Package org.apache.commons.jexl3

Interface JxltEngine.Template

Enclosing class:
JxltEngine
public static interface JxltEngine.Template
A template is a JEXL script that evaluates by writing its content through a Writer.

The source text is parsed considering each line beginning with '$$' (as default pattern) as JEXL script code and all others as Unified JEXL expressions; those expressions will be invoked from the script during evaluation and their output gathered through a writer. It is thus possible to use looping or conditional construct "around" expressions generating output.

For instance: 
 $$ for(var x : [1, 3, 5, 42, 169]) {
 $$   if (x == 42) {
 Life, the universe, and everything
 $$   } else if (x > 42) {
 The value $(x} is over forty-two
 $$   } else {
 The value ${x} is under forty-two
 $$   }
 $$ }

Will evaluate as:

 The value 1 is under forty-two
 The value 3 is under forty-two
 The value 5 is under forty-two
 Life, the universe, and everything
 The value 169 is over forty-two

During evaluation, the template context exposes its writer as '$jexl' which is safe to use in this case. This allows writing directly through the writer without adding new-lines as in:

 $$ for(var cell : cells) { $jexl.print(cell); $jexl.print(';') }

A template is expanded as one JEXL script and a list of template expressions; each template expression is being replaced in the script by a call to jexl:print(expr) (the expr is in fact the expr number in the template). This integration uses a specialized JexlContext (TemplateContext) that serves as a namespace (for jexl:) and stores the template expression array and the writer (java.io.Writer) that the 'jexl:print(...)' delegates the output generation to.

Since:
3.0

  • Method Details

    • asString

      String asString()
      Recreate the template source from its inner components.
      Returns:
      the template source rewritten

    • evaluate

      void evaluate(JexlContext context, Writer writer)
      Evaluates this template.
      Parameters:
      context - the context to use during evaluation
      writer - the writer to use for output

    • evaluate

      void evaluate(JexlContext context, Writer writer, Object... args)
      Evaluates this template.
      Parameters:
      context - the context to use during evaluation
      writer - the writer to use for output
      args - the arguments

    • getParameters

      String[] getParameters()
      Gets the list of parameters expected by this template.
      Returns:
      the parameter names array

    • getPragmas

      Map<String,Object> getPragmas()
      Gets this script pragmas.
      Returns:
      the (non null, may be empty) pragmas map
      Since:
      3.1

    • getVariables

      Set<List<String>> getVariables()
      Gets the list of variables accessed by this template.

      This method will visit all nodes of the sub-expressions and extract all variables whether they are written in 'dot' or 'bracketed' notation. (a.b is equivalent to a['b']).

      Returns:
      the set of variables, each as a list of strings (ant-ish variables use more than 1 string) or the empty set if no variables are used

    • prepare

      JxltEngine.Template prepare(JexlContext context)
      Prepares this template by expanding any contained deferred TemplateExpression.
      Parameters:
      context - the context to prepare against
      Returns:
      the prepared version of the template