My hacking journal

SimpleTemplateEngine escaping

· by admin · Read in about 2 min · (226 Words)
escaping groovy

The method createTemplate() inside SimpleTemplateEngine builds a template from a String, and then make(bindings) replaces placeholders with values from the hash.

As advertised in the documentation, placeholders are given in JSP or GString style, so the problem is: how do we escape JSP and GString delimiters? That is, how can we insert a plain $foo or a literal <%=bar%> without the engine complaining about missing keys when binding?

First, the GString part. Your first bet would be using a backslash to escape the dollar. The intuition is right, but the implementation is tricky. For example using:


won’t work, because the backslash is taken from the GString before converting to String, and then you have a "$foo" which can be evaluated as a GString placeholder from the template engine. We need to keep the backslash in that String, and the solution is a triple backslash:


The first \\ is a literal \, the \$ is a literal $, so the engine receives a \$foo, and won’t attempt to do any substitution. If you don’t like the triple escape, another option is:


which, to my understanding, means that the code will be evaluated as a GString, but instead of the name of a variable it finds a literal string, so doesn’t look for a value for the given name.


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