java深入探究16-mybatis

链接：http://pan.baidu.com/s/1skJ4TNB 密码：koo9

1.引入mybatis

　　jsbc简单易学,上手快,非常灵活构建SQL，效率高但代码繁琐，难以写出高质量的代码

　　hibernate不用写SQL，完全以面向对象的方式设计和访问但处理复杂业务时，灵活度差

　　所以中间产物：mybatis就应运而生

2.mybatis说法和特定

　　1）MyBatis 本是apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code，并且改名为MyBatis 。2013年11月迁移到Github。

　　2）iBATIS一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。iBATIS提供的持久层框架包括SQL Maps和Data Access Objects（DAO）

　　3）jdbc/dbutils/springdao，hibernate/springorm，mybaits同属于ORM解决方案之一

3.mybatis快速入门

　　1)导入jar包（5个核心包+2个数据库访问包）：asm-3.3.1.jar；cglib-2.2.2.jar；commons-logging-1.1.1.jar；log4j-1.2.16.jar；mybatis-3.1.1.jar；mysql-connector-java-5.1.7-bin.jar；ojdbc5.jar

　　2）创建sql:

--mysql语法
create table students(
   id  int() primary key,
   name varchar(),
   sal double(,)
);
--oracle语法
create table students(
   id  number() primary key,
   name varchar2(),
   sal number(,)
);

　创建Student.java

/**
 * 学生
 * @author AdminTC
 */
public class Student {
    private Integer id;
    private String name;
    private Double sal;
    public Student(){}
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Double getSal() {
        return sal;
    }
    public void setSal(Double sal) {
        this.sal = sal;
    }
}

　　3)配置映射文件StudentMapper.xml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="mynamespace">
    <insert id="add1">
        insert into students(id,name,sal) values(,'哈哈',)
    </insert>
    <insert id="add2" parameterType="cn.itcast.javaee.mybatis.app05.Student">
        insert into students(id,name,sal) values(#{id},#{name},#{sal})
    </insert>
</mapper>

　　4）配置mybatis.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://127.0.0.1:3306/mybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="cn/itcast/javaee/mybatis/app05/StudentMapper.xml"/>
    </mappers>
</configuration>

　　5）创建MyBatisUtil工具类

/**
 * MyBatis工具类
 * @author AdminTC
 */
public class MyBatisUtil {
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            Reader reader = Resources.getResourceAsReader("mybatis.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    private MyBatisUtil(){}
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession == null){
            sqlSession = sqlSessionFactory.openSession();
            threadLocal.set(sqlSession);
        }
        return sqlSession;
    }
    public static void closeSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession != null){
            sqlSession.close();
            threadLocal.remove();
        }
    }
    public static void main(String[] args) {
        Connection conn = MyBatisUtil.getSqlSession().getConnection();
        System.out.println(conn!=null?"连接成功":"连接失败");
    }
}

　　6）创建StudentDao

/**
 * 持久层
 * @author AdminTC
 */
public class StudentDao {
    /**
     * 增加学生（无参）
     */
    public void add1() throws Exception{
        SqlSession sqlSession = MyBatisUtil.getSqlSession();
        try{
            sqlSession.insert("mynamespace.add1");
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            sqlSession.commit();
        }
        MyBatisUtil.closeSqlSession();
    }
    /**
     * 增加学生（有参）
     */
    public void add2(Student student) throws Exception{
        SqlSession sqlSession = MyBatisUtil.getSqlSession();
        try{
            sqlSession.insert("mynamespace.add2",student);
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            sqlSession.commit();
        }
        MyBatisUtil.closeSqlSession();
    }
    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();
        dao.add1();
        dao.add2(new Student(,"呵呵",8000D));
    }
}

4. mybatis工作流程

　　1)通过Reader对象读取src目录下的mybatis.xml配置文件（改文件的名字和位置可变）
　　2)通过SqlSessionFactoryBuilder对象创建sqlSessionFactory对象
　　3)从当前线程中获取SqlSession对象
　　4)事务开始，mybatis中默认
　　5)通过sqlSession对象读取StudentMapper.xml映射文件中操作编号，从而读取sql语句
　　6)事务提交必写
　　7)关闭SqlSession对象并且分离当前线程与sqlSession对象，让GC尽早回收

