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今天小編給大家分享一下Mybatis基礎(chǔ)概念與高級(jí)應(yīng)用方法的相關(guān)知識(shí)點(diǎn),內(nèi)容詳細(xì),邏輯清晰,相信大部分人都還太了解這方面的知識(shí),所以分享這篇文章給大家參考一下,希望大家閱讀完這篇文章后有所收獲,下面我們一起來了解一下吧。
數(shù)據(jù)庫:mysql5.7
jdk:15
<!--引入依賴--> <dependencies> <!--mybatis坐標(biāo)--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.5</version> </dependency> <!--mysql驅(qū)動(dòng)坐標(biāo)--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.6</version> <scope>runtime</scope> </dependency> <!--單元測試坐標(biāo)--> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.22</version> </dependency> </dependencies>
User實(shí)體
@Data public class User { private Integer id; private String username; }
jdbc.driver=com.mysql.jdbc.Driver jdbc.url=jdbc:mysql://127.0.0.1/zdy_mybatis jdbc.username=root jdbc.password=root
<?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> <!--加載外部的properties文件--> <properties resource="jdbc.properties"></properties> <!--給實(shí)體類的全限定類名給別名--> <typeAliases> <!--給單獨(dú)的實(shí)體起別名--> <!-- <typeAlias type="com.yun.pojo.User" alias="user"></typeAlias>--> <!--批量起別名:該包下所有的類的本身的類名:別名還不區(qū)分大小寫--> <package name="com.yun.pojo"/> </typeAliases> <!--environments:運(yùn)行環(huán)境--> <environments default="development"> <environment id="development"> <!--當(dāng)前事務(wù)交由JDBC進(jìn)行管理--> <transactionManager type="JDBC"></transactionManager> <!--當(dāng)前使用mybatis提供的連接池--> <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> <!--引入映射配置文件--> <mappers> <mapper resource="UserMapper.xml"></mapper> </mappers> </configuration>
UserMapper.xml
<mapper namespace="user"> <!--select--> <select id="findAll" resultType="com.yun.pojo.User"> select * from user </select> </mapper>
@Test public void test1() throws IOException { //1.Resources工具類,配置文件的加載,把配置文件加載成字節(jié)輸入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件,并創(chuàng)建了sqlSessionFactory工廠 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生產(chǎn)sqlSession // 默認(rèn)開啟一個(gè)事務(wù),但是該事務(wù)不會(huì)自動(dòng)提交 //在進(jìn)行增刪改操作時(shí),要手動(dòng)提交事務(wù) SqlSession sqlSession = sqlSessionFactory.openSession(); //4.sqlSession調(diào)用方法:查詢所有selectList 查詢單個(gè):selectOne 添加:insert 修改:update 刪除:delete List<User> users = sqlSession.selectList("user.findAll"); users.forEach(item ->{ System.out.println(item); }); sqlSession.close(); }
輸出結(jié)果
User(id=1, username=Tom)
User(id=2, username=Jerry)
UserMapper.xml
<!--parameterType:參數(shù)類型--> <insert id="saveUser" parameterType="com.yun.pojo.User"> insert into user Values (#{id},#{username}) </insert>
@Test public void test2() throws IOException { InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); User user = new User(); user.setId(3); user.setUsername("jack"); sqlSession.insert("user.saveUser",user); sqlSession.commit(); sqlSession.close(); }
數(shù)據(jù)庫結(jié)果:
UserMapper.xml
<update id="updateUser" parameterType="com.yun.pojo.User"> update user set username = #{username} where id = #{id} </update>
@Test public void test3() throws IOException { InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); User user = new User(); user.setId(3); user.setUsername("rose"); sqlSession.update("user.updateUser",user); sqlSession.commit(); sqlSession.close(); }
數(shù)據(jù)庫結(jié)果:
UserMapper.xml
<delete id="deleteUser" parameterType="java.lang.Integer"> delete from user where id =#{id} </delete>
@Test public void test4() throws IOException { InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); User user = new User(); user.setId(3); sqlSession.delete("user.deleteUser",3); sqlSession.commit(); sqlSession.close(); }
數(shù)據(jù)庫結(jié)果:
public interface IUserDao { //查詢所有用戶 List<User> findAll() throws IOException; }
UserDaoImpl
public class UserDaoImpl implements IUserDao { @Override public List<User> findAll() throws IOException { InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); SqlSession sqlSession = sqlSessionFactory.openSession(); List<User> users = sqlSession.selectList("user.findAll"); sqlSession.close(); return users; } }
