如何获得Mybatis
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.5.6version>
dependency>
123456
数据持久化
为什么需要持久化?
Dao层,Service层,Controller层…
最重要的一点:使用的人多!
Spring-SpringMVC-SpringBoot
思路:搭建环境–>导入Mybatis–>编写代码–>测试
搭建数据库
CREATE DATABASE `mybatis`;
USE `mybatis`;
CREATE TABLE `user`(
`id` INT(20) NOT NULL PRIMARY KEY,
`name` VARCHAR(30) DEFAULT NULL,
`pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8
INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'袁志松','123456'),
(2,'张三','123456'),
(3,'李四','123456')
新建项目
<dependencies>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>5.1.47version>
dependency>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.5.6version>
dependency>
<dependency>
<groupId>junitgroupId>
<artifactId>junitartifactId>
<version>4.12version>
dependency>
dependencies>
DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="123456"/>
dataSource>
environment>
environments>
<mappers>
<mapper resource="com/kuang/dao/UserMapper.xml"/>
mappers>
configuration>
此处设useSSL=false。
//SqlSessionFactory -->SqlSession
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static {
try {
//使用Mybaties第一步:获取sqlSessionFactory对象
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (Exception e) {
e.printStackTrace();
}
}
//既然有了 SqlSessionFactory,顾名思义,我们可以从中获得 SqlSession 的实例。
// SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
public static SqlSession getSqlSession(){
// SqlSession sqlSession = sqlSessionFactory.openSession();
// return sqlSession;
return sqlSessionFactory.openSession();
}
}
//实体类
public class User {
private int id;
private String name;
private String pwd;
public User() {
}
public User(int id, String name, String pwd) {
this.id = id;
this.name = name;
this.pwd = pwd;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPwd() {
return pwd;
}
public void setPwd(String pwd) {
this.pwd = pwd;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
", pwd='" + pwd + '\'' +
'}';
}
}
public interface UserDao {
List<User> getUserList();
}
DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.kuang.dao.UserDao">
<select id="getUserList" resultType="com.kuang.pojo.User">
select * from mybatis.user
select>
mapper>
注意点:
MapperRegistry是什么?
核心配置文件中注册mappers
@Test
public void test(){
//第一步:获得SqlSession对象
SqlSession sqlSession = MybatisUtils.getSqlSession();
//方式一:getMapper
UserDao userDao = sqlSession.getMapper(UserDao.class);
List<User> userList = userDao.getUserList();
for (User user : userList) {
System.out.println(user);
}
//关闭SqlSession
sqlSession.close();
}
可能遇到的问题:
<build>
<resources>
<resource>
<directory>src/main/resourcesdirectory>
<excludes>
<exclude>**/*.propertiesexclude>
<exclude>**/*.xmlexclude>
excludes>
<filtering>truefiltering>
resource>
<resource>
<directory>src/main/javadirectory>
<includes>
<include>**/*.propertiesinclude>
<include>**/*.xmlinclude>
includes>
<filtering>truefiltering>
resource>
resources>
build>
namespace中的包名要和Dao/Mapper接口的包名一致!
选择,查询语句;
1.编写接口
//根据id查询用户
User getUserById(int id);
2.编写对应的mapper中的sql语句
<select id="getUserById" parameterType="int" resultType="com.kuang.pojo.User">
select * from mybatis.user where id = #{id}
select>
3.测试
@Test
public void getUserById(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User user = mapper.getUserById(1);
System.out.println(user);
//关闭SqlSession
sqlSession.close();
}
<insert id="addUser" parameterType="com.kuang.pojo.User">
insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd})
insert>
<update id="updateUser" parameterType="com.kuang.pojo.User">
update mybatis.user set name=#{name},pwd=#{pwd} where id = #{id}
update>
<delete id="deleteUser" parameterType="int">
delete from mybatis.user where id = #{id}
delete>
注意点:
即可成功测试。
假设,我们的实体类,或者数据库中的表,字段或者参数过多,我们应当考虑使用Map!
