环境:
回顾:
SSM框架:配置文件,最好的方式看官网文档
MyBatis 是一款优秀的持久层框架
它支持自定义 SQL、存储过程以及高级映射。
MyBatis避免了除了几乎所有的 JDBC 代码以及设置参数和获取结果集
MyBatis可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO(Plain Old Java Objects,普通老式 Java 对象)为数据库中的记录。
MyBatis 本是**apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code**,并且改名为MyBatis 。2013年11月迁移到Github。
maven仓库:
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.5.2version>
dependency>
github:https://github.com/mybatis/mybatis-3
中文文档:https://mybatis.org/mybatis-3/
数据持久化
为什么需要持久化?
Dao层,Serbvice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,'小王子','123456'),
(2,'小玫瑰','156312'),
(3,'张三','123456')
新建项目
新建一个普通的maven项目
删除src目录
导入maven依赖
<dependencies>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>5.1.47version>
dependency>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.5.2version>
dependency>
<dependency>
<groupId>junitgroupId>
<artifactId>junitartifactId>
<version>4.12version>
dependency>
dependencies>
<build>
<resources>
<resource>
<directory>src/main/resourcesdirectory>
<includes>
<include>**/*.propertiesinclude>
<include>**/*.xmlinclude>
includes>
<filtering>truefiltering>
resource>
<resource>
<directory>src/main/javadirectory>
<includes>
<include>**/*.propertiesinclude>
<include>**/*.xmlinclude>
includes>
<filtering>truefiltering>
resource>
resources>
build>
IDEA数据库连接URL:jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC
编写mybatis的核心配置文件
<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=true&useUnicode=true&characterEncoding=utf8"/>
<property name="username" value="root"/>
<property name="password" value="chen19990217...+"/>
dataSource>
environment>
environments>
<mappers>
<mapper resource="com/chen/dao/userMapper.xml"/>
mappers>
configuration>
编写mybatis的工具类
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
//sqlSessionFactory --> sqlSession
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static {
try {
//1.使用Mybatis获取sqlSessionFactory对象
String resource = "org/mybatis/example/mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException 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(){
return sqlSessionFactory.openSession();
}
}
实体类
package com.chen.util;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
//sqlSessionFactory --> sqlSession
public class MybatisUtils {
private static SqlSessionFactory sqlSessionFactory;
static {
try {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
//获取SqlSession连接
public static SqlSession getSession(){
return sqlSessionFactory.openSession();
}
/*
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。
*/
}
Dao接口
public interface UserDao {
List<User> getUserList();
}
接口实现类由原来的UserDaoImpl转变为一个Mapper配置文件
<mapper namespace="com.chen.dao.UserDao">
<select id="getUserList" resultType="com.chen.pojo.User">
select * from user
select>
mapper>
Junit测试
MapperRegister是什么
核心配置文件中注册mappers
可能会遇到的问题:
配置文件没有注册
绑定接口错误
方法名不对
返回类型不对
Maven静态资源过滤问题
<build>
<resources>
<resource>
<directory>src/main/resourcesdirectory>
<includes>
<include>**/*.propertiesinclude>
<include>**/*.xmlinclude>
includes>
<filtering>truefiltering>
resource>
<resource>
<directory>src/main/javadirectory>
<includes>
<include>**/*.propertiesinclude>
<include>**/*.xmlinclude>
includes>
<filtering>truefiltering>
resource>
resources>
build>
测试类代码
package com.chen.dao;
import com.chen.pojo.User;
import com.chen.util.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class UserDaoTest {
@Test
public void test(){
SqlSession session = MybatisUtils.getSession();
//方式一:不推荐使用
// List userList1 = sqlSession.selectList("com.chen.dao.UserDao.getUserList");
// for (User user : userList1) {
// System.out.println(user);
// }
//方法二:
UserDao mapper = session.getMapper(UserDao.class);
List<User> users = mapper.getUserList();
for (User user: users){
System.out.println(user);
}
session.close();
}
}
namespace的包名要和Dao/mappper接口的包名一致
选择,查询语句;
id:就是对应的namespace中的方法名
resultType:Sql语句执行的返回值!
