今天开始学习我自己总结的 Java-学习路线 中的《MyBatis》,小简从 0 开始学 Java 知识,并不定期更新所学笔记,期待一年后的蜕变吧!<有同样想法的小伙伴,可以联系我一起交流学习哦!>
和 Hibernate 相比,MyBatis 封装性低于 Hibernate,但性能优秀、小巧、简单易学、应用广泛。
和 JDBC 相比,MyBatis 减少了 50% 以上的代码量,并且满足高并发和高响应的要求。
<packaging>jar</packaging>
<dependencies>
<!-- Mybatis核心 -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.9</version>
</dependency>
<!-- junit测试 -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<!-- MySQL驱动 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.27</version>
</dependency>
</dependencies>
习惯上命名为
mybatis-config.xml
,存放的位置是src/main/resources目录下
<?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>
<!--设置连接数据库的环境-->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/MyBatis"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<!--引入映射文件-->
<mappers>
<mapper resource="mappers/UserMapper.xml"/>
</mappers>
</configuration>
MyBatis中的mapper接口相当于以前的dao。区别在于mapper仅仅是接口,我们不需要提供实现类
package com.jianjian.mapper;
public interface UserMapper {
/**
* 添加用户信息
*/
int insertUser();
}
Java概念 | 数据库概念 |
---|---|
类 | 表 |
属性 | 字段/列 |
对象 | 记录/行 |
映射文件的命名规则:表所对应的实体类的类名+Mapper.xml,存放的位置是src/main/resources/mappers目录下
MyBatis中面向接口操作数据,要保证两个一致
<?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="com.jianjian.mapper.UserMapper"> <!--条件1-->
<insert id="insertUser"> <!--条件2-->
insert into t_user values(null,'张三','123',23,'女')
</insert>
</mapper>
DROP TABLE IF EXISTS `t_user`;
CREATE TABLE `t_user` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(255) CHARACTER SET utf8 DEFAULT NULL,
`password` varchar(255) CHARACTER SET utf8 DEFAULT NULL,
`age` int(11) DEFAULT NULL,
`sex` char(1) CHARACTER SET utf8 DEFAULT NULL,
`email` varchar(255) CHARACTER SET utf8 DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
package com.jianjian.pojo;
public class User {
private Integer id;
private String username;
private String password;
private Integer age;
private String sex;
private String email;
//...构造器、get、set、toString方法
}
public class UserMapperTest {
@Test
public void testInsertUser() throws IOException {
//读取MyBatis的核心配置文件
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
//获取SqlSessionFactoryBuilder对象
SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
//通过核心配置文件所对应的字节输入流创建工厂类SqlSessionFactory,生产SqlSession对象
SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
//获取sqlSession,此时通过SqlSession对象所操作的sql都必须手动提交或回滚事务
//SqlSession sqlSession = sqlSessionFactory.openSession();
//创建SqlSession对象,此时通过SqlSession对象所操作的sql都会自动提交
SqlSession sqlSession = sqlSessionFactory.openSession(true);
//通过代理模式创建UserMapper接口的代理实现类对象
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
//调用UserMapper接口中的方法,就可以根据UserMapper的全类名匹配元素文件,通过调用的方法名匹配映射文件中的SQL标签,并执行标签中的SQL语句
int result = userMapper.insertUser();
//提交事务
//sqlSession.commit();
System.out.println("result:" + result);
}
}
SqlSession sqlSession = sqlSessionFactory.openSession(true);
,传入一个Boolean类型的参数,值为true,这样就可以自动提交新建utils/SqlSessionUtils.java
public class SqlSessionUtils {
public static SqlSession getSqlSession(){
SqlSession sqlSession = null;
try {
//读取MyBatis的核心配置文件
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
//获取SqlSessionFactoryBuilder对象
SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
//通过核心配置文件所对应的字节输入流创建工厂类SqlSessionFactory,生产SqlSession对象
SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
//创建SqlSession对象,此时通过SqlSession对象所操作的sql都会自动提交
sqlSession = sqlSessionFactory.openSession(true);
} catch (IOException e) {
throw new RuntimeException(e);
}
return sqlSession;
}
}
<!-- log4j日志 -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="STDOUT" class="org.apache.log4j.ConsoleAppender">
<param name="Encoding" value="UTF-8" />
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%-5p %d{MM-dd HH:mm:ss,SSS} %m (%F:%L) \n" />
</layout>
</appender>
<logger name="java.sql">
<level value="debug" />
</logger>
<logger name="org.apache.ibatis">
<level value="info" />
</logger>
<root>
<level value="debug" />
<appender-ref ref="STDOUT" />
</root>
</log4j:configuration>
核心配置文件中的标签必须按照固定的顺序(有的标签可以不写,但顺序一定不能乱): 顺序为:properties、settings、typeAliases、typeHandlers、objectFactory、objectWrapperFactory、reflectorFactory、plugins、environments、databaseIdProvider、mappers
<!--引入properties文件,此时就可以${属性名}的方式访问属性值-->
<properties resource="jdbc.properties"></properties>
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/Mybatis
jdbc.username=root
jdbc.password=root
<settings>
<!--将表中字段的下划线自动转换为驼峰-->
<setting name="mapUnderscoreToCamelCase" value="true"/>
<!--开启延迟加载-->
<setting name="lazyLoadingEnabled" value="true"/>
</settings>
a>设置单个对象别名
<typeAliases>
<typeAlias type="com.jianjian.pojo.User"></typeAlias> <!--默认别名,类名-->
<typeAlias type="com.jianjian.pojo.User" alias="user"></typeAlias><!--自定义别名-->
