mybatis入门（介绍、mybatis入门程序（增、删、改、查））

1、介绍

（1）mybatis的优势：

MyBatis是apache的一个开源项目，对jdbc操作数据库的过程进行了封装，开发者只需关注sql本身，而不需要去处理注册驱动、创建连接、创建执行者对象、手动设置参数等复杂的代码。可以通过xml或注解的方式将要执行的各种statement配置起来，最终由mybatis框架执行sql并将结果映射成java对象返回。

（2）传统的jdbc的不足：

public class JdbcDemo {
    public static void main(String[] args) {
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            // 加载数据库驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 通过驱动管理类获取数据库链接
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/stu_mangement", "root", "root");
            // 定义sql语句 ?表示占位符
            String sql = "select * from student where studentno = ?";
            // 获取预处理statement
            preparedStatement = connection.prepareStatement(sql);
            // 设置参数，第一个参数为sql语句中参数的序号（从1开始），第二个参数为设置的参数值
            preparedStatement.setString(1, "201811");
            // 向数据库发出sql执行查询，查询出结果集
            resultSet = preparedStatement.executeQuery();
            // 遍历查询结果集
            while (resultSet.next()) {
                System.out.println(resultSet.getString("studentno") + "  " + resultSet.getString("sname"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            // 释放资源
            if (resultSet != null) {
                try {
                    resultSet.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }

}

201811  zhai

数据库连接创建、释放频繁造成系统资源浪费，从而影响系统性能，使用数据库连接池可解决此问题。

sql语句在代码中硬编码，造成代码不易维护，实际应用中sql变化的可能较大，sql变动需要改变java代码。

使用preparedStatement向占有位符号传参数存在硬编码，因为sql语句的where条件不一定，可能多也可能少，修改sql还要修改代码，不易维护。

对结果集解析存在硬编码（查询列名），sql变化导致解析代码变化，系统不易维护，如果能将数据库记录封装成pojo对象解析比较方便。

（3）mybatis框架：

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2、mybatis入门程序

（1）导包：

核心包、依赖包、数据库驱动包

 （2）书写pojo：

public class Student implements Serializable {
    private static final long serialVersionUID = 1L;
    private String studentno;
    private String sname;
    private String sex;
    private String birthday;
    private String classno;
    private String point;
    private String phone;
    private String email;
    public String getStudentno() {
        return studentno;
    }
    public void setStudentno(String studentno) {
        this.studentno = studentno;
    }
    public String getSname() {
        return sname;
    }
    public void setSname(String sname) {
        this.sname = sname;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public String getBirthday() {
        return birthday;
    }
    public void setBirthday(String birthday) {
        this.birthday = birthday;
    }
    @Override
    public String toString() {
        return "Student [studentno=" + studentno + ", sname=" + sname + ", sex="
                + sex + ", birthday=" + birthday + ", classno=" + classno
                + ", point=" + point + ", phone=" + phone + ", email=" + email
                + "]";
    }
    public String getClassno() {
        return classno;
    }
    public void setClassno(String classno) {
        this.classno = classno;
    }
    public String getPoint() {
        return point;
    }
    public void setPoint(String point) {
        this.point = point;
    }
    public String getPhone() {
        return phone;
    }
    public void setPhone(String phone) {
        this.phone = phone;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
}

（3）核心配置文件：

<?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>
    <!-- 和spring整合后 environments配置将废除    -->
    <environments default="development">
        <environment id="development">
            <!-- 使用jdbc事务管理 -->
            <transactionManager type="JDBC" />
            <!-- 数据库连接池 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://localhost:3306/student" />
                <property name="username" value="root" />
                <property name="password" value="root" />
            </dataSource>
        </environment>
    </environments>
</configuration>

（4）日志文件（在控制台打印信息）：

# Global logging configuration
log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

（5）书写Student.xml配置文件，并将该文件引入到核心配置文件：

<?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="test">
    <select id="findStudentById" parameterType="Integer" resultType="pers.zhb.pojo.Student">
        select * from student where studentno = #{v}
    </select>
</mapper>