parameterType:参数类型
编写接口
//根据id查询用户
User getUserById(int id);
编写对应的mapper中的sql
<select id="getUserById" parameterType="int" resultType="com.chen.pojo.User">
select * from mybatis.user where id = #{id}
select>
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);
}
//insert 一个用户
int addUser(User user);
//修改一个用户
int updateUser(User user);
//删除一个用户
int deleteUser(int id);
<insert id="addUser" parameterType="com.chen.pojo.User">
insert into mybatis.user(id, name, pwd) values (#{
id},#{
name},#{
pwd});
</insert>
<update id="updateUser" parameterType="com.chen.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>
//增删改需要提交事务
@Test
public void addUser(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
int res = mapper.addUser(new User(4, "死猪", "123"));
if (res > 0){
System.out.println("插入成功");
}
//提交事务!!!
sqlSession.commit();
sqlSession.close();
}
@Test
public void updateUser(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
mapper.updateUser(new User(4,"呵呵","123123"));
sqlSession.commit();
sqlSession.close();
}
@Test
public void deleteUser(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
mapper.deleteUser(4);
sqlSession.commit();
sqlSession.close();
}
假设我们的实体类,或者额数据库中的表,字段或者参数过多,我们应当考虑使用Map!
<insert id="addUser" parameterType="map">
insert into mybatis.user(id, name, pwd) values (#{userId},#{userName},#{passWord});
insert>
@Test
public void addUser2(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
HashMap<String, Object> map = new HashMap<String, Object>();
map.put("userId",5);
map.put("userName","小灰灰");
map.put("passWord","2222222");
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?
Java代码执行的时候,传递通配符%%
<select id="getUserLike" resultType="com.chen.pojo.User">
select * from mybatis.user where name like #{
value};
</select>
@Test
public void getUserLike(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> list = mapper.getUserLike("%小%");
for (User user : list) {
System.out.println(user);
}
sqlSession.commit();
sqlSession.close();
}
在sql拼接中使用通配符
select * from mybatis.user where name like "%"{value}"%"
mybatis-config.xml
mybatis的配置文件包含了会深深影响mybatis行为的设置和属性信息
MyBatis 的配置文件包含了会深深影响 MyBatis 行为的设置和属性信息。 配置文档的顶层结构如下:
configuration(配置)
properties(属性)
settings(设置)
typeAliases(类型别名)
typeHandlers(类型处理器)
objectFactory(对象工厂)
plugins(插件)
environments(环境配置)
environment(环境变量)
transactionManager(事务管理器)
dataSource(数据源)
databaseIdProvider(数据库厂商标识)
mappers(映射器)
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
学会使用多种enviroment配置方案
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
这些属性可以在外部进行配置,并可以进行动态替换。你既可以在典型的 Java 属性文件中配置这些属性,也可以在 properties 元素的子元素中设置。
编写一个配置文件
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=utf8
username=root
password=chen19990217...+
在核心配置文件中引用
//引入外部配置文件
<properties resource="db.properties"/>
类型别名可为 Java 类型设置一个缩写名字。
它仅用于 XML 配置,意在降低冗余的全限定类名书写。
//可以给实体类起别名
<typeAliases>
<typeAlias type="com.chen.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 Java Bean
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>
<typeAlias type="com.chen.pojo.User" alias="User"/>
<package name="com.chen.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,需要在实体类上添加注解
@Alias("hello")
下面是一些为常见的 Java 类型内建的类型别名。它们都是不区分大小写的,注意,为了应对原始类型的命名重复,采取了特殊的命名风格。
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 |
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。
typeHandlers(类型处理器)
objectFactory(对象工厂)
plugins(插件)
MapperRegistry:注册绑定我们的Mapper文件
方式一:使用相对于类路径的资源引用
<mappers>
<mapper resource="com/chen/dao/userMapper.xml"/>
mappers>
方式二:使用class文件绑定
<mapper class="com.chen.dao.UserMapper" />
注意点:
方式三:使用扫描包进行注入绑定
<package name="com.chen.dao"/>
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生命周期,和作用域是至关重要的,因为错误的使用会导致并发运行的错误
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这里面的每一个Mapper,代表一个具体的业务
修改实体类的属性名为不一致
public class User {
private int id;
private String name;
private String password;}
测试出现问题:password为空
//select * from mybatis.user where id = #{id};
//类型处理器
//select id,name,pwd from mybatis.user where id = #{id};
解决方案:
起别名
select id,name,pwd as password from mybatis.user where id = #{id};
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" resultMap="UserMap">
select * from mybatis.user where id = #{id};
select>
如果一个数据粗操作,出现了异常,我们需要拍错,日志就是最好的助手
曾经:sout、debug
在Mybatis中具体使用哪一个日志实现,在设置中设置
STDOUT_LOGGING标准日志输入
在Mybatis核心配置文件中,配置我们的日志!
