MyBatis作用在持久层,是一款负责数据库访问的框架,它内部封装了 jdbc,使开发者只需要关注 sql 语句本身,而不需要去处理加载驱动、创建连接、创建 statement 等繁杂的过程。
MyBatis通过 xml或注解的方式 将要执行的各种 statement 配置起来,并通过java对象和statement中sql的动态参数进行映射生成最终执行的sql语句,最后由 mybatis 框架执行sql并将结果映射为java对象并返回。
MyBatis采用 ORM 思想解决了实体和数据库映射的问题,对jdbc进行了封装,屏蔽了jdbc api底层访问细节,使我们不用编写调用jdbc api,就可以完成对数据库的持久化操作。
ORM:对象关系映射思想。是指把Java对象和数据库的表和字段进行关联映射,即操作Java对象,就相当于操作了数据库。
单一的使用Mybatis 框架,不涉及客户端,所以这里使用Maven创建Java项目,搭建 Mybatis 开发环境并查询数据库用户表所有用户信息。
<dependencies>
<!--Junit单元测试-->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<!--<scope>test</scope>-->
</dependency>
<!--MySql的数据库驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.46</version>
</dependency>
<!--Mybatis的jar包-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.6</version>
</dependency>
<!--Mybatis依赖的日志包-->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
</dependencies>
/*注意:
①JavaBean的属性名和数据库的字段名保持一致(有些情况不一致,则数据库的字段名可起别名与JavaBean的属性名保持一致)。
②属性类型使用包装类,不使用基本数据类型
*/
public class User {
private Integer id;
private String username;
private String password;
private String email;
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 getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", username='" + username + '\'' +
", password='" + password + '\'' +
", email='" + email + '\'' +
", birthday=" + birthday +
'}';
}
}
/*注意:
①映射器:在Mybatis里,把持久层(dao层)接口称为映射器。
②映射器类名取名规范:可以取名为`XXXMapper`,也可以写成`XXXDao`。
③使用Mybatis框架只要创建接口即可,不需要创建接口的实现类,是通过代理对象来实现功能的。
*/
public interface UserMapper {
//查询所有用户
List<User> queryAllUser();
}
映射配置文件(UserMapper.xml)
映射配置文件规范:
<mapper namespace="com.mycode.dao.UserMapper">
<select id="queryAllUser" resultType="com.mycode.domain.User">
select * from t_user
select>
mapper>
<configuration>
<environments default="mybatis01">
<environment id="mybatis01">
<transactionManager type="JDBC">transactionManager>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql:///stusmanager"/>
<property name="username" value="root"/>
<property name="password" value="1998"/>
dataSource>
environment>
<environment id="mybatis02">
<transactionManager type="JDBC">transactionManager>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql:///stusmanager"/>
<property name="username" value="root"/>
<property name="password" value="1998"/>
dataSource>
environment>
environments>
<mappers>
<mapper resource="com/mycode/dao/UserMapper.xml" />
mappers>
configuration>
# 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.
#控制台输出
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
#日志文件存放路径
log4j.appender.LOGFILE.File=d:\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
/*
思路:读取配置文件,得到一个输入流,构造者根据输入流流构造一个工厂,工厂生产一个SqlSession对象,
SqlSession对象得到映射器的代理对象,由代理对象执行sql语句。
*/
public class QuickStartTest {
@Test
public void quickStartTest() throws IOException {
//读取核心配置文件(SqlMapConfig.xml),得到输入流
InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
//创建构造者对象
SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
//构造者根据输入流构造一个工厂,得到SqlSessionFactory工厂对象【构造者模式】
SqlSessionFactory factory = sqlSessionFactoryBuilder.build(inputStream);
//工厂对象生产一个SqlSession对象【工厂模式】
SqlSession sqlSession = factory.openSession();
//使用SqlSession对象获取映射器UserMapper接口的代理对象(有接口,没有实现类,生成代理对象,由代理对象完成功能)【代理模式】
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
//调用UserMapper代理对象的方法(即调用代理对象行为),查询所有用户.
List<User> userList = mapper.queryAllUser();
for (User user:userList) {
System.out.println(user);
}
sqlSession.close();
inputStream.close();
}
}
运行输出:<××××>为注释
[main] DEBUG ache.ibatis.logging.LogFactory - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
[main] DEBUG source.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
[main] DEBUG source.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
[main] DEBUG source.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
[main] DEBUG source.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
[main] DEBUG ansaction.jdbc.JdbcTransaction - Opening JDBC Connection <打开JDBC连接>
[main] DEBUG source.pooled.PooledDataSource - Created connection 1131645570.<创建连接>
[main] DEBUG ansaction.jdbc.JdbcTransaction - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@43738a82]<取消自动提交事务>
[main] DEBUG de.dao.UserMapper.queryAllUser - ==> Preparing: select * from t_user <准备执行sql语句>
[main] DEBUG de.dao.UserMapper.queryAllUser - ==> Parameters:
[main] DEBUG de.dao.UserMapper.queryAllUser - <== Total: 37<查询到37条记录>
User{id=1, username='张三', password='1', email='null', birthday=null}
User{id=2, username='李四', password='1', email='null', birthday=null}
User{id=3, username='王五', password='1', email='null', birthday=null}
User{id=4, username='上官婉儿', password='1', email='null', birthday=null}
User{id=5, username='上官锅儿', password='1', email='null', birthday=null}
User{id=6, username='上官瓢儿', password='1', email='null', birthday=null}
.....
.....
User{id=37, username='小乔', password='1', email='null', birthday=null}
User{id=38, username='伽罗', password='1', email='null', birthday=null}
User{id=39, username='迪迦', password='1', email='null', birthday=null}
User{id=43, username='百里', password='123', email='[email protected]', birthday=Thu Jan 02 00:00:00 CST 2020}
[main] DEBUG ansaction.jdbc.JdbcTransaction - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@43738a82] <恢复自动提交状态>
[main] DEBUG ansaction.jdbc.JdbcTransaction - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@43738a82]<关闭JDBC连接>
[main] DEBUG source.pooled.PooledDataSource - Returned connection 1131645570 to pool.<连接归还给数据库连接池>
从运行日志信息就可以看出,这正对应前面概述所说:MyBatis内部封装了 jdbc,使开发者只需关注 sql 语句本身,而不需要去处理加载驱动、创建连接、创建 statement 等过程,同时MyBatis还采用 ORM 思想解决了实体和数据库映射的问题,这使我们可以更为方便的完成对数据的持久化操作。