org.apache.ibatis.exceptions.PersistenceException: 
### Error building SqlSession.
### The error may exist in User.xml
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: java.lang.NullPointerException
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.qf.test.Demo01.test01(Demo01.java:31)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
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:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: java.lang.NullPointerException
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
Caused by: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. Cause: java.lang.NullPointerException
at 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)
... 27 more
Caused by: java.lang.NullPointerException
at org.apache.ibatis.builder.xml.XMLMapperBuilder.configurationElement(XMLMapperBuilder.java:109)
... 30 more

解決方法一：

檢視User.xml y對映檔案mapper中是否定義了名稱空間  namespace="test”，如果沒有加上namespace="test”就可以

<?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="test">
     
     <!-- 根據id查詢使用者，UesrById(int id)
     select:配置查詢語句
     id:可以通過id找到執行的statement，（ststement是唯一標識）
     praramentType:輸入引數的型別
     resultType:輸出結果型別
      -->
      
      <select id="findById" parameterType="int" resultType="com.qf.domain.User">
         select * from user where id=#{id}
         
   </select>      
</mapper>
 

解決方法二：（原文地址：http://blog.csdn.NET/lkwan123/article/details/59043923）

1. org.apache.ibatis.exceptions.PersistenceException:   
2. ### Error building SqlSession.  
3. ### The error may exist in cn.itcast.mybatis.mapper/UserMapper.xml  
4. ### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource cn.itcast.mybatis.mapper/UserMapper.xml  
5.     出現這個問題大多數都是找不到對映檔案，這和沒有遵循mybatis的mapper代理配置規範有關，對於我這個問題仔細看java.io.IOException:Could not find resource   
6. cn.itcast.mybatis.mapper/UserMapper.xml,就是檔案讀寫出現問題，系統找不到這個檔案，需要檢查，mapper介面與對映的mapper.xml 的命名是否一致，是否在同一目錄下。  
7. 如果還沒解決就在看SqlMapConfig.xml配置檔案載入mapper介面檔案的路徑有沒有錯誤，一般有兩種方試，第一掃描類<mapperclass=:"類路徑和類名"/>第二種批量掃描載入：選擇掃描包<packagename="包名"/>經過不懈努力問題終於解決。
8. 開發mybatis時要注意四點開發規範：  
9. 1、在mapper.xml中namespace等於mapper介面地址  
10. 2、mapper.java介面中的方法名和mapper.xml中statement的id一致  
11. 3、mapper.java介面中的方法輸入引數型別和mapper.xml中statement的parameterType指定的型別一致。  
12. 4、mapper.java介面中的方法返回值型別和mapper.xml中statement的resultType指定的型別一致。