</typeAliases>
b>设置某包下所有对象拥有默认别名
<typeAliases>
<!--以包为单位,设置改包下所有的类型都拥有默认的别名,即类名且不区分大小写-->
<package name="com.jianjian.pojo"/>
</typeAliases>
在MyBatis中,对于Java中常用的类型都设置了类型别名
别名 | 映射的类型 |
---|---|
_byte | byte |
_long | long |
_short | short |
_int | int |
_integer | int |
_double | double |
_float | float |
_boolean | boolean |
string | String |
byte | Byte |
long | Long |
short | Short |
int | Integer |
integer | Integer |
double | Double |
float | Float |
boolean | Boolean |
date | Date |
decimal | BigDecimal |
bigdecimal | BigDecimal |
object | Object |
map | Map |
hashmap | HashMap |
list | List |
arraylist | ArrayList |
collection | Collection |
iterator | Iterator |
<plugins>
<plugin interceptor="org.mybatis.example.ExamplePlugin">
<property name="someProperty" value="100"/>
</plugin>
</plugins>
<environments default="mysql_test">
<!--
environment:设置具体的连接数据库的环境信息
属性:id:设置环境的唯一标识,可通过environments标签中的default设置某一个环境的id,表示默认使用的环境
-->
<environment id="mysql_test">
<!--
transactionManager:设置事务管理方式
属性:
type:设置事务管理方式,type="JDBC|MANAGED"
type="JDBC":设置当前环境的事务管理都必须手动处理
type="MANAGED":设置事务被管理,例如spring中的AOP
-->
<transactionManager type="JDBC"/>
<!--
dataSource:设置数据源
属性:
type:设置数据源的类型,type="POOLED|UNPOOLED|JNDI"
type="POOLED":使用数据库连接池,即会将创建的连接进行缓存,下次使用可以从缓存中直接获取,不需要重新创建
type="UNPOOLED":不使用数据库连接池,即每次使用连接都需要重新创建
type="JNDI":调用上下文中的数据源
-->
<dataSource type="POOLED">
<!--设置驱动类的全类名-->
<property name="driver" value="${jdbc.driver}"/>
<!--设置连接数据库的连接地址-->
<property name="url" value="${jdbc.url}"/>
<!--设置连接数据库的用户名-->
<property name="username" value="${jdbc.username}"/>
<!--设置连接数据库的密码-->
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
a>引入单个映射文件
<!--引入映射文件-->
<mappers>
<mapper resource="UserMapper.xml"/>
</mappers>
a>引入包下所有映射文件
<!--引入映射文件-->
<mappers>
<package name="com.jianjian.mapper"/>
</mappers>
IDEA偏好设置→编辑器→文件和代码模版→点击“+”号新建模版→名字设置为mybatis-config→扩展设置为xml→复制下面代码并保存
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!--引入properties-->
<properties resource="jdbc.properties"></properties>
<!--设置别名-->
<typeAliases>
<package name="com.jianjian.pojo"/>
</typeAliases>
<!--设置连接数据库的环境-->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!--引入映射文件-->
<mappers>
<package name="com.jianjian.mapper"/>
</mappers>
</configuration>
package com.jianjian.mapper;
public interface UserMapper {
int insertUser();
}
<!--int insertUser();-->
<insert id="insertUser">
insert into t_user values(null,'admin','123456',23,'男','12345@qq.com')
</insert>
@Test
public void testInsertUser(){
SqlSession sqlsession = SqlSessionUtils.getSqlSession();
UserMapper userMapper = sqlsession.getMapper(UserMapper.class);
int result = userMapper.insertUser();
System.out.println("result:" + result);
}
package com.jianjian.mapper;
public interface UserMapper {
int insertUser();
int deleteUser();
}
<!--int deleteUser();-->
<delete id="deleteUser">
delete from t_user where id = 6
</delete>
@Test
public void testDeleteUser(){
SqlSession sqlsession = SqlSessionUtils.getSqlSession();
UserMapper userMapper = sqlsession.getMapper(UserMapper.class);
int result = userMapper.deleteUser();
System.out.println("result:" + result);
}
<!--int updateUser();-->
<update id="updateUser">
update t_user set username = '张三' where id = 5
</update>
<!--User getUserById();-->
<select id="getUserById" resultType="com.jianjian.pojo.User">
select * from t_user where id = 2
</select>
<!--List<User> getUserList();-->
<select id="getUserList" resultType="User">
select * from t_user
</select>
注意:
TooManyResultsException
;但是若查询的数据只有一条,可以使用实体类或集合作为返回值
${}
和#{}
${}
的本质就是字符串拼接
${}
使用字符串拼接的方式拼接sql,若为字符串类型或日期类型的字段进行赋值时,需要手动添加单引号#{}
的本质就是占位符赋值
#{}
使用占位符赋值的方式拼接sql,若为字符串类型或日期类型的字段进行赋值时,可以自动添加单引号若mapper接口中的方法参数为单个的字面量类型,此时可以使用${}
和#{}
${}
需要手动加单引号<!--User getUserByUsername(String username);-->
<select id="getUserByUsername" resultType="User">
select * from t_user where username = #{username}
</select>
<!--User getUserByUsername(String username);-->
<select id="getUserByUsername" resultType="User">
select * from t_user where username = '${username}'
</select>
@Test
public void testUserByUsername(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
User user = userMapper.getUserByUsername("admin");
System.out.println("result:" + user);
}
若mapper接口中的方法参数为多个时,此时MyBatis会自动将这些参数放在一个map集合中
<!--User checkLogin(String username,String password);-->
<select id="checkLogin" resultType="User">
select * from t_user where username = #{arg0} and password = #{arg1}
</select>
<!--User checkLogin(String username,String password);-->
<select id="checkLogin" resultType="User">
select * from t_user where username = '${param1}' and password = '${param2}'
</select>
@Test