5.mybatis配置文件解析

　　1）StudentMapper.xml文件，提倡放在与实体同目录下，文件名任意
　　2）environments连接环境信息优化：
　　　　1.建一个db.properties用来存放连接信息
　　　　2.在mybatis中properties属性可以加载这个配置信息
　　　　3.连接环境配置属性值就可以用${mysql.url}形式从配置文件中获取了
　　3)StudentMapper.xml中insert标签parameterType="app04.Student"每次要类全路径
　　　　简化方式：
　　　　　　1.mybatis中添加
　　　　　　<!-- 设置类型别名 -->
　　　　　　<typeAliases>
　　　　　　<typeAlias type="app04.Student" alias="student"/>
　　　　　　</typeAliases>
　　　　　　2.之后在StudentMapper.xml中写类型时都可以用简称student了

<?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="mynamespace">
    <insert id="add1">
        insert into students(id,name,sal) values(,'哈哈',)
    </insert>
    <insert id="add2" parameterType="cn.itcast.javaee.mybatis.app05.Student">
        insert into students(id,name,sal) values(#{id},#{name},#{sal})
    </insert>
</mapper>

6.mybatis映射文件祥解(StudentMapper.xml)

　　StudentMapper:存放表映射；sql语句
　　mybatis:连接环境信息，加载映射文件

7.基于MybatisUtil工具类，完成CURD操作

StudentMapper.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="app09.Student">

    <resultMap type="app09.Student" id="studentMap">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="sal" column="sal"/>
    </resultMap>

    <!-- 增加学生 -->
    <insert id="add" parameterType="app09.Student">
        insert into students(id,name,sal) values(#{id},#{name},#{sal})
    </insert>
    <!-- 根据ID查询学生
         如果参数不是一个实体的话，只是一个普通变量，例如:int,double,String
         这里的#{中间的变量名可以随便写}，不过提倡就用方法的形参
     -->
    <select id="findById" parameterType="int" resultType="app09.Student">
        select * from students where id=#{id}
    </select>
    <!-- 查询所有学生
         理论上resultType要写List<Student>
         但这里只需书写List中的类型即可，即只需书写Student的全路径名
    -->
    <select id="findAll" resultType="app09.Student">
        select id,name,sal from students
    </select>
    <!-- 更新学生 -->
    <update id="update" parameterType="app09.Student">
        update students set name=#{name},sal=#{sal}  where id=#{id}
    </update>
    <!-- 删除学生 -->
    <delete id="delete" parameterType="app09.Student">
        delete form students where id=#{id}
    </delete>

    <!--
        注意：这个insert/update/delete标签只是一个模板，在做操作时，其实是以SQL语句为核心的
             即在做增/删/时，insert/update/delete标签可通用，
             但做查询时只能用select标签
             我们提倡什么操作就用什么标签
    -->
</mapper>

StudentDao.java

package app09;

import java.util.List;

import org.apache.ibatis.session.SqlSession;
import util.MybatisUtil;

public class StudentDao {
    /**
     * 增加学生
     */
    public void add(Student student)throws Exception{
        SqlSession sqlSession=null;
        try{
            sqlSession=MybatisUtil.getSqlSession();
            //开始事务
            sqlSession.insert(Student.class.getName()+".add",student);
            sqlSession.commit();
            //提交
        }catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        }finally{
            //解除关系让GC处理sqlSession对象
            MybatisUtil.closeSqlSession();
        }
    }
    /**
     *根据ID 查询学生
     */
    public Student findById(int id)throws Exception{
        SqlSession sqlSession=null;
        try{
            sqlSession=MybatisUtil.getSqlSession();
            //开始事务
            Student student=sqlSession.selectOne(Student.class.getName()+".findById", id);
            sqlSession.commit();
            return student;
            //提交
        }catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
            throw new RuntimeException();
        }finally{
            //解除关系让GC处理sqlSession对象
            MybatisUtil.closeSqlSession();
        }
    }
    /**
     *    查询所有学生
     */
    public List<Student> findAll()throws Exception{
        SqlSession sqlSession=null;
        try{
            sqlSession=MybatisUtil.getSqlSession();
            //开始事务
            return sqlSession.selectOne(Student.class.getName()+".findAll");

