Mybatis的mapper接口函數重載問題

Mybatis的接口函數能不能進行重載？

mybatis版本：3.4x
java版本：java 8

語法層面：

1、接口的方法可以進行重載，因爲 java 語法可以讓接口函數進行重載。

Mybatis框架方面：

1、結論：可以有條件的進行重載。
2、爲什麼會有這個問題？：mybatis裏面將接口裏面的方法名稱和配置文件裏面的id屬性進行唯一配對，在同一個命名空間下只能有一個id，那麼所有函數名稱相同的重載函數都會被綁定到一個id上，所以，如果要實現函數的重載，必須讓一個SQL語句去適應多個函數的參數，如果是單純的重載是肯定不行的（重載函數的定義就是參數相關），但是得益於mybatis的多種傳參方式和隱性的分頁功能，可以在接口裏面進行函數重載，但是還是需要將所有的重載函數適配到同一個id的SQL上面去，仍然有很大的侷限性，並不是可以隨意的進行重載。

測試：

1、數據庫環境

DROP TABLE IF EXISTS sys_user;
CREATE TABLE sys_user(
  id BIGINT NOT NULL AUTO_INCREMENT COMMENT '用戶的ID',
  user_name VARCHAR(50) COMMENT '用戶名稱',
  user_password VARCHAR(50) COMMENT '密碼',
  user_email VARCHAR(50) COMMENT '郵箱',
  user_info TEXT COMMENT '簡介',
  head_img BLOB COMMENT '頭像',
  create_time DATETIME COMMENT '創建時間',
  PRIMARY KEY (id)
)DEFAULT CHARSET utf8;
ALTER TABLE sys_user COMMENT '用戶表';

INSERT INTO sys_user VALUES ('1','admin','123456','[email protected]','管理員',null,'2016-04-01 17:00:58');
INSERT INTO sys_user VALUES ('1001','test','123456','[email protected]','測試用戶',null,'2016-04-01 17:01:52');

2、實體類

public class SysUser {

    private Long id;
    private String userName;
    private String userPassword;
    private String userEmail;
    private String userInfo;
    private byte[] headImg;
    private Date createTime;

    public SysUser(){
    }
    /**setter and getter*/
}

3、測試
3.1、測試模板代碼

public class SysUserDaoTest {

    private static SqlSessionFactory sqlSessionFactory;
    private SqlSession sqlSession;

    @BeforeClass
    public static void beforeClass(){
        String resource = "plus/mybatis-config.xml";
        try{
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        }catch(IOException e){
            e.printStackTrace();
        }
    }

    @Before
    public void before(){
        //事物手動提交
        sqlSession = sqlSessionFactory.openSession(false);
    }

    @After
    public void after(){
        //回滾事物
        sqlSession.rollback(true);
        //關閉會話
        sqlSession.close();
    }
}

3.2、測試場景一

重載實現分頁、參數類型轉換實現重載。

3.2.1、接口

public interface SysUserDao {

    SysUser selectById(Long id);

