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Mybatis终极案例之注解开发
一、注解开发实现CURD操作
1.环境搭建
参考入门案例，环境搭建主要分为如下几步：
1、配置pom.xml
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.19</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.6</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13</version>
</dependency>
</dependencies>
2、配置SqlMapConfig.xml
<?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>
<!-- 导入数据库连接信息 -->
<properties resource="jdbcConfig.properties"></properties>
<!-- 配置延迟加载和二级缓存 -->
<settings>
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="aggressiveLazyLoading" value="false"/>
<setting name="cacheEnabled" value="true"/>
</settings>
<!-- 给实体类取别名，该包下的实体类都会具有别名 -->
<typeAliases>
<package name="domain"/>
</typeAliases>
<environments default="mysql">
<environment id="mysql">
<transactionManager type="JDBC"></transactionManager>
<!-- 连接数据库信息 -->
<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 dao 接口的位置，它有两种方式
第一种:使用 mapper 标签配置 class 属性
第二种:使用 package 标签，直接指定 dao 接口所在的包
-->
<mappers>
<package name="dao"/>
</mappers>
</configuration>
之所以采用外部文件(jdbcConfig.propertities)的方式对数据连接信息进行修改，是为了之后修改时更加方便，内容如下：
jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis
jdbc.username=root
jdbc.password=12345678
log4j的配置文件(log4j.properties)如下：
# Set root category priority to INFO and its only appender to CONSOLE.
#log4j.rootCategory=INFO, CONSOLE debug info warn error fatal
log4j.rootCategory=debug, CONSOLE, LOGFILE
# Set the enterprise logger category to FATAL and its only appender to CONSOLE.
log4j.logger.org.apache.axis.enterprise=FATAL, CONSOLE
# CONSOLE is set to be a ConsoleAppender using a PatternLayout.
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n
# LOGFILE is set to be a File appender using a PatternLayout.
log4j.appender.LOGFILE=org.apache.log4j.FileAppender
log4j.appender.LOGFILE.File=axis.log
log4j.appender.LOGFILE.Append=true
log4j.appender.LOGFILE.layout=org.apache.log4j.PatternLayout
log4j.appender.LOGFILE.layout.ConversionPattern=%d{ISO8601} %-6r [%15.15t] %-5p %30.30c %x - %m\n
上述三个文件都在Resources目录下，同时注意：对于同一个dao接口映射配置文件和注解的方式只能选一种，如果采用注解的方式，该dao接口对应得resource就不能包括映射配置文件。
3、新建实体类
在src/main/java目录下，新建实体类domain.User。
public class User implements Serializable {
private Integer userId;
private String userName;
private String userAddress;
private Date userBirthday;
private String userSex;
public Integer getUserId() {
return userId;
}
public void setUserId(Integer userId) {
this.userId = userId;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getUserAddress() {
return userAddress;
}
public void setUserAddress(String userAddress) {
this.userAddress = userAddress;
}
public Date getUserBirthday() {
return userBirthday;
}
public void setUserBirthday(Date userBirthday) {
this.userBirthday = userBirthday;
}
public String getUserSex() {
return userSex;
}
public void setUserSex(String userSex) {
this.userSex = userSex;
}
@Override
public String toString() {
return "User{" +
"userId=" + userId +
", userName='" + userName + '\'' +
", userAddress='" + userAddress + '\'' +
", userBirthday=" + userBirthday +
", userSex='" + userSex + '\'' +
'}';
}
}
2.配置数据库列名和实体关系类名的映射
由于实体类属性名和数据库列名并不一致，所以不能像入门案例一样，只使用Select标签。需要使用Results标签。在src/main/java目录下，新建接口dao.IUserDao:
public interface IUserDao {
/**
* 查询所有用户
* 实体类属性名和数据库列名不一致，通过Results注解进行配置
* @return
*/
@Select("select * from user")
//Results的id相当于名称，value属性是实体类属性和数据库列名的映射关系
@Results(id = "userMap", value = {
//Result的id表示是否是主键，默认为false，column是数据库列名，property是实体类属性
@Result(id = true, column = "id", property = "userId"),
@Result(column = "username", property = "userName"),
@Result(column = "sex", property = "userSex"),