            //提交
        }catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
            throw new RuntimeException();
        }finally{
            //解除关系让GC处理sqlSession对象
            MybatisUtil.closeSqlSession();
        }
    }
    /**
     * 更新学生
     */
    public void update(Student student) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.update(Student.class.getName()+".update",student);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }
    /**
     * 删除学生
     */
    public void delete(Student student) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.delete(Student.class.getName()+".delete",student);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }

    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();
        //dao.add(new Student(1,"哈哈",7000D));
        //dao.add(new Student(2,"呵呵",8000D));
        //dao.add(new Student(3,"班长",9000D));
        //dao.add(new Student(4,"键状高",10000D));
        //Student student = dao.findById(4);
        //List<Student> studentList = dao.findAll();
        //for(Student student : studentList){
        //    System.out.print(student.getId()+":"+student.getName()+":"+student.getSal());
        //    System.out.println();
        //}
        Student student = dao.findById();
        System.out.println(student.getName());
        //student.setName("靓班长");
        //dao.update(student);

        //Student student = dao.findById(3);
        //System.out.print(student.getId()+":"+student.getName()+":"+student.getSal());

        //dao.delete(student);
    }
}

8.分页查询

package app10;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import org.apache.ibatis.session.SqlSession;
import util.MybatisUtil;

public class StudentDao {
    public void add(Student student)throws Exception{
        SqlSession sqlSession=null;
        try{
            sqlSession.insert(Student.class.getName()+".add",student);
            sqlSession.commit();
        }catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }
    /**
     * 分页
     * 在映射文件中参数不能是多个，对个多个参数需要封装用map
     * @param start
     * @param size
     * @return
     */
    public List<Student> findAllWithFy(int start,int size){
        SqlSession sqlSession=null;
        try{
            sqlSession = MybatisUtil.getSqlSession();

            Map<String,Object> map = new LinkedHashMap<String,Object>();
            map.put("pstart",start);
            map.put("psize",size);
            return sqlSession.selectList(Student.class.getName()+".findAllWithFy", map);
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw new RuntimeException();
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }
    /**
     * 分页有条件
     * 在映射文件中参数不能是多个，对个多个参数需要封装用map
     * @param start
     * @param size
     * @return
     */
    public List<Student> findAllWithFy(String name,int start,int size){
        SqlSession sqlSession=null;
        try{
            sqlSession = MybatisUtil.getSqlSession();

            Map<String,Object> map = new LinkedHashMap<String,Object>();
            map.put("pstart",start);
            map.put("psize",size);
            map.put("pname", "%"+name+"%");
            return sqlSession.selectList(Student.class.getName()+".findAllByNameWithFy", map);
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw new RuntimeException();
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }

    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();

        //for(int i=1;i<=10;i++){
        //    dao.add(new Student(i,"哈哈",7000D));
        //}

        System.out.println("--------------------第一页");
        List<Student> studentList1=dao.findAllWithFy("xiao",, );

        //List<Student> studentList1 = dao.findAllByNameWithFy("哈",0,3);
        for(Student s : studentList1){
            System.out.println(s.getId()+":"+s.getName()+":"+s.getSal());
        }
        //System.out.println("--------------------第二页");
        //List<Student> studentList2 = dao.findAllByNameWithFy("哈",3,3);
        //for(Student s : studentList2){
        //    System.out.println(s.getId()+":"+s.getName()+":"+s.getSal());
        //}
        //System.out.println("--------------------第三页");
        //List<Student> studentList3 = dao.findAllByNameWithFy("哈",6,3);
        //for(Student s : studentList3){
        //    System.out.println(s.getId()+":"+s.getName()+":"+s.getSal());
        //}