//标志的日志工厂实现
<settings>
<setting name="logImpl" value="STDOUT_LOGGING"/>
settings>
什么是LOG4J?
<dependency>
<groupId>log4jgroupId>
<artifactId>log4jartifactId>
<version>1.2.17version>
dependency>
#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/chen.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
<settings>
<setting name="logImpl" value="LOG4J"/>
settings>
D:\java\jdk-8\bin\java.exe -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:D:\idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar=55179:D:\idea\IntelliJ IDEA 2019.1\bin" -Dfile.encoding=UTF-8 -classpath "D:\idea\IntelliJ IDEA 2019.1\lib\idea_rt.jar;D:\idea\IntelliJ IDEA 2019.1\plugins\junit\lib\junit-rt.jar;D:\idea\IntelliJ IDEA 2019.1\plugins\junit\lib\junit5-rt.jar;D:\java\jdk-8\jre\lib\charsets.jar;D:\java\jdk-8\jre\lib\deploy.jar;D:\java\jdk-8\jre\lib\ext\access-bridge-64.jar;D:\java\jdk-8\jre\lib\ext\cldrdata.jar;D:\java\jdk-8\jre\lib\ext\dnsns.jar;D:\java\jdk-8\jre\lib\ext\jaccess.jar;D:\java\jdk-8\jre\lib\ext\jfxrt.jar;D:\java\jdk-8\jre\lib\ext\localedata.jar;D:\java\jdk-8\jre\lib\ext\nashorn.jar;D:\java\jdk-8\jre\lib\ext\sunec.jar;D:\java\jdk-8\jre\lib\ext\sunjce_provider.jar;D:\java\jdk-8\jre\lib\ext\sunmscapi.jar;D:\java\jdk-8\jre\lib\ext\sunpkcs11.jar;D:\java\jdk-8\jre\lib\ext\zipfs.jar;D:\java\jdk-8\jre\lib\javaws.jar;D:\java\jdk-8\jre\lib\jce.jar;D:\java\jdk-8\jre\lib\jfr.jar;D:\java\jdk-8\jre\lib\jfxswt.jar;D:\java\jdk-8\jre\lib\jsse.jar;D:\java\jdk-8\jre\lib\management-agent.jar;D:\java\jdk-8\jre\lib\plugin.jar;D:\java\jdk-8\jre\lib\resources.jar;D:\java\jdk-8\jre\lib\rt.jar;F:\JavaWebProjects\mybatis\October-Mybatis\mybatis-04\target\test-classes;F:\JavaWebProjects\mybatis\October-Mybatis\mybatis-04\target\classes;F:\maven\jarpool\maven_repository\log4j\log4j\1.2.17\log4j-1.2.17.jar;F:\maven\jarpool\maven_repository\mysql\mysql-connector-java\5.1.47\mysql-connector-java-5.1.47.jar;F:\maven\jarpool\maven_repository\org\mybatis\mybatis\3.5.2\mybatis-3.5.2.jar;F:\maven\jarpool\maven_repository\junit\junit\4.12\junit-4.12.jar;F:\maven\jarpool\maven_repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit4 com.chen.dao.UserMapperTest,test
[org.apache.ibatis.logging.LogFactory]-Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
[org.apache.ibatis.logging.LogFactory]-Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
[org.apache.ibatis.io.VFS]-Class not found: org.jboss.vfs.VFS
[org.apache.ibatis.io.JBoss6VFS]-JBoss 6 VFS API is not available in this environment.
[org.apache.ibatis.io.VFS]-Class not found: org.jboss.vfs.VirtualFile
[org.apache.ibatis.io.VFS]-VFS implementation org.apache.ibatis.io.JBoss6VFS is not valid in this environment.
