Resolved: Not to hardcode in annotations

In this post, we will see how to resolve Not to hardcode in annotations

Question:

Utils

public class GeneralUtils {    

    public static String getUrlWithId(String urlsPartStr) {
        // Get a relative URL like /delete/{id} .
        String result = String.format("%s/{id}", urlsPartStr);
        return result;
    }
}

UrlsParts

public class UrlsParts {   

    public static final String delete = "/delete";

    public static final String deleteById = GeneralUtils.getUrlWithId(delete);

}

Controller

@PostMapping(UrlsParts.deleteById)
public String delete(@PathVariable Integer id,
                     Model model) {
    authorRepository.deleteById(id);

    return "redirect:" + Urls.AUTHORS_LIST.getHref();
}

FYI: this is Spring. But anyway, the question is about core Java.
Error

Attribute value must be constant

Problem
I try not to hardcode strings in annotations. In the last video there is a partial solution. But, frankly speaking, I failed miserably.
Could you help me? Any solution will suit me (Enums etc.).

Best Answer:

As the error message says, the argument for an annotation must be a constant expression. You can see the definition of a “constant” expression in the JLS:

A constant expression is an expression denoting a value of primitive type or a String that does not complete abruptly

It then goes on to list the necessary and sufficient conditions for a constant expression. Here are some of the relevant ones:

(a constant expression) is composed using only the following: Literals of primitive type (§3.10.1, §3.10.2, §3.10.3, §3.10.4), string literals (§3.10.5), and text blocks (§3.10.6) The additive operators + and – (§15.18) Simple names (§6.5.6.1) that refer to constant variables (§4.12.4). Qualified names (§6.5.6.2) of the form TypeName . Identifier that refer to constant variables (§4.12.4). […]

And a “constant variable” is (§4.12.4):

a final variable of primitive type or type String that is initialized with a constant expression (§15.29).

Notably, method calls are not constant expressions. One reason is that methods could “complete abruptly”, by throwing an exception for example.
Therefore, deleteById is not a constant variable, and so the expression deleteById is not a constant expression.
On the other hand, the expressions delete + "/{id}" is a constant expression because delete and "/{id}" are constant expressions, and + applied to constant expressions is also a constant expression.
I’d suggest declaring a separate constant called byId, if you don’t want to repeatedly write "/{id}".

public static final String byId = "/{id}";
public static final String deleteById = delete + byId;

Or use delete + byId directly as the annotation argument.

If you have better answer, please add a comment about this, thank you!

Source: Stackoverflow.com

Resolved: Not to hardcode in annotations

Resolved: How to stop a thread that has a blocking function from easygui in python

Resolved: Removing null keys from a json array of objects

Resolved: How can I generate at compile-time a separate OpenAPI Swagger.json file for each Controller in my ASP.NET project?

Question:

Best Answer:

Related Posts

Resolved: How to stop a thread that has a blocking function from easygui in python

Resolved: Removing null keys from a json array of objects

Resolved: How can I generate at compile-time a separate OpenAPI Swagger.json file for each Controller in my ASP.NET project?