Java 反射工具類 ReflectionUtils

import lombok.extern.slf4j.Slf4j;

import java.lang.reflect.*;

/**
 * 反射的 Utils 函數集合
 * 提供通路私有變量, 擷取泛型類型 Class, 提取集合中元素屬性等 Utils 函數
 */
@Slf4j
public class ReflectionUtils {


    /**
     * 直接讀取對象的屬性值, 忽略 private/protected 修飾符, 也不經過 getter
     *
     * @param object
     * @param fieldName
     * @return
     */
    public static Object getFieldValue(Object object, String fieldName) {
        Field field = getDeclaredField(object, fieldName);

        if (field == null) {
            throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");
        }

        makeAccessible(field);

        Object result = null;

        try {
            result = field.get(object);
        } catch (IllegalAccessException e) {
            log.error("getFieldValue:", e);
        }

        return result;
    }

    /**
     * 直接設定對象屬性值, 忽略 private/protected 修飾符, 也不經過 setter
     *
     * @param object
     * @param fieldName
     * @param value
     */
    public static void setFieldValue(Object object, String fieldName, Object value) {
        Field field = getDeclaredField(object, fieldName);

        if (field == null) {
            throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");
        }

        makeAccessible(field);

        try {
            field.set(object, value);
        } catch (IllegalAccessException e) {
            log.error("setFieldValue:", e);
        }
    }


    /**
     * 通過反射, 獲得定義 Class 時聲明的父類的泛型參數的類型
     * 如: public EmployeeDao extends BaseDao<Employee, String>
     *
     * @param clazz
     * @param index
     * @return
     */
    @SuppressWarnings("unchecked")
    public static Class getSuperClassGenricType(Class clazz, int index) {
        Type genType = clazz.getGenericSuperclass();

        if (!(genType instanceof ParameterizedType)) {
            return Object.class;
        }

        Type[] params = ((ParameterizedType) genType).getActualTypeArguments();

        if (index >= params.length || index < 0) {
            return Object.class;
        }

        if (!(params[index] instanceof Class)) {
            return Object.class;
        }

        return (Class) params[index];
    }

    /**
     * 通過反射, 獲得 Class 定義中聲明的父類的泛型參數類型
     * 如: public EmployeeDao extends BaseDao<Employee, String>
     *
     * @param <T>
     * @param clazz
     * @return
     */
    @SuppressWarnings("unchecked")
    public static <T> Class<T> getSuperGenericType(Class clazz) {
        return getSuperClassGenricType(clazz, 0);
    }

    /**
     * 循環向上轉型, 擷取對象的 DeclaredMethod
     *
     * @param object
     * @param methodName
     * @param parameterTypes
     * @return
     */
    public static Method getDeclaredMethod(Object object, String methodName, Class<?>[] parameterTypes) {

        for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()) {
            try {
                return superClass.getDeclaredMethod(methodName, parameterTypes);
            } catch (NoSuchMethodException e) {
                //Method 不在目前類定義, 繼續向上轉型
            }
        }

        return null;
    }

    /**
     * 使 filed 變為可通路
     *
     * @param field
     */
    public static void makeAccessible(Field field) {
        if (!Modifier.isPublic(field.getModifiers())) {
            field.setAccessible(true);
        }
    }

    /**
     * 循環向上轉型, 擷取對象的 DeclaredField
     *
     * @param object
     * @param filedName
     * @return
     */
    public static Field getDeclaredField(Object object, String filedName) {

        for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()) {
            try {
                return superClass.getDeclaredField(filedName);
            } catch (NoSuchFieldException e) {
                //Field 不在目前類定義, 繼續向上轉型
            }
        }
        return null;
    }

    /**
     * 直接調用對象方法, 而忽略修飾符(private, protected)
     *
     * @param object
     * @param methodName
     * @param parameterTypes
     * @param parameters
     * @return
     * @throws InvocationTargetException
     * @throws IllegalArgumentException
     */
    public static Object invokeMethod(Object object, String methodName, Class<?>[] parameterTypes,
                                      Object[] parameters) throws InvocationTargetException {

        Method method = getDeclaredMethod(object, methodName, parameterTypes);

        if (method == null) {
            throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + object + "]");
        }

        method.setAccessible(true);

        try {
            return method.invoke(object, parameters);
        } catch (IllegalAccessException e) {
            log.error("invokeMethod:", e);
        }

        return null;
    }
}      

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