    }
}

<?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="app10.Student">

    <resultMap type="app10.Student" id="studentMap">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="sal" column="sal"/>
    </resultMap>

    <insert id="add" parameterType="app10.Student">
        insert into students(id,name,sal) values(#{id},#{name},#{sal})
    </insert>
    <select id="findAllWithFy" parameterType="map" resultMap="studentMap">
        select id,name,sal from students limit #{pstart},#{psize}
    </select>
    <select id="findAllByNameWithFy" parameterType="map" resultMap="studentMap">
        select id,name,sal from students where name like #{pname} limit #{pstart},#{psize}
    </select>
</mapper>

9。动态SQL操作

　　1）动态查询：select id,name,sal from students where 1=1 and name=? and sal=?

<where>
            <if test="pid!=null">
                and id=#{pid}
            </if>
            <if test="pname!=null">
                and name=#{pname}
            </if>
            <if test="psal=null">
                and sal=#{psal}
            </if>
</where>

StudentMapper.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="app11.Student">

    <resultMap type="app11.Student" id="studentMap">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="sal" column="sal"/>
    </resultMap>

    <select id="findAll" parameterType="map" resultMap="studentMap">
        select * from students
        <where>
            <if test="pid!=null">
                and id=#{pid}
            </if>
            <if test="pname!=null">
                and name=#{pname}
            </if>
            <if test="psal=null">
                and sal=#{psal}
            </if>
        </where>
    </select>

</mapper>

StudentDao.java

package app11;

import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.session.SqlSession;

import util.MybatisUtil;

/**
 * 持久层
 * @author AdminTC
 */
public class StudentDao {
    /**
     * 有条件的查询所有学生
     */
    public List<Student> findAll(Integer id,String name,Double sal) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();

            Map<String,Object> map = new LinkedHashMap<String,Object>();
            map.put("pid",id);
            map.put("pname",name);
            map.put("psal",sal);

            return sqlSession.selectList(Student.class.getName()+".findAll",map);
        }catch(Exception e){
            e.printStackTrace();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }

    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();
        List<Student> studentList = dao.findAll(,null,null);
        for(Student s : studentList){
            System.out.println(s.getId()+":"+s.getName()+":"+s.getSal());
        }
    }
}

　　2）动态更新：update students set name=?,sal=? where id=?

StudentDao.java

package app12;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.session.SqlSession;

import util.MybatisUtil;

/**
 * 持久层
 * @author AdminTC
 */
public class StudentDao {
    /**
     * 有条件更新学生
     */
    public void dynaUpdate(Integer id,String name,Double sal) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();

            Map<String,Object> map = new HashMap<String, Object>();
            map.put("pid",id);
            map.put("pname",name);
            map.put("psal",sal);
            sqlSession.update("studentNamespace.dynaUpdate",map);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }

    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();
        //关注SQL的变化
        //dao.dynaUpdate(1,null,9000D);//update students set sal=? where id=?
        //dao.dynaUpdate(1,"笨笨",null);//update students set name=? where id=?
        dao.dynaUpdate(,"笨笨",10000D);//update students set name=? and sal=? where id=?
    }
}

StudentMapper.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="studentNamespace">    

    <resultMap type="app12.Student" id="studentMap">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="sal" column="sal"/>
    </resultMap>

    <!-- set标签自动判断哪个是最后一个字段，会自动去掉最后一个,号 -->
    <update id="dynaUpdate" parameterType="map">
        update students
        <set>
            <if test="pname!=null">
                students_name = #{pname},
            </if>
            <if test="psal!=null">
                students_sal = #{psal},
            </if>
        </set>
        where students_id = #{pid}
    </update>

</mapper>

　　3）动态删除

delete from students where id in (1,3,5,7)
select id,name,sal from students where id in (2,4,6,8)

