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Core Katharsis library
There is a newer version: 3.0.2
package io.katharsis.utils;

import io.katharsis.resource.annotations.JsonApiResource;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.*;

/**
 * Provides reflection methods for parsing information about a class.
 */
public class ClassUtils {

    private static final ClassUtils INSTANCE = new ClassUtils();

    private ClassUtils() {
    }

    /**
     * Returns a list of class fields. Supports inheritance and doesn't return synthetic fields.
     *
     * @param beanClass class to be searched for
     * @return a list of found fields
     */
    public static List getClassFields(Class beanClass) {
        Map result = new HashMap<>();

        Class currentClass = beanClass;
        while (currentClass != null && currentClass != Object.class) {
            for (Field field : currentClass.getDeclaredFields()) {
                if (!field.isSynthetic()) {
                    result.putIfAbsent(field.getName(), field);
                }
            }
            currentClass = currentClass.getSuperclass();
        }

        return new LinkedList<>(result.values());
    }

    /**
     * Tries to find a class fields. Supports inheritance and doesn't return synthetic fields.
     *
     * @param beanClass class to be searched for
     * @param fieldName field name
     * @return a list of found fields
     */
    public static Field findClassField(Class beanClass, String fieldName) {
        Class currentClass = beanClass;
        while (currentClass != null && currentClass != Object.class) {
            for (Field field : currentClass.getDeclaredFields()) {
                if (field.isSynthetic()) {
                    continue;
                }

                if (field.getName().equals(fieldName)) {
                    return field;
                }
            }
            currentClass = currentClass.getSuperclass();
        }

        return null;
    }

    /**
     * 
     * Return a list of class getters. Supports inheritance and overriding, that is when a method is found on the
     * lowest level of inheritance chain, no other method can override it.
     * 

     * A getter:
     * 

     * Starts with an is if returns boolean or {@link Boolean} value
     * Starts with a get if returns non-boolean value
     * 
     *
     * @param beanClass class to be searched for
     * @return a list of found getters
     */
    public static List getClassGetters(Class beanClass) {
        Map result = new HashMap<>();

        Class currentClass = beanClass;
        while (currentClass != null && currentClass != Object.class) {
            for (Method method : currentClass.getDeclaredMethods()) {
                if (INSTANCE.isGetter(method)) {
                    result.putIfAbsent(method.getName(), method);
                }
            }
            currentClass = currentClass.getSuperclass();
        }

        return new LinkedList<>(result.values());
    }

    /**
     * Return a list of class setters. Supports inheritance and overriding, that is when a method is found on the
     * lowest level of inheritance chain, no other method can override it.
     *
     * @param beanClass class to be searched for
     * @return a list of found getters
     */
    public static List getClassSetters(Class beanClass) {
        Map result = new HashMap<>();

        Class currentClass = beanClass;
        while (currentClass != null && currentClass != Object.class) {
            for (Method method : currentClass.getDeclaredMethods()) {
                if (INSTANCE.isSetter(method)) {
                    result.putIfAbsent(method.getName(), method);
                }
            }
            currentClass = currentClass.getSuperclass();
        }

        return new LinkedList<>(result.values());
    }

    /**
     * Return a first occurrence of a method annotated with specified annotation
     * @param searchObject instance to be searched
     * @param annotationClass annotation class
     * @return annotated method or null
     */
    public static Method findMethodWith(Object searchObject, Class annotationClass) {
        Method foundMethod = null;
        Class currentClass = searchObject.getClass();
        methodFinder:
        while (currentClass != null && currentClass != Object.class) {
            for (Method method : currentClass.getDeclaredMethods()) {
                if (method.isAnnotationPresent(annotationClass)) {
                    foundMethod = method;
                    break methodFinder;
                }
            }
            currentClass = currentClass.getSuperclass();
        }

        return foundMethod;
    }

    /**
     * Returns the first clazz in the ancestory hierarchy with the JsonApiResource annotation
     * @param data instance
     * @param  instance type
     * @return class or null
     */
    public static  Class getJsonApiResourceClass(final T data) {
        return getJsonApiResourceClass((Class)data.getClass());
    }

    public static  Class getJsonApiResourceClass(final Class candidateClass) {
        Class currentClass = candidateClass;
        while (currentClass != null && currentClass != Object.class) {
            if (currentClass.isAnnotationPresent(JsonApiResource.class)) {
                return currentClass;
            }
            currentClass = currentClass.getSuperclass();
        }

        return null;
    }

    private boolean isGetter(Method method) {
        return isBooleanGetter(method) || isNonBooleanGetter(method);
    }

    public static boolean isBooleanGetter(Method method) {
        if (!method.getName().startsWith("is"))
            return false;
        if (method.getName().length() < 3)
            return false;
        if (method.getParameterTypes().length != 0) return false;
        return boolean.class.equals(method.getReturnType()) || Boolean.class.equals(method.getReturnType());
    }

    private boolean isNonBooleanGetter(Method method) {
        if (!method.getName().startsWith("get"))
            return false;
        if (method.getName().length() < 4)
            return false;
        if (method.getParameterTypes().length != 0)
            return false;
        return !void.class.equals(method.getReturnType());
    }

    private boolean isSetter(Method method) {
        if (!method.getName().startsWith("set"))
            return false;
        if (method.getName().length() < 4)
            return false;
        return method.getParameterTypes().length == 1;
    }
}