Mybatis (一)

1 DAO层框架

• 框架：是一种整体的解决方案。

1.1 JDBC的步骤

1.2 Hibernate执行的步骤

1.3 MyBaits

2 Mybatis简介

• Mybatis是支持定制化SQL、存储过程以及高级映射的优秀的持久层框架。
• Mybatis避免了几乎所有的JDBC代码和手动设置参数以及获取结果集。
• Mybatis可以使用简单的XML或者注解用于配置和原始映射，将接口和Java的POJO映射成数据库中的记录。

3 为什么需要Mybatis？

• Mybatis是一个半自动的持久层框架。
• JDBC
  • SQL夹在Java代码中，耦合度高导致硬编码内伤。
  • 维护不易且实际开发需求中SQL是有变化的，频繁修改的情况多见。
• Hibernate和JPA
  • 长难复杂的SQL，对于Hibernate而言处理并不容易。
  • 内部自动生成的SQL，不容易做优化处理。
  • 基于全映射的全自动框架，大量字段的POJO进行部分映射的时候比较困难，导致数据库性能下降。　　　　
• 对于开发人员而言，核心SQL还是需要自己优化的。
• SQL和Java代码分开，功能边界清晰，一个专注业务，一个专注数据。

4 下载Mybatis

• https://github.com/mybatis/mybatis-3

5 Mybatis之HelloWorld

5.1 编写SQL脚本

DROP DATABASE mybatis;
CREATE DATABASE mybatis;
USE mybatis;
DROP TABLE employee;
CREATE TABLE employee(
    id INT PRIMARY KEY AUTO_INCREMENT,
    last_name ),
    gender ),
    email )
);
INSERT INTO employee (last_name,gender,email) VALUES ('许威威','男','1975356467@qq.com');

5.2 创建javabean

• Employee.java

package com.xuweiwei.mybatis.pojo;

public class Employee {
    private Integer id;
    private String lastName;
    private String gender;
    private String email;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

5.3 在src下加入log4j.properties文件

og4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.err
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

### direct messages to file mylog.log ###
log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.File=c\:mylog.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

### set log levels - for more verbose logging change 'info' to 'debug' ###

log4j.rootLogger=debug, stdout 

5.4 在src下新建mybatis-config.xml文件

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>

    </mappers>
</configuration>

5.5 新建EmployeeMapper.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.xuweiwei.mybatis.pojo.Employee">
    <select id="selectEmployeeById" resultType="com.xuweiwei.mybatis.pojo.Employee">
        select id,last_name lastName,gender,email  from employee where id = #{id}
    </select>
</mapper>

5.6 将EmployeeMapper.xml文件加入到mybatis-config.xml文件中

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/xuweiwei/mybatis/mapper/EmployeeMapper.xml"/>
    </mappers>
</configuration>

5.7 测试

package com.xuweiwei.mybatis.test;

import com.xuweiwei.mybatis.pojo.Employee;
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.Test;

import java.io.IOException;
import java.io.InputStream;

public class MybatisTest {
    @Test
    public void test() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        try {
            Employee employee = (Employee) session.selectOne("com.xuweiwei.mybatis.pojo.Employee.selectEmployeeById", 1);
            System.out.println(employee);
        } finally {
            session.close();
        }

    }

}

6 接口编程

6.1 编写EmployeeMapper.java

package com.xuweiwei.mybatis.mapper;

import com.xuweiwei.mybatis.pojo.Employee;

public interface EmployeeMapper {

    public Employee getEmployeeById(Integer id);
}

6.2 修改EmployeeMapper.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.xuweiwei.mybatis.mapper.EmployeeMapper">
    <select id="getEmployeeById" resultType="com.xuweiwei.mybatis.pojo.Employee">
        select id,last_name lastName,gender,email  from employee where id = #{id}
    </select>
</mapper>

6.3 测试

package com.xuweiwei.mybatis.test;

import com.xuweiwei.mybatis.mapper.EmployeeMapper;
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.Test;

import java.io.IOException;
import java.io.InputStream;

public class MybatisTest {
    @Test
    public void test() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        try {
            EmployeeMapper employeeMapper = session.getMapper(EmployeeMapper.class);
            System.out.println(employeeMapper.getEmployeeById(1));
        } finally {
            session.close();
        }

    }

}

7 SqlSession

• SqlSession的实例不是线程安全的，因此不能共享。
• SqlSession每次使用完之后必须正确的关闭。

8 全局配置文件

• 在全局配置文件中可以通过settings设置是否开启驼峰规则映射。

• Employee.java

package com.xuweiwei.mybatis.pojo;

public class Employee {
    private Integer id;
    private String lastName;
    private String gender;
    private String email;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "id=" + id +
                ", lastName='" + lastName + '\'' +
                ", gender='" + gender + '\'' +
                ", email='" + email + '\'' +
                '}';
    }
}

• mybatis-config.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>
    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/xuweiwei/mybatis/mapper/EmployeeMapper.xml"/>
    </mappers>
</configuration>

• log4j.properties

og4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.err
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

### direct messages to file mylog.log ###
log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.File=c\:mylog.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

### set log levels - for more verbose logging change 'info' to 'debug' ###

log4j.rootLogger=debug, stdout 

• EmployeeMapper.java

package com.xuweiwei.mybatis.mapper;

import com.xuweiwei.mybatis.pojo.Employee;

public interface EmployeeMapper {

    public Employee getEmployeeById(Integer id);
}

• EmployeeMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.xuweiwei.mybatis.mapper.EmployeeMapper">
    <select id="getEmployeeById" resultType="com.xuweiwei.mybatis.pojo.Employee">
        select id,last_name ,gender,email  from employee where id = #{id}
    </select>
</mapper>

• 测试

package com.xuweiwei.mybatis.test;

import com.xuweiwei.mybatis.mapper.EmployeeMapper;
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.Test;

import java.io.IOException;
import java.io.InputStream;

public class MybatisTest {
    @Test
    public void test() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        try {
            EmployeeMapper employeeMapper = session.getMapper(EmployeeMapper.class);
            System.out.println(employeeMapper.getEmployeeById(1));
        } finally {
            session.close();
        }

    }

}