Mybatis学习笔记
Mybatis学习笔记
笔记地址：https://github.com/userwusir/study-notes
资源
官网
https://mybatis.org/mybatis-3/zh/index.html
项目地址
https://github.com/mybatis/mybatis-3/releases
Maven配置
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.6</version>
</dependency>
第一个Mybatis程序
文件结构
-
sql
create table user ( id int(10) not null primary key, name varchar(15) null, pwd varchar(15) null ); -
pom.xml
<dependencies> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.6</version> </dependency> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.13</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.23</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.18</version> </dependency> </dependencies> <build> <!--在build中配置resources，来防止我们资源导出失败的问题--> <resources> <resource> <directory>src/main/resources</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> </resource> <resource> <directory>src/main/java</directory> <includes> <include>**/*.properties</include> <include>**/*.xml</include> </includes> <filtering>true</filtering> </resource> </resources> </build> -
Mybatis核心配置文件
<?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> <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=utf-8"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> <!--每一个Mapper文件都需要在核心配置文件中配置！--> <mappers> <mapper resource="com/wll/dao/UserMapper.xml"/> </mappers> </configuration> -
util工具类
/** * @author wulele */ public class MybatisUtil { /** * 每个基于 MyBatis 的应用都是以一个 SqlSessionFactory 的实例为核心的。SqlSessionFactory 的实例 * 可以通过 SqlSessionFactoryBuilder 获得。而 SqlSessionFactoryBuilder 则可以从 XML 配置文件 * 或一个预先配置的 Configuration 实例来构建出 SqlSessionFactory 实例 */ private static SqlSessionFactory sqlSessionFactory; static { try { String resource = "mybaties-config.xml"; InputStream inputStream = Resources.getResourceAsStream(resource); sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); } catch (IOException e) { e.printStackTrace(); } } /** * SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。 * @return SqlSession */ public SqlSession getSqlSession() { return sqlSessionFactory.openSession(); //可以设置autocommit，设置为自动提交事务，不用sqlsession.commit() //return sqlSessionFactory.openSession(true); } } -
pojo层
/** * @author wulele */ @Getter @Setter @NoArgsConstructor @AllArgsConstructor @ToString public class User { private int id; private String name; private String pwd; } -
UserDao--->UserMapper
/** * @author wulele */ public interface UserDao { /** * User list * @return User list */ public List<User> getUerList(); } -
UserDaoImpl--->UserMapper.xml
<?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.wll.dao.UserDao"> <select id="getUerList" resultType="com.wll.pojo.User"> select * from mybatis.user </select> </mapper> -
test
public class UserDaoTest { @Test public void test(){ //建议写法，保证sqlSession能在finally被关闭 SqlSession sqlSession = null; try { sqlSession = new MybatisUtil().getSqlSession(); UserDao mapper = sqlSession.getMapper(UserDao.class); List<User> userList = mapper.getUerList(); //不推荐使用 //List<User> userList = sqlSession.selectList("com.wll.dao.UserDao.getUerList"); for (User user : userList) { System.out.println(user); } } catch (Exception e) { e.printStackTrace(); } finally { sqlSession.close(); } } } -
注意点！
-
util工具类
String resource = "mybaties-config.xml";
不要写全路径
-
如果自己写的xml在sources文件夹中，不能被打包到发布文件夹，记得pom.xml配置build的resources
-
Mapper.xml文件的namespace、resultType写完整包名，id为namespace对应包下的方法
-
每一个Mapper文件都需要在核心配置文件中配置！
-
-
运行结果
增删改查
注意：增删改需要提交事务！
传递多个参数使用Map或者注解
增
/**
* add user
* @param user
*/
public void addUser(User user);
<insert id="addUser" parameterType="com.wll.pojo.User">
insert into mybatis.user(id, name, pwd) value (#{id},#{name},#{pwd})
