[JAVA] Summary of how to write annotation arguments


As I wrote in another article, I didn't touch Java very much during the heyday of annotation (?), So I didn't understand the argument rules of annotation well, and even if I googled, there was nothing that met the demand, so I will write it myself. For those who have the same question in the future.

Below, the annotation shown in the example uses @RequestMapping.

Term definition

It may not be accurate, but I use it in this sense below.

The name that associates the value you specify when writing the annotation.
The name that the annotation accepts in the reference.

Rule 1: Those with default values can be omitted

Looking at the reference of @RequestMapping, some elements are written, but since the default values are all specified, you can write as follows. The default value for each element is used.


Rule 2: Can be omitted if the argument name is value

The following have the same meaning

@RequestMapping(value = "/")

In the case of Spring, @AliasFor is prepared, and the place where" What does the value of Mapping mean? "Can be written as path. See the reference for which element is an alias for value. I think that something that is almost as perceived is another name.

@RequestMapping(path = "/")

Rule 3: Arguments may be written as scalar values even if the element type is an array

The compiler extends it to an array.

// value -> {"/"}

You may or may not write your own {}. However, {} is required when writing two or more arguments as explained below.

// value -> {"/", "/index"}
@RequestMapping("/", "/index")
// value -> {"/", "/index"}
@RequestMapping({"/", "/index"})

Rule 4: Argument name required if there are two or more arguments

It was hard to understand because I thought it was like a required argument and an optional argument like Python's default value argument.

@RequestMapping(value = "/", method = RequestMethod.GET)

//I want to decorate Python I can't write as follows
@RequestMapping("/", method = RequestMethod.GET)

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