[org.apache.ibatis.io.VFS]-Using VFS adapter org.apache.ibatis.io.DefaultVFS
[org.apache.ibatis.io.DefaultVFS]-Find JAR URL: file:/F:/JavaWebProjects/mybatis/October-Mybatis/mybatis-04/target/classes/com/chen/pojo
[org.apache.ibatis.io.DefaultVFS]-Not a JAR: file:/F:/JavaWebProjects/mybatis/October-Mybatis/mybatis-04/target/classes/com/chen/pojo
[org.apache.ibatis.io.DefaultVFS]-Reader entry: User.class
[org.apache.ibatis.io.DefaultVFS]-Listing file:/F:/JavaWebProjects/mybatis/October-Mybatis/mybatis-04/target/classes/com/chen/pojo
[org.apache.ibatis.io.DefaultVFS]-Find JAR URL: file:/F:/JavaWebProjects/mybatis/October-Mybatis/mybatis-04/target/classes/com/chen/pojo/User.class
[org.apache.ibatis.io.DefaultVFS]-Not a JAR: file:/F:/JavaWebProjects/mybatis/October-Mybatis/mybatis-04/target/classes/com/chen/pojo/User.class
[org.apache.ibatis.io.DefaultVFS]-Reader entry: ���� 1 @
[org.apache.ibatis.io.ResolverUtil]-Checking to see if class com.chen.pojo.User matches criteria [is assignable to Object]
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.datasource.pooled.PooledDataSource]-PooledDataSource forcefully closed/removed all connections.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Opening JDBC Connection
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Created connection 500179317.
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@1dd02175]
[com.chen.dao.UserMapper.getUserById]-==> Preparing: select * from mybatis.user where id = ?;
[com.chen.dao.UserMapper.getUserById]-==> Parameters: 1(Integer)
[com.chen.dao.UserMapper.getUserById]-<== Total: 1
User{id=1, name='小王子', pwd='123456'}
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@1dd02175]
[org.apache.ibatis.transaction.jdbc.JdbcTransaction]-Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@1dd02175]
[org.apache.ibatis.datasource.pooled.PooledDataSource]-Returned connection 500179317 to pool.
Process finished with exit code 0
简单使用
在要使用Log4j的类中,导入包import org.apache.log4j.Logger;
日志对象,参数为当前类的class
Logger logger = Logger.getLogger(UserMapperTest.class);
日志级别
@Test
public void testLog4j(){
logger.info("info:进入了testLog4j方法");
logger.debug("debug:进入了testLog4j");
logger.error("error:进入了testLog4j");
}
思考:为什么要分页?
语法:select * from user limit startIndex,pageSize
使用Mybatis实现分页,核心就是SQL
接口
//分页
List<User> getUserByLimit(Map<String,Integer> map);
Mapper.XML
<select id="getUserByLimit" parameterType="map" resultType="user">
select * from mybatis.user limit #{startIndex},#{pageSize};
select>
测试
@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> userByLimit = mapper.getUserByLimit(map);
for (User user : userByLimit) {
System.out.println(user);
}
}
不再使用SQL实现分页
接口
//分页2
List<User> getUserByRowBounds();
mapper.xml
<select id="getUserByRowBounds" resultType="user">
select * from mybatis.user ;
select>
测试
@Test
public void getUserByRowBounds(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
//RowBounds实现
RowBounds rowBounds = new RowBounds(1, 2);
//通过java代码层面实现分页
List<User> list = sqlSession.selectList("com.chen.dao.UserMapper.getUserByRowBounds",null,rowBounds);
for (User user : list) {
System.out.println(user);
}
sqlSession.close();
}
了解即可,以后有用再拿出来
关于接口的理解
三个面向区别
@Select("select * from user")
List<User> getUsers();
<mappers>
<mapper class="com.chen.dao.UserMapper" />
mappers>
@Test
public void test(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
//核心:底层主要使用反射
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> users = mapper.getUsers();
for (User user : users) {
System.out.println(user);
}
sqlSession.close();
}
本质:反写机制实现
底层:动态代理!
