MyBatis 注解开发+缓存

注：前两部分只是大概介绍
重点是第三部分的 MyBatis注解方式进行开发

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一、MyBatis 中的延迟加载

1. 延迟加载

在真正使用数据时才发起查询，不用的时候不查询；按需加载（懒加载）；

2. 立即加载

不管用不用，只要一调用方法，马上发起查询；

在对应的四种表关系中：

• 一对多、一对多：通常用 延迟加载；
• 多对一、一对一：通常用 立即加载；

二、MyBatis 中的缓存

1. 一级缓存

一级缓存是 SQLSession 范围的缓存，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；

2. 二级缓存

三、MyBatis 的注解开发

用注解方式进行开发，可替代原来的配置文件 IUserDao.xml；

1. 环境搭建

（1）创建新项目

（2）编辑 pom.xml 文件

这里直接给出整个项目的文件目录

pom.xml 文件内容如下：

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0modelVersion>

    <groupId>org.examplegroupId>
    <artifactId>MyBatisTest2artifactId>
    <version>1.0-SNAPSHOTversion>

    <packaging>jarpackaging>

    <dependencies>
        <dependency>
            <groupId>org.mybatisgroupId>
            <artifactId>mybatisartifactId>
            <version>3.5.6version>
        dependency>
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>8.0.15version>
        dependency>
        <dependency>
            <groupId>log4jgroupId>
            <artifactId>log4jartifactId>
            <version>1.2.12version>
        dependency>
        <dependency>
            <groupId>junitgroupId>
            <artifactId>junitartifactId>
            <version>3.8.2version>
        dependency>
        <dependency>
            <groupId>junitgroupId>
            <artifactId>junitartifactId>
            <version>RELEASEversion>
            <scope>testscope>
        dependency>
    dependencies>

project>

（3）导入两个配置文件：

jdbcConfig.properties 和 log4j.properties

• jdbcConfig.properties 文件内容如下：
  （该文件内容就是连接数据库用到的信息）

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatisdata?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC
jdbc.username=root
jdbc.password=root

• log4j.properties 内容如下：

log4j.rootLogger=INFO,CONSOLE
log4j.addivity.org.apache=true
 
# console
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Threshold=INFO
log4j.appender.CONSOLE.Target=System.out
log4j.appender.CONSOLE.Encoding=UTF-8
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=[demo] %-5p %d{
     yyyy-MM-dd HH\:mm\:ss} - %C.%M(%L)[%t] - %m%n
 
# all
log4j.logger.com.demo=INFO, DEMO
log4j.appender.DEMO=org.apache.log4j.RollingFileAppender
log4j.appender.DEMO.File=${catalina.base}/logs/demo.log
log4j.appender.DEMO.MaxFileSize=50MB
log4j.appender.DEMO.MaxBackupIndex=3
log4j.appender.DEMO.Encoding=UTF-8
log4j.appender.DEMO.layout=org.apache.log4j.PatternLayout
log4j.appender.DEMO.layout.ConversionPattern=[demo] %-5p %d{
     yyyy-MM-dd HH\:mm\:ss} - %C.%M(%L)[%t] - %m%n

（4）创建 SqlMapConfig.xml 文件

• SqlMapConfig.xml 内容如下：

<configuration>
    
    <properties resource="jdbcConfig.properties">properties>
    
    <typeAliases>
        <package name="domain">package>
    typeAliases>

    
    <environments default="mysql">
        <environment id="mysql">
            <transactionManager type="JDBC">transactionManager>
            <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>

    
    <mappers>
        <package name="dao">package>
    mappers>

configuration>

2. 单表 CRUD 操作

（1）准备数据库

CREATE TABLE `user`(
	`id` int(11) NOT NULL auto_increment,
	`username` varchar(32) NOT NULL COMMENT '用户名称',
	`birthday` datetime DEFAULT NULL COMMENT '生日',
	`sex` char(1) DEFAULT NULL COMMENT '性别',
	`address` varchar(256) DEFAULT NULL COMMENT '地址',
	PRIMARY KEY (`id`),
)ENGINE=INNODB DEFAULT CHARSET=utf8;

（2）创建 User.java 类

（根据前面的目录，在适当位置创建即可）

• User.java 内容如下：
  定义变量，以及相应的 get 和 set 方法，toString 方法；

package domain;

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;

    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;
    }

    @Override
    public String toString() {
     
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

（3）创建 IUserDao.java 接口

• IUserDao.java 内容如下：

package dao;

import domain.User;
import org.apache.ibatis.annotations.*;
import org.apache.ibatis.mapping.FetchType;

import java.util.List;