</insert>
@Test
public void addUser(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
mapper.addUser(new User(4,"bob","1234"));
//提交事务！！！
sqlSession.commit();
sqlSession.close();
}
删
<delete id="delUserById" parameterType="int">
delete
from mybatis.user
where id = #{id}
</delete>
改
<update id="updateUser" parameterType="com.wll.pojo.User">
update mybatis.user
set name = #{name},
pwd = #{pwd}
where id = #{id}
</update>
查
<select id="getUserById" parameterType="int" resultType="com.wll.pojo.User">
select *
from mybatis.user
where id = #{id}
</select>
配置进阶
配置顺序
配置有先后顺序
environments
可以配置多个environment但只能使用一个
使用场景：正式+测试
<environments default="test">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url"
value="jdbc:mysql://192.144.231.70:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=utf-8"/>
<property name="username" value="root"/>
<property name="password" value="123123"/>
</dataSource>
</environment>
<environment id="test">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url"
value="jdbc:mysql://192.144.231.70:3306/mybatis?useSSL=true&useUnicode=true&characterEncoding=utf-8"/>
<property name="username" value="root"/>
<property name="password" value="123123"/>
</dataSource>
</environment>
</environments>
properties
<!--假如外部配置文件也含有username属性，优先使用外部配置文件-->
<properties resource="db.properties">
<property name="username" value="root"/>
</properties>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
settings
别名（typeAliases）
-
指定实体类取别名
<typeAliases> <typeAlias type="com.wll.pojo.User" alias="User"/> </typeAliases> -
扫描包
扫描实体类所在包，如果不使用注解，其默认别名就是类首字母小写
<typeAliases> <package name="com.wll.pojo"/> </typeAliases>对比，第一种方式可以自定义别名，第二种需要在实体类加注解才可以自定义别名
@Alias("hello")
映射器（mappers）
-
类路径资源引用
-
mapper文件完全限定类名
-
mapper文件包名
注意点：第一种使用无特殊要求，第二三种使用需要 接口和mapper配置文件同名，并且在一个文件夹下！
结果映射（ResultMap）
如果pojo层对象名不与数据库列名一一对应，可以使用ResultMap来解决。
日志
标准日志配置
<settings>
<setting name="logImpl" value="STDOUT_LOGGING"/>
</settings>
LOG4J配置
-
导包
<dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency> -
log4j.properties
#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/wll.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 # 输出消息编码 log4j.appender.LOGFILE.encoding=UTF-8 -
核心配置文件
<settings> <setting name="logImpl" value="LOG4J"/> </settings> -
补充
Logger logger = Logger.getLogger(UserMapper.class); logger.info("开始了"); logger.debug("哦哦哦"); logger.error("错错错");
-
注意
mybatis核心配置文件中不要使用或中使用package来指定要扫描的包，否则log文件打不开
分页
limit
-
limit格式
select * from user limit startIndex,pageSize;example--从0开始，一页三行 select * from user limit 0,3; -
UserMapper
/** * limit user list * @param map * @return List */ List<User> limitUserList(Map<String, Integer> map); -
UserMapper.xml
<select id="limitUserList" parameterType="map" resultType="User"> select * from mybatis.user limit #{startIndex},#{pageSize} </select> -
Test
@Test public void limitUserList(){ SqlSession sqlSession = new MybatisUtil().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> users = mapper.limitUserList(map); for (User user : users) { System.out.println(user); } sqlSession.close(); }
RowBounds
-
UserMapper
/** * rowBounds user list * @return List */ List<User> rowBoundsUserList(); -
UserMapper.xml
<select id="rowBoundsUserList" resultType="User"> select * from mybatis.user </select> -
Test
@Test public void rowBoundsUserList(){ RowBounds rowBounds = new RowBounds(0,2); SqlSession sqlSession = new MybatisUtil().getSqlSession(); List<User> userList = sqlSession.selectList("com.wll.dao.UserMapper.rowBoundsUserList", null, rowBounds); for (User user : userList) { System.out.println(user); } sqlSession.close(); }
Mybatis PageHelper插件
