On Nov 17, 2013, at 6:00 AM, Konstantin Kolinko wrote:
> 2013/11/17 Nick Williams <nicho...@nicholaswilliams.net>:
>> I have an EL 3.0 edge case that I need help understanding. Am I doing
>> something wrong (I don't think so) or is the Tomcat 8.0 implementation
>> missing something?
>>
>> Consider the following EL expression:
>>
>> ${users.stream()
>> .filter(u -> fn:contains(u.username, '1'))
>> .sorted((u1, u2) -> u1.lastName.compareTo(u2.lastName) == 0 ?
>> u1.firstName.compareTo(u2.firstName) : u1.lastName.compareTo(u2.lastName))
>> .toList()}
>>
>> This works as expected. However, it results in potentially evaluating
>> u1.lastName.compareTo(u2.lastName) twice. My understanding is that the
>> right-hand side of a lambda expression can be any valid EL expression, so I
>> believe this should also work:
>>
>> ${users.stream()
>> .filter(u -> fn:contains(u.username, '1'))
>> .sorted((u1, u2) -> x = u1.lastName.compareTo(u2.lastName); x
>> == 0 ? u1.firstName.compareTo(u2.firstName) : x)
>> .toList()}
>>
>> However, this doesn't evaluate. I get the following error instead:
>>
>> org.apache.el.parser.ParseException: Encountered " "=" "= "" at line 3,
>> column 38.
>> Was expecting one of:
>> "." ...
>> ")" ...
>> etc ...
>>
>
> What if you add "(" ")" ?
> What operator has higher priority, "->" or ";" ?
"->" has higher priority than both "=" and ";", according to the spec. In this
particular case, I'm not sure whether that means parenthesis are absolutely
required or not. However, I can confirm that adding parenthesis here solves
this problem, so perhaps that's what I was doing wrong for this error. This
expression now works:
${users.stream()
.filter(u -> fn:contains(u.username, '1'))
.sorted((u1, u2) -> (x = u1.lastName.compareTo(u2.lastName); x
== 0 ? u1.firstName.compareTo(u2.firstName) : x))
.toList()}
>> Next I tried to reduce the properties present in each user using the stream
>> "map" method. Once again, with the understanding that the right-hand side of
>> a lambda expression can be any valid EL expression, I use an EL Map literal
>> to construct a reduced set of properties:
>>
>> ${users.stream()
>> .filter(u -> fn:contains(u.username, '1'))
>> .map(u -> {'username':u.username, 'first':u.firstName,
>> 'last':u.lastName})
>> .sorted((u1, u2) -> u1.lastName.compareTo(u2.lastName) == 0 ?
>> u1.firstName.compareTo(u2.firstName) : u1.lastName.compareTo(u2.lastName))
>> .toList()}
>>
>> However, that doesn't work and I get this error:
>>
>> org.apache.el.parser.ParseException: Encountered "<EOF>" at line 3, column
>> 88.
>> Was expecting one of:
>> "." ...
>> ")" ...
>> etc ...
>>
>
> I do not understand the above. Can you provide a simple test case?
> Which one of the expressions does not work? Can you remove the others?
So, as mentioned above, the following expression works:
${users.stream()
.filter(u -> fn:contains(u.username, '1'))
.sorted((u1, u2) -> (x = u1.lastName.compareTo(u2.lastName); x
== 0 ? u1.firstName.compareTo(u2.firstName) : x))
.toList()}
If I now add the "map" operation to it, I get the EOF error. Nothing else about
the expression changed:
${users.stream()
.filter(u -> fn:contains(u.username, '1'))
.sorted((u1, u2) -> (x = u1.lastName.compareTo(u2.lastName);
x == 0 ? u1.firstName.compareTo(u2.firstName) : x))
.map(u -> {'username':u.username, 'first':u.firstName,
'last':u.lastName})
.toList()}
javax.el.ELException: Failed to parse the expression [${users.stream()
.filter(u -> fn:contains(u.username, '1'))
.sorted((u1, u2) -> (x = u1.lastName.compareTo(u2.lastName);
x == 0 ? u1.firstName.compareTo(u2.firstName) : x))
.map(u -> {'username':u.username, 'first':u.firstName,
'last':u.lastName}]
...
<root cause>
org.apache.el.parser.ParseException: Encountered "<EOF>" at line 6, column 38.
Was expecting one of:
"." ...
")" ...
etc...
Notice that it thinks the expression is ending after the closing } of the
map-literal. Now the example in 2.3.6.4 of the specification alludes to the
fact that my use of the map-literal here is correct. In that example they use a
list-literal instead (.map(p->[p.name, p.unitPrice])). I tried changing to use
a list-literal instead of a map-literal, and that's when I got the
NumberFormatException described earlier. I _believe_ both should be legal; the
specification clearly intends that at least using the list-literal should be
legal. Neither work in Tomcat.
Does this make sense?
>> Section 2.3.6.4 of the specification uses the following example, where a
>> LIST literal is used as the right-hand side of the mapping lambda expression:
>>
>> products.stream().filter(p->p.unitPrice >= 10).
>> .map(p->[p.name, p.unitPrice])
>> .toList()
>>
>> I tried to use this exact syntax, as shown in the spec, with my example:
>>
>> ${users.stream()
>> .filter(u -> fn:contains(u.username, '1'))
>> .map(u -> [u.username, u.firstName, u.lastName])
>> .sorted((u1, u2) -> u1.lastName.compareTo(u2.lastName) == 0 ?
>> u1.firstName.compareTo(u2.firstName) : u1.lastName.compareTo(u2.lastName))
>> .toList()}
>>
>> And now I get this lovely error:
>>
>> javax.el.ELException: java.lang.NumberFormatException: For input string:
>> "lastName"
>> javax.el.BeanELResolver.invoke(BeanELResolver.java:185)
>>
>> org.apache.jasper.el.JasperELResolver.invoke(JasperELResolver.java:147)
>> org.apache.el.parser.AstValue.getValue(AstValue.java:158)
>> ...
>>
>> I'm sure I'm doing something wrong here, but I'm not exactly sure what. On
>> the other hand, it's possible that the Tomcat 8.0 implementation is just
>> wrong. Can someone shed some light on this?
>>
>
> Best regards,
> Konstantin Kolinko
Thanks,
Nick
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