Hello.java

package com.example;
class Hello {
  // Simple example (unknown field name, namespace "com/example/Hello", id "noop")
  @Logged
  native void noop(int a);

  // Complex example (known field names, namespace "com/example", id "fooed")
  @Logged(id="fooed", namespace="com/example", fields=["from", "to"])
  void foo(@LogFormat(As.HASHCODE) Bar source, @LogFormat(As.IDENTITY) Baz dest);
}

LogFormat.java

package java.lang.annotation;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PARAMETER})
public @interface LogFormat {
  As value;
  
  public enum As {
    STRING,   // default, uses Object#toString()
    HASHCODE, // uses Object#hashCode()
    IDENTITY, // uses System.identityHashCode()
    STRUCT,   // uses recursive representation of public fields
    IGNORED,  // completely skipped
  }
}

Logged.java

package java.lang.annotation;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface Logged {
  // defaults to method name, eg logMyEvent
  String id() default null;

  // defaults to class descriptor, eg com/example/Foo
  String namespace() default null;

  // name of each field; defaults to undefined
  String[] fields[];
}

NOTES

Supports primitive types & strings, LogFormat.As for other classes.

SharedPrefix.java

package java.lang.annotation;

// Pool it, t
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PARAMETER, ElementType.FIELD})
public @interface Pooled {
    Boolean sharedPrefix() default false;
}