在核心配置文件中引入该文件：

<mappers>
        <mapper resource="sqlmap/student.xml"/>
</mappers>

（6）书写测试类：

public class Test {
    public void testMybatis() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //执行Sql语句
        Student student = sqlSession.selectOne("test.findStudentById", 201811);
        System.out.println(student);
    }
    public static void main(String args []){
        Test test=new Test();
        try {
            test.testMybatis();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 2094411587.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@7cd62f43]
DEBUG [main] - ==>  Preparing: select * from student where studentno = ? 
DEBUG [main] - ==> Parameters: 201811(Integer)
DEBUG [main] - <==      Total: 1
Student [studentno=201811, sname=zhai, sex=男, birthday=1998-11-11, classno=tx171, point=890, phone=1234567890, email=null]

（7）模糊查询：

<select id="findStudentBysname" parameterType="String" resultType="pers.zhb.pojo.Student">
        select * from student where sname like '%${value}%'
</select>

public void testfindUserBysname() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //执行Sql语句
        List<Student> students = sqlSession.selectList("test.findStudentBysname", "zh");
        for (Student student : students) {
            System.out.println(student);

        }
    }

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 1555690610.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@5cb9f472]
DEBUG [main] - ==>  Preparing: select * from student where sname like '%zh%' 
DEBUG [main] - ==> Parameters: 
DEBUG [main] - <==      Total: 4
Student [studentno=201811, sname=zhai, sex=男, birthday=1998-11-11, classno=tx171, point=890, phone=1234567890, email=null]
Student [studentno=201812, sname=zhai2, sex=男, birthday=1998-11-11, classno=tx171, point=893, phone=19837372533, email=null]
Student [studentno=201813, sname=zhai3, sex=男, birthday=1998-11-11, classno=tx171, point=892, phone=19837372534, email=null]
Student [studentno=201814, sname=zhai3, sex=男, birthday=1998-11-11, classno=tx101, point=892, phone=19837372534, email=null]

上面的方式不能防止sql注入，可以更改配置文件，如下：

<select id="findStudentBysname" parameterType="String" resultType="pers.zhb.pojo.Student">
        select * from student where sname like "%"#{value}"%"
</select>

（8）添加：

<insert id="insertStudent" parameterType="pers.zhb.pojo.Student">
        insert into student (studentno,sname,sex,phone)
        values (#{studentno},#{sname},#{sex},#{phone})
</insert>

  public void testInsertStudent() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //执行Sql语句
        Student student=new Student();
        student.setStudentno("2020319");
        student.setSname("ma");
        student.setPhone("18733356671");
        student.setSex("男");
        int i = sqlSession.insert("test.insertStudent", student);
        sqlSession.commit();
    }

最后需要提交。

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 152134087.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@91161c7]
DEBUG [main] - ==>  Preparing: insert into student (studentno,sname,sex,phone) values (?,?,?,?) 
DEBUG [main] - ==> Parameters: 2020319(String), ma(String), 男(String), 18733356671(String)
DEBUG [main] - <==    Updates: 1
DEBUG [main] - Committing JDBC Connection [com.mysql.jdbc.JDBC4Connection@91161c7]

（9）更新：

    <update id="updateStudentById" parameterType="pers.zhb.pojo.Student">
        update student
        set sname = #{sname}
        where studentno = #{studentno}
    </update>

 public void testUpdateUserById() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        Student student=new Student();
        student.setStudentno("2020319");
        student.setSname("ma2011");
        int i = sqlSession.update("test.updateStudentById", student);
        sqlSession.commit();
    }

10、删除

<delete id="deleteStudentById" parameterType="Integer">
        delete from student
        where studentno = #{value}
</delete>

 public void testDelete() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();

        sqlSession.delete("test.deleteStudentById", 2020319);
        sqlSession.commit();
    }

DEBUG [main] - Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - PooledDataSource forcefully closed/removed all connections.
DEBUG [main] - Opening JDBC Connection
DEBUG [main] - Created connection 152134087.
DEBUG [main] - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@91161c7]
DEBUG [main] - ==>  Preparing: delete from student where studentno = ? 
DEBUG [main] - ==> Parameters: 2020319(Integer)
DEBUG [main] - <==    Updates: 1
DEBUG [main] - Committing JDBC Connection [com.mysql.jdbc.JDBC4Connection@91161c7]