@Test public void test5() throws IOException { UserDaoImpl dao = new UserDaoImpl(); List<User> users = dao.findAll(); System.out.println(users); }
打印結(jié)果:
[User(id=1, username=Tom), User(id=2, username=Jerry)]
Mapper接口開發(fā)需要遵行以下規(guī)范:
mapper.xml文件中的namespace與mapper接口的全限定名相同;
2. mapper接口方法名和mapper.xml中定義的每個(gè)statement的id相同
3. mapper接口方法的輸入?yún)?shù)類型和mapper.xml中定義的每個(gè)sql的parameterType的類型相同
4. mapper接口方法的輸出參數(shù)類型和mapper.xml中定義的每個(gè)sql的resultType的類型相同
根據(jù)上述的規(guī)范修改UserMapper.xml
<mapper namespace="com.yun.dao.IUserDao"> <!--select--> <select id="findAll" resultType="com.yun.pojo.User"> select * from user </select> </mapper>
public interface IUserDao { //查詢所有用戶 List<User> findAll() throws IOException; }
@Test public void test6() throws IOException { InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); IUserDao mapper = sqlSession.getMapper(IUserDao.class); List<User> all = mapper.findAll(); all.forEach(item ->{ System.out.println(all); }); }
輸出結(jié)果:
User(id=1, username=Tom)
User(id=2, username=Jerry)
public interface IUserDao { //多條件組合查詢:演示if public List<User> findByCondition(User user); }
<!--抽取sql片段--> <sql id="selectUser"> select * from user </sql> <!--多條件組合查詢:演示if--> <select id="findByCondition" parameterType="user" resultType="user"> <include refid="selectUser"></include> <where> <if test="id !=null"> and id = #{id} </if> <if test="username !=null"> and username = #{username} </if> </where> </select>
@Test public void test7() throws IOException { InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); IUserDao mapper = sqlSession.getMapper(IUserDao.class); User user1 = new User(); user1.setId(1); user1.setUsername("Tom"); List<User> all = mapper.findByCondition(user1); for (User user : all) { System.out.println(user); } }
輸出結(jié)果:
User(id=1, username=Tom)
動(dòng)態(tài)sql語句 foreach標(biāo)簽
public interface IUserDao { //多值查詢:演示foreach public List<User> findByIds(int[] ids); }
<!--多值查詢:演示foreach--> <select id="findByIds" parameterType="list" resultType="user"> <include refid="selectUser"></include> <where> <foreach collection="array" open="id in (" close=")" item="id" separator=","> #{id} </foreach> </where> </select>
@Test public void test8() throws IOException { InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); IUserDao mapper = sqlSession.getMapper(IUserDao.class); int[] arr = {1,2}; List<User> all = mapper.findByIds(arr); for (User user : all) { System.out.println(user); } }
輸出結(jié)果:
User(id=1, username=Tom)
User(id=2, username=Jerry)
User實(shí)體
@Data public class User { private Integer id; private String username; //該用戶所具有的訂單信息 private List<Order> orders; //該用戶所具有的角色信息 private List<Role> roles; }
Order實(shí)體
@Data public class Order { private Integer id; private String orderTime; private BigDecimal total; //表明該訂單屬于哪個(gè)用戶 private User user; }
Role實(shí)體
@Data public class Role { private Integer id; private String roleName; }
public interface IOrderMapper { /** * 查詢訂單的同時(shí)還查詢該訂單所屬的用戶 * @return */ public List<Order> findOrderAndUser(); }
<resultMap id="orderMap" type="com.yun.pojo.Order"> <result property="id" column="id"></result> <result property="orderTime" column="order_time"></result> <result property="total" column="total"></result> <association property="user" javaType="com.yun.pojo.User"> <result property="id" column="uid"></result> <result property="username" column="username"></result> </association> </resultMap> <!--resultMap:手動(dòng)來配置實(shí)體屬性與表字段的映射關(guān)系--> <select id="findOrderAndUser" resultMap="orderMap"> select * from orders o,user u where o.uid = u.id </select>
@Test public void test1() throws IOException { //1.Resources工具類,配置文件的加載,把配置文件加載成字節(jié)輸入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件,并創(chuàng)建了sqlSessionFactory工廠 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生產(chǎn)sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); IOrderMapper mapper = sqlSession.getMapper(IOrderMapper.class); List<Order> orderAndUser = mapper.findOrderAndUser(); orderAndUser.forEach(order -> { System.out.println(order); }); }