地址：https://pagehelper.github.io/
注解开发
example
UserMapper.java
@Select("select * from user")
List<User> getUerList();
本质：反射机制
底层：动态代理
使用场景：sql语句较为简单
增删改查
/**
* get User By id
*
* @param id
* @return
*/
@Select("select * from user where id = #{uid}")
User getUserById(@Param("uid") int id);
/**
* add user
*
* @param user
*/
@Insert("insert into user(id,name,pwd) values(#{id},#{name},#{pwd})")
void addUser(User user);
/**
* update user
*
* @param user
*/
@Update("update user set name = #{name}, pwd = #{pwd} where id = #{id}")
void updateUser(User user);
/**
* delete user
*
* @param id
*/
@Delete("delete from user where id = #{uid}")
void delUser(@Param("uid") int id);
#{}与${}的区别:
{}方式能够很大程度防止sql注入(安全)，${}方式无法防止Sql注入
多对一操作
create table student
(
id int(10) not null
primary key,
name varchar(30) null,
tid int(10) null,
constraint fktid
foreign key (tid) references teacher (id)
);
create table teacher
(
id int(10) not null
primary key,
name varchar(30) null
);
sql
select s.id,s.name,t.name from student s, teacher t where s.tid = t.id;
public class Student {
private int id;
private String name;
//一个学生对应多个老师
private Teacher teacher;
}
public class Teacher {
private int id;
private String name;
}
查询嵌套
StudentMapper
/**
* student list
* @return List
*/
List<Student> studentList();
StudentMapper.xml
<!--查询全部学生信息，学生tid对应老师id-->
<select id="studentList" resultMap="StudentTeacher">
select * from student
</select>
<!--map集结果映射-->
<resultMap id="StudentTeacher" type="com.wll.pojo.Student">
<id property="id" column="id"/>
<id property="name" column="name"/>
<!--对象处理association，映射老师对象到学生tid属性-->
<!--集合处理collection-->
<association property="teacher" column="tid" select="teacherList" javaType="com.wll.pojo.Teacher"/>
</resultMap>
<!--查询全部老师信息-->
<select id="teacherList" resultType="com.wll.pojo.Teacher">
select * from teacher where id = #{tid}
</select>
结果：
结果嵌套
<select id="studentList2" resultMap="StudentTeacher2">
select s.id sid, s.name sname, t.name tname, t.id tid
from student s,
teacher t
where s.tid = t.id;
</select>
<resultMap id="StudentTeacher2" type="com.wll.pojo.Student">
<id property="id" column="sid"/>
<id property="name" column="sname"/>
<!--嵌套结果-->
<association property="teacher" javaType="com.wll.pojo.Teacher">
<!--返回teacher的id和name-->
<id property="id" column="tid"/>
<id property="name" column="tname"/>
</association>
</resultMap>
结果：
一对多
实体类：
public class Student {
private int id;
private String name;
private int tid;
}
public class Teacher {
private int id;
private String name;
private List<Student> students;
}
结果嵌套
/**
* get Teacher
* @param id
* @return
*/
Teacher getTeacher(@Param("tid") int id);
/**
* get teacher
* @param id
* @return
*/
Teacher getTeacher2(@Param("tid")int id);
<select id="getTeacher" resultMap="TeacherStudent">
select s.id sid, s.name sname, t.id tid, t.name tname
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"/>
<!--javaType: 指定属性的类型
集合中的泛型信息，我们使用ofType-->
<collection property="students" ofType="student">
<result property="id" column="sid"/>
<result property="name" column="sname"/>
<result property="tid" column="tid"/>
</collection>
</resultMap>
结果：
Teacher(id=1, name=吴老师,
students=[Student(id=1, name=小明, tid=1),
Student(id=2, name=小红, tid=1),
Student(id=3, name=小张, tid=1),
Student(id=4, name=小李, tid=1),
Student(id=5, name=小王, tid=1)])
查询嵌套
<select id="getTeacher2" resultMap="TeacherStudent2">
select *
from teacher
where id = #{tid}
</select>
<resultMap id="TeacherStudent2" type="teacher">
<result property="id" column="id"/>
<collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId"
column="id"/>
</resultMap>
<select id="getStudentByTeacherId" resultType="student">
select *