    List<SysUser> selectById(Long id,RowBounds rowBound);
 }

3.2.2、mapper配置文件

<!--
    id：注意事項：接口方法不能進行重載，在3.4版本後是錯的！！！！！，因爲至少可以分頁！！！
            1、接口中的所有重載方法對應XML裏面的同一個ID，但是3.4之後有一個分頁的插件，所以至少可以接受一個org.apache.ibatis.session.RowBounds的隱性參數。
            2、雖然接口裏面的方法可以進行重載，但是需要一個前提：不要指定 parameterType 屬性！！
                接口方法如下：
                SysUser selectById(Long id);
                List<SysUser> selectById(Long id,RowBounds rowBound);
                SysUser selectById(String name);
                測試代碼如下：
                SysUserDao sysUserDao = sqlSession.getMapper(SysUserDao.class);
                SysUser sysUser = sysUserDao.selectById(1L);
                Assert.assertEquals("admin",sysUser.getUserName());
                SysUser sysUser1 = sysUserDao.selectById("1");
                Assert.assertEquals("admin",sysUser1.getUserName());
                /*
                plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
                plus.dao.SysUserDao.selectById - ==> Parameters: 1(Long)
                plus.dao.SysUserDao.selectById - <==      Total: 1
                plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
                plus.dao.SysUserDao.selectById - ==> Parameters: 1(String)
                plus.dao.SysUserDao.selectById - <==      Total: 1
                 */
                 RowBounds rowBound = new RowBounds(0,2);
                List<SysUser> sysUsers = sysUserDao.selectById(1L,rowBound);
                Assert.assertEquals(1,sysUsers.size());
                /*
                plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
                plus.dao.SysUserDao.selectById - ==> Parameters: 1(Long)
                plus.dao.SysUserDao.selectById - <==      Total: 1
                 */
                事實證明，當不指定參數類型的時候（也僅僅當不指定參數類型的時候纔可以，因爲重載重載的是參數），是可以進行
                接口方法重載的，因爲mybatis的參數類型推斷會自動的轉換參數類型，比如：
                    sysUserDao.selectById("楚雲飛");
                因爲ID的類型是Long類型，所以數據類型的自動轉換失敗，但是是不會出現異常的，只是它選取出來的數據集爲null,因爲ID的類型是bigint，沒有bigint值爲楚雲飛，所以爲null結果集。
    -->
    <select id="selectById" resultMap="sysUser" flushCache="true">
        SELECT * FROM sys_user WHERE id = #{id};
    </select>
    <resultMap id="sysUser" type="plus.pojo.SysUser">
        <id property="id" column="id"/>
        <result property="userName" column="user_name"/>
        <result property="userPassword" column="user_password"/>
        <result property="userEmail" column="user_email"/>
        <result property="userInfo" column="user_info"/>
        <result property="headImg" column="head_img" jdbcType="BLOB"/>
        <result property="createTime" column="create_time" jdbcType="TIMESTAMP"/>
    </resultMap>

3.3、測試場景二

參數傳遞方式實現重載，map參數傳遞和固定參數名的參數傳遞方式

3.3.1、接口

public interface SysUserDao {

    SysUser selectByCondition(@Param("id")Long id,@Param("userName")String userName,@Param("userPassword")String userPassword);

    SysUser selectByCondition(Map params);
}

3.3.2、mapper配置文件

<!--
    固定參數傳遞：
       函數接口：
           SysUser selectByCondition(@Param("id")Long id,@Param("userName")String userName,@Param("userPassword")String userPassword);
           SysUser selectByCondition(Map params);
       測試函數：
            @Test
            public void selectByCondition(){

                SysUserDao sysUserDao = sqlSession.getMapper(SysUserDao.class);

                SysUser sysUser = sysUserDao.selectByCondition(1L,"admin","123456");

                Assert.assertEquals("[email protected]",sysUser.getUserEmail());

                /*
                plus.dao.SysUserDao.selectByCondition - ==>  Preparing: SELECT * FROM sys_user WHERE id = ? AND user_name = ? AND user_password = ?;
                plus.dao.SysUserDao.selectByCondition - ==> Parameters: 1(Long), admin(String), 123456(String)
                plus.dao.SysUserDao.selectByCondition - <==      Total: 1
                 */

                Map<String,Object> params = new HashMap<String,Object>(3);
                //傳入的鍵值必須和SQL語句裏面的以及重載函數的參數名稱相同纔可以實現正確的重載，否則將重載出錯。
                params.put("id",1L);
                params.put("userName","admin");
                params.put("userPassword","123456");

                SysUser sysUser1 = sysUserDao.selectByCondition(params);
                /*
                plus.dao.SysUserDao.selectByCondition - ==>  Preparing: SELECT * FROM sys_user WHERE id = ? AND user_name = ? AND user_password = ?;
                plus.dao.SysUserDao.selectByCondition - ==> Parameters: 1(Long), admin(String), 123456(String)
                plus.dao.SysUserDao.selectByCondition - <==      Total: 1
                 */

                Assert.assertEquals("[email protected]",sysUser1.getUserEmail());
            }
-->
    <select id="selectByCondition" resultMap="sysUser" flushCache="true">
        SELECT * FROM sys_user WHERE id = #{id} AND user_name = #{userName} AND user_password = #{userPassword};
    </select>

3.4、完整的測試代碼

package plus.dao;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.*;
import org.junit.*;
import plus.pojo.SysUser;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class SysUserDaoTest {

    private static SqlSessionFactory sqlSessionFactory;
    private SqlSession sqlSession;

    @BeforeClass
    public static void beforeClass(){
        String resource = "plus/mybatis-config.xml";
        try{
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        }catch(IOException e){
            e.printStackTrace();
        }
    }

    @Before
    public void before(){
        //事物手動提交
        sqlSession = sqlSessionFactory.openSession(false);
    }