我们可以在工具类创建的时候实现自动提交事务
//获取SqlSession连接
public static SqlSession getSqlSession(){
return sqlSessionFactory.openSession(true);
}
编写接口增加注解
//方法存在多个参数,所有的参数前面必须加上@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},#{pwd})")
int addUser(User user);
@Update("update user set name=#{name},pwd=#{pwd} where id=#{id}")
int updateUser(User user);
@Delete("delete from user where id = #{uid}")
int deleteUser(@Param("uid") int id);
测试类
@Test
public void test1(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
//核心:底层主要使用反射
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User userById = mapper.getUserById(2);
System.out.println(userById);
sqlSession.close();
}
@Test
public void test2(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
//核心:底层主要使用反射
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
mapper.addUser(new User(5,"啧啧啧","1111111"));
sqlSession.close();
}
@Test
public void test3(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
//核心:底层主要使用反射
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
mapper.updateUser(new User(5,"to","21313"));
sqlSession.close();
}
@Test
public void test4(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
//核心:底层主要使用反射
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
mapper.deleteUser(5);
sqlSession.close();
}
【注意:我们必须要将接口注册绑定到我们的核心配置中】
关于@Param注解
通过注解生成getter和setter等方法
使用步骤:
1. 在IDEA中安装LOmbok插件
2. 在项目中导入lombok的jar包
<dependency>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
<version>1.18.12version>
<scope>providedscope>
dependency>
lombok中的注解:
@NonNull
@Getter and @Setter
@Accessors
@AllArgsConstructor
@RequiredArgsConstructor
@NoArgsConstructor
@ToString和@EqualsAndHashCode
@Data
@Value
@Builder和@Singular
@Singular
@Builder
@Cleanup
@ExtensionMethod : 可以扩展已有的类(不建议使用)
@FieldDefaults (官方待转正)
@Delegate (不建议使用)
@Wither(不推荐)
说明:
@Data :无参构造,get,set,toString,hashCode,equals
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,'王老师');
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,'小张',1);
INSERT INTO student (`id` , `name` , `tid`) VALUES(3,'小宏',1);
INSERT INTO student (`id` , `name` , `tid`) VALUES(4,'小李',1);
INSERT INTO student (`id` , `name` , `tid`) VALUES(5,'小龙',1);
SELECT * FROM student;
SELECT * FROM teacher;
<mapper namespace="com.chen.dao.StudentMapper">
<select id="getStudent" resultMap="StudentTeacher">
select * from 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 teacher where id = #{id}
select>
mapper>
<select id="getStudent2" resultMap="StudentTeacher2">
select s.id sid,s.name sname,t.name tname
from student s,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>
回顾Mysql多对一查询方式:
和之前方法一样
实体类有所改变
@Data
public class Teacher {
private int id;
private String name;
//一个老师又有多个学生
private int tid;
}
@Data
public class Student {
private int id;
private String name;
private int tid;
}
<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 student where tid=#{tid}
select>
注意点:
面试高频
动态SQL就是指根据不同的条件生成不同的SQL语句
动态 SQL 元素和JSTL标签或基于XML的文本处理器类似。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
SQL:
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:
导包
编写配置文件
编写实体类
@Data
public class Blog {
private int id;
private String title;
private String author;
private Date createTime;
private int views;
}
表写实体类对应Mapper接口和Mapper.XML文件
<mapper namespace="com.chen.dao.BlogMapper">
<insert id="addBlog" parameterType="blog">
insert into blog (id, title, author,create_time, views)
values (#{id},#{title},#{author},#{createTime},#{views});
insert>
测试类
@Test
public void addInitBlog(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
Blog blog = new Blog();
blog.setId(IDUtils.getId());
blog.setTitle("Mybatis如此简单");
blog.setAuthor("小王子");
blog.setCreateTime(new Date());
blog.setViews(9999);
mapper.addBlog(blog);
