The compiler says that the annotation value should be constant,
I have an annotated Spring 1 class @Controller
with annotated methods @RequestMapping
. I want to reference the parameter values @RequestMapping
, value
and method
, from another class, not hard-code them into an annotation.
Example
Instead
@Controller
public class MyController {
@RequestMapping(value="my/path", method=RequestMethod.GET)
public String handlePath() {
// etc...
}
}
I want two files,
@Controller
public class MyController {
@RequestMapping(value=Constants.PATH, method=Constants.PATH_METHOD)
public String handlePath() {
// etc...
}
}
and
public class Constants {
public static final String PATH = "my/path";
public static final RequestMethod PATH_METHOD = RequestMethod.GET;
}
Unfortunately this fails on the following compile-time error:
error: an enum annotation value must be an enum constant @RequestMapping(value=Constants.PATH, method=Constants.PATH_METHOD) ^
Question
Why does this work for the case String
, but not for enum
s?
Notes
- This question is not Spring specific, it is just (hopefully) an accessible example of this problem.
- I am using Java 8
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We need to see what the Java Language spec says an acceptable value for an annotation method .
It is a compile-time error if the element type is not commensurate with the element size. The element type is
T
commensurate with the element valueV
if and only if one of the following conditions is met:
- If
T
is a primitive type orString
, then itV
is a constant expression (§15.28).- If
T
is a typeenum
(§8.9), then V is a constantenum
(§8.9.1).
PATH_METHOD
is not constant enum
. RequestMethod.GET
is a constant enum
. For String
this
public static final String PATH = "my/path";
- constant variable, which is a constant expression and therefore can be used.
It shouldn't work even if the constant was declared in the same file. Please review.
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