详细出错代码：
org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. Cause: org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'cn.mgy.mapper.UserMapper.findById'. It's likely that neither a Result Type nor a Result Map was specified. ### The error may exist in cn/mgy/mapper/xml/UserMapper.xml ### The error may involve cn.mgy.mapper.UserMapper.findById ### The error occurred while handling results ### SQL: SELECT * FROM t_user where uid = ? ### Cause: org.apache.ibatis.executor.ExecutorException: A query was run and no Result Maps were found for the Mapped Statement 'cn.mgy.mapper.UserMapper.findById'. It's likely that neither a Result Type nor a Result Map was specified. at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77) at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:82) at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53) at com.sun.proxy.$Proxy4.findById(Unknown Source) at cn.mgy.test.UserTest.findById(UserTest.java:52) 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.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:538) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:760) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:460) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)
解决方案：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "mybatis-3-mapper.dtd" > 3 <mapper namespace="cn.mgy.mapper.UserMapper"> 4 <insert id="insert"> 5 INSERT INTO t_user (uname, pwd, age) VALUES (#{uname}, #{pwd}, #{age}); 6 </insert> 7 <delete id="deleteById"> 8 DELETE FROM t_user WHERE uid=#{uid} 9 </delete> 10 <update id="upUnameById"> 11 UPDATE t_user SET uname=#{uname} WHERE uid=#{uid} 12 </update> 13 <select id="findById"> 修改为：<select id="findById" resultType="cn.mgy.pojo.User">
14 SELECT * FROM t_user where uid = #{uid}
15 </select> 16 </mapper>