運(yùn)行結(jié)果:
Order(id=1, orderTime=2022-05-01, total=1000.00, user=User(id=1, username=Tom, orders=null, roles=null))
Order(id=2, orderTime=2022-05-10, total=2000.00, user=User(id=2, username=Jerry, orders=null, roles=null))
Order(id=3, orderTime=2022-05-20, total=3000.00, user=User(id=2, username=Jerry, orders=null, roles=null))
public interface IUserMapper { /** * 查詢所有用戶信息,同時(shí)查詢出每個(gè)用戶關(guān)聯(lián)的訂單信息 * @return */ public List<User> findAll(); }
<resultMap id="userMap" type="com.yun.pojo.User"> <id property="id" column="id"></id> <result property="username" column="username"></result> <collection property="orders" ofType="com.yun.pojo.Order"> <id property="id" column="oid"></id> <result property="orderTime" column="order_time"></result> <result property="total" column="total"></result> </collection> </resultMap> <!--resultMap:手動(dòng)來配置實(shí)體屬性與表字段的映射關(guān)系--> <select id="findAll" resultMap="userMap"> select u.*,o.id oid,o.order_time,o.total,o.uid from user u left join orders o on u.id = o.uid </select>
@Test public void test2() throws IOException { //1.Resources工具類,配置文件的加載,把配置文件加載成字節(jié)輸入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件,并創(chuàng)建了sqlSessionFactory工廠 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生產(chǎn)sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); IUserMapper mapper = sqlSession.getMapper(IUserMapper.class); List<User> users = mapper.findAll(); users.forEach(user -> { System.out.println(user.getUsername()); System.out.println(user.getOrders()); }); }
運(yùn)行結(jié)果:
Tom
[Order(id=1, orderTime=2022-05-01, total=1000.00, user=null)]
Jerry
[Order(id=2, orderTime=2022-05-10, total=2000.00, user=null), Order(id=3, orderTime=2022-05-20, total=3000.00, user=null)]
public interface IUserMapper { /** * 查詢所有用戶信息,同事查詢出每個(gè)用戶關(guān)聯(lián)的角色信息 * @return */ public List<User> findUserAndRole(); }
<resultMap id="userAndRoleMap" type="com.yun.pojo.User"> <result property="id" column="userId"></result> <result property="username" column="username"></result> <collection property="roles" ofType="com.yun.pojo.Role"> <result property="id" column="roleId"></result> <result property="roleName" column="rolename"></result> </collection> </resultMap> <select id="findUserAndRole" resultMap="userAndRoleMap"> SELECT * FROM USER u LEFT JOIN sys_user_role sur ON u.id = sur.user_id LEFT JOIN sys_role sr ON sur.role_id = sr.id </select>
@Test public void test3() throws IOException { //1.Resources工具類,配置文件的加載,把配置文件加載成字節(jié)輸入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件,并創(chuàng)建了sqlSessionFactory工廠 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生產(chǎn)sqlSession SqlSession sqlSession = sqlSessionFactory.openSession(); IUserMapper mapper = sqlSession.getMapper(IUserMapper.class); List<User> users = mapper.findUserAndRole(); users.forEach(user -> { System.out.println(user.getUsername()); System.out.println(user.getRoles()); }); }
運(yùn)行結(jié)果:
Tom
[Role(id=null, roleName=董事長), Role(id=null, roleName=經(jīng)理)]
Jerry
[Role(id=null, roleName=董事長), Role(id=null, roleName=經(jīng)理)]
@Insert: 實(shí)現(xiàn)新增 @Update: 實(shí)現(xiàn)更新 @Delete: 實(shí)現(xiàn)刪除 @Select: 實(shí)現(xiàn)查詢 @Result: 實(shí)現(xiàn)結(jié)果集封裝;他代替的是標(biāo)簽<resultMap>,該注解中可以使用單個(gè)@Result注解,也可以使用@Result集合, 使用格式:@Results({@Result(),@Result()}) 或 @Results(@Result()) @Results: 可以與@Result一起使用,封裝多個(gè)結(jié)果集 @One: 實(shí)現(xiàn)一對(duì)一結(jié)果集封裝 @Many: 實(shí)現(xiàn)一對(duì)多結(jié)果集封裝
測試案例
public interface IUserMapper { //添加用戶 @Insert("insert into user values(#{id},#{username})") public void addUser(User user); //更新用戶 @Update("update user set username = #{} where id = #{id}") public void updateUser(User user); //查詢用戶 @Select("select * from user") public List<User> getAllUser(); //刪除用戶 @Delete("delete from user where id=#{id}") public void delUser(Integer id); }