@Result(column = "address", property = "userAddress"),
@Result(column = "birthday", property = "userBirthday"),
}
)
List<User> findAllUsers();
}
3.测试
在test/java目录下，新建测试类UserTest：
public class UserTest {
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();
}
@Test
public void testFindAllUsers() {
List<User> users = userDao.findAllUsers();
for (User user : users
) {
System.out.println(user);
}
}
4、更加复杂的查询
我们已经实现了最基本的查询操作，现在在IUserDao接口中，添加更多的方法，以实现更加复杂的CRUD：
/**
* 根据用户id查询用户
* 无需再次重写Results注解，可以通过ResultMap注解引用Results
* @param userId
*/
@Select("select * from user where id = #{uid}")
@ResultMap("userMap")
User findById(Integer userId);
/**
* 模糊查询
* 参数是基本属性，#{}中的名称随意
* @param userName
* @return
*/
@Select("select * from user where username like #{username}")
@ResultMap("userMap")
List<User> findByName(String userName);
/**
* 查询用户总数
*
* @return
*/
@Select("select count(id) from user")
int findTotal();
/**
* 插入用户
*
* @param user
*/
@Insert("insert into user(username, sex, address, birthday) values " +
"(#{userName}, #{userSex}, #{userAddress}, #{userBirthday}) ")
@ResultMap("userMap")
void insertUser(User user);
/**
* 删除用户
*
* @param userId
*/
@Delete("delete from user where id = #{id} ")
@ResultMap("userMap")
void deleteUser(Integer userId);
/**
* 更新用户
* 参数是实体类，使用的OGNL表达式，因此#{}中的名称必须是属性名
* @param user
*/
@Update("update user set username = #{userName}, address = #{userAddress}, " +
" sex = #{userSex}, birthday = #{userBirthday} where id = #{userId}")
@ResultMap("userMap")
void updateUser(User user);
/**
* 保存操作
* 通过SelectKey可以获取保存用户时，数据库自动更新的id字段
* @param user
* @return 影响数据库记录的行数
*/
@Insert("insert into user(username, sex, birthday, address) values (#" +
"{userName}, #{userSex},#{userBirthday},#{userAddress} )")
@SelectKey(keyColumn = "id", keyProperty = "userId", resultType = Integer.class,
before = false, statement = {"select last_insert_id()"})
int saveUser(User user);
在测试类UserTest中添加测试：
/**
* 测试根据id查询用户
*/
@Test
public void testFindById(){
User user = userDao.findById(41);
System.out.println(user);
}
/**
* 测试根据名字进行模糊查询
*/
@Test
public void testFindByName(){
List<User> users = userDao.findByName("%王%");
for (User user : users
) {
System.out.println(user);
}
}
/**
* 查询数据库中用户总数
*/
@Test
public void testFindTotal(){
int total = userDao.findTotal();
System.out.print("数据库中用户总数为：");
System.out.println(total);
}
/**
* 测试插入用户
*/
@Test
public void testInsertUser(){
User user = new User();
user.setUserName("插入的用户");
user.setUserAddress("湖北省武汉市洪山区");
userDao.insertUser(user);
}
/**
* 测试更新用户
*/
@Test
public void testUpdateUser(){
User user = new User();
user.setUserId(59);
user.setUserName("更新的用户");
user.setUserAddress("北京市海淀区");
user.setUserSex("男");
user.setUserBirthday(new Date());
userDao.updateUser(user);
}
/**
* 测试删除用户
*/
@Test
public void testDeleteUser(){
User user = new User();
userDao.deleteUser(60);
}
/**
* 测试保存用户
*/
@Test
public void testSaveUser(){
User user = new User();
user.setUserName("保存的用户");
user.setUserAddress("武汉市武昌区");
user.setUserSex("女");
user.setUserBirthday(new Date());
int res = userDao.saveUser(user);
System.out.println("影响数据库记录的行数:"+res);
System.out.println("插入的主键值:"+user.getUserId());
}
二、注解开发实现复杂关系映射
1.一对一多表查询
1、新建Account类
在src/main/java目录下的domain包下，新建实体类Account：
public class Account implements Serializable {
private Integer uid;
private Integer id;
private Double money;
//从表实体应包含主表实体的引用
private User user;
public Integer getUid() {
return uid;
}
public void setUid(Integer uid) {
this.uid = uid;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
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{" +
"uid=" + uid +
", id=" + id +
", money=" + money +
'}';
}
}
2、添加dao接口
在src/main/java目录下的dao包下，新建接口IAccountDao：
