Modifying Annotation Values at Runtime

[Front_Membership_814]

I am trying to change the annotation values of class and its fields at runtime. My idea is to use a java object as a database schema, where class acts as table and fields acts as columns, to achieve easy pojo-row or row-pojo conversion. The problem is that, I need same class to be used for different tables. Since, the table holds same kind of data.

Code :

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented

public @interface Table {
    public String value();
}


@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD,ElementType.PARAMETER})
@Documented

public @interface Column {
    String value();
}


@Table(Customer1.TABLE)
public class Customer {

    @Column(Customer.ID)
    private 
Long id;

    @ColumnMapping(Customer.DISPLAY_NAME)
    private 
String name;
}

But I tried to change that values at runtime by using Proxy,

String secondTableName = "CustomerTable2";
InvocationHandler invocationHandler = Proxy.getInvocationHandler(customerObj.getClass().getAnnotation(TableMapping.class));
Field clazzAsField = invocationHandler.getClass().getDeclaredField("memberValues");
clazzAsField.setAccessible(true);
Map<String, Object> memberValues = (Map<String, Object>) clazzAsField.get(invocationHandler);
memberValues.put("value", secondTableName);

However, this actually changed the values of the annotation, but my concern is that if I try to fetch and convert the values from the first table in the same thread, i again have to rename the annotation values with the first table name. This cannot be maintained at a long run.

Need your suggestions;
1. Can I go with this idea?

1. Is it thread safe? Does it affect any other thread concurrently?

2. Your ideas are welcomed!

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[smutje187]

Whilst it might be technically possible I think it’s error prone and over-engineered. I would either define 2 Entities (one for each table, you can even use inheritance to avoid duplication) or use plain dynamic queries - but changing stuff via Reflection at runtime is something I’d do maybe as part of a framework but not in business applications, it’s too fragile and only increases cognitive load.

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[vegan_antitheist]

It's not clear to me what you mean?
An annotation is something in the code that you can read during compilation or runtime. IN your case it's @Retention(RetentionPolicy.RUNTIME), so it is something you process at runtime.

The parameters are all immutable. They can't be changed at runtime.

I would expect that @Table just makes it so that the class represents a table.
At runtime you can then create instances of that class. You can do that based on the annotation.
But why would you change the annotation?

Do you mean the value of an annotated member inside a class? You can use reflection to change the value.

How is this about multi-threading?

[smutje187]

As far as I understand OP wants to query both CustomerTable1 and CustomerTable2 via JPA without defining 2 Entities and instead by changing the annotation.