Spring Property Injection in a final attribute @Value - Java

Question

A simple question on Spring injection from a properties file for a final attribute.

I have a properties file which I want to store a file path in. Generally when I use properties files I setup class attributes using something like this:

private @Value("#{someProps['prop.field']}") String someAttrib ;

Then in my spring.xml I would have something like:

<util:properties id="someProps"   
    location="classpath:/META-INF/properties/somePropFile.properties" />

This works well, is simple and makes code nice and neat. But I'm not sure what is the neatest pattern to use when trying to inject properties values into final class attributes?

Obviously something like:

private static final @Value("#{fileProps['dict.english']}") String DICT_PATH; 

will not work. Is there another way?

Solution 1

The only way you can inject values into a final field is through Constructor Injection. Everything else would be an awful hack on Spring's side.

Solution 2

If you are looking for an example here is one:

public class Test {
    private final String value;

    public Test(@Value("${some.value}") String value){
        this.value=value;
        System.out.println(this.value);
    }
}

Comments

[skaffman]

No, the two approaches are incompatible.

[wheeler]

Is there an example of this?

[giannis christofakis]

How are you gonna initialize this class? Are you gonna annotate it as a Component and let the container do it or in any other way ?

[Austin Poole]

Using @Component annotation or any of the other stereotypes will work

[giannis christofakis]

Any idea how to do the same in a static property?

[Austin Poole]

You can't. You can only initialize a static final property in two ways. In a static block or in the declaration statement. static { STATIC_VARIABLE = "value";} or private static final String FOO = "bar"