前面我们介绍了Mybatis动态SQL的使用；本篇我们介绍使用mybatis-velocity动态语言生成动态SQL。

如果您对Mybatis动态SQL不太了解，建议您先进行了解后再阅读本篇，可以参考：

Mybatis 动态SQL – 使用if,where标签动态生成条件语句

Mybatis 动态SQL – 使用if,set标签动态生成更新语句

Mybatis 动态SQL – 使用choose标签动态生成条件语句

Mybatis 动态SQL – 使用choose标签动态生成更新语句

Mybatis 动态SQL - 使用foreach标签查询数据、批量新增、批量修改、删除数据

一、数据准备

这里我们直接使用脚本初始化数据库中的数据

-- 如果数据库不存在则创建数据库
CREATE DATABASE IF NOT EXISTS demo DEFAULT CHARSET utf8;
-- 切换数据库
USE demo;
-- 创建用户表
CREATE TABLE IF NOT EXISTS T_TEACHER(
  ID INT PRIMARY KEY COMMENT '教师编号',
  TEACHER_NAME VARCHAR(64) NOT NULL COMMENT '教师名称',
  DEPARTMENT VARCHAR(16) NOT NULL COMMENT '所属部门',
  BIRTH DATE NOT NULL COMMENT '出生年月',
  DEGREE VARCHAR(16) NOT NULL COMMENT '学历(ZK:专科, BK:本科, YJS:研究生, BS:博士)'
);
-- 插入用户数据
INSERT INTO T_TEACHER(ID, TEACHER_NAME, DEPARTMENT, BIRTH, DEGREE)
VALUES(1, '张三1', '001', '1990-06-12', 'BK'),
      (2, '李四1', '002', '1992-05-10', 'BK'),
      (3, '张三2', '003', '1988-