public void testcheckLogin(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
User user = userMapper.checkLogin("admin","123456");
System.out.println("result:" + user);
}
若mapper接口中的方法需要的参数为多个时,此时可以手动创建map集合
将这些数据放在map中只需要通过{}和#{}访问map集合的键就可以获取相对应的值,注意{}需要手动加单引号
<!--User checkLoginByMap(Map<String,Object> map);-->
<select id="checkLoginByMap" resultType="User">
select * from t_user where username = #{username} and password = #{password}
</select>
@Test
public void checkLoginByMap() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
Map<String,Object> map = new HashMap<>();
map.put("usermane","admin");
map.put("password","123456");
User user = userMapper.checkLoginByMap(map);
System.out.println(user);
}
若mapper接口中的方法参数为实体类对象时此时可以使用${}
和#{}
,通过访问实体类对象中的属性名获取属性值
<!--int insertUser(User user);-->
<insert id="insertUser">
insert into t_user values(null,#{username},#{password},#{age},#{sex},#{email})
</insert>
@Test
public void insertUser() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
User user = new User(null,"Tom","123456",12,"男","123@321.com");
userMapper.insertUser(user);
}
可以通过@Param注解标识mapper接口中的方法参数,此时会将这些参数放在map集合中
只需要通过{}和#{}访问map集合的键就可以获取相对应的值,注意{}需要手动加单引号
<!--User CheckLoginByParam(@Param("username") String username, @Param("password") String password);-->
<select id="CheckLoginByParam" resultType="User">
select * from t_user where username = #{username} and password = #{password}
</select>
<!--User CheckLoginByParam(@Param("username") String username, @Param("password") String password);-->
<select id="CheckLoginByParam" resultType="User">
select * from t_user where username = #{param1} and password = #{param2}
</select>
@Test
public void checkLoginByParam() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
mapper.CheckLoginByParam("admin","123456");
}
建议分成两种情况进行处理
User
List<User>
Map<String, Object>
List<User>
List<Map<String, Object>>
@MapKey("id")
//根据用户id查询用户信息
User getUserById(@Param("id") int id);
<!--User getUserById(@Param("id") int id);-->
<select id="getUserById" resultType="User">
select * from t_user where id = #{id}
</select>
//查询所有用户信息
List<User> getUserList();
<!--List<User> getUserList();-->
<select id="getUserList" resultType="User">
select * from t_user
</select>
// 查询用户的总记录数
int getCount();
<!--int getCount();-->
<select id="getCount" resultType="integer">
select count(id) from t_user
</select>
//根据用户id查询用户信息为map集合
Map<String, Object> getUserToMap(@Param("id") int id);
<!--Map<String, Object> getUserToMap(@Param("id") int id);-->
<select id="getUserToMap" resultType="map">
select * from t_user where id = #{id}
</select>
<!--结果:{password=123456, sex=男, id=1, age=23, username=admin}-->
//查询所有用户信息为map集合
//将表中的数据以map集合的方式查询,一条数据对应一个map;若有多条数据,就会产生多个map集合,此时可以将这些map放在一个list集合中获取
List<Map<String, Object>> getAllUserToMap();
<!--Map<String, Object> getAllUserToMap();-->
<select id="getAllUserToMap" resultType="map">
select * from t_user
</select>
<!--
结果:
[{password=123456, sex=男, id=1, age=23, username=admin},
{password=123456, sex=男, id=2, age=23, username=张三},
{password=123456, sex=男, id=3, age=23, username=张三}]
-->
//查询所有用户信息为map集合
//通过@MapKey注解设置map集合的键,值是每条数据所对应的map集合
@MapKey("id")
Map<String, Object> getAllUserToMap();
<!--Map<String, Object> getAllUserToMap();-->
<select id="getAllUserToMap" resultType="map">
select * from t_user
</select>
<!--
结果:
{
1={password=123456, sex=男, id=1, age=23, username=admin},
2={password=123456, sex=男, id=2, age=23, username=张三},
3={password=123456, sex=男, id=3, age=23, username=张三}
}
-->
//根据用户名进行模糊查询
List<User> getUserByLike(@Param("fuzzy_name") String username);
<!--List<User> getUserByLike(@Param("fuzzy_name") String username);-->
<select id="getUserByLike" resultType="User">
<!--select * from t_user where username like '%${fuzzy_name}%'-->
<!--select * from t_user where username like concat('%',#{fuzzy_name},'%')-->
select * from t_user where username like "%"#{fuzzy_name}"%"<!--最常用-->
</select>
只能使用${}
,如果使用#{}
,则解析后的sql语句为delete from t_user where id in ('1,2,3')
,这样是将1,2,3
看做是一个整体,只有id为1,2,3
的数据会被删除。正确的语句应该是delete from t_user where id in (1,2,3)
,或者delete from t_user where id in ('1','2','3')
//根据id批量删除
int deleteMore(@Param("ids") String ids);
!--int deleteMore(@Param("ids") String ids);-->
<delete id="deleteMore">
delete from t_user where id in (${ids})
</delete>
@Test
public void deleteMore() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
int result = mapper.deleteMore("1,2,3,8");
System.out.println(result);
}
只能使用${}
,因为表名不能加单引号
//查询指定表中的数据
List<User> getUserByTable(@Param("tableName") String tableName);
<!--List<User> getUserByTable(@Param("tableName") String tableName);-->
<select id="getUserByTable" resultType="User">