blog.setId(IDUtils.getId());
blog.setTitle("Java如此简单");
mapper.addBlog(blog);
blog.setId(IDUtils.getId());
blog.setTitle("Spring如此简单");
mapper.addBlog(blog);
blog.setId(IDUtils.getId());
blog.setTitle("微服务如此简单");
mapper.addBlog(blog);
sqlSession.close();
}
<setting name="mapUnderscoreToCamelCase" value="true"/>
mapUnderscoreToCamelCase 是否开启驼峰命名自动映射,即从经典数据库列名 A_COLUMN 映射到经典 Java 属性名 aColumn。
<select id="queryBlogIF" parameterType="map" resultType="Blog">
select * from 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 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 blog
<where>
<if test="title != null">
title = #{title}
if>
<if test="author != null">
and author = #{author}
if>
where>
select>
<update id="updateBlog" parameterType="map" >
update 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层面取执行一些逻辑代码
<select id="queryBlogForeach" parameterType="map" resultType="blog">
select * from blog
<where>
<foreach collection="ids" item="id" open="and (" close=")" separator="or">
id = #{id}
foreach>
where>
select>
测试类
@Test
public void queryBlogForeach(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
HashMap map = new HashMap();
ArrayList<Integer> ids = new ArrayList<Integer>();
map.put("ids",ids);
List<Blog> blogs = mapper.queryBlogForeach(map);
for (Blog blog : blogs) {
System.out.println(blog);
}
sqlSession.close();
}
有的时候,我们可能会将一些公共的部分抽取出来作为一个SQL片段,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 blog
<where>
<include refid="if-title-author">include>
where>
select>
注意事项:
建议:
查询 : ;连接数据库,好资源
一次查询的结果,给他暂存在一个可以直接取到的地方-->内存:缓存
我们再次查询相同数据的时候,直接走缓存,就不用了走数据库了
1、什么是缓存 [ Cache ]?
2、为什么使用缓存?
3、什么样的数据能使用缓存?
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
一级缓存也叫本地缓存:
测试步骤:
开启日志
测试在一个Session中查询两次相同的记录
查看日志输出发现值进行了一次查询:
缓存失效的情况:
查询不同的东西
增删改操作,可能会改变原来的数据,所以必定会刷新缓存
查询不同的Mapper.xml
手动清除缓存!
//手动清理缓存
sqlSession.clearCache();
**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的这个区间段!
一级缓存就相当一个Map
二级缓存也叫全局缓存,一级缓存作用域太低了,所以诞生了二级缓存
基于namespace级别的缓存,一个名称空间,对应一个二级缓存;
工作机制
步骤:
开启全局缓存
设置名 | 描述 | 有效值 | 默认值 |
---|---|---|---|
cacheEnabled | 全局性地开启或关闭所有映射器配置文件中已配置的任何缓存。 | true | false | true |
//显示的开启全局缓存
<setting name="cacheEnabled" value="true"/>
也可以自定义参数
<cache eviction="FIFO"
flushInterval="60000"
size="512"
readOnly="true"/>
测试
问题:我们需要将实体类序列化!否则报错
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User implements Serializable {
private int id;
private String name;
private String pwd;
}
测试类代码
@Test
public void test1(){
SqlSession sqlSession = MybatisUtils.getSqlSession();
SqlSession sqlSession2 = MybatisUtils.getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User user1 = mapper.queryUserById(1);
System.out.println(user1);
sqlSession.close();
UserMapper mapper1 = sqlSession2.getMapper(UserMapper.class);
User user2 = mapper1.queryUserById(1);
System.out.println(user2);
System.out.println(user1 == user2);
sqlSession2.close();
}
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!
<dependency>
<groupId>org.mybatis.cachesgroupId>
<artifactId>mybatis-ehcacheartifactId>
<version>1.1.0version>
dependency>
在Mapper.xml中指定我们的ehcache缓存实现
<cache type="org.mybatis.caches.ehcache.EhcacheCache"/>
ehcache.xml
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="http://ehcache.org/ehcache.xsd"
updateCheck="false">
<diskStore path="./tmpdir/Tmp_EhCache"/>
<defaultCache
eternal="false"
maxElementsInMemory="10000"
overflowToDisk="false"
diskPersistent="false"
timeToIdleSeconds="1800"
timeToLiveSeconds="259200"
memoryStoreEvictionPolicy="LRU"/>
<cache
name="cloud_user"
eternal="false"
maxElementsInMemory="5000"
overflowToDisk="false"
diskPersistent="false"
timeToIdleSeconds="1800"
timeToLiveSeconds="1800"
memoryStoreEvictionPolicy="LRU"/>
ehcache>
目前最多的用Redis数据库来做缓存