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excel import and export utils.
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package top.yumbo.excel.util;

import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils;
import top.yumbo.excel.interfaces.SerializableFunction;

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;

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);
  }
}