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
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