/**
 * 在 mybatis 中针对 CRUD ，一共有四个注解
 * @Select @Insert @Update @Delete
 */
public interface IUserDao {
     
    /**
     * 查询所有用户
     * @return
     */
    @Select("select * from user")
    List<User> findAll();

    /**
     * 保存用户
     * @param user
     */
    @Insert("insert into user(username,address,sex,birthday)values(#{username},#{address},#{sex},#{birthday})")
    void saveUser(User user);

    /**
     * 更新用户
     * @param user
     */
    @Update("update user set username=#{username},sex=#{sex},birthday=#{birthday},address=#{address} where id=#{id}")
    void updateUser(User user);

    /**
     * 删除用户
     * @param userId
     */
    @Delete("delete from user where id=#{id}")
    void deleteUser(Integer userId);

    /**
     * 根据 Id 查询用户
     * @param userId
     * @return
     */
    @Select("select * from user where id=#{id}")
    User findById(Integer userId);

    /**
     * 根据用户名称模糊查询
     * @param username
     * @return
     */
    //两种写法（AnnotationCRUDTest.java 中也要改写）
//    @Select("select * from user where username like #{username}")
    @Select("select * from user where username like '%${value}%'")
    List<User> findUserByName(String username);

    /**
     * 查询用户数量
     * @return
     */
    @Select("select count(*) from user")
    int findTotalUser();
}

（4）创建 测试类：AnnotationCRUDTest.java

• AnnotationCRUDTest.java 内容如下

import dao.IUserDao;
import 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.Date;
import java.util.List;

public class AnnotationCRUDTest {
     
    private InputStream in;
    private SqlSessionFactory factory;
    private SqlSession sqlSession;
    private IUserDao userDao;

    @Before
    public void init() throws Exception{
     
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        factory = new SqlSessionFactoryBuilder().build(in);
        sqlSession = factory.openSession();
        userDao = sqlSession.getMapper(IUserDao.class);
    }

    @After
    public void destroy() throws Exception{
     
        sqlSession.commit();
        sqlSession.close();
        in.close();
    }

    /**
     * 查询所有
     */
    @Test
    public void testFindAll(){
     
        List<User> users = userDao.findAll();
        for (User user : users){
     
            //System.out.println("----------每个用户的信息----------");
            System.out.println(user);
            //System.out.println(user.getAccounts());
        }
    }

    /**
     * 保存用户
     */
    @Test
    public void testSave(){
     
        User user = new User();
        user.setUsername("zzz");
        user.setAddress("北京");

        userDao.saveUser(user);
    }

    /**
     * 更新用户
     */
    @Test
    public void testUpdate(){
     
        User user = new User();
        user.setId(27);
        user.setUsername("eee");
        user.setAddress("上海");
        user.setSex("男");
        user.setBirthday(new Date());

        userDao.updateUser(user);
    }

    /**
     * 删除用户
     */
    @Test
    public void testDelete(){
     
        userDao.deleteUser(27);
    }

    /**
     * 根据 Id 查询用户信息
     */
    @Test
    public void testFindOne(){
     
        User user = userDao.findById(26);
        System.out.println(user);
    }

    /**
     * 根据用户名称模糊查询
     */
    @Test
    public void testFindByName(){
     
        //两种写法（IUserDao.java 中也要改写）
//        List users = userDao.findUserByName("%c%");
        List<User> users = userDao.findUserByName("c");
        for (User user : users){
     
            System.out.println(user);
        }
    }

    /**
     * 查询用户数量
     */
    @Test
    public void testFindTotal(){
     
        int total = userDao.findTotalUser();
        System.out.println(total);
    }
}

（5）测试结果

• 依次运行测试类中的每个测试方法
  以 testFindAll() 方法为例：
  

3. 多表查询操作

（1）准备数据库

• 在之前数据库的基础上，创建一张 account 表
  

CREATE TABLE `account`(
	`ID` int(11) NOT NULL COMMENT '编号',
	`UID` int(11) DEFAULT NULL COMMENT '用户编号',
	`MONEY` DOUBLE DEFAULT NULL COMMENT '金额',
	PRIMARY KEY (`ID`),
	KEY `FK_Reference_8` (`UID`),
	CONSTRAINT `FK_Reference_8` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
)ENGINE=INNODB DEFAULT CHARSET=utf8;

（2）创建 Account.java 类 & 修改 User.java 类

• Account.java 内容如下：

package domain;

import java.io.Serializable;

public class Account implements Serializable {
     
    private Integer id;
    private Integer uid;
    private Double money;

    //多对一（MyBatis 中称之为一对一）的映射：一个账户只能属于一个用户
    private User user;

    public User getUser() {
     
        return user;
    }

    public void setUser(User user) {
     
        this.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;
    }

    @Override
    public String toString() {
     
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money=" + money +
                '}';
    }
}

