Create custom code in a constructor created with ByteBuddy

Question

I'm new with byteBudd and doing first test to learn about it I got a solution for a "problem" but I would like to improve it. I would like to generate a this code:

public class A {
  private String value;
  public A(){}
  public A(Map<String, Object> p){
    this.value=p.get("value");
  }
  //getter and setter
}

I made it work using MethodDelegation.to and use of reflection with this code

@Test
    public void withReflection() throws Exception {


        DynamicType.Builder builder = new ByteBuddy()
                .subclass(Object.class, ConstructorStrategy.Default.NO_CONSTRUCTORS)
                .name("cat.altimiras.dynamic.AAA") //must be same package
                .defineField("value", String.class, Visibility.PRIVATE)
                .defineMethod("getValue", String.class, Visibility.PUBLIC)
                .intercept(FieldAccessor.ofBeanProperty())
                .defineMethod("setValue", void.class, Visibility.PUBLIC)
                .withParameters(String.class)
                .intercept(FieldAccessor.ofBeanProperty())
                .defineConstructor(Visibility.PUBLIC)
                .intercept(MethodCall.invoke(Object.class.getDeclaredConstructor()))
                .defineConstructor(Visibility.PUBLIC)
                .withParameter(Map.class)
                .intercept(
                        MethodCall.invoke(Object.class.getDeclaredConstructor())
                                .andThen(
                                    MethodDelegation.to(
                                            new Object() {
                                                public void assign(@RuntimeType Map<String, Object> value, @This Object o) throws Exception {
                                                    Field f = o.getClass().getDeclaredField("value");
                                                    f.setAccessible(true);
                                                    f.set(o, value.get("value")); // Reflection
                                                }
                                            }
                                    )
                                )
                );

        Class cl = builder.make().load(this.getClass().getClassLoader(), ClassLoadingStrategy.Default.INJECTION).getLoaded();

        Map<String, String> p = new HashMap<>();
        p.put("value", "lala");

        Object o = cl.getConstructor(Map.class).newInstance(p);

        Assert.assertEquals("lala", o.getClass().getDeclaredMethod("getValue").invoke(o));

This is working but I don't like because : 1 - I would like to avoid the use of reflection 2 - "A" can't not be to a random package "xyzA" for instance

Do you know if this is possible? And how to do it?

Thanks in advance

Answer 1

You are using a method delegation to an anonymous type which is defined as package-private by the Java compiler. If you define a named, public class, you can invoke the delegator from any package.

Also, use the @FieldValue annotation rather than reflection to access the field in question.