[jira] [Comment Edited] (JEXL-256) Jexl should not try to resolve a variable from Context when Context.has() returns false

["Dmitri Blinov (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/JEXL-256?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16428367#comment-16428367 ] 

Dmitri Blinov edited comment on JEXL-256 at 4/6/18 2:06 PM:
------------------------------------------------------------

I understand your logic, but I thought that if JexlContext has defined two methods for variables, like {{get()}} and {{has()}}, that would mean if we check for a variable, we should first call {{has()}} and only if it returns {{true}} we should call {{get()}}. Your explanation has your reason, that we optimistically try to {{get()}} first and if {{null}} has returned, we use {{has()}} to check if there is the variable missing or its value is {{null}}. I have implemented the context {{get()}} method to log an error message if there is an attempt to address the variable that does not exist within context. And as wrote previously, I noticed that there are log messages about missing context variables which names are parts of a longer antish style variable names. The idea is to check for {{has()}} first, so that developers writing their own context implementation could rely on {{has()}} as a guarding method. I think this is similar to {{ConcurrentHashMap}} implementation where {{get()}} method can throw NPE if there is no key, so we should rely on {{containsKey()}} before we actually try to get anything from the map


was (Author: dmitri_blinov):
I understand your logic, but I thought that if JexlContext has defined two methods for variables, like {{get()}} and {{has()}}, that would mean if we check for a variable, we should first call {{has()}} and only if it returns {{true}} we should call {{get()}}. Your explanation has your reason, that we optimistically try to {{get()}} first and if {{null}} has returned, we use {{has()}} to check if there is the variable missing or its value is {{nul}}l. I have implemented the context {{get()}} method to log an error message if there is an attempt to address the variable that does not exist within context. And as wrote previously, I noticed that there are log messages about missing context variables which names are parts of a longer antish style variable names. The idea is to check for {{has()}} first, so that developers writing their own context implementation could rely on {{has()}} as a guarding method. I think this is similar to {{ConcurrentHashMap}} implementation where {{get()}} method can throw NPE if there is no key, so we should rely on {{containsKey()}} before we actually try to get anything from the map

> Jexl should not try to resolve a variable from Context when Context.has() returns false
> ---------------------------------------------------------------------------------------
>
>                 Key: JEXL-256
>                 URL: https://issues.apache.org/jira/browse/JEXL-256
>             Project: Commons JEXL
>          Issue Type: Improvement
>    Affects Versions: 3.1
>            Reporter: Dmitri Blinov
>            Priority: Major
>
> I have bumped into the problem when my {{Context.get()}} sometimes reports access to variables that are reported by the {{Context.has()}} method as not existent, and are not supposed to be in the context, mainly parts of ant-ish variable paths. I assume that once {{Context.has()}} have reported {{false}} no attempt from the Jexl to call {{Context.get()}} with the same parameter should be made.
> I think the problem lies in {{Interpreter.java}} which first calls {{Context.get()}} and only if it returns null, which should not necceserily mean the variable does not exist, checks {{Context.has()}}. 
> {code}
>     @Override
>     protected Object visit(ASTIdentifier node, Object data) {
>         cancelCheck(node);
>         String name = node.getName();
>         if (data == null) {
>             int symbol = node.getSymbol();
>             if (symbol >= 0) {
>                 return frame.get(symbol);
>             }
>             Object value = context.get(name);
>             if (value == null
>                     && !(node.jjtGetParent() instanceof ASTReference)
>                     && !context.has(name)
>                     && !node.isTernaryProtected()) {
>                 return unsolvableVariable(node, name, true);
>             }
>             return value;
>         } else {
>             return getAttribute(data, name, node);
>         }
>     }
> {code}
> So I suggest to change the code to something like this
> {code}
>     @Override
>     protected Object visit(ASTIdentifier node, Object data) {
>         cancelCheck(node);
>         String name = node.getName();
>         if (data == null) {
>             int symbol = node.getSymbol();
>             if (symbol >= 0) {
>                 return frame.get(symbol);
>             }
>             if (!context.has(name)
>                     && !(node.jjtGetParent() instanceof ASTReference)
>                     && !node.isTernaryProtected()) {
>                 return unsolvableVariable(node, name, true);
>             }
>             return context.get(name);
>         } else {
>             return getAttribute(data, name, node);
>         }
>     }
> {code}



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