public interface IAccountDao {
/**
* 查询带有用户信息的账户信息
* 并且使用延迟加载的方式
* @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的one属性，表示是一对一的关系
//此时column表示查询所需要的参数所对应的数据库列名
//property表示的是从表实体对主表实体的引用的属性名
@Result(column = "uid", property = "user",
//One的select属性，表示对于主表实体所对应的查询方法
//fetchType属性是加载的方式：LAZY(延迟)、EAGER(立即)、DEFAULT(默认)
//一对一默认是立即加载，一对多默认是延迟加载
one = @One(select = "dao.IUserDao.findById",
fetchType = FetchType.LAZY)
)
})
List<Account> findAccountsWithUser();
}
3、测试
在test/java目录下，新建测试类AccountTest：
public class AccountTest {
private InputStream in;
private SqlSessionFactory factory;
private SqlSession session;
private IAccountDao accountDao;
@Before
public void init() throws Exception {
in = Resources.getResourceAsStream("SqlMapConfig.xml");
factory = new SqlSessionFactoryBuilder().build(in);
session = factory.openSession();
accountDao = session.getMapper(IAccountDao.class);
}
@After
public void destroy() throws Exception {
session.commit();
session.close();
in.close();
}
/**
* 测试查询带有用户信息的账户信息
*/
@Test
public void testFindAccountsWithUser() {
List<Account> accounts = accountDao.findAccountsWithUser();
for (Account account : accounts
) {
System.out.println(account.getId());
if(account.getUid() == 41)
System.out.println(account.getUser());
}
}
}
2.一对多多表查询
1、在IAccountDao接口中添加根据用户id查询的方法
/**
* 根据用户Id查询账户信息
* @param uerId
* @return
*/
@Select("select * from account where uid = #{uid}")
List<Account> findByUid(Integer uerId);
2、在IUserDao接口中添加一对多查询的方法
/**
* 查询带有账户信息的用户信息
* @return
*/
@Select("select * from user")
@Results(id = "userMap1", value = {
@Result(id = true, column = "id", property = "userId"),
@Result(column = "username", property = "userName"),
@Result(column = "sex", property = "userSex"),
@Result(column = "address", property = "userAddress"),
@Result(column = "birthday", property = "userBirthday"),
@Result(column = "id", property = "accounts",
//many表示对应关系是一对多
many = @Many(select = "dao.IAccountDao.findByUid",
fetchType = FetchType.LAZY))
}
)
List<User> findUsersWithAccounts();
3、测试
在测试类UserTest中添加测试：
/**
* 测试查询带有账户信息的用户信息
* 延迟加载的方式
*/
@Test
public void testFindUsersWithAccounts(){
List<User> users = userDao.findUsersWithAccounts();
for (User user : users
) {
System.out.println(user.getUserId());
if(user.getUserId() == 41)
System.out.println(user.getAccounts());
}
}
三、基于注解的二级缓存
1.开启二级缓存配置
1、在主配置文件SqlMapConfig.xml中添加二级缓存的支持
<setting name="cacheEnabled" value="true"/>
2、对应的接口开启二级缓存的支持
在接口IUserDao接口名的上方添加：
@CacheNamespace(blocking=true) //mybatis 基于注解方式实现配置二级缓存
2.测试运行
在测试类UserTest中添加测试：
@Test
public void testL1Cache() {
User user1 = userDao.findById(41);
System.out.println("第一次查询的用户:" + user1);
User user2 = userDao.findById(41);
System.out.println("第二次查询用户:" + user2);
System.out.print("第一次和第二次是否是同一对象：");
System.out.println(user1 == user2);
sqlSession.clearCache();//清空缓存
User user3 = userDao.findById(41);
System.out.println("第三次查询用户:" + user3);
System.out.print("第二次和第三次是否是同一对象：");
System.out.println(user2 == user3);
sqlSession.close();//close操作会清空缓存
//再次获取 SqlSession 对象
sqlSession = factory.openSession();
userDao = sqlSession.getMapper(IUserDao.class);
User user4 = userDao.findById(41);
System.out.println("第四次查询用户:" + user4);
System.out.print("第三次和第四次是否是同一对象：");
System.out.println(user3 == user4);
}
/**
* 测试二级缓存
*/
@Test
public void testL2Cache() {
User user1 = userDao.findById(41);
System.out.println("第一次查询的用户:" + user1);
sqlSession.close(); //关闭一级缓存
sqlSession = factory.openSession();
userDao = sqlSession .getMapper(IUserDao.class);
User user2 = userDao .findById(41);
System.out.println("第二次查询用户:" + user2);
System.out.print("第一次和第二次是否是同一对象：");
System.out.println(user1 == user2);
}