    @After
    public void after(){
        //回滾事物
        sqlSession.rollback(true);
        //關閉會話
        sqlSession.close();
    }

    @Test
    public void selectById(){
        SysUserDao sysUserDao = sqlSession.getMapper(SysUserDao.class);

        SysUser sysUser = sysUserDao.selectById(1L);

        Assert.assertEquals("admin",sysUser.getUserName());

        SysUser sysUser1 = sysUserDao.selectById("1");

        Assert.assertEquals("admin",sysUser1.getUserName());

        /*
        plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
        plus.dao.SysUserDao.selectById - ==> Parameters: 1(Long)
        plus.dao.SysUserDao.selectById - <==      Total: 1
        plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
        plus.dao.SysUserDao.selectById - ==> Parameters: 1(String)
        plus.dao.SysUserDao.selectById - <==      Total: 1
         */

        RowBounds rowBound = new RowBounds(0,2);

        List<SysUser> sysUsers = sysUserDao.selectById(1L,rowBound);

        Assert.assertEquals(1,sysUsers.size());
        /*
        plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
        plus.dao.SysUserDao.selectById - ==> Parameters: 1(Long)
        plus.dao.SysUserDao.selectById - <==      Total: 1
         */
    }

    @Test
    public void selectByCondition(){

        SysUserDao sysUserDao = sqlSession.getMapper(SysUserDao.class);

        SysUser sysUser = sysUserDao.selectByCondition(1L,"admin","123456");

        Assert.assertEquals("[email protected]",sysUser.getUserEmail());

        /*
        plus.dao.SysUserDao.selectByCondition - ==>  Preparing: SELECT * FROM sys_user WHERE id = ? AND user_name = ? AND user_password = ?;
        plus.dao.SysUserDao.selectByCondition - ==> Parameters: 1(Long), admin(String), 123456(String)
        plus.dao.SysUserDao.selectByCondition - <==      Total: 1
         */

        Map<String,Object> params = new HashMap<String,Object>(3);
        params.put("id",1L);
        params.put("userName","admin");
        params.put("userPassword","123456");

        SysUser sysUser1 = sysUserDao.selectByCondition(params);
        /*
        plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
        plus.dao.SysUserDao.selectById - ==> Parameters: 1(Long)
        plus.dao.SysUserDao.selectById - <==      Total: 1
         */

        Assert.assertEquals("[email protected]",sysUser1.getUserEmail());
    }
}

3.5、完整的mapper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="plus.dao.SysUserDao">

    <!--
    id：當使用接口時，屬性值必須爲接口裏面的方法名稱,在同一個命名空間裏面不重複，否則將啓動報錯；
        在任何情況下，id屬性不能出現英文句點 '.' (Caused by: org.apache.ibatis.builder.BuilderException: Dots are not allowed in element names, please remove it) ;
        注意事項：接口方法不能進行重載，在3.4版本後是錯的！！！！！，因爲可以分頁！！！
            1、接口中的所有重載方法對應XML裏面的同一個ID，但是3.4之後有一個分頁的插件，所以可以接受一個org.apache.ibatis.session.RowBounds的隱性參數。
            2、雖然接口裏面的方法可以進行重載，但是如果要在運行的時候依然不報錯的話，需要一個前提：不要指定 parameterType 屬性！！
                接口方法如下：
                SysUser selectById(Long id);
                List<SysUser> selectById(Long id,RowBounds rowBound);
                SysUser selectById(String name);
                測試代碼如下：
                SysUserDao sysUserDao = sqlSession.getMapper(SysUserDao.class);
                SysUser sysUser = sysUserDao.selectById(1L);
                Assert.assertEquals("admin",sysUser.getUserName());
                SysUser sysUser1 = sysUserDao.selectById("1");
                Assert.assertEquals("admin",sysUser1.getUserName());
                /*
                plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
                plus.dao.SysUserDao.selectById - ==> Parameters: 1(Long)
                plus.dao.SysUserDao.selectById - <==      Total: 1
                plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
                plus.dao.SysUserDao.selectById - ==> Parameters: 1(String)
                plus.dao.SysUserDao.selectById - <==      Total: 1
                 */
                 RowBounds rowBound = new RowBounds(0,2);
                List<SysUser> sysUsers = sysUserDao.selectById(1L,rowBound);
                Assert.assertEquals(1,sysUsers.size());
                /*
                plus.dao.SysUserDao.selectById - ==>  Preparing: SELECT * FROM sys_user WHERE id = ?;
                plus.dao.SysUserDao.selectById - ==> Parameters: 1(Long)
                plus.dao.SysUserDao.selectById - <==      Total: 1
                 */
                事實證明，當不指定參數類型的時候（也僅僅當不指定參數類型的時候纔可以，因爲重載重載的是參數），是可以進行
                接口方法重載的，因爲mybatis的參數類型推斷會自動的轉換參數類型，比如：
                    sysUserDao.selectById("楚雲飛");
                因爲ID的類型是Long類型，所以數據類型的自動轉換失敗，但是是不會出現異常的，只是它選取出來的數據集爲null
    -->
    <select id="selectById" resultMap="sysUser" flushCache="true">
        SELECT * FROM sys_user WHERE id = #{_parameter};
    </select>

