How to extend java @Interface with it's param

Question

In a spring boot application where I have two dataSources,

I need to select the proper dataSource using @Transactional annotation with the following parameters:

String value (required)
Boolean readOnly (default: false)

I want to create an @interface so I do not have to type the value (chances a developer make a mistake is motivating the decision)

So this needs to be written in a class :

@Transactional("transactionManager2")

I have created the following @interface:

@Target({ElementType.METHOD, ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Transactional("transactionManager2") public @interface TransactionManager2Tx { }

This annotation replace @Transactional("transactionManager2") and it is working well.

However, I cannot pass the other parameters. For example, this is not possible:

@TransactionManager2Tx(readOnly = true)

How can I achieve this?

See my next update =))

Andremoniy
– Andremoniy

2017-11-03 15:38:26 +00:00
Commented Nov 3, 2017 at 15:38 — Andremoniy
– Andremoniy, Commented Nov 3, 2017 at 15:38

Andremoniy · Accepted Answer · 2017-11-03 15:37:11Z

Generally - that's not possible to do, because annotation's elements values are defined at compile-time. You can not dynamically pass the values there.

But, in Spring there is a tricky annotation type @AliasFor.

You can try do the following:

@Target({ElementType.METHOD, ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Transactional("transactionManager2") public @interface TransactionManager2Tx { @AliasFor(annotation = Transactional.class, attribute = "readOnly") boolean readOnly() default false; }

If it doesn't work, you can always define the two distinct annotations, kind of:

@Target({ElementType.METHOD, ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Transactional(value = "transactionManager2", readOnly = true) public @interface ReadOnlyTransactionManager2Tx { } @Target({ElementType.METHOD, ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Transactional(value = "transactionManager2", readOnly = false) public @interface NonReadOnlyTransactionManager2Tx { }

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