select * from ${tableName}
</select>
例如:添加班级信息 ,获取新添加的班级的id ,为班级分配学生,即将某学生的班级id修改为新添加的班级的id
在mapper.xml中设置两个属性
//添加用户信息
void insertUser(User user);
<!--void insertUser(User user);-->
<insert id="insertUser" useGeneratedKeys="true" keyProperty="id">
insert into t_user values (null,#{username},#{password},#{age},#{sex},#{email})
</insert>
@Test
public void insertUser() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User user = new User(null, "ton", "123", 23, "男", "123@321.com");
mapper.insertUser(user);
System.out.println(user);
}
//输出:user{id=10, username='ton', password='123', age=23, sex='男', email='123@321.com'},自增主键存放到了user的id属性中
建立两张表,员工表t_emp,部门表t_dept
CREATE TABLE `t_emp` (
`eid` int(11) NOT NULL AUTO_INCREMENT,
`emp_name` varchar(20) DEFAULT NULL,
`age` int(11) DEFAULT NULL,
`sex` char(1) DEFAULT NULL,
`email` varchar(20) DEFAULT NULL,
`did` int(11) DEFAULT NULL,
PRIMARY KEY (`eid`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
CREATE TABLE `t_dept` (
`did` int(11) NOT NULL AUTO_INCREMENT,
`dept_name` varchar(20) DEFAULT NULL,
PRIMARY KEY (`did`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
数据库字段一般采用下划线,Java属性一般采用驼峰,所以就会造成字段名和属性名不一致,导致映射不了,并不会报错,只是无法映射的字段会显示null
<!--List<Emp> getAllEmp();-->
<select id="getAllEmp" resultType="Emp">
<!--select * from t_emp-->
select eid,emp_name empName,age,sex,email from t_emp <!--设置emp_name别名empName-->
</select>
@Test
public void testGetAllEmp(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
List<Emp> list = mapper.getAllEmp();
list.forEach(emp -> System.out.println(emp));
}
<settings>
<!--将表中字段的下划线自动转换为驼峰 emp_name:empName-->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
<!--List<Emp> getAllEmp();-->
<select id="getAllEmp" resultType="Emp">
select * from t_emp
</select>
若数据库表中字段名和实体类中的属性名不一致,则可以通过resultMap设置自定义映射
注:部分字段名和属性名一致的属性可以不用映射
<resultMap id="empResultMap" type="Emp">
<id property="eid" column="eid"></id>
<result property="empName" column="emp_name"></result>
<result property="age" column="age"></result>
<result property="sex" column="sex"></result>
<result property="email" column="email"></result>
</resultMap>
<select id="getAllEmp" resultMap="empResultMap">
select * from t_emp
</select>
resultMap:设置自定义映射
查询员工信息以及员工所对应的部门信息
public class Emp {
private Integer eid;
private String empName;
private Integer age;
private String sex;
private String email;
private Dept dept;
//...构造器、get、set、toString方法
}
<resultMap id="empAndDeptResultMapOne" type="Emp">
<id property="eid" column="eid"></id>
<result property="empName" column="emp_name"></result>
<result property="age" column="age"></result>
<result property="sex" column="sex"></result>
<result property="email" column="email"></result>
<result property="dept.did" column="did"></result>
<result property="dept.deptName" column="dept_name"></result>
</resultMap>
<!--Emp getEmpAndDept(@Param("eid")Integer eid);-->
<select id="getEmpAndDept" resultMap="empAndDeptResultMapOne">
select * from t_emp left join t_dept on t_emp.did = t_dept.did where t_emp.eid = #{eid}
</select>
<resultMap id="empAndDeptResultMapTwo" type="Emp">
<id property="eid" column="eid"></id>
<result property="empName" column="emp_name"></result>
<result property="age" column="age"></result>
<result property="sex" column="sex"></result>
<result property="email" column="email"></result>
<association property="dept" javaType="Dept">
<id property="did" column="did"></id>
<result property="deptName" column="dept_name"></result>
</association>
</resultMap>
<!--Emp getEmpAndDept(@Param("eid")Integer eid);-->
<select id="getEmpAndDept" resultMap="empAndDeptResultMapTwo">
select * from t_emp left join t_dept on t_emp.did = t_dept.did where t_emp.eid = #{eid}
</select>
//EmpMapper里的方法
/**
* 通过分步查询,员工及所对应的部门信息
* 分步查询第一步:查询员工信息
*/
Emp getEmpAndDeptByStepOne(@Param("eid") Integer eid);
<resultMap id="empAndDeptByStepResultMap" type="Emp">
<id property="eid" column="eid"></id>
<result property="empName" column="emp_name"></result>
<result property="age" column="age"></result>
<result property="sex" column="sex"></result>
<result property="email" column="email"></result>
<association property="dept"
select="com.jianjian.mapper.DeptMapper.getEmpAndDeptByStepTwo" column="did">
</association>
</resultMap>
<!--Emp getEmpAndDeptByStepOne(@Param("eid") Integer eid);-->
<select id="getEmpAndDeptByStepOne" resultMap="empAndDeptByStepResultMap">
select * from t_emp where eid = #{eid}
</select>
//DeptMapper里的方法
/**
* 通过分步查询,员工及所对应的部门信息
* 分步查询第二步:通过did查询员工对应的部门信息
*/
Dept getEmpAndDeptByStepTwo(@Param("did") Integer did);
<!--此处的resultMap仅是处理字段和属性的映射关系-->
<resultMap id="EmpAndDeptByStepTwoResultMap" type="Dept">