//万能的Map
int addUser2(Map<String,Object> map);
<insert id="addUser2" parameterType="map">
insert into mybatis.user (id,pwd) values (#{userid},#{password})
insert>
@Test
public void addUser2(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
Map<String,Object> map = new HashMap<String, Object>();
map.put("userid",4);
map.put("password","123321");
mapper.addUser2(map);
sqlSession.commit();
sqlSession.close();
}
Map传递参数,直接在sql中取出key即可!【parameterType=“map”】
对象传递参数,直接在sql中取对象的属性即可!【parameterType=“Object”】
只有一个基本类型参数的情况下,可以直接在sql中取到!
多个参数用Map,或者注解!
模糊查询怎么写?
List<User> userList = mapper.getUserLike("%李%");
select * from mybatis.user where name like "%"#{value}"%"
Mybatis可以配置成适应多种环境
不过要记住:尽管可以配置多个环境,但每个SqlSessionFactory实例只能选择一种环境。
在 MyBatis 中有两种类型的事务管理器(type="[JDBC|MANAGED]")
Mybatis默认的事务管理器就是JDBC,连接池:POOLED
我们可以通过properties属性来实现引用配置文件
这些属性都是可外部配置且可动态替换的,既可以在典型的Java属性文件中配置,亦可通过properties元素的子元素来传递。【db.properties】
编写一个配置文件
db.properties
driver=com.mysql.jdbc.Driverurl=jdbc:mysql://localhost:3306/mybatis?
useSSL=false&useUnicode=true&characterEncoding=UTF-8
username=root
password=1234561234
在核心配置文件中映入
<properties resource="db.properties">
<property name="username" value="root"/>
<property name="pwd" value="123123"/>
properties>
<typeAliases>
<typeAlias type="com.kuang.pojo.User" alias="User" />
typeAliases>
也可以指定一个包名,MyBatis会在包名下面搜索需要的JavaBean,比如:
扫描实体类的包,它的默认别名就为这个类的类名,首字母小写!
<typeAliases>
<package name="com.kuang.pojo"/>
typeAliases>
在实体类比较少的时候,使用第一种方式。
如果实体类十分多,建议使用第二种。
第一种可以DIY别名,第二种则不行,如果非要改,需要在实体上增加注解
@Alias("user")
//实体类
public class User {}
这是MyBatis中极为重要的调整设置,它们会改变MyBatis的运行时行为。
MapperRegistry:注册绑定我们的Mapper文件;
方式一:【推荐使用】
<mappers>
<mapper resource="com/kuang/dao/UserMapper.xml"/>
mappers>
方式二:使用class文件绑定注册
<mappers>
<mapper class="com.kuang.dao.UserMapper"/>
mappers>
注意点:
方式三:使用扫描包进行注入绑定
<mappers>
<package name="com.kuang.dao"/>
mappers>
注意点:
练习:
生命周期和作用域是至关重要的,因为错误的使用会导致非常严重的并发问题。
SqlSessionFactoryBuilder:
SqlSessionFactory:
SqlSession:
数据库中的字段
新建一个项目,拷贝之前的,测试实体类字段不一致的情况
public class User {
private int id;
private String name;
private String password;
}
测试出现问题
// select * from mybatis.user where id = #{id}
// 类型处理器
// select id,name,pwd from mybatis.user where id = #{id}
解决方法:
起别名
<select id="getUserById" parameterType="int" resultType="user">
select id,name,pwd as password from mybatis.user where id = #{id}
select>
resultMap解决
结果集映射
id name pwd
id name password
<resultMap id="UserMap" type="User">
<result column="id" property="id" />
<result column="name" property="name" />
<result column="pwd" property="password" />
resultMap>
<select id="getUserById" parameterType="int" resultMap="UserMap">
select * from mybatis.user where id = #{id}
select>
如果一个数据库操作出现了异常,我们需要排错。日志就是最好的助手!
