PropertyDescriptor

Reflection or runtime introspection is a powerful feature in Java. some cool features we use in Spring like copyProperties, core concepts are come from Jdk only.

Under JDK java.beans package, there are some key classes used for reflection.

• Introspector
• BeanInfo
• PropertyDescriptor
• MethodDescriptor

• Introspector: It conducts introspective analysis of a JavaBean class through the getBeanInfo method and generates a BeanInfo object.
• BeanInfo: It contains an array of property descriptors and an array of method descriptors of a JavaBean.
• PropertyDescriptor: It represents a property of a JavaBean and includes the property name, property type, the reading method (getter), and the writing method (setter).
• MethodDescriptor: It represents a method in a JavaBean and contains a Method object.
• Method: It is a class in the Java reflection mechanism. Both the PropertyDescriptor and MethodDescriptor reference it, which is used to call methods at runtime.

class Person {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

public class PropertyDescriptorExample {
    public static void main(String[] args) throws Exception {

        BeanInfo beanInfo = Introspector.getBeanInfo(Person.class);

        PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();

        for (PropertyDescriptor propertyDescriptor : propertyDescriptors) {
            String propertyName = propertyDescriptor.getName();
            Class<?> propertyType = propertyDescriptor.getPropertyType();
            Method readMethod = propertyDescriptor.getReadMethod();
            Method writeMethod = propertyDescriptor.getWriteMethod();

            System.out.println("Property Name: " + propertyName);
            System.out.println("Property Type: " + propertyType);
            System.out.println("Read Method: " + readMethod);
            System.out.println("Write Method: " + writeMethod);
            System.out.println("----------------------");
        }

        Person person = new Person();

        PropertyDescriptor nameDescriptor = new PropertyDescriptor("name", Person.class);

        Method setNameMethod = nameDescriptor.getWriteMethod();

        setNameMethod.invoke(person, "John");

        Method getNameMethod = nameDescriptor.getReadMethod();

        String name = (String) getNameMethod.invoke(person);
        System.out.println("Person's name: " + name);
    }
}