private IUserMapper mapper; @Before public void before() throws IOException { //1.Resources工具類,配置文件的加載,把配置文件加載成字節(jié)輸入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件,并創(chuàng)建了sqlSessionFactory工廠 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生產(chǎn)sqlSession true:事務(wù)自動(dòng)提交 SqlSession sqlSession = sqlSessionFactory.openSession(true); mapper = sqlSession.getMapper(IUserMapper.class); } @Test public void addUser(){ User user = new User(); user.setId(3); user.setUsername("jack"); mapper.addUser(user); } @Test public void updateUser(){ User user = new User(); user.setId(3); user.setUsername("rose"); mapper.updateUser(user); } @Test public void getAllUser(){ List<User> userList = mapper.getAllUser(); userList.forEach(item -> { System.out.println(item); }); } @Test public void delUser(){ mapper.delUser(3); }
運(yùn)行結(jié)果:
一對(duì)一
public interface IOrderMapper { /** * 查詢訂單的同時(shí)還查詢該訂單所屬的用戶 * @return */ @Results({ @Result(property = "id",column = "id"), @Result(property = "orderTime",column = "order_time"), @Result(property = "total",column = "total"), @Result(property = "user",column = "uid",javaType = User.class, one = @One(select = "com.yun.mapper.IUserMapper.getUserById")), }) @Select("select * from orders") public List<Order> findOrderAndUser(); } public interface IUserMapper { @Select("select * from user where id = #{id}") public User getUserById(Integer id); }
@Test public void oneToOne(){ List<Order> orderAndUser = orderMapper.findOrderAndUser(); orderAndUser.forEach(item -> { System.out.println(item); }); }
運(yùn)行結(jié)果:
Order(id=1, orderTime=2022-05-01, total=1000.00, user=User(id=1, username=Tom, orders=null, roles=null))
Order(id=2, orderTime=2022-05-10, total=2000.00, user=User(id=2, username=Jerry, orders=null, roles=null))
Order(id=3, orderTime=2022-05-20, total=3000.00, user=User(id=2, username=Jerry, orders=null, roles=null))
一對(duì)多
public interface IUserMapper { /** * 查詢所有用戶信息,同時(shí)查詢出每個(gè)用戶關(guān)聯(lián)的訂單信息 * @return */ @Select("select * from user") @Results({ @Result(property = "id",column = "id"), @Result(property = "username",column = "username"), @Result(property = "orders",column = "id",javaType = List.class, many = @Many(select = "com.yun.mapper.IOrderMapper.getOrderByUid")) }) public List<User> findAll(); } public interface IOrderMapper { @Select("select * from orders where uid = #{uid}") public List<Order> getOrderByUid(Integer uid); }
@Test public void oneToMore(){ List<User> users = mapper.findAll(); users.forEach(item -> { System.out.println(item); }); }
運(yùn)行結(jié)果:
User(id=1, username=Tom, orders=[Order(id=1, orderTime=null, total=1000.00, user=null)], roles=null)
User(id=2, username=Jerry, orders=[Order(id=2, orderTime=null, total=2000.00, user=null), Order(id=3, orderTime=null, total=3000.00, user=null)], roles=null)
多對(duì)多
public interface IUserMapper { /** * 查詢所有用戶信息,同事查詢出每個(gè)用戶關(guān)聯(lián)的角色信息 * @return */ @Select("select * from user") @Results({ @Result(property = "id",column = "id"), @Result(property = "username",column = "username"), @Result(property = "roles",column = "id",javaType = List.class, many = @Many(select ="com.yun.mapper.IRoleMapper.getAll")) }) public List<User> findUserAndRole(); } public interface IRoleMapper { @Select("select * from sys_role sr,sys_user_role sur where sr.id = sur.role_id and sur.user_id = #{uid}") public List<Role> getAll(Integer uid); }
@Test public void moreToMore(){ List<User> users = mapper.findUserAndRole(); users.forEach(item -> { System.out.println(item); }); }
運(yùn)行結(jié)果:
User(id=1, username=Tom, orders=null, roles=[Role(id=1, roleName=董事長), Role(id=2, roleName=經(jīng)理)])
User(id=2, username=Jerry, orders=null, roles=[Role(id=1, roleName=董事長), Role(id=2, roleName=經(jīng)理)])
緩存就是內(nèi)存中的數(shù)據(jù),常常來自對(duì)數(shù)據(jù)庫查詢結(jié)果的保存,使用緩存,我們可以避免頻繁的與數(shù)據(jù)庫進(jìn)行交互,進(jìn)而提高響應(yīng)速度.
