Reflection

---

Motivation

@NoArgsConstructor
@Getter
class User {
    private String name;
    private String email;
}

var user = entitiyManager.find(User.class, 42);
System.out.println(user.getName()); -> "Max"

Wie?

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Class

Class<User> clazz = User.class;
clazz = user.getClass();

class Class {
    String getName()       // -> at.htlstp.domain.User
    String getSimpleName() // -> User
    Field[] getDeclaredFields()
    Constructor[] getDeclaredConstructors()
    Method[] getDeclaredMethods()
    Field getField(String name)
    Constructor getConstructor(Class<?>... parameterTypes)
    Method getMethod(String name, Class<?>... parameterTypes)
    A getAnnotation(Class<A> annotationClass)
    ...

• getMethods() -> alle public Methoden
• getDeclaredMethods() -> alle Methoden
• Constructor, Field, Method analog

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Annotations

public @interface Entity {
   String name default "";
   String table();
   String[] constraints();
}

@Entity(table = "users", constraints = {"UNIQUE(name)"})
class User {}

Class clazz = User.class
Entity entity = clazz.getAnnotation(Entity.class);
String table = null;
if (entity.table().equals(""))
    table = clazz.getSimpleName();
else
    table = entity.table();
connection.prepareStatement("create table ? ...")
        .setString(1, table);