StudentDao.java

package app13;

import java.util.ArrayList;
import java.util.List;

import org.apache.ibatis.session.SqlSession;

import app13.StudentDao;

import util.MybatisUtil;

/**
 * 持久层
 * @author AdminTC
 */
public class StudentDao {
    /**
     * 根据ID批量删除学生(数组版本)
     * @param ids
     * @throws Exception
     */
    public void dynaDeleteArray(int ...ids)throws Exception{
        SqlSession sqlSession=null;
        try{
            sqlSession=MybatisUtil.getSqlSession();
            sqlSession.delete(Student.class.getName()+".dynaDeleteArray",ids);
            sqlSession.commit();
        }catch (Exception e) {
            e.printStackTrace();
            sqlSession.rollback();
            throw new RuntimeException();
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }

    public void dynaDeleteList(List<Integer> ids)throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.delete("studentNamespace.dynaDeleteList",ids);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }

    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();
        dao.dynaDeleteArray(,);

        //List<Integer> ids = new ArrayList<Integer>();
        //ids.add(6);
        //ids.add(8);
        //ids.add(9);
        //dao.dynaDeleteList(ids);
    }
}

StudentMapper.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="app13.Student">    

    <resultMap type="app13.Student" id="studentMap">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="sal" column="sal"/>
    </resultMap>

    <delete id="dynaDeleteArray">
        delete from students where id in
        <!-- foreach用于迭代数组元素
             open表示开始符号
             close表示结束符合
             separator表示元素间的分隔符
             item表示迭代的数组，属性值可以任意，但提倡与方法的数组名相同
             #{ids}表示数组中的每个元素值
         -->
         <foreach collection="array" open="(" close=")" separator="," item="ids">
             #{ids}
         </foreach>
    </delete>

    <delete id="dynaDeleteList">
        delete from students where id in
        <foreach collection="list" open="(" close=")" separator="," item="ids">
            #{ids}
        </foreach>
    </delete>
</mapper>

　　4）动态插入：insert into student(id,name,sal) values(?,?,?)

StudentMapper.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="studentNamespace">    

    <resultMap type="app14.Student" id="studentMap">
        <id property="id" column="id"/>
        <result property="name" column="name"/>
        <result property="sal" column="sal"/>
    </resultMap>

    <!-- 定义sql片段   字段名,id属性值任意写-->
    <sql id="key">
        <trim suffixOverrides=",">
            <if test="id!=null">
                id,
            </if>
            <if test="name!=null">
                name,
            </if>
            <if test="sal!=null">
                sal,
            </if>
        </trim>

    </sql>
    <!-- 定义sql片段 ？ -->
    <sql id="value">
        <!-- 去掉最后一个， -->
        <trim suffixOverrides=",">
            <if test="id!=null">
                #{},
            </if>
            <if test="name!=null">
                #{},
            </if>
            <if test="sal!=null">
                #{},
            </if>
        </trim>

    </sql>

    <insert id="dynaInsert" parameterType="day14.Student">
        insert into students(<include refid="key"></include>) values(<include refid="value"></include>)
    </insert>

</mapper>

StudentDao.java

package app14;

import java.util.ArrayList;
import java.util.List;

import org.apache.ibatis.session.SqlSession;

import app13.Student;

import util.MybatisUtil;

/**
 * 持久层
 * @author AdminTC
 */
public class StudentDao {
    /**
     * 动态插入学生
     */
    public void dynaInsert(Student student) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();
            sqlSession.insert("studentNamespace.dynaInsert",student);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            //MybatisUtil.closeSqlSession();
        }
    }

    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();
        //dao.dynaInsert(new Student(1,"哈哈",7000D));//insert into 表名(*,*,*) values(?,?,?)
        dao.dynaInsert(new Student(,"哈哈",null));//insert into 表名(*,*) values(?,?)
        //dao.dynaInsert(new Student(3,null,7000D));//insert into 表名(*,*) values(?,?)
        //dao.dynaInsert(new Student(4,null,null));//insert into 表名(*) values(?)
    }
}