关于mybatis:MyBatis查询Error-instantiating-class-types-or-values

在学习mybatis时的关联关系时遇到了这个问题。

Error instantiating class com.springmvc_mybatis.pojo.Items with invalid types () or values ().

实例化具备有效类型（）或值（）的类com.springmvc_mybatis.pojo.items时出错

解决办法：

实例化失败，阐明pojo类的构造函数有问题，本次谬误地点在于我的实体类上，没有提供一个mybatis的resultMap后果集构造函数，我将此构造函数加上就不报错了。

因为mapper.xml中有一个resultMap须要用到这个构造函数：

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" ><mapper namespace="com.star.mapper.NewsMapper"> <resultMap id="BaseResultMap" type="com.star.model.News"> <constructor> <idArg column="news_id" jdbcType="INTEGER" javaType="java.lang.Integer"/> <arg column="title" jdbcType="VARCHAR" javaType="java.lang.String"/> </constructor> </resultMap> <!-- 新闻对应多个类型标签：一对多关系 --> <resultMap id="newsManyToMany" type="com.star.model.News" extends="BaseResultMap"><!--        <id column="news_id" property="newsId"/>--><!--        <result column="title" property="title"/>--> <collection property="categories" column="newsId" ofType="com.star.model.Category" select="com.star.mapper.CategoryMapper.queryNewsByCategoryId"> </collection> </resultMap> <sql id="Base_Column_List"> news_id, title    </sql> <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer"> select        <include refid="Base_Column_List"/> from t_news        where news_id = #{newsId,jdbcType=INTEGER} </select> <select id="queryCategoryByNewId" resultMap="newsManyToMany"> select * from t_news nws left join t_news_category nct on nws.news_id = nct.nid        left join t_category ctg on ctg.category_id = nct.cid        where nws.news_id = #{newsId} </select> <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer"> delete from t_news    where news_id = #{newsId,jdbcType=INTEGER} </delete> <insert id="insert" parameterType="com.star.model.News"> insert into t_news (news_id, title) values (#{newsId,jdbcType=INTEGER}, #{title,jdbcType=VARCHAR}) </insert> <insert id="insertSelective" parameterType="com.star.model.News"> insert into t_news        <trim prefix="(" suffix=")" suffixOverrides=","> <if test="newsId != null"> news_id,            </if> <if test="title != null"> title,            </if> </trim> <trim prefix="values (" suffix=")" suffixOverrides=","> <if test="newsId != null"> #{newsId,jdbcType=INTEGER},            </if> <if test="title != null"> #{title,jdbcType=VARCHAR},            </if> </trim> </insert> <update id="updateByPrimaryKeySelective" parameterType="com.star.model.News"> update t_news        <set> <if test="title != null"> title = #{title,jdbcType=VARCHAR},            </if> </set> where news_id = #{newsId,jdbcType=INTEGER} </update> <update id="updateByPrimaryKey" parameterType="com.star.model.News"> update t_news    set title = #{title,jdbcType=VARCHAR} where news_id = #{newsId,jdbcType=INTEGER} </update></mapper>