一直碰到这个问题，学不了了

java.lang.NoClassDefFoundError: Could not initialize class com.imooc.mybatis.uitls.MybatisUtils

    at com.imooc.mybatis.MybatisTestor.testSelectAll(MybatisTestor.java:50)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)


前面好端端的，加了<mapper>之后，不仅selectAll()这个报错，之前测试成功的也报错，都是报这个错

源代码

goods.xml

<?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>
   <select id="selectAll" resultType="com.imooc.mybatis.entity.Goods">
  /* useCache="false"代表不使用缓存*/
       select * from t_goods order by goods_id desc limit 10
   </select>
</mapper>

mabatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
       PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
       "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
   <environments default="dev">
   <!--        配置环境，不同的环境不同的id名字-->
   <environment id="dev">
       <!--采用JDBC方式对数据库事务进行commit/rollback-->
       <transactionManager type="JDBC"></transactionManager>
       <!--            采用连接池方式管理数据库连接-->
       <dataSource type="POOLED">
           <!--            <dataSource type="com.imooc.mybatis.entity.C3P0DataSourceFactory">-->
           <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
           <property name="url"
                     value="jdbc:mysql://localhost:3306/babytun?useUnicode=true&amp;characterEncoding=UTF-8"/>
           <property name="username" value="root"/>
           <property name="password" value="123"/>
           <!--                <property name="initialPoolSize" value="5"/>-->
           <!--                <property name="maxPoolSize" value="20"/>-->
           <!--                <property name="minPollSize" value="5"/>-->
       </dataSource>
   </environment>
   </environments>
   <mappers>
       <mapper resource="mappers/goods.xml"></mapper>
   </mappers>
</configuration>

工具类

package com.imooc.mybatis.uitls;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.Reader;

public class MybatisUtils {
   //    利用static（静态）属于类不属于对象，且全局唯一
   private static SqlSessionFactory sqlSessionFactory = null;
   //    利用静态块在初始类时实例化sqlSessionFactory
   static {
       Reader reader =null;
       try {
            reader = Resources.getResourceAsReader("mybatis-config.xml");
           sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
       } catch (IOException e) {
           e.printStackTrace();
//            初始化错误时，通过抛出异常ExceptionInInitializerError通知调用者
           throw new ExceptionInInitializerError(e);
       }
   }

   public static SqlSession openSession(){
       return sqlSessionFactory.openSession();
   }

   public static void closeSession(SqlSession sqlSession){
       if (sqlSession!=null){
           sqlSession.close();
       }
   }
}