目录

项目搭建前置准备

1.1 typeHandlers标签

 1.2 plugins标签-分页

 1.3知识小结

---

项目搭建前置准备

相关依赖

  <dependencies>
        <!-- mysql驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.17</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>4.12</version>
        </dependency>
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper</artifactId>
            <version>3.7.5</version>
        </dependency>
        <dependency>
            <groupId>com.github.jsqlparser</groupId>
            <artifactId>jsqlparser</artifactId>
            <version>0.9.1</version>
        </dependency>

    </dependencies>

user表 

实体类

package com.itheima.domain;

import java.util.Date;

public class User {

    private int id;
    private String username;
    private String password;
    private Date birthday;

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public int getId() {
        return id;
    }

    public void setId(int 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;
    }

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

UserMapper接口

package com.itheima.mapper;

import com.itheima.domain.User;
import java.util.List;
public interface UserMapper {
    public void save(User user);
    public User findById(int id);
    public List<User> findAll();

}

配置

com.itheima.mapper/UserMapper.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.itheima.mapper.UserMapper">
    <insert id="save" parameterType="user">
        insert into user values(#{id},#{username},#{password},#{birthday})
    </insert>
    <select id="findById" parameterType="int" resultType="user">
        select * from user where id=#{id}
    </select>
</mapper>

日志log4j.properties

### direct log messages to stdout ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
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

jdbc.proerties

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test?useSSL=false&serverTimezone=Asia/Shanghai
jdbc.username=root
jdbc.password=root

mybatis配置

<?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>
    <!--通过properties标签加载外部properties文件-->
    <properties resource="jdbc.properties"></properties>
    <!--自定义别名-->
    <typeAliases>
        <typeAlias type="com.itheima.domain.User" alias="user"></typeAlias>
    </typeAliases>
    <!--注册类型处理器-->
    <typeHandlers>
        <typeHandler handler="com.itheima.handler.DateTypeHandler"></typeHandler>
    </typeHandlers>
    <!--配置分页助手插件-->
    <plugins>
        <plugin interceptor="com.github.pagehelper.PageHelper">
            <property name="dialect" value="mysql"></property>
        </plugin>
    </plugins>
    <!--数据源环境-->
    <environments default="developement">
        <environment id="developement">
            <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>
    <!--加载映射文件-->
    <mappers>
        <mapper resource="com/itheima/mapper/UserMapper.xml"></mapper>
    </mappers>
</configuration>

1.1 typeHandlers标签

无论是MyBatis在预处理语句(PreparedStatement)中设置一个参数时，还是从结果集中取出一个值时，都会用类型处理器将获取的值以合适的方式转换成v类型。下表描述了一些默认的类型处理器 

你可以重写类型处理器或创建你自己的类型处理器来处理不支持的或非标的类型。具体做法为：实现org.apache.ibatis.type.TypeHandler接口，或继承一个很便利的类org.apach能。ibatis.type.BaseTypeHandler,然后可以选择性地将它映射到一个DBC类型。例如需求：一个Jva中的Date数据类型，我想将之存到数据库的时候存成个1970年至今的毫秒数，取出来时转换成java的Date,即java的Date与数据库的varchar毫秒值之间转换。
开发步骤：
①定义转换类继承类BaseTypeHandler<T>
②覆盖A个未实现的方法，其中setNonNullParameter为java程序设置数据到数据库的回调方法，getNullableResult为查询时mysqlE的字符串类型转换成java的Type类型的方法

package com.itheima.handler;

import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Date;
public class DateTypeHandler extends BaseTypeHandler<Date> {
    //将java类型 转换成 数据库需要的类型
    public void setNonNullParameter(PreparedStatement preparedStatement, int i, Date date, JdbcType jdbcType) throws SQLException {
        long time = date.getTime();
        preparedStatement.setLong(i,time);
    }
    //将数据库中类型 转换成java类型
    //String参数  要转换的字段名称
    //ResultSet 查询出的结果集
    public Date getNullableResult(ResultSet resultSet, String s) throws SQLException {
        //获得结果集中需要的数据(long) 转换成Date类型 返回
        long aLong = resultSet.getLong(s);
        Date date = new Date(aLong);
        return date;
    }
    //将数据库中类型 转换成java类型
    public Date getNullableResult(ResultSet resultSet, int i) throws SQLException {
        long aLong = resultSet.getLong(i);
        Date date = new Date(aLong);
        return date;
    }
    //将数据库中类型 转换成java类型
    public Date getNullableResult(CallableStatement callableStatement, int i) throws SQLException {
        long aLong = callableStatement.getLong(i);
        Date date = new Date(aLong);
        return date;
    }
}

③在MyBatis核心配置文件中进行注册

<?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>
    </typeAliases>
    <!--注册类型处理器-->
    <typeHandlers>
        <typeHandler handler="com.itheima.handler.DateTypeHandler"></typeHandler>
    </typeHandlers>
   
    <!--加载映射文件-->
    <mappers>
        <mapper resource="com/itheima/mapper/UserMapper.xml"></mapper>
    </mappers>
</configuration>

④测试1 插入数据库的日期是long类型

 @Test
    public void test1() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //创建user
        User user = new User();
        user.setUsername("ceshi");
        user.setPassword("abc");
        user.setBirthday(new Date());
        //执行保存造作
        mapper.save(user);
        sqlSession.commit();
        sqlSession.close();
    }

 测试2 打印输出转换类型Date

    
    @Test
    public void test2() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.findById(5);
        System.out.println("user中的birthday："+user.getBirthday());
        sqlSession.commit();
        sqlSession.close();
    }

 1.2 plugins标签-分页

MyBatis可以使用第三方的插件来对功能进行扩展，分页助手PageHelper是将分页的复操作进行封装，使用简单的方式即可获得分页的相关数据
开发步骤：
①导入通用PageHelper的坐标

        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper</artifactId>
            <version>3.7.5</version>
        </dependency>
        <dependency>
            <groupId>com.github.jsqlparser</groupId>
            <artifactId>jsqlparser</artifactId>
            <version>0.9.1</version>
        </dependency>

②在mybatisi核心配置文件中配置PageHelper插件

   <!--配置分页助手插件-->
    <plugins>
        <plugin interceptor="com.github.pagehelper.PageHelper">
            <property name="dialect" value="mysql"></property>
        </plugin>
    </plugins>

③测试分页数据获取

 @Test
    public void test3() throws IOException {
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //设置分页相关参数   当前页+每页显示的条数
        PageHelper.startPage(3,3);

        List<User> userList = mapper.findAll();
        for (User user : userList) {
            System.out.println(user);
        }
        //获得与分页相关参数
        PageInfo<User> pageInfo = new PageInfo<User>(userList);
        System.out.println("当前页："+pageInfo.getPageNum());
        System.out.println("每页显示条数："+pageInfo.getPageSize());
        System.out.println("总条数："+pageInfo.getTotal());
        System.out.println("总页数："+pageInfo.getPages());
        System.out.println("上一页："+pageInfo.getPrePage());
        System.out.println("下一页："+pageInfo.getNextPage());
        System.out.println("是否是第一个："+pageInfo.isIsFirstPage());
        System.out.println("是否是最后一个："+pageInfo.isIsLastPage());
        sqlSession.close();
    }

 

 1.3知识小结

MyBatis核心配置文件常用标签：
1、propertiest标签：该标签可以加载外的properties.文件
2、typeAliases标签：设置类型别名
3、environments标签：数据源环境配置标签
4、typeHandlers标签：配置自定义类型处理器
5、plugins标签：配置MyBatis的插件