    <!--
    參數傳遞問題：
    1、接口函數：
        SysUser selectByCondition(Long id,String userName,String userPassword);
    參數傳遞：
        1、默認參數傳遞：默認的參數的命名爲 param + 序位，SQL語句如下：
            SELECT * FROM sys_user WHERE id = #{param1} AND user_name = #{param2} AND user_password = #{param3};
        2、默認參數傳遞：直接序列參數，SQL語句如下：
            SELECT * FROM sys_user WHERE id = #{0} AND user_name = #{1} AND user_password = #{2};
        3、固定參數傳遞：
            函數接口：
                SysUser selectByCondition(@Param("id")Long id,@Param("userName")String userName,@Param("userPassword")String userPassword);
            SQL語句如下：
                SELECT * FROM sys_user WHERE id = #{id} AND user_name = #{userName} AND user_password = #{userPassword};
        4、使用Map傳遞參數：
            函數接口：SysUser selectByCondition(Map params);
            調用代碼段：
                Map<String,Object> params = new HashMap<String,Object>(3);
                params.put("id",1L);
                params.put("userName","admin");
                params.put("userPassword","123456");
                SysUser sysUser1 = sysUserDao.selectByCondition(params);
                Assert.assertEquals("[email protected]",sysUser1.getUserEmail());
            SQL語句：
                SELECT * FROM sys_user WHERE id = #{id} AND user_name = #{userName} AND user_password = #{userPassword};
            思考：
                1、與固定參數的SQL相比，沒有改變SQL語句，而且兩個接口實現重載。
                2、接口函數可以實現重載，但是需要SQL語句來兼容這個函數的重載，也就是可以進行有條件的重載。
        5、使用 $ 和 # 進行取值的區別：
            1. #將傳入的數據都當成一個字符串，會對自動傳入的數據加一個雙引號。如：order by #user_id#，如果傳入的值是111,那麼解析成sql時的值爲order by "111", 如果傳入的值是id，則解析成的sql爲order by "id".
            2. $將傳入的數據直接顯示生成在sql中。如：order by $user_id$，如果傳入的值是111,那麼解析成sql時的值爲order by user_id,  如果傳入的值是id，則解析成的sql爲order by id.
            3. #方式能夠很大程度防止sql注入。
            4.$方式無法防止Sql注入。
            5.$方式一般用於傳入數據庫對象，例如傳入表名.
            6.一般能用#的就別用$.
            SELECT * FROM sys_user WHERE id = ${id} AND user_name = '${userName}' AND user_password = '${userPassword}';
    -->
    <select id="selectByCondition" resultMap="sysUser" flushCache="true">
        SELECT * FROM sys_user WHERE id = #{id} AND user_name = #{userName} AND user_password = #{userPassword};
    </select>



    <resultMap id="sysUser" type="plus.pojo.SysUser">
        <id property="id" column="id"/>
        <result property="userName" column="user_name"/>
        <result property="userPassword" column="user_password"/>
        <result property="userEmail" column="user_email"/>
        <result property="userInfo" column="user_info"/>
        <result property="headImg" column="head_img" jdbcType="BLOB"/>
        <result property="createTime" column="create_time" jdbcType="TIMESTAMP"/>
    </resultMap>
</mapper>

3.6、完整的接口

public interface SysUserDao {

    SysUser selectById(Long id);

    List<SysUser> selectById(Long id,RowBounds rowBound);

    SysUser selectById(String name);

    SysUser selectByCondition(@Param("id")Long id,@Param("userName")String userName,@Param("userPassword")String userPassword);

    SysUser selectByCondition(Map params);
}