MyBatis注解开发

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，当咱们执行查询以后，查询的结果会同时存入到SqlSession为咱们提供一块区域中。

该区域的结构是一个Map。当咱们再次查询一样的数据，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对象建立的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.让当前的操做支持二级缓存（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); }

 

注解开发就不须要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)); } }

总的来讲，简单的查询能够用注解，方便快速，可是太复杂的sql仍是用xml

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