<id property="did" column="did"></id>
<result property="deptName" column="dept_name"></result>
</resultMap>
<!--Dept getEmpAndDeptByStepTwo(@Param("did") Integer did);-->
<select id="getEmpAndDeptByStepTwo" resultMap="EmpAndDeptByStepTwoResultMap">
select * from t_dept where did = #{did}
</select>
<!--核心配置文件中开启下划线自动转换为驼峰,可直接用resultType-->
<!--Dept getEmpAndDeptByStepTwo(@Param("did") Integer did);-->
<select id="getEmpAndDeptByStepTwo" resultType="Dept">
select * from t_dept where did = #{did}
</select>
@Test
public void testGetEmpAndDeptByStep(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Emp empAndDeptByStepOne = mapper.getEmpAndDeptByStepOne(4);
System.out.println("empAndDeptByStepOne = " + empAndDeptByStepOne);
}
查询部门以及所对应的员工信息
public class Dept {
private Integer did;
private String deptName;
private List<Emp> emps;
//...构造器、get、set、toString方法
}
collection:用来处理一对多的映射关系
<resultMap id="DeptAndEmpResultMap" type="Dept">
<id property="did" column="did"></id>
<result property="deptName" column="dept_name"></result>
<collection property="emps" ofType="Emp">
<id property="eid" column="eid"></id>
<result property="empName" column="emp_name"></result>
<result property="age" column="age"></result>
<result property="sex" column="sex"></result>
<result property="email" column="email"></result>
</collection>
</resultMap>
<!--Dept getDeptAndEmp(@Param("did") Integer did);-->
<select id="getDeptAndEmp" resultMap="DeptAndEmpResultMap">
select * from t_dept left join t_emp on t_dept.did = t_emp.did where t_dept.did = #{did}
</select>
@Test
public void testGetEmpAndDept2(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
DeptMapper mapper = sqlSession.getMapper(DeptMapper.class);
Dept deptAndEmp = mapper.getDeptAndEmp(3);
System.out.println("deptAndEmp = " + deptAndEmp);
}
/**
* 通过分步查询,查询部门及对应的所有员工信息
* 分步查询第一步:查询部门信息
*/
Dept getDeptAndEmpByStepOne(@Param("did") Integer did);
<resultMap id="DeptAndEmpByStepOneResultMap" type="Dept">
<id property="did" column="did"></id>
<result property="deptName" column="dept_name"></result>
<collection property="emps"
select="com.jianjian.mapper.EmpMapper.getDeptAndEmpByStepTwo" column="did">
</collection>
</resultMap>
<!--Dept getDeptAndEmpByStepOne(@Param("did") Integer did);-->
<select id="getDeptAndEmpByStepOne" resultMap="DeptAndEmpByStepOneResultMap">
select * from t_dept where did = #{did}
</select>
/**
* 通过分步查询,查询部门及对应的所有员工信息
* 分步查询第二步:根据部门id查询部门中的所有员工
*/
List<Emp> getDeptAndEmpByStepTwo(@Param("did") Integer did);
<!--List<Emp> getDeptAndEmpByStepTwo(@Param("did") Integer did);-->
<select id="getDeptAndEmpByStepTwo" resultType="Emp">
select * from t_emp where did = #{did}
</select>
分步查询的优点:可以实现延迟加载,但是必须在核心配置文件中设置全局配置信息:
<settings>
<!--开启延迟加载-->
<setting name="lazyLoadingEnabled" value="true"/>
</settings>
<!--此时就可以实现按需加载,获取的数据是什么,就只会执行相应的sql-->
@Test
public void getEmpAndDeptByStepOne() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Emp emp = mapper.getEmpAndDeptByStepOne(1);
System.out.println(emp.getEmpName());
}
@Test
public void getEmpAndDeptByStepOne() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Emp emp = mapper.getEmpAndDeptByStepOne(1);
System.out.println(emp.getEmpName());
System.out.println("----------------");
System.out.println(emp.getDept());
}
有的功能不想设置延迟加载,可通过association和collection中的fetchType属性手动设置当前的分步查询延迟加载效果
<resultMap id="empAndDeptByStepResultMap" type="Emp">
<id property="eid" column="eid"></id>
<result property="empName" column="emp_name"></result>
<result property="age" column="age"></result>
<result property="sex" column="sex"></result>
<result property="email" column="email"></result>
<association property="dept"
select="com.jianjian.mapper.DeptMapper.getEmpAndDeptByStepTwo"
column="did"
fetchType="eager">
</association>
</resultMap>
Mybatis框架的动态SQL技术是一种根据特定条件动态拼装SQL语句的功能,它存在的意义是为了解决拼接SQL语句字符串时的痛点问题
if标签可通过test属性(即传递过来的数据)的表达式进行判断,若表达式的结果为true,则标签中的内容会执行;反之标签中的内容不会执行
<!--List<Emp> getEmpByCondition(Emp emp);-->
<select id="getEmpByCondition" resultType="Emp">
select * from t_emp where 1=1
<if test="empName != null and empName !=''">
and emp_name = #{empName}
</if>
<if test="age != null and age !=''">
and age = #{age}
</if>
<if test="sex != null and sex !=''">
and sex = #{sex}
</if>
<if test="email != null and email !=''">
and email = #{email}
</if>
</select>
@Test
public void testGetEmpByCondition(){
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
List<Emp> empByCondition = mapper.getEmpByCondition(new Emp(null,"张三",null,null,null));
System.out.println("empByCondition = " + empByCondition);
}
在where后面添加一个恒成立条件1=1
,这个恒成立条件并不会影响查询的结果,这个1=1
可以用来拼接and
语句,例如:当empName为null时
select * from t_emp where and age = ? and sex = ? and email = ?
