org.apache.ibatis.reflection.ReflectionException: Error instantiating class mybatis.config.UserBeanForConfig with invalid types () or values (). 这个异常表示通过反射创建你自定的JavaBean失败,因为你没有默认的构造方法,或者是你使用了<constructor>标签,但是没有符合该标签结构的构造函数。
方式一:直接使用Setter方法进行映射
<resultMap id="userBeanMap" type="mybatis.config.UserBeanForConfig"> <id column="n_userid" property="nUserId" jdbcType="INTEGER" /> <result column="c_name" property="cName" jdbcType="VARCHAR" /> <result column="c_sex" property="cSex" jdbcType="VARCHAR" /> <result column="n_age" property="nAge" jdbcType="INTEGER" /> </resultMap>
上面这种方式对Bean进行映射,必须存在一个默认的构造函数,否则就会抛出这个错误。
方式二:使用构造函数进行映射
<resultMap id="userBeanMap" type="mybatis.config.UserBeanForConfig"> <constructor> <idArg column="n_userid" jdbcType="INTEGER" javaType="int" /> <arg column="c_name" jdbcType="VARCHAR" javaType="java.lang.String" /> </constructor> <result column="c_sex" property="cSex" jdbcType="VARCHAR" /> <result column="n_age" property="nAge" jdbcType="INTEGER" /> </resultMap>
注意:使用上面这种方式时,你必须在JavaBena中创建一个类型完全匹配的构造方法(如果是基本类型,则使用包装类型。如:int应该为Integer),才能进行映射。
public UserBeanForConfig(Integer nUserId, String cName) { this.nUserId = nUserId; this.cName = cName; }
详细错误信息:
log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory). log4j:WARN Please initialize the log4j system properly. log4j:WARN See https://logging.apache.org/log4j/1.2/faq.html#noconfig for more info. Exception in thread "main" org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. Cause: org.apache.ibatis.reflection.ReflectionException: Error instantiating class mybatis.config.UserBeanForConfig with invalid types () or values (). Cause: java.lang.NoSuchMethodException: mybatis.config.UserBeanForConfig.<init>() ### The error may exist in mybatis/config/StudentForConfigMapper.xml ### The error may involve mybatis.config.StudentForConfigMapper.selectStudentListSimple-Inline ### The error occurred while setting parameters ### SQL: SELECT n_userid, c_name, c_sex, n_age FROM t_user ### Cause: org.apache.ibatis.reflection.ReflectionException: Error instantiating class mybatis.config.UserBeanForConfig with invalid types () or values (). Cause: java.lang.NoSuchMethodException: mybatis.config.UserBeanForConfig.<init>() at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:23) at org.apache.ibatis.session.defaults.DefaultSqlSession.select(DefaultSqlSession.java:126) at org.apache.ibatis.session.defaults.DefaultSqlSession.select(DefaultSqlSession.java:114) at mybatis.config.ClientForConfig.invoke(ClientForConfig.java:34) at mybatis.config.ClientForConfig.main(ClientForConfig.java:22) Caused by: org.apache.ibatis.reflection.ReflectionException: Error instantiating class mybatis.config.UserBeanForConfig with invalid types () or values (). Cause: java.lang.NoSuchMethodException: mybatis.config.UserBeanForConfig.<init>() at org.apache.ibatis.reflection.factory.DefaultObjectFactory.instantiateClass(DefaultObjectFactory.java:83) at org.apache.ibatis.reflection.factory.DefaultObjectFactory.create(DefaultObjectFactory.java:45) at org.apache.ibatis.reflection.factory.DefaultObjectFactory.create(DefaultObjectFactory.java:38) at org.apache.ibatis.executor.resultset.FastResultSetHandler.createResultObject(FastResultSetHandler.java:387) at org.apache.ibatis.executor.resultset.FastResultSetHandler.createResultObject(FastResultSetHandler.java:366) at org.apache.ibatis.executor.resultset.FastResultSetHandler.getRowValue(FastResultSetHandler.java:266) at org.apache.ibatis.executor.resultset.FastResultSetHandler.handleRowValues(FastResultSetHandler.java:221) at org.apache.ibatis.executor.resultset.FastResultSetHandler.handleResultSet(FastResultSetHandler.java:196) at org.apache.ibatis.executor.resultset.FastResultSetHandler.handleResultSets(FastResultSetHandler.java:159) at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:57) at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:70) at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:57) at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:259) at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:132) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:105) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:81) at org.apache.ibatis.session.defaults.DefaultSqlSession.select(DefaultSqlSession.java:124) ... 3 more Caused by: java.lang.NoSuchMethodException: mybatis.config.UserBeanForConfig.<init>() at java.lang.Class.getConstructor0(Class.java:2706) at java.lang.Class.getDeclaredConstructor(Class.java:1985) at org.apache.ibatis.reflection.factory.DefaultObjectFactory.instantiateClass(DefaultObjectFactory.java:57) ... 19 more
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