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, possibly 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

    • prepare

      default JxltEngine.Template prepare(JexlContext context, Object... args)
      Prepares this template by expanding any contained deferred TemplateExpression with optional arguments.

      This binds arguments to template parameters for immediate expressions when the template also uses deferred/nested expressions.

      Parameters:
      context - the context to prepare against
      args - the arguments to bind (optional)
      Returns:
      the prepared version of the template
      Since:
      3.6.2