曾经:sout、debug
现在:日志工厂!
在Mybatis中具体使用哪一个日志实现,在设置中设定!
STDOUT_LOGGING标准日志输出
在mybatis-config.xml核心配置文件中,配置我们的日志!
<settings>
<setting name="logImpl" value="STDOUT_LOGGING"/>
settings>
什么是Log4j?
1.先在pom.xml文件中导入log4j的依赖包
<dependencies>
<dependency>
<groupId>log4jgroupId>
<artifactId>log4jartifactId>
<version>1.2.17version>
dependency>
dependencies>
2.在resources文件夹下建立log4j.properties文件进行配置
#将等级为DEBUG的日志信息输出到console和file这两个目的地,console和file的定义在下面的代码
log4j.rootLogger = DEBUG,console ,file
#控制台输出的相关设置
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.Target = System.out
log4j.appender.console.Threshold = DEBUG
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern = [%c]-%m%n
#文件输出的相关设置
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File = ./log/kuang.log
log4j.appender.file.MaxFileSize = 10mb
log4j.appender.file.Threshold = DEBUG
log4j.appender.file.layout = org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern = [%p][%d{yy-MM-dd}][%c]%m%n
#日志输出级别
log4j.logger.org.mybatis=DEBUG
log4j.logger.java.sql=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.ResultSet=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG
3.在mybatis-config.xml核心配置文件中,配置log4j为日志的实现!
<settings>
<setting name="logImpl" value="LOG4J"/>
settings>
4.Log4j的使用,直接测试运行
简单使用
static Logger logger = Logger.getLogger(UserDaoTest.class);
logger.info("info:进入了testLog4j");
logger.debug("DEBUG:进入了testLog4j");
logger.error("erro:进入了testLog4j");
思考:为什么要分页!
语法:SELECT * from user limit startIndex,pageSize
SELECT * from user limit 3 #[0,n]
使用Mybatis实现分页,核心SQL
//分页
List<User> getUserByLimit(Map<String,Integer> map);
<select id="getUserByLimit" parameterType="map" resultMap="UserMap">
select * from mybatis.user limit #{startIndex},#{pageSize}
select>
@Test
public void getUserByLimit(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
HashMap<String, Integer> map = new HashMap<String, Integer>();
map.put("startIndex",0);
map.put("pageSize",2);
List<User> userList = mapper.getUserByLimit(map);
for (User user : userList) {
System.out.println(user);
}
sqlSession.close();
}
不再使用SQL实现分页
//分页2
List<User> getUserByRowBounds();
<select id="getUserByRowBounds" resultMap="UserMap">
select * from mybatis.user
select>
@Test
public void getUserByRowBounds(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
//RowBounds实现
RowBounds rowBounds = new RowBounds(0, 2);
//通过java代码层面实现分页
List<User> userList = sqlSession.selectList("com.kuang.dao.UserMapper.getUserByRowBounds",null,rowBounds);
for (User user : userList) {
System.out.println(user);
}
sqlSession.close();
}
了解即可,使用时,需要知道是什么东西!
@Select("select * from user")
List<User> getUsers();
<mappers>
<mapper class="com.kuang.dao.UserMapper" />
mappers>
@Test
public void getUsers(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> users = mapper.getUsers();
for (User user : users) {
System.out.println(user);
}
sqlSession.close();
}
本质:反射机制实现
底层:动态代理!