,此时where
会与and
连用,SQL语句会报错select * from t_emp where 1= 1 and age = ? and sex = ? and email = ?
,此时不报错where和if一般结合使用
<!--List<Emp> getEmpByCondition(Emp emp);-->
<select id="getEmpByCondition" resultType="Emp">
select * from t_emp
<where>
<if test="empName != null and empName !=''">
emp_name = #{empName}
</if>
<if test="age != null and age !=''">
and age = #{age}
</if>
<if test="sex != null and sex !=''">
and sex = #{sex}
</if>
<if test="email != null and email !=''">
and email = #{email}
</if>
</where>
</select>
注意:where标签不能去掉条件后多余的and/or
<!--这种用法是错误的,只能去掉条件前面的and/or,条件后面的不行-->
<where>
<if test="empName != null and empName !=''">
emp_name = #{empName} and
</if>
<if test="age != null and age !=''">
age = #{age}
</if>
</where>
trim用于去掉或添加标签中的内容
若trim中的标签都不满足条件,则trim标签没有任何效果,也就是只剩下select * from t_emp
<!--List<Emp> getEmpByCondition(Emp emp);-->
<select id="getEmpByCondition" resultType="Emp">
select * from t_emp
<trim prefix="where" suffixOverrides="and|or">
<if test="empName != null and empName !=''">
emp_name = #{empName} and
</if>
<if test="age != null and age !=''">
age = #{age} and
</if>
<if test="sex != null and sex !=''">
sex = #{sex} or
</if>
<if test="email != null and email !=''">
email = #{email}
</if>
</trim>
</select>
<!--List<Emp> getEmpListByChoose(Emp emp);-->
<select id="getEmpByChoose" resultType="Emp">
select * from t_emp
<where>
<choose>
<when test="empName != null and empName != ''">
emp_name = #{empName}
</when>
<when test="age != null and age != ''">
age = #{age}
</when>
<when test="sex != null and sex != ''">
sex = #{sex}
</when>
<otherwise>
did = 1
</otherwise>
</choose>
</where>
</select>
相当于if a else if b else if c else d
,只会执行其中一个
对集合进行遍历
属性:
,
批量删除
<!--int deleteMoreByArray(@Param("eids") Integer[] eids);-->
<delete id="deleteMoreByArray">
delete from t_emp where eid in
<foreach collection="eids" item="eid" separator="," open="(" close=")">
#{eid}
</foreach>
</delete>
@Test
public void deleteMoreByArray() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
int result = mapper.deleteMoreByArray(new Integer[]{1,2,3});
System.out.println(result);
}
批量添加
<!--int insertMoreByList(@Param("emps") List<Emp> emps);-->
<insert id="insertMoreByList">
insert into t_emp values
<foreach collection="emps" item="emp" separator=",">
(null,#{emp.empName},#{emp.age},#{emp.sex},#{emp.email})
</foreach>
</insert>
@Test
public void insertMoreByList() {
SqlSession sqlSession = SqlSessionUtils.getSqlSession();
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
Emp emp1 = new Emp(null,"a",1,"男","123@321.com");
Emp emp2 = new Emp(null,"b",1,"男","123@321.com");
Emp emp3 = new Emp(null,"c",1,"男","123@321.com");
List<Emp> emps = Arrays.asList(emp1, emp2, emp3);
int result = mapper.insertMoreByList(emps);
System.out.println(result);
}
sql语句可以记录一段公共sql片段,在使用的地方通过include标签进行引入
<sql>
标签<sql id="empColumns">eid,emp_name,age,sex,email</sql>
<include>
标签<!--List<Emp> getEmpByCondition(Emp emp);-->
<select id="getEmpByCondition" resultType="Emp">
select <include refid="empColumns"></include> from t_emp
</select>
一级缓存是SqlSession级别的,通过同一个SqlSession查询的数据会被缓存,下次查询相同的数据,就会从缓存中直接获取,不会从数据库重新访问
一级缓存失效的四种情况:
sqlSession.clearCache();
二级缓存是SqlSessionFactory级别,通过同一个SqlSessionFactory创建的SqlSession查询的结果会被缓存;此后若再次执行相同的查询语句,结果就会从缓存中获取
二级缓存开启的条件:
<cache />
sqlSession.close();
sqlSession.commit();
二级缓存失效的情况:两次查询之间执行了任意的增删改,会使一级和二级缓存同时失效
二级缓存的相关配置
在mapper配置文件中添加的cache标签可以设置一些属性
<!-- Mybatis EHCache整合包 -->
<dependency>
<groupId>org.mybatis.caches</groupId>
<artifactId>mybatis-ehcache</artifactId>
<version>1.2.1</version>
</dependency>
<!-- slf4j日志门面的一个具体实现 -->
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.3</version>
</dependency>
<?xml version="1.0" encoding="utf-8" ?>
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="../config/ehcache.xsd">
<!-- 磁盘保存路径 -->
<diskStore path="/Users/jianjian/ehcache"/>
<defaultCache
maxElementsInMemory="1000"
maxElementsOnDisk="10000000"
eternal="false"
overflowToDisk="true"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
diskExpiryThreadIntervalSeconds="120"
