错误一开始也是同样空指针，然后报错链接过去的却是其他项目的工具类，后面把其他项目给删掉了，但还是报错空指针，这回链接的就是本项目的了，但问题是测试类运行了前三个方法的时候是没有问题的，但到了第四个方法就报错了，不知道是中途休息的时候点到了哪里还是怎么样，接着同类下其他的测试方法也开始报同样的错误。
结构
配置环境
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- 1 配置环境，默认的环境id为mysql -->
<environments default="mysql">
<!-- 1.2 配置id，为mysql的数据库环境 -->
<environment id="mysql">
<!-- 使用JDBC的事务管理 -->
<transactionManager type="JDBC" />
<!-- 数据库连接池 -->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
<property name="username" value="root" />
<property name="password" value="123456" />
</dataSource>
</environment>
</environments>
<!-- 2 配置Mapper的位置 -->
<mappers>
<!-- 可以配置多个Mapper -->
<mapper resource="com/itheima/mapper/CustomerMapper.xml" />
</mappers>
</configuration>
映射文件
<?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">
<!-- namespace表示命名空间 -->
<mapper namespace="com.itheima.mapper.CustomerMapper">
<!-- <if>元素的使用 -->
<select id="findCustomerByNameAndJobs"
parameterType="com.itheima.po.Customer"
resultType="com.itheima.po.Customer">
select * from t_customer
<where>
<if test="username != null and username != '' ">
and username like concat('%',#{username},'%')
</if>
<if test="jobs != null and jobs != '' ">
and jobs = #{jobs}
</if>
</where>
</select>
<!-- <choose>(<when>,<otherwise>)元素使用 -->
<select id="findCustomerByNameOrJobs"
parameterType="com.itheima.po.Customer"
resultType="com.itheima.po.Customer">
select * from t_customer
<trim prefix="where" prefixOverrides="and">
<choose>
<when test="username != null and username != '' ">
and username like concat('%',#{username},'%')
</when>
<when test="jobs != null and jobs != '' ">
and jobs = #{jobs}
</when>
<otherwise>
and phone is null
</otherwise>
</choose>
</trim>
</select>
<!-- <set>元素 -->
<update id="updateCustomer" parameterType="c">
update t_customer
<set> <!-- <set>元素会去掉多余的逗号 -->
<if test="username != null and username != ''">
username = #{username},
</if>
<if test="jobs != null and jobs != ''">
jobs = #{jobs},
</if>
<if test="phone != null and phone != ''">
phone = #{phone},
</if>
</set>
where id = #{id}
</update>
<!-- <foreach>元素使用 -->
<select id="findCustomerByIds" parameterType="List"
resultType="com.itheima.po.Customer">
select * from t_customer where id in
<foreach item="id" index="index" collection="list" open="("
separator="," close=")">
#{id}
</foreach>
</select>
</mapper>
测试类
package com.itheima.test;
import java.util.ArrayList;
import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import com.itheima.po.Customer;
import com.itheima.utils.MybatisUtils;
/**
* 入门程序测试类
*/
public class MybatisTest {
/**
* 根据客户姓名和职业组合条件查询客户信息列表
*/
@Test
public void findCustomerByNameAndJobsTest() {
//通过工具类生成SqlSession对象
SqlSession sqlSession = MybatisUtils.getSession();
//创建Customer对象，封装需要组合查询的条件
Customer customer = new Customer();
customer.setUsername("jack");
customer.setJobs("teacher");
//执行SqlSession的查询方法，返回结果集
List<Customer> customers = sqlSession.selectList("com.itheima.mapper.CustomerMapper.findCustomerByNameAndJobs", customer);
//输出查询结果
for(Customer cust : customers) {
//打印输出结果
System.out.println(cust);
}
//关闭SqlSession
sqlSession.close();
}
@Test
public void findCustomerByNameOrJobsTest() {
SqlSession sqlSession = MybatisUtils.getSession();
Customer customer = new Customer();
customer.setUsername("jack");
customer.setJobs("teacher");
List<Customer> customers = sqlSession.selectList("com.itheima.mapper.CustomerMapper.findCustomerByNameOrJobs", customer);
for(Customer customers2 : customers) {
System.out.println(customers2);
}
sqlSession.close();
}
/**
* 更新客户信息
*/
@Test
public void updateCustomerTest() {
SqlSession sqlSession = MybatisUtils.getSession();
Customer customer = new Customer();
customer.setId(4);
customer.setJobs("waiter");
customer.setPhone("17777777777");
int rows = sqlSession.update("com.itheima.mapper.CustomerMapper.updateCustomer", customer);
if(rows>0) {
System.out.println("成功更新了" +rows+ "条语句！");
}else {
System.out.println("更新失败！");
}
//提交事务
sqlSession.commit();
//关闭SqlSession
sqlSession.close();
}
/**
* 根据客户编号批量查询客户信息
*/
@Test
public void findCustomerByIdsTest() {
//获取SqlSession
SqlSession sqlSession = MybatisUtils.getSession();
//创建List集合，封装查询id
List<Integer> ids = new ArrayList<>();
for(int i=0; i>3; i++) {
ids.add(i);
}
//执行SqlSession的查询方法，返回结果集
List<Customer> customers = sqlSession.selectList("com.itheima.mapper.CustomerMapper.findCustomerByIds", ids);
//输出查询结果信息
for(Customer customer : customers) {
//打印输出结果
System.out.println(customer);
}
//关闭SqlSession
sqlSession.close();
}
}
工具类
package com.itheima.utils;
import java.io.Reader;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory = null;
static {
try {
Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
} catch (Exception e) {
// TODO: handle exception
}
}
public static SqlSession getSession() {
return sqlSessionFactory.openSession();
}
}