from student
where tid = #{tid}
</select>
动态sql
学习环境
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'
);
mybaties-config.xml
<!--开启数据库映射到实体类驼峰命名-->
<setting name="mapUnderscoreToCamelCase" value="true"/>
pojo
public class Blog {
private String id;
private String title;
private String author;
private Date createTime;
private int views;
}
BlogMapper
/**
* add blog
* @param blog
*/
void addBlog(Blog blog);
BlogMapper.xml
<insert id="addBlog" parameterType="blog">
insert into blog(id, title, author, create_time, views)
values (#{id}, #{title}, #{author}, #{createTime}, #{views})
</insert>
UuidUtil
public class UuidUtil {
public String getId(){
return UUID.randomUUID().toString().replaceAll("-","");
}
}
Test
public void test(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
Blog blog = new Blog();
blog.setId(new UuidUtil().getId());
blog.setTitle("study");
blog.setAuthor("wll");
blog.setCreateTime(new Date());
blog.setViews(1000);
mapper.addBlog(blog);
blog.setId(new UuidUtil().getId());
blog.setTitle("mybatis");
blog.setCreateTime(new Date());
mapper.addBlog(blog);
blog.setId(new UuidUtil().getId());
blog.setTitle("servlet");
blog.setCreateTime(new Date());
mapper.addBlog(blog);
sqlSession.commit();
sqlSession.close();
}
结果：
if
BlogMapper
/**
* IF find blog
* @param map
* @return
*/
List<Blog> findBlogIF(Map map);
BlogMapper.xml
<select id="findBlogIF" parameterType="map" resultType="blog">
select * from blog where 1=1
<if test="title != null">
title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</select>
Test
public void test(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
HashMap map = new HashMap();
map.put("author","wll");
List<Blog> blogList = mapper.findBlogIF(map);
for (Blog blog : blogList) {
System.out.println(blog);
}
sqlSession.close();
}
结果：
where & trim & sql片段
消除第一个查询条件为空的情况下第二个查询条件前的AND或OR，类似于where 1=1
BlogMapper.xml & where
<select id="findBlogIF" 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>
BlogMapper.xml & trim
<select id="findBlogIF" parameterType="map" resultType="blog">
select * from blog
<trim prefix="where" prefixOverrides="AND|OR">
<if test="title != null">
title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</trim>
</select>
BlogMapper.xml & sql片段
提取公用部分sql
-
最好基于单表来定义sql片段
-
不要存在where标签
<sql id="IF-title-author">
<if test="title != null">
title = #{title}
</if>
<if test="author != null">
and author = #{author}
</if>
</sql>
<select id="findBlogIF" parameterType="map" resultType="blog">
select * from blog
<trim prefix="where" prefixOverrides="AND|OR">
<include refid="IF-title-author"></include>
</trim>
</select>
choose
条件成立就执行，第一个成立就退出后面不执行，以此类推
BlogMapper
/**
* choose find blog
* @param map
* @return
*/
List<Blog> findBlogChoose(Map map);
BlogMapper.xml & where
<select id="findBlogChoose" 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>
BlogMapper.xml & trim
<select id="findBlogChoose" parameterType="map" resultType="blog">
select * from blog
<trim prefix="where" prefixOverrides="AND|OR">
<choose>
<when test="title != null">
title = #{title}
</when>
<when test="author != null">
and author = #{author}
</when>
<otherwise>
and views = ${views}
</otherwise>
</choose>
</trim>
</select>
Test
public void test(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
HashMap map = new HashMap();
map.put("title","study");
map.put("author","wll");
map.put("views",1000);
List<Blog> blogList = mapper.findBlogChoose(map);
for (Blog blog : blogList) {
System.out.println(blog);
}
sqlSession.close();
}
结果：
set
BlogMapper
/**
* update blog
* @param map
*/
void updateBlog(Map map);
BlogMapper.xml & set
<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}