memoryStoreEvictionPolicy="LRU">
</defaultCache>
</ehcache>
EHCache配置文件说明
属性名 | 是否必须 | 作用 |
---|---|---|
maxElementsInMemory | 是 | 在内存中缓存的element的最大数目 |
maxElementsOnDisk | 是 | 在磁盘上缓存的element的最大数目,若是0表示无穷大 |
eternal | 是 | 设定缓存的elements是否永远不过期。 如果为true,则缓存的数据始终有效, 如果为false那么还要根据timeToIdleSeconds、timeToLiveSeconds判断 |
overflowToDisk | 是 | 设定当内存缓存溢出的时候是否将过期的element缓存到磁盘上 |
timeToIdleSeconds | 否 | 当缓存在EhCache中的数据前后两次访问的时间超过timeToIdleSeconds的属性取值时, 这些数据便会删除,默认值是0,也就是可闲置时间无穷大 |
timeToLiveSeconds | 否 | 缓存element的有效生命期,默认是0.,也就是element存活时间无穷大 |
diskSpoolBufferSizeMB | 否 | DiskStore(磁盘缓存)的缓存区大小。默认是30MB。每个Cache都应该有自己的一个缓冲区 |
diskPersistent | 否 | 在VM重启的时候是否启用磁盘保存EhCache中的数据,默认是false |
diskExpiryThreadIntervalSeconds | 否 | 磁盘缓存的清理线程运行间隔,默认是120秒。每个120s, 相应的线程会进行一次EhCache中数据的清理工作 |
memoryStoreEvictionPolicy | 否 | 当内存缓存达到最大,有新的element加入的时候, 移除缓存中element的策略。 默认是LRU(最近最少使用),可选的有LFU(最不常使用)和FIFO(先进先出 |
在xxxMapper.xml文件中设置二级缓存类型
<cache type="org.mybatis.caches.ehcache.EhcacheCache"/>
存在SLF4J时,作为简易日志的log4j将失效,此时我们需要借助SLF4J的具体实现logback来打印日志。创建logback的配置文件logback.xml
,名字固定,不可改变
<?xml version="1.0" encoding="UTF-8"?>
<configuration debug="true">
<!-- 指定日志输出的位置 -->
<appender name="STDOUT"
class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<!-- 日志输出的格式 -->
<!-- 按照顺序分别是:时间、日志级别、线程名称、打印日志的类、日志主体内容、换行 -->
<pattern>[%d{HH:mm:ss.SSS}] [%-5level] [%thread] [%logger] [%msg]%n</pattern>
</encoder>
</appender>
<!-- 设置全局日志级别。日志级别按顺序分别是:DEBUG、INFO、WARN、ERROR -->
<!-- 指定任何一个日志级别都只打印当前级别和后面级别的日志。 -->
<root level="DEBUG">
<!-- 指定打印日志的appender,这里通过“STDOUT”引用了前面配置的appender -->
<appender-ref ref="STDOUT" />
</root>
<!-- 根据特殊需求指定局部日志级别 -->
<logger name="com.jianjian.mapper" level="DEBUG"/>
</configuration>
<dependencies>
<!-- MyBatis核心依赖包 -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.9</version>
</dependency>
<!-- junit测试 -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13.2</version>
<scope>test</scope>
</dependency>
<!-- MySQL驱动 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.29</version>
</dependency>
<!-- log4j日志 -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
</dependencies>
<!-- 控制Maven在构建过程中相关配置 -->
<build>
<!-- 构建过程中用到的插件 -->
<plugins>
<!-- 具体插件,逆向工程的操作是以构建过程中插件形式出现的 -->
<plugin>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-maven-plugin</artifactId>
<version>1.3.0</version>
<!-- 插件的依赖 -->
<dependencies>
<!-- 逆向工程的核心依赖 -->
<dependency>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-core</artifactId>
<version>1.3.2</version>
</dependency>
<!-- 数据库连接池 -->
<dependency>
<groupId>com.mchange</groupId>
<artifactId>c3p0</artifactId>
<version>0.9.5.5</version>
</dependency>
<!-- MySQL驱动 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.29</version>
</dependency>
</dependencies>
</plugin>
</plugins>
</build>
<?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>
<!--引入properties-->
<properties resource="jdbc.properties"></properties>
<settings>
<!--将表中字段的下划线自动转换为驼峰-->
<setting name="mapUnderscoreToCamelCase" value="true"/>
<!--开启延迟加载-->
<setting name="lazyLoadingEnabled" value="true"/>
</settings>
<!--设置别名-->
<typeAliases>
<package name="com.xxx.pojo"/>
</typeAliases>
<!--设置连接数据库的环境-->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!--引入映射文件-->
<mappers>
<package name="com.xxx.mapper"/>
</mappers>
</configuration>
jdbc.properties
jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/Mybatis
jdbc.username=root
jdbc.password=root
文件名必须是:generatorConfig.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
"http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
<!--
targetRuntime: 执行生成的逆向工程的版本
MyBatis3Simple: 生成基本的CRUD(清新简洁版)
MyBatis3: 生成带条件的CRUD(奢华尊享版)
-->
<context id="DB2Tables" targetRuntime="MyBatis3Simple">
<!-- 数据库的连接信息 -->
<jdbcConnection driverClass="com.mysql.cj.jdbc.Driver"
connectionURL="jdbc:mysql://localhost:3306/Mybatis"
userId="root"
password="root">
</jdbcConnection>
<!-- javaBean的生成策略-->
<javaModelGenerator targetPackage="com.jianjian.pojo"
targetProject="./src/main/java">
<property name="enableSubPackages" value="true" />
<property name="trimStrings" value="true" />