一級(jí)緩存是SqlSession,在操作數(shù)據(jù)庫時(shí)需要構(gòu)造sqlSession對(duì)象,在對(duì)象中有一個(gè)數(shù)據(jù)結(jié)構(gòu)(HashMap)用于存儲(chǔ)緩存數(shù)據(jù).不同的sqlSession之間互不影響.
二級(jí)緩存是mapper級(jí)別的緩存,多個(gè)sqlSession去操作同一個(gè)mapper的sql語句,多個(gè)sqlSession可以共用二級(jí)緩存,二級(jí)緩存是跨sqlSession的.
demo
public class CacheTest { private IUserMapper mapper; private SqlSession sqlSession; @Before public void before() throws IOException { //1.Resources工具類,配置文件的加載,把配置文件加載成字節(jié)輸入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件,并創(chuàng)建了sqlSessionFactory工廠 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生產(chǎn)sqlSession true:事務(wù)自動(dòng)提交 sqlSession = sqlSessionFactory.openSession(true); mapper = sqlSession.getMapper(IUserMapper.class); } @Test public void test1() { //第一次查詢id為1的用戶 User user1 = mapper.getUserById(1); //第二次查詢id為1的用戶 User user2 = mapper.getUserById(1); System.out.println(user1 == user2); } }
現(xiàn)在我們變換一下上面的demo
public class CacheTest { private IUserMapper mapper; private SqlSession sqlSession; @Before public void before() throws IOException { //1.Resources工具類,配置文件的加載,把配置文件加載成字節(jié)輸入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件,并創(chuàng)建了sqlSessionFactory工廠 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生產(chǎn)sqlSession true:事務(wù)自動(dòng)提交 sqlSession = sqlSessionFactory.openSession(); mapper = sqlSession.getMapper(IUserMapper.class); } @Test public void test1() { //第一次查詢id為1的用戶 User user1 = mapper.getUserById(1); User user = new User(); user.setId(1); user.setUsername("Lucy"); mapper.updateUser(user); sqlSession.commit(); //第二次查詢id為1的用戶 User user2 = mapper.getUserById(1); System.out.println(user1 == user2); } }
結(jié)論:做增刪改操作,并進(jìn)行了事物的提交,就會(huì)刷新以及緩存;或者還可以通過 sqlSession.clearCache()清楚緩存;這樣做的目的就是為了讓緩存中存儲(chǔ)的是最新的信息,避免臟讀;
二級(jí)緩存的原理和一級(jí)緩存原理一樣,第一次查詢會(huì)將數(shù)據(jù)放入緩存中,然后第二次查詢則會(huì)直接從緩存中獲取,但是一級(jí)緩存是基于sqlSession的,而二級(jí)緩存是基于mapper文件的namespace,也就是說,多個(gè)sqlSession可以共享一個(gè)mapper中的二級(jí)緩存,并且如果兩個(gè)mapper的namespace相同,即使是兩個(gè)mapper,那么這兩個(gè)mapper執(zhí)行sql查詢到的數(shù)據(jù)也將存在相同的二級(jí)緩存區(qū)域中.
