初学Mybatis时遇到 Error building SqlSession.的原因，看了半天，终于成功解决了

1、我出现的的错误

Exception in thread "main" java.lang.ExceptionInInitializerErrorCaused by: org.apache.ibatis.exceptions.PersistenceException: ### Error building SqlSession.### The error may exist in com/lhj/mapper/PersonMapper.xml### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Person'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Personat org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:26)at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:54)at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:38)at com.lhj.test.Test.<clinit>(Test.java:21)Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Person'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Personat org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:109)at org.apache.ibatis.builder.xml.XMLConfigBuilder.parse(XMLConfigBuilder.java:92)at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:52)... 2 moreCaused by: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Person'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Personat org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:120)at org.apache.ibatis.builder.xml.XMLMapperBuilder.parse(XMLMapperBuilder.java:92)at org.apache.ibatis.builder.xml.XMLConfigBuilder.mapperElement(XMLConfigBuilder.java:322)at org.apache.ibatis.builder.xml.XMLConfigBuilder.parseConfiguration(XMLConfigBuilder.java:107)... 4 moreCaused by: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Person'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Personat org.apache.ibatis.builder.BaseBuilder.resolveClass(BaseBuilder.java:103)at org.apache.ibatis.builder.xml.XMLStatementBuilder.parseStatementNode(XMLStatementBuilder.java:72)at org.apache.ibatis.builder.xml.XMLMapperBuilder.buildStatementFromContext(XMLMapperBuilder.java:135)at org.apache.ibatis.builder.xml.XMLMapperBuilder.buildStatementFromContext(XMLMapperBuilder.java:128)at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:118)... 7 moreCaused by: org.apache.ibatis.type.TypeException: Could not resolve type alias 'Person'.  Cause: java.lang.ClassNotFoundException: Cannot find class: Personat org.apache.ibatis.type.TypeAliasRegistry.resolveAlias(TypeAliasRegistry.java:117)at org.apache.ibatis.builder.BaseBuilder.resolveAlias(BaseBuilder.java:130)at org.apache.ibatis.builder.BaseBuilder.resolveClass(BaseBuilder.java:101)... 11 moreCaused by: java.lang.ClassNotFoundException: Cannot find class: Personat org.apache.ibatis.io.ClassLoaderWrapper.classForName(ClassLoaderWrapper.java:190)at org.apache.ibatis.io.ClassLoaderWrapper.classForName(ClassLoaderWrapper.java:89)at org.apache.ibatis.io.Resources.classForName(Resources.java:256)at org.apache.ibatis.type.TypeAliasRegistry.resolveAlias(TypeAliasRegistry.java:113)... 13 more

2、我的配置文件

mybatis-config.xml：

<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><!-- 元素允许在主配置文件之外提供一个properties格式对应文件，从而使得主配置文件更加通用。这样对部署非常有用  --><properties resource="db.properties"></properties><!-- 设置别名，一定要放在properties下面  --><typeAliases><typeAlias alias="per" type="com.lhj.entity.Person"/></typeAliases><!-- 配置数据源相关的信息  --><environments default="development"><environment id="development"><transactionManager type="JDBC"></transactionManager><dataSource type="POOLED"><property name="driver" value="${driver}"/><property name="url" value="${url}"/><property name="username" value="${username}"/><property name="password" value="${password}"/></dataSource></environment></environments><!-- 映射文件 --><mappers><mapper resource="com/lhj/mapper/PersonMapper.xml"/></mappers></configuration>

PersonMapper.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 namespace="com.lhj"><!-- 查找 --><select id="findPerson" parameterType="int" resultType="Person">select * from per where id=#{id}</select><!-- 插入 --><insert id="addPerson" parameterType="Person"useGeneratedKeys="true" keyProperty="id">insert into per value(null,#{name},#{age})</insert><!-- 删除 --><delete id="delPerson" parameterType="int">delete from per where id=#{id}</delete><!-- 修改 --><update id="updatePerson" parameterType="Person">update per set name=#{name},age=#{age} where id=#{id}</update></mapper>

3、错误原因

我在mybatis-config.xml的这个配置文件里给实体类设置了别名<typeAliases>
        <typeAlias alias="per" type="com.lhj.entity.Person"/>
    </typeAliases>，而在PersonMapper.xml这个配置文件中的resultType="Person"、parameterType="Person"，我却没有用到这个别名。

解决办法就是把PersonMapper.xml这个配置文件中的修改成resultType="per"、parameterType="per"或者不用别名，直接用包名加类名，例如：resultType="com.lhj.entity.Person"、parameterType="com.lhj.entity.Person"。

哈哈，这样就完美解决了。