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package cn.cucc.reflection;

import java.beans.Introspector;
import java.lang.invoke.SerializedLambda;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;

public class ReflectionUtil {
	
	private static Map, Field> cache = new ConcurrentHashMap<>();

	public static  String getFieldName(SerializableFunction function) {
		Field field = ReflectionUtil.getField(function);
		return field.getName();
	}

	public static Field getField(SerializableFunction function) {
		return cache.computeIfAbsent(function, ReflectionUtil::findField);
	}

	public static Field findField(SerializableFunction function) {
		Field field = null;
		String fieldName = null;
		try {
			// 第1步 获取SerializedLambda
			Method method = function.getClass().getDeclaredMethod("writeReplace");
			method.setAccessible(Boolean.TRUE);
			SerializedLambda serializedLambda = (SerializedLambda) method.invoke(function);
			// 第2步 implMethodName 即为Field对应的Getter方法名
			String implMethodName = serializedLambda.getImplMethodName();
			if (implMethodName.startsWith("get") && implMethodName.length() > 3) {
				fieldName = Introspector.decapitalize(implMethodName.substring(3));

			} else if (implMethodName.startsWith("is") && implMethodName.length() > 2) {
				fieldName = Introspector.decapitalize(implMethodName.substring(2));
			} else if (implMethodName.startsWith("lambda$")) {
				throw new IllegalArgumentException("SerializableFunction不能传递lambda表达式,只能使用方法引用");

			} else {
				throw new IllegalArgumentException(implMethodName + "不是Getter方法引用");
			}
			// 第3步 获取的Class是字符串，并且包名是“/”分割，需要替换成“.”，才能获取到对应的Class对象
			String declaredClass = serializedLambda.getImplClass().replace("/", ".");
			Class aClass = Class.forName(declaredClass, false, ClassUtils.getDefaultClassLoader());

			// 第4步 Spring 中的反射工具类获取Class中定义的Field
			field = ReflectionUtils.findField(aClass, fieldName);

		} catch (Exception e) {
			e.printStackTrace();
		}
		// 第5步 如果没有找到对应的字段应该抛出异常
		if (field != null) {
			return field;
		}
		throw new NoSuchFieldError(fieldName);
	}
	
	
}