nested exception is org.apache.ibatis.exceptions.PersistenceException

spring与mybatis整合，测试时异常：

两小时找答案（在底部）

nested exception is org.apache.ibatis.exceptions.PersistenceException

Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!

Caused by: org.apache.ibatis.exceptions.PersistenceException:

Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.

详细错误如下：

org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException: 
 Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
 The error may exist in com/hl/ld/mapper/UserMapper.xml
 The error may involve com.hl.ld.mapper.UserMapper.findUserById
 The error occurred while executing a query
 Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
  at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:77)
  at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:446)
  at com.sun.proxy.$Proxy9.selectOne(Unknown Source)

  at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
  at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
  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.exceptions.PersistenceException: 
Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
The error may exist in com/hl/ld/mapper/UserMapper.xml
 The error may involve com.hl.ld.mapper.UserMapper.findUserById
The error occurred while executing a query
 Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
  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 sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:606)
  at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433)
  ... 30 more
Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
  at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:80)
  at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:82)
  at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:68)
  at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:336)
  at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:84)
  at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:62)
  at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
  at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
  at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
  at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
  at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
  ... 37 more
Caused by: java.sql.SQLException: Connections could not be acquired from the underlying database!
  at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:118)
  at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:689)
  at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:140)
  at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:111)
  at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:77)
  ... 47 more
Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.
  at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1418)
  at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:606)
  at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:526)
  at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutAndMarkConnectionInUse(C3P0PooledConnectionPool.java:755)
  at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:682)
  ... 50 more

原来是在spring配置文件中配置mapper接口扫描器

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <!-- 指定扫描的包名 -->
    <property name="basePackage" value="com.hl.ld.mapper"/>

    <property name="sqlSessionFactory" ref="sqlSessionFactory"/>
            
 </bean>

因为扫描的执行比下面配置优先级要高

<!-- 加载数据库配置信息 -->
<context:property-placeholder location="classpath:db.properties"/>
 <!-- 数据源配置 -->
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
      <property name= "driverClass" value="${jdbc.driver}"></property>
       <property name="jdbcUrl" value="${jdbc.url}" />
      <property name="user" value="${jdbc.username}"/>
      <property name="password" value="${jdbc.password}"/>
</bean>

导致执行时连接数据库的配置文件还未加载，连接不到数据库，引发异常；
解决方法：将spring扫描mapper接口配置改为如下:

bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<!-- 指定扫描的包名 -->
  <property name="basePackage" value="com.hl.ld.mapper"/>
  <!-- <property name="sqlSessionFactory" ref="sqlSessionFactory"/>-->
   <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
          
</bean>

哈哈哈哈，为我们的粗心大意，干杯！