefix> <surName>";

         assertEquals(
                   "Max Planck",
                   new ST(personTemplate).add("firstName", "Max")
                            .add("surName", "Planck").render());
         assertEquals("Einstein",
                   new ST(personTemplate).add("surName", "Einstein").render());
         assertEquals("Albert", new ST(personTemplate)
                   .add("firstName", "Albert").render());
         assertEquals("Johannes Diderik van der Waals",
                   new ST(personTemplate).add("firstName", "Johannes Diderik")
                            .add("surNamePrefix", "van der")
                            .add("surName", "Waals"), vanDerWaals);
     }

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