</javaModelGenerator>
<!-- SQL映射文件的生成策略 -->
<sqlMapGenerator targetPackage="com.jianjian.mapper"
targetProject="./src/main/resources">
<property name="enableSubPackages" value="true" />
</sqlMapGenerator>
<!-- Mapper接口的生成策略 -->
<javaClientGenerator type="XMLMAPPER"
targetPackage="com.jianjian.mapper"
targetProject="./src/main/java">
<property name="enableSubPackages" value="true" />
</javaClientGenerator>
<!-- 逆向分析的表 -->
<!-- tableName设置为*号,可以对应所有表,此时不写domainObjectName -->
<!-- domainObjectName属性指定生成出来的实体类的类名 -->
<table tableName="t_emp" domainObjectName="Emp"/>
<table tableName="t_dept" domainObjectName="Dept"/>
</context>
</generatorConfiguration>
双击运行
运行结果
生成的实体类需要手动添加构造器、toString方法
一般使用奢华尊享版,即 targetRuntime设置为MyBatis3
QBC 即 Quary By Criteria,在sql语句相当于查询条件。QBC查询是将查询条件通过Java对象进行模块化封装。
selectByExample
:按条件查询,需要传入一个example对象或者null;如果传入一个null,则表示没有条件,也就是查询所有数据example.createCriteria().xxx
:创建条件对象,通过andXXX方法为SQL添加查询添加,每个条件之间是and关系example.or().xxx
:将之前添加的条件通过or拼接其他条件@Test
public void testMBG() throws IOException {
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
SqlSession sqlSession = sqlSessionFactory.openSession(true);
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
EmpExample example = new EmpExample();
//名字为张三,且年龄大于等于20
example.createCriteria().andEmpNameEqualTo("张三").andAgeGreaterThanOrEqualTo(20);
//或者did不为空
example.or().andDidIsNotNull();
List<Emp> emps = mapper.selectByExample(example);
emps.forEach(System.out::println);
}
updateByPrimaryKey
:通过主键进行数据修改,如果某一个值为null,也会将对应的字段改为nullmapper.updateByPrimaryKey(new Emp(1,"admin",22,null,"456@qq.com",3));
updateByPrimaryKeySelective()
:通过主键进行选择性数据修改,如果某个值为null,则不修改这个字段mapper.updateByPrimaryKeySelective(new Emp(2,"admin2",22,null,"456@qq.com",3));
<!-- https://mvnrepository.com/artifact/com.github.pagehelper/pagehelper -->
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper</artifactId>
<version>5.2.0</version>
</dependency>
在MyBatis的核心配置文件(mybatis-config.xml)中配置插件
<plugins>
<!--设置分页插件-->
<plugin interceptor="com.github.pagehelper.PageInterceptor"></plugin>
</plugins>
在查询功能之前使用PageHelper.startPage(int pageNum, int pageSize)
开启分页功能
@Test
public void testPageHelper() throws IOException {
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
SqlSession sqlSession = sqlSessionFactory.openSession(true);
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
//访问第一页,每页四条数据
Page<Object> page = PageHelper.startPage(1, 4);
List<Emp> emps = mapper.selectByExample(null);
//在查询到List集合后,打印分页数据
System.out.println(page);
}
Page{count=true, pageNum=1, pageSize=4, startRow=0, endRow=4, total=8, pages=2, reasonable=false, pageSizeZero=false}[Emp{eid=1, empName='admin', age=22, sex='男', email='456@qq.com', did=3}, Emp{eid=2, empName='admin2', age=22, sex='男', email='456@qq.com', did=3}, Emp{eid=3, empName='王五', age=12, sex='女', email='123@qq.com', did=3}, Emp{eid=4, empName='赵六', age=32, sex='男', email='123@qq.com', did=1}]
在查询获取list集合之后,使用PageInfo<T> pageInfo = new PageInfo<>(List<T> list, intnavigatePages)
获取分页相关数据
@Test
public void testPageHelper() throws IOException {
InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
SqlSession sqlSession = sqlSessionFactory.openSession(true);
EmpMapper mapper = sqlSession.getMapper(EmpMapper.class);
PageHelper.startPage(1, 4);
List<Emp> emps = mapper.selectByExample(null);
PageInfo<Emp> page = new PageInfo<>(emps,5);
System.out.println(page);
}
PageInfo{
pageNum=1, pageSize=4, size=4, startRow=1, endRow=4, total=8, pages=2,
list=Page{count=true, pageNum=1, pageSize=4, startRow=0, endRow=4, total=8, pages=2, reasonable=false, pageSizeZero=false}[Emp{eid=1, empName='admin', age=22, sex='男', email='456@qq.com', did=3}, Emp{eid=2, empName='admin2', age=22, sex='男', email='456@qq.com', did=3}, Emp{eid=3, empName='王五', age=12, sex='女', email='123@qq.com', did=3}, Emp{eid=4, empName='赵六', age=32, sex='男', email='123@qq.com', did=1}],
prePage=0, nextPage=2, isFirstPage=true, isLastPage=false, hasPreviousPage=false, hasNextPage=true, navigatePages=5, navigateFirstPage=1, navigateLastPage=2, navigatepageNums=[1, 2]}