• User.java 给原来的文件中添加了如下内容：
  

• 修改后的 User.java 内容如下：

package domain;

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;

    //一对多关系映射，一个用户对应多个账户
    private List<Account> accounts;

    public List<Account> getAccounts() {
     
        return accounts;
    }

    public void setAccounts(List<Account> accounts) {
     
        this.accounts = 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;
    }

    @Override
    public String toString() {
     
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", address='" + address + '\'' +
                ", sex='" + sex + '\'' +
                ", birthday=" + birthday +
                '}';
    }
}

（3）创建 IAccountDao.java 接口 & 修改 IUserDao.java 接口

• IAccountDao.java 内容如下：

package dao;

import domain.Account;
import domain.User;
import org.apache.ibatis.annotations.*;
import org.apache.ibatis.mapping.FetchType;

import java.util.List;

public interface IAccountDao {
     
    /**
     * 查询所有账户，并且获取每个账户所所属的用户信息
     * @return
     */
    @Select("select * from account")
    @Results(id="accountMap",value = {
     
            @Result(id = true, column = "id", property = "id"),
            @Result(column = "uid", property = "uid"),
            @Result(column = "money", property = "money"),
            @Result(property = "user", column = "uid",
                    one = @One(select = "dao.IUserDao.findById",
                                fetchType = FetchType.EAGER))
    })
    List<Account> findAll();

    /**
     * 根据 用户Id 查询 账户信息
     * @param
     * @return
     */
    @Select("select * from account where uid = #{userId}")
    List<Account> findAccountByUid(Integer userId);
}

• IUserDao.java 添加了如下内容：
  

• 修改后的 IUserDao.java 如下：

package dao;

import domain.User;
import org.apache.ibatis.annotations.*;
import org.apache.ibatis.mapping.FetchType;

import java.util.List;

/**
 * 在 mybatis 中针对 CRUD ，一共有四个注解
 * @Select @Insert @Update @Delete
 */
public interface IUserDao {
     
    /**
     * 查询所有用户
     * @return
     */
    @Select("select * from user")
    @Results(id = "userMap", value = {
     
            @Result(id = true, column = "id", property = "id"),
            @Result(column = "username", property = "username"),
            @Result(column = "address", property = "address"),
            @Result(column = "sex", property = "sex"),
            @Result(column = "birthday", property = "birthday"),
            @Result(property = "accounts", column = "id",
                    many = @Many(select = "dao.IAccountDao.findAccountByUid",
                                fetchType = FetchType.LAZY))
    })
    List<User> findAll();

    /**
     * 保存用户
     * @param user
     */
    @Insert("insert into user(username,address,sex,birthday)values(#{username},#{address},#{sex},#{birthday})")
    void saveUser(User user);

    /**
     * 更新用户
     * @param user
     */
    @Update("update user set username=#{username},sex=#{sex},birthday=#{birthday},address=#{address} where id=#{id}")
    void updateUser(User user);

    /**
     * 删除用户
     * @param userId
     */
    @Delete("delete from user where id=#{id}")
    void deleteUser(Integer userId);

    /**
     * 根据 Id 查询用户
     * @param userId
     * @return
     */
    @Select("select * from user where id=#{id}")
    User findById(Integer userId);

    /**
     * 根据用户名称模糊查询
     * @param username
     * @return
     */
    //两种写法（AnnotationCRUDTest.java 中也要改写）
//    @Select("select * from user where username like #{username}")
    @Select("select * from user where username like '%${value}%'")
    List<User> findUserByName(String username);

    /**
     * 查询用户数量
     * @return
     */
    @Select("select count(*) from user")
    int findTotalUser();
}

（4）创建 测试类：AccountTest.java & 修改 测试类：AnnotationCRUDTest.java

• AccountTest.java 内容如下：

import dao.IAccountDao;
import dao.IUserDao;
import domain.Account;
import 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.Date;
import java.util.List;

public class AccountTest {
     

    private InputStream in;
    private SqlSessionFactory factory;
    private SqlSession sqlSession;
    private IAccountDao accountDao;

    @Before
    public void init() throws Exception{
     
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        factory = new SqlSessionFactoryBuilder().build(in);
        sqlSession = factory.openSession();
        accountDao = sqlSession.getMapper(IAccountDao.class);
    }

    @After
    public void destroy() throws Exception{
     
        sqlSession.commit();
        sqlSession.close();
        in.close();
    }

    /**
     * 查询所有信息
     */
    @Test
    public void testFindAll(){
     
        List<Account> accounts = accountDao.findAll();
        for (Account account : accounts){
     