Mybatis详细的执行流程!(之后应用的多了详细再走一遍)
public static SqlSession getSqlSession(){
return sqlSessionFactory.openSession(true);
}
public interface UserMapper {
@Select("select * from user")
List<User> getUsers();
//方法存在多个参数,所有参数前面必须加上@Param("id")注解
@Select("select * from user where id=#{id}")
User getUserById(@Param("id") int id);
@Insert("insert into user (id,name,pwd) values(#{id},#{name},#{password})")
int addUser(User user);
@Update("update user set name=#{name},pwd=#{password} where id=#{id}")
int updateUser(User user);
@Delete("delete from user where id = #{uid}")
int deleteUser(@Param("uid") int id);
}
【注意:我们必须要将接口注册绑定到我们的核心配置文件中!】
关于@Param()注解
使用步骤:
<dependency>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
<version>1.18.10version>
dependency>
@Data
@AllArgsConstructor
@NoArgsConstructor
@Getter and @Setter
@FieldNameConstants
@ToString
@EqualsAndHashCode
@AllArgsConstructor, @RequiredArgsConstructor and @NoArgsConstructor
@Log, @Log4j, @Log4j2, @Slf4j, @XSlf4j, @CommonsLog, @JBossLog, @Flogger, @CustomLog
@Data
@Builder
@SuperBuilder
@Singular
@Delegate
@Value
@Accessors
@Wither
@With
@SneakyThrows
说明:
@Data:无参构造、get、set、toString、hashCode、equals
@AllArgsConstructor
@NoArgsConstructor
@EqualsAndHashCode
@ToString
@Getter and @Setter
多对一:
SQL语句:
CREATE TABLE `teacher` (
`id` INT(10) NOT NULL,
`name` VARCHAR(30) DEFAULT NULL,
PRIMARY KEY (`id`)
)ENGINE = INNODB DEFAULT CHARSET=utf8
INSERT INTO teacher(`id`,`name`) VALUES (1,'秦老师');
CREATE TABLE `student` (
`id` INT(10) NOT NULL,
`name` VARCHAR(30) DEFAULT NULL,
`tid` INT(10) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `fktid`(`tid`),
CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
)ENGINE = INNODB DEFAULT CHARSET=utf8
INSERT INTO `student`(`id`,`name`,`tid`) VALUES ('1','小明','1');
INSERT INTO `student`(`id`,`name`,`tid`) VALUES ('2','小红','1');
INSERT INTO `student`(`id`,`name`,`tid`) VALUES ('3','小张','1');
INSERT INTO `student`(`id`,`name`,`tid`) VALUES ('4','小李','1');
INSERT INTO `student`(`id`,`name`,`tid`) VALUES ('5','小王','1');
<select id="getStudent2" resultMap="StudentTeacher2">
select s.id sid,s.name sname,t.name tname
from mybatis.student s,mybatis.teacher t
where s.tid = t.id
select>
<resultMap id="StudentTeacher2" type="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<association property="teacher" javaType="Teacher">
<result property="name" column="tname"/>
association>
resultMap>
<select id="getStudent" resultMap="StudentTeacher">
select * from mybatis.student
select>
<resultMap id="StudentTeacher" type="Student">
<result property="id" column="id"/>
<result property="name" column="name"/>
<association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
resultMap>
<select id="getTeacher" resultType="Teacher">
select * from mybatis.teacher where id = #{id}
select>
回顾Mysql多对一查询方式:
比如:一个老师拥有多个学生!
对于老师而言,就是一对多的关系!
