1、主要异常：The error occurred while setting parameters，找不到可以set的参数
异常提示
org.apache.ibatis.exceptions.PersistenceException:
### Error querying database. Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'items' in 'class com.java.mybatis.po.User'
### The error may exist in com/java/mybatis/mapper/UserMapper.xml
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: SELECT orders.id,orders.user_id,orders.number,user.username,user.sex, orderdetail.id detailId,orderdetail.items_id,orderdetail.items_num, items.price,items.name FROM orders,USER,orderdetail,items WHERE orders.user_id = user.id AND orders.id = orderdetail.orders_id AND orderdetail.items_id = items.id
### Cause: org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'items' in 'class com.java.mybatis.po.User'
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:26)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:111)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:102)
at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:119)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:63)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:52)
at $Proxy5.findUserAndItemsRstMap(Unknown Source)
at com.java.mybatis.mapper.UserMapperTest.testFindUserAndItemsRstMap(UserMapperTest.java:153)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:69)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:48)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:292)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
异常分析：
测试类运行时出错，原因在于配置文件中pojo类之间的关系不正确，在User表中找不到Items对象成员变量，
正确的配置如下：
2、配置文件中的标签位置不正确
异常提示：
org.apache.ibatis.exceptions.PersistenceException:
### Error building SqlSession.
### The error may exist in com/java/mybatis/mapper/UserMapper.java (best guess)
### The error occurred while processing mapper_resultMap[OrdersAndDetailRstMap]_collection[detailList]
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration.
Cause: org.apache.ibatis.builder.BuilderException: Error creating document instance. Cause: org.xml.sax.SAXParseException: The content of element type "resultMap" must match "(constructor?,id*,result*,association*,collection*,discriminator?)".
at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:26)
at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:82)
at org.apache.ibatis.session.SqlSessionFactoryBuilder.build(SqlSessionFactoryBuilder.java:66)
at com.java.mybatis.mapper.OrdersMapperTest.setUp(OrdersMapperTest.java:35)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:27)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:69)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:48)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:292)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error creating document instance. Cause: org.xml.sax.SAXParseException: The content of element type "resultMap" must match "(constructor?,id*,result*,association*,collection*,discriminator?)".
at 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:80)
... 25 more
异常分析：
关于这个异常，在网上查到一些原因是：元素类型为 “resultMap” 的内容必须匹配 (constructor?,id*,result*,association*,collection*,discriminator?)” ，即pojo类之间的关系要按这个顺序写下来；这是其中一个可能的原因；
另一个原因：我犯的错是第一个原因解决后还有问题，结果发现还要解决上面提到的第一个异常，因为我没有把对应的pojo类嵌套进对应的</collection>中，导致有的pojo类没有直接关系而出现第一个异常，所以记得不要粗心大意啊。