            System.out.println("-------每个账户的信息-------");
            System.out.println(account);
            System.out.println(account.getUser());
        }
    }

}

• AnnotationCRUDTest.java 内容如下：

import dao.IUserDao;
import 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.Date;
import java.util.List;

public class AnnotationCRUDTest {
     
    private InputStream in;
    private SqlSessionFactory factory;
    private SqlSession sqlSession;
    private IUserDao userDao;

    @Before
    public void init() throws Exception{
     
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        factory = new SqlSessionFactoryBuilder().build(in);
        sqlSession = factory.openSession();
        userDao = sqlSession.getMapper(IUserDao.class);
    }

    @After
    public void destroy() throws Exception{
     
        sqlSession.commit();
        sqlSession.close();
        in.close();
    }

    /**
     * 查询所有
     */
    @Test
    public void testFindAll(){
     
        List<User> users = userDao.findAll();
        for (User user : users){
     
            System.out.println("----------每个用户的信息----------");
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }

    /**
     * 保存用户
     */
    @Test
    public void testSave(){
     
        User user = new User();
        user.setUsername("zzz");
        user.setAddress("北京");

        userDao.saveUser(user);
    }

    /**
     * 更新用户
     */
    @Test
    public void testUpdate(){
     
        User user = new User();
        user.setId(27);
        user.setUsername("eee");
        user.setAddress("上海");
        user.setSex("男");
        user.setBirthday(new Date());

        userDao.updateUser(user);
    }

    /**
     * 删除用户
     */
    @Test
    public void testDelete(){
     
        userDao.deleteUser(27);
    }

    /**
     * 根据 Id 查询用户信息
     */
    @Test
    public void testFindOne(){
     
        User user = userDao.findById(26);
        System.out.println(user);
    }

    /**
     * 根据用户名称模糊查询
     */
    @Test
    public void testFindByName(){
     
        //两种写法（IUserDao.java 中也要改写）
//        List users = userDao.findUserByName("%c%");
        List<User> users = userDao.findUserByName("c");
        for (User user : users){
     
            System.out.println(user);
        }
    }

    /**
     * 查询用户数量
     */
    @Test
    public void testFindTotal(){
     
        int total = userDao.findTotalUser();
        System.out.println(total);
    }
}

（5）测试结果

• 运行 AnnotationCRUDTest.java 文件 中的 testFindAll() 方法：
  
• 运行 AccountTest.java 中的 testFindAll() 方法：
  

4. 缓存的配置

（1）修改配置文件 SqlMapConfig.xml

• 增加如下内容：
  

• 修改后的文件内容如下：

<configuration>
    
    <properties resource="jdbcConfig.properties">properties>
    
    <settings>
        <setting name="cacheEnabled" value="true"/>
    settings>
    
    <typeAliases>
        <package name="domain">package>
    typeAliases>

    
    <environments default="mysql">
        <environment id="mysql">
            <transactionManager type="JDBC">transactionManager>
            <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>

    
    <mappers>
        <package name="dao">package>
    mappers>

configuration>

（2）修改 IUserDao.java 文件

• 添加内容及位置如下：

@CacheNamespace(blocking = true)    //开启二级缓存

（3）添加 测试类：SecondLevelCatchTest.java

• SecondLevelCatchTest.java 内容如下：

import dao.IUserDao;
import 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.Date;
import java.util.List;

public class SecondLevelCatchTest {
     
    private InputStream in;
    private SqlSessionFactory factory;
    private SqlSession sqlSession;
    private IUserDao userDao;

    @Before
    public void init() throws Exception{
     
        in = Resources.getResourceAsStream("SqlMapConfig.xml");
        factory = new SqlSessionFactoryBuilder().build(in);
        sqlSession = factory.openSession();
        userDao = sqlSession.getMapper(IUserDao.class);
    }

    @After
    public void destroy() throws Exception{
     

        in.close();
    }

    /**
     * 查询所有
     */
    @Test
    public void testFindAll(){
     
        List<User> users = userDao.findAll();
        for (User user : users){
     
            System.out.println("----------每个用户的信息----------");
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }

    /**
     * 根据 Id 查询用户信息
     */
    @Test
    public void testFindOne(){
     
        User user = userDao.findById(24);
        System.out.println(user);

        sqlSession.close(); //释放一级缓存
        sqlSession = factory.openSession(); //再次打开session
        IUserDao userDao1 = sqlSession.getMapper(IUserDao.class);
        User user1 = userDao1.findById(24);
        System.out.println(user1);

        System.out.println(user == user1);
        sqlSession.close();

    }

}

（4）测试结果

• 运行 该测试类的 testFindAll() 方法：
  

备注