@Data
public class Student {
private int id;
private String name;
private int tid;
}
@Data
public class Teacher {
private int id;
private String name;
//一个老师拥有多个学生
private List<Student> students;
}
<select id="getTeacher" resultMap="TeacherStudent">
SELECT s.id sid,s.name sname,t.name tname,t.id,tid
from student s,teacher t
where s.tid = t.id and t.id = #{tid}
select>
<resultMap id="TeacherStudent" type="Teacher">
<result property="id" column="tid"/>
<result property="name" column="tname"/>
<collection property="students" ofType="Student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<result property="tid" column="tid"/>
collection>
resultMap>
<select id="getTeacher2" resultMap="TeacherStudent2">
select * from mybatis.teacher where id = #{tid}
select>
<resultMap id="TeacherStudent2" type="Teacher">
<collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>
resultMap>
<select id="getStudentByTeacherId" resultType="Student">
select * from mybatis.student where tid = #{tid}
select>
注意点:
面试高频
什么是动态SQL:动态SQL就是 指根据不同的条件生成不同的SQL语句
利用动态SQL这一特性可以彻底摆脱这种痛苦。
在 MyBatis 之前的版本中,需要花时间了解大量的元素。借助功能强大的基于 OGNL 的表达式,MyBatis 3 替换了之前的大部分元素,大大精简了元素种类,现在要学习的元素种类比原来的一半还要少。
if
choose (when, otherwise)
trim (where, set)
foreach
CREATE TABLE `blog`(
`id` VARCHAR(50) NOT NULL COMMENT '博客id',
`title` VARCHAR(100) NOT NULL COMMENT '博客标题',
`author` VARCHAR(30) NOT NULL COMMENT '博客作者',
`create_time` DATETIME NOT NULL COMMENT '创建时间',
`views` INT(30) NOT NULL COMMENT '浏览量'
)ENGINE=INNODB DEFAULT CHARSET=utf8
创建一个基础工程
@Data
public class Blog {
private String id;
private String title;
private String author;
private Date createTime; //属性名和字段名不一致
private int views;
}
<select id="queryBlogIF" parameterType="map" resultType="Blog">
select * from mybatis.blog where 1=1
<if test="title != null">
and title = #{title}
if>
<if test="author != null">
and author = #{author}
if>
select>
<select id="queryBlogChoose" parameterType="map" resultType="Blog">
select * from mybatis.blog
<where>
<choose>
<when test="title != null">
title = #{title}
when>
<when test="author != null">
and author = #{author}
when>
<otherwise>
and views = #{views}
otherwise>
choose>
where>
select>
<select id="queryBlogIF" parameterType="map" resultType="Blog">
select * from mybatis.blog
<where>
<if test="title != null">
and title = #{title}
if>
<if test="author != null">
and author = #{author}
if>
where>
select>
<update id="updateBlog" parameterType="map">
update mybatis.blog
<set>
<if test="title != null">
title = #{title},
if>
<if test="author != null">
author = #{author}
if>
set>
where id = #{id}
update>
所谓的动态SQL,本质还是SQL语句,只是我们可以在SQL层面,去执行一个逻辑代码
<select id="queryBlogForeach" parameterType="map" resultType="Blog">
select * from mybatis.blog
<where>
<foreach collection="ids" item="id" open="and (" close=")" separator="or">
id = #{id}
foreach>
where>
select>
动态SQL就是在拼接SQL语句,我们只要保证SQL的正确性,按照SQL的格式,去排列组合就可以了。
建议:
有的时候,我们可以能会将一些功能的部分抽取出来,方便复用!
<sql id="if-title-author">
<if test="title != null">
title = #{title}
if>
<if test="author != null">
and author = #{author}
if>
sql>
<select id="queryBlogIF" parameterType="map" resultType="Blog">
select * from mybatis.blog
<where>
<include refid="if-title-author">include>
where>
select>
注意事项:
10月28和29日因为身体不舒服耽搁了两天
Mybatis包含一个非常强大的查询缓存特性,它可以非常方便地定制和配置缓存。缓存可以极大的提升查询效率。
Mybatis系统中默认定义了两级缓存:
一级缓存
和
二级缓存
测试步骤:
缓存失效的情况:
小结:一级缓存默认是开启的,只在一次SqlSession中有效,也就是拿到连接到关闭连接这个区间段!
一级缓存相当于一个Map。
步骤:
<setting name="cacheEnabled" value="true"/>
<cache/>
也可以自定义参数
<cache
eviction="FIFO"
flushInterval="60000"
size="512"
readOnly="true"/>
测试
Cause: java.io.NotSerializableException: com.kuang.pojo.User
小结:
Ehcache是一种广泛使用的开源Java分布式缓存,主要面向通用缓存。
要在程序中使用ehcache,先要导包!
在mapper中指定使用我们的ehcache缓存实现!
目前:Redis数据库来做缓存!K-V