MyBatis注解开发
- 2019 年 10 月 7 日
- 筆記
延迟加载（按需加载、懒加载）在真正使用数据时才发起查询，不用的时候不查询
MyBatis一级缓存：
指的是MyBatis中SqlSession对象的缓存，当我们执行查询之后，查询的结果会同时存入到SqlSession为我们提供一块区域中。
该区域的结构是一个Map。当我们再次查询同样的数据，mybatis会先去sqlsession中查询是否有，有的话直接拿出来用。 当SqlSession对象消失时，mybatis的一级缓存也就消失了
当调用SqlSession的修改、添加、删除、commit()、close()等方法时，就会清空一级缓存
MyBatis二级缓存
MyBatis中SqlSessionFactory对象的缓存。由同一个SqlSessionFactory对象创建的SqlSession共享其缓存 二级缓存使用步骤：
1.让MyBatis框架支持二级缓存（在sqlmapconfig.xml中配置）
<setting name="cacheEnabled" value="true"/>
2.让当前的映射文件支持二级缓存（在UserDao.xml中配置）
<cache/>
3.让当前的操作支持二级缓存（在select标签中配置）
useCache="true"
二级缓存中存放的内容是数据，而不是对象
另外一种是使用注解，在Dao类上面
@CacheNamespace(blocking = true)
实体类
import java.io.Serializable; public class Account implements Serializable { private Integer id; private Integer uid; private Double money; private User user; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public Integer getUid() { return uid; } public void setUid(Integer uid) { this.uid = uid; } public Double getMoney() { return money; } public void setMoney(Double money) { this.money = money; } public User getUser() { return user; } public void setUser(User user) { this.user = user; } @Override public String toString() { return "Account{" + "id=" + id + ", uid=" + uid + ", money=" + money + '}'; }}
import java.io.Serializable;import java.util.Date;import java.util.List; public class User implements Serializable { private Integer id; private String username; private String address; private String sex; private Date birthday; private List<Account> accounts; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } public List<Account> getAccounts() { return accounts; } public void setAccounts(List<Account> accounts) { this.accounts = accounts; } @Override public String toString() { return "User{" + "id=" + id + ", username='" + username + ''' + ", address='" + address + ''' + ", sex='" + sex + ''' + ", birthday=" + birthday + '}'; }}
Dao层
import com.jinke.domain.Account;import org.apache.ibatis.annotations.One;import org.apache.ibatis.annotations.Result;import org.apache.ibatis.annotations.Results;import org.apache.ibatis.annotations.Select;import org.apache.ibatis.mapping.FetchType; import java.util.List; public interface AccountDao { @Select("select * from account") @Results(id = "accountMap", value = { @Result(id = true, property = "id", column = "id"), @Result(property = "uid", column = "uid"), @Result(property = "money", column = "money"), @Result(property = "user", column = "uid", one = @One(select = "com.jinke.dao.UserDao.findById", fetchType = FetchType.LAZY)) }) List<Account> findAll(); @Select("select * from account where uid = #{uid}") List<Account> findAccountByUid(Integer uid);}
import com.jinke.domain.User;import org.apache.ibatis.annotations.*;import org.apache.ibatis.mapping.FetchType; import java.util.List; /*开启二级缓存*/@CacheNamespace(blocking = true)public interface UserDao { @Select("select * from user") @Results(id = "userMap", value = {@Result(id = true, property = "id", column = "id"), @Result(property = "username", column = "username"), @Result(property = "sex", column = "sex"), @Result(property = "address", column = "address"), @Result(property = "birthday", column = "birthday"), @Result(property = "accounts", column = "id", many = @Many(select = "com.jinke.dao.AccountDao.findAccountByUid", fetchType = FetchType.EAGER))} ) List<User> findAll(); @Select("select * from user where id = #{id}") @ResultMap(value = "userMap") User findById(Integer id); }
注解开发就不需要xml配置映射关系了
<?xml version="1.0" encoding="utf-8" ?><!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 2.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration> <properties resource="jdbcConfig.properties"/> <settings> <setting name="lazyLoadingEnabled" value="true"/> <setting name="aggressiveLazyLoading" value="true"/> <!--配置开启二级缓存--> <setting name="cacheEnabled" value="true"/> </settings> <typeAliases> <!--用于配置别名的包，该包下实体类都会注册别名，即类名，且不区分大小写--> <package name="com.jinke.domain"/> </typeAliases> <!--配置环境--> <environments default="mysql"> <!--配置mysql的环境--> <environment id="mysql"> <!--配置事务--> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driver}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </dataSource> </environment> </environments> <!--配置映射文件的位置--> <mappers> <package name="com.jinke.dao"/> </mappers></configuration>
测试类
import com.jinke.dao.AccountDao;import com.jinke.dao.RoleDao;import com.jinke.dao.UserDao;import com.jinke.domain.Account;import com.jinke.domain.Role;import com.jinke.domain.User;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 org.junit.After;import org.junit.Before;import org.junit.Test; import java.io.InputStream;import java.util.List; public class MyBatisTest { private InputStream in; private SqlSession sqlSession; private UserDao userDao; private AccountDao accountDao; private RoleDao roleDao; private SqlSessionFactory factory; @Before public void init() throws Exception { in = Resources.getResourceAsStream("SqlMapConfig.xml"); SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder(); factory = builder.build(in); sqlSession = factory.openSession(); userDao = sqlSession.getMapper(UserDao.class); accountDao = sqlSession.getMapper(AccountDao.class); roleDao = sqlSession.getMapper(RoleDao.class); } @After public void destroy() throws Exception { sqlSession.commit(); sqlSession.close(); in.close(); } @Test public void testFindAccount() { List<Account> accounts = accountDao.findAll(); for (Account account : accounts) { System.out.println(account + " " + account.getUser()); } } @Test public void testFindUser() { List<User> users = userDao.findAll(); for (User user : users) { System.out.println(user + " " + user.getAccounts()); } } @Test public void testFindRole() { List<Role> roles = roleDao.findAll(); for (Role role : roles) { System.out.println(role + " " + role.getUsers()); } } @Test public void testFirstLevelCache() { User user = userDao.findById(1); System.out.println(user); //清除一级缓存 sqlSession.clearCache(); User user2 = userDao.findById(1); System.out.println(user2); System.out.println("user==user2?" + (user == user2)); } @Test public void testClearCache() { //测试二级缓存 SqlSession session1 = factory.openSession(); UserDao userDao1 = session1.getMapper(UserDao.class); User user1 = userDao1.findById(1); System.out.println(user1); session1.close(); SqlSession session2 = factory.openSession(); UserDao userDao2 = session2.getMapper(UserDao.class); User user2 = userDao2.findById(1); System.out.println(user2); session1.close(); System.out.println("user==user2?" + (user1 == user2)); }}
总的来说，简单的查询可以用注解，方便快速，但是太复杂的sql还是用xml
