Java使用注解实现BigDecimal的四舍五入

public static void main(String[] args) {
    BigDecimal bigDecimalValue = new BigDecimal("9.455");
    BigDecimal result = bigDecimalValue.setScale(2, RoundingMode.FLOOR);
    System.out.println("FLOOR: " + result);

    BigDecimal result2 = bigDecimalValue.setScale(2, RoundingMode.CEILING);
    System.out.println("CEILING: " + result2);

    BigDecimal result3 = bigDecimalValue.setScale(2, RoundingMode.HALF_UP);
    System.out.println("HALF_UP: " + result3);

    BigDecimal result4 = bigDecimalValue.setScale(2, RoundingMode.HALF_EVEN);
    System.out.println("HALF_EVEN: " + result4);

    BigDecimal result5 = bigDecimalValue.setScale(2, RoundingMode.HALF_DOWN);
    System.out.println("HALF_DOWN: " + result5);

    BigDecimal result6 = bigDecimalValue.setScale(3, RoundingMode.UNNECESSARY);
    System.out.println("UNNECESSARY: " + result6);
}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface DecimalScale {
    int value() default 2; // 默认截取到两位小数
}

package com.imile.ops.analysis.config.myabtis;

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import com.imile.ops.analysis.annotation.DecimalScale;
import com.imile.ops.analysis.context.RequestInfoHolder;
import com.imile.ops.analysis.context.UserContext;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.stereotype.Component;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.time.LocalDateTime;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

/**
 * MybatisPlus自定义填充公共字段
 *
 * @author Andrew
 * @date 2020/08/11
 */
@Component
public class MybatisMetaObjectHandler implements MetaObjectHandler {
    private final static String USER_CODE = "USER_CODE";
    private final static String USER_NAME = "USER_NAME";

    private Map<String, String> getOperator() {
        Map<String, String> userMap = new HashMap<>();
        UserContext userInfo = RequestInfoHolder.getLoginInfo();
        if (userInfo == null) {
            userMap.put(USER_CODE, "");
            userMap.put(USER_NAME, "");
        } else {
            userMap.put(USER_CODE, userInfo.getUserCode());
            userMap.put(USER_NAME, userInfo.getUserName());
        }
        return userMap;
    }

    @Override
    public void insertFill(MetaObject metaObject) {
        Map<String, String> userMap = getOperator();
        // 如果用户不为数据迁移
        Object createUserCode = getFieldValByName("createUserCode", metaObject);
        Object id = getFieldValByName("id", metaObject);
        if (createUserCode == null) {
            setFieldValByName("createUserCode", userMap.get(USER_CODE), metaObject);
        }
        Object createUserName = getFieldValByName("createUserName", metaObject);
        if (createUserName == null) {
            setFieldValByName("createUserName", userMap.get(USER_NAME), metaObject);
        }
        Object createDate = getFieldValByName("createDate", metaObject);
        if (createDate == null) {
            setFieldValByName("createDate", LocalDateTime.now(), metaObject);
        }
        Object lastUpdUserCode = getFieldValByName("lastUpdUserCode", metaObject);
        if (lastUpdUserCode == null) {
            setFieldValByName("lastUpdUserCode", userMap.get(USER_CODE), metaObject);
        }
        Object lastUpdUserName = getFieldValByName("lastUpdUserName", metaObject);
        if (lastUpdUserName == null) {
            setFieldValByName("lastUpdUserName", userMap.get(USER_NAME), metaObject);
        }
        Object lastUpdDate = getFieldValByName("lastUpdDate", metaObject);
        if (lastUpdDate == null) {
            setFieldValByName("lastUpdDate", LocalDateTime.now(), metaObject);
        }
        // 处理带有 @DecimalScale() 注解的字段
        processDecimalFields(metaObject);
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        Map<String, String> userMap = getOperator();
        setFieldValByName("lastUpdUserCode", userMap.get(USER_CODE), metaObject);
        setFieldValByName("lastUpdUserName", userMap.get(USER_NAME), metaObject);
        setFieldValByName("lastUpdDate", LocalDateTime.now(), metaObject);

        processDecimalFields(metaObject);
    }

    /**
     * 处理带有 @DecimalScale() 注解的字段
     *
     * @param metaObject
     */
    private void processDecimalFields(MetaObject metaObject) {
        Arrays.stream(metaObject.getOriginalObject().getClass().getDeclaredFields())
                .filter(field -> field.isAnnotationPresent(DecimalScale.class))
                .forEach(field ->
                {
                    try {
                        field.setAccessible(true);
                        // 获取字段值
                        Object value = field.get(metaObject.getOriginalObject());
                        if (value != null) {
                            // 检查字段值是否为 BigDecimal
                            if (value instanceof BigDecimal) {
                                // 是 -> 截取(向下)指定位数小数
                                BigDecimal v = new BigDecimal(value.toString());
                                // 赋值
                                field.set(metaObject.getOriginalObject(),
                                        v.setScale(field.getAnnotation(DecimalScale.class).value(), RoundingMode.FLOOR));
                            } else {
                                throw new IllegalArgumentException("The field annotated with @DecimalScale must be a Number type.");
                            }
                        }
                    } catch (IllegalAccessException e) {
                        throw new RuntimeException(e);
                    }
                });
    }
}