</where>
</update>
BlogMapper.xml & trim
<update id="updateBlog" parameterType="map">
update blog
<trim prefix="set" suffixOverrides=",">
<if test="title != null">
title = #{title},
</if>
<if test="author != null">
author = #{author}
</if>
</trim>
<where>
id = #{id}
</where>
</update>
Test
public void test(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
HashMap map = new HashMap();
map.put("title","studying");
map.put("author","wll");
map.put("id","3d14b89488284b0892bfdc51938d1d31");
mapper.updateBlog(map);
sqlSession.commit();
sqlSession.close();
}
Foreach
sql
--两种方式查询id是1，2，3中的信息
select * from blog where id in (1,2,3);
select * from blog where 1 = 1 and (id = 1 or id = 2 or id =3);
BlogMapper
/**
* dynamic sql
* @param map
* @return
*/
List<Blog> DynamicSql(Map map);
BlogMapper.xml
<select id="DynamicSql" parameterType="map" resultType="blog">
select * from blog
<where>
<!--方式一-->
<!-- <foreach collection="ids" item="id" open="id in(" separator="," close=")">-->
<!-- #{id}-->
<!-- </foreach>-->
<!--方式二-->
<foreach collection="ids" item="id" open="and (" separator="or" close=")">
id = #{id}
</foreach>
</where>
</select>
Test
public void test(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
HashMap map = new HashMap();
ArrayList<Integer> ids = new ArrayList<>();
ids.add(1);
ids.add(2);
map.put("ids",ids);
List<Blog> blogIF = mapper.DynamicSql(map);
for (Blog blog : blogIF) {
System.out.println(blog);
}
sqlSession.close();
}
Mybatis缓存
My Batis系统中默认定义了两级缓存:一级缓存和二级缓存
-
默认情况下,只有一级缓存开启。( Sqlsession级别的缓存,也称为本地缓存)
-
二级缓存需要手动开启和配置,他是基于 namespace级别的缓存
为了提高扩屐性, MyBatis定义了缓存接口 Cache。我们可以通过实现 Cache接口来自定义二级缓存
一级缓存
public void myTest(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User user = mapper.getUserById(1);
System.out.println(user);
User user2 = mapper.getUserById(1);
System.out.println(user2);
sqlSession.close();
}
查询两次id都为1的user，发现之查询了一次
查询一次id为1，一次为2的user，发现查询了两次
public void myTest(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
User user = mapper.getUserById(1);
System.out.println(user);
mapper.updateUser(new User(2,"kkk","123"));
User user2 = mapper.getUserById(1);
System.out.println(user2);
sqlSession.close();
}
查询两次同一个人过程中更新另一个人信息，发现查询两次
总结：
- 映射语句文件中的所有 select 语句的结果将会被缓存。
- 映射语句文件中的所有 insert、update 和 delete 语句会刷新缓存。
- 缓存会使用最近最少使用算法（LRU, Least Recently Used）算法来清除不需要的缓存。
- 缓存不会定时进行刷新（也就是说，没有刷新间隔）。
- 主动清理缓存（sqlSession.clearCache()）
二级缓存
mybaties-config.xml
<!--默认是开启的，显示地表达开启缓存-->
<setting name="cacheEnabled" value="true"/>
在想开启二级缓存地Mapper.xml文件中
<cache/>
也可扩展
创建了一个 FIFO 缓存，每隔 60 秒刷新，最多可以存储结果对象或列表的 512 个引用，而且返回的对象被认为是只读的，因此对它们进行修改可能会在不同线程中的调用者产生冲突
<cache
eviction="FIFO"
flushInterval="60000"
size="512"
readOnly="true"/>
注意：若是不配置readOnly="true"，且pojo没有序列化，会报错Cause: java.io.NotSerializableException: com.wll.pojo.User
Test
public void myTest(){
SqlSession sqlSession = new MybatisUtil().getSqlSession();
SqlSession sqlSession2 = new MybatisUtil().getSqlSession();
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
UserMapper mapper2 = sqlSession2.getMapper(UserMapper.class);
User user = mapper.getUserById(1);
System.out.println(user);
sqlSession.close();
User user2 = mapper2.getUserById(1);
System.out.println(user2);
sqlSession2.close();
}
两个sqlSession，第一个关闭后第二个查询，发现只查询一次（一级缓存存到二级缓存中去了）
Ehcache
pom.xml
<dependency>
<groupId>org.mybatis.caches</groupId>
<artifactId>mybatis-ehcache</artifactId>
<version>1.2.1</version>
</dependency>
UserMapper.xml
<cache type="org.mybatis.caches.ehcache.EhcacheCache"/>
mybatis-config.xml
<?xml version="1.0" encoding="UTF-8"?>
<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>
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