首先在全局配置文件sqlMapconfig.xml文件加入如下代碼
<settings> <setting name="cacheEnabled" value="true"/> </settings>
注意,該配置需要放在properties標(biāo)簽下,具體順序,可百度了解
其次,在xxxMapper.xml文件中開啟緩存(如果當(dāng)前操作時(shí)基于注解開發(fā)的話,使用注解@CacheNamespace)
<cache></cache>
demo2
public class CacheTest { private IUserMapper mapper; private SqlSession sqlSession; private SqlSessionFactory sqlSessionFactory; @Before public void before() throws IOException { //1.Resources工具類,配置文件的加載,把配置文件加載成字節(jié)輸入流 InputStream inputStream = Resources.getResourceAsStream("sqlMApConfig.xml"); //2.解析了配置文件,并創(chuàng)建了sqlSessionFactory工廠 sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //3.生產(chǎn)sqlSession sqlSession = sqlSessionFactory.openSession(); mapper = sqlSession.getMapper(IUserMapper.class); } @Test public void test2() { SqlSession sqlSession1 = sqlSessionFactory.openSession(); SqlSession sqlSession2 = sqlSessionFactory.openSession(); SqlSession sqlSession3 = sqlSessionFactory.openSession(); IUserMapper mapper1 = sqlSession1.getMapper(IUserMapper.class); IUserMapper mapper2 = sqlSession2.getMapper(IUserMapper.class); IUserMapper mapper3 = sqlSession3.getMapper(IUserMapper.class); User user1 = mapper1.getUserById(1); //清空一級(jí)緩存 sqlSession1.close(); User user2 = mapper2.getUserById(1); System.out.println(user1 == user2); } }
運(yùn)行結(jié)果為 false
結(jié)論:通過debug斷點(diǎn)顯示,實(shí)際上,第二次查詢則會(huì)直接從緩存中獲取用戶信息了,不過二級(jí)緩存緩存的不是對(duì)象,而是緩存的對(duì)象中的數(shù)據(jù),所以查詢結(jié)果為false;
注意,二級(jí)緩存底層還是HashMap結(jié)構(gòu),所以 po類需要實(shí)現(xiàn)序列化接口 ;因?yàn)槎?jí)緩存數(shù)據(jù)存儲(chǔ)介質(zhì)多種多樣,不一定只存在內(nèi)存中,有可能存在硬盤中,如果我們要在取這個(gè)緩存的話,就需要反序列化了,所以mybatis中的pojo都去實(shí)現(xiàn)Serializable接口;
變換一下demo2
@Test public void test2() { SqlSession sqlSession1 = sqlSessionFactory.openSession(); SqlSession sqlSession2 = sqlSessionFactory.openSession(); SqlSession sqlSession3 = sqlSessionFactory.openSession(); IUserMapper mapper1 = sqlSession1.getMapper(IUserMapper.class); IUserMapper mapper2 = sqlSession2.getMapper(IUserMapper.class); IUserMapper mapper3 = sqlSession3.getMapper(IUserMapper.class); User user1 = mapper1.getUserById(1); //清空一級(jí)緩存 sqlSession1.close(); User user = new User(); user.setId(1); user.setUsername("Tom"); mapper3.updateUser(user); sqlSession3.commit(); User user2 = mapper2.getUserById(1); System.out.println(user1 == user2); }
結(jié)論:做增刪改操作,并進(jìn)行了事物的提交,就會(huì)刷新以及緩存;這樣做的目的就是為了讓緩存中存儲(chǔ)的是最新的信息,避免臟讀;
此外mybatis中還可以配置useCache和flushCache等配置項(xiàng);
useCache
是用來設(shè)置是否禁用二級(jí)緩存的,在statement中設(shè)置useCache=false可以禁用當(dāng)前select語句的二級(jí)緩存,即每次查詢都會(huì)會(huì)發(fā)出sql去查詢,默認(rèn)情況是true,即該sql使用二級(jí)緩存,例如
<select id="findAll" useCache = "false" resultMap="userMap"> select u.*,o.id oid,o.order_time,o.total,o.uid from user u left join orders o on u.id = o.uid </select>
使用sql注解方式可以使用@Options(useCache = false)的方式
flushCache
在mapper的同一個(gè)namespace中,如果有其他的insert,update,delete操作數(shù)據(jù)后需要刷新緩存,如果不執(zhí)行刷新緩存會(huì)出現(xiàn)臟讀,設(shè)置statememt配置中的
flushCache = "true"屬性,默認(rèn)情況下為true,即刷新緩存,如果改成false則不會(huì)刷新,使用緩存時(shí)如果手動(dòng)修改數(shù)據(jù)庫表中的查詢數(shù)據(jù)會(huì)出現(xiàn)臟讀 例如
<select id="findAll" flushCache = "true" useCache = "false" resultMap="userMap"> select u.*,o.id oid,o.order_time,o.total,o.uid from user u left join orders o on u.id = o.uid </select>
一般下執(zhí)行完commit操作都需要刷新緩存,flushCache=true表示刷新緩存,這樣可以避免數(shù)據(jù)庫臟讀,所以我們不用設(shè)置,默認(rèn)即可
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