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From "Henri Biestro (JIRA)" <j...@apache.org>
Subject [jira] [Created] (JEXL-197) Add annotations
Date Fri, 27 May 2016 09:00:22 GMT
Henri Biestro created JEXL-197:
----------------------------------

             Summary: Add annotations
                 Key: JEXL-197
                 URL: https://issues.apache.org/jira/browse/JEXL-197
             Project: Commons JEXL
          Issue Type: Improvement
            Reporter: Dmitri Blinov
            Assignee: Henri Biestro
             Fix For: 3.1


Another train of thoughts...

As an implementation to the extension of statement executions in JEXL we could introduce the
use of annotations to each statement or block in the script, i.e. 

{code}
@synchronized(items) {for (x : items) ...}
{code}

Each statement block should be allowed to have only one annotation but it would be convenient
to allow the syntax 
{code}
@silent @lenient {null.tryMe()}
{code}

which should be syntaxically equivalent to:

{code}
@silent {@lenient {null.tryMe()}}
{code}

>From the JexlEngine point of view, each annotation could be implemented in the form of
Interceptor interface, for example

{code}
public interface Interceptor {
   public Object onExecute(JexlStatement block, String annotation, Object.. args);
}
{code}

The annotation syntax should allow for zero, one or more parameters. Those parameters should
be evaluated before interceptor execution and submitted to the Interceptor.onExecute() method
via args parameter.

JexlEngine should be given a method to register annotation interceptor based on annotation
name, and the one for default interceptor, which should be called before each statement execution
as if @default annotation is declared in each statement in script. 

{code}
@silent {@default {...}}
{code}

The JexlStatement is the proposed new interface to somehow identify the statement or block
of code which may also provide some info about it's stack frame.

{code}
public interface JexlStatement {
   public Object interpret();

   // ..
}
{code}

The JexlStatement.interpret() method should trigger the execution of the statement block,
returning statement's result as its return value.

In the absence of a matching interceptor corresponding to the annotation name, JexlEngine
should simply ignore that, or write some diagnostic message in the log file.

Such implementation could provide developers with excellent tool to add various checks and
enhancements to scripting without pushing for new features that eventually would mess up the
basic code. The JEXL-185 issue could also be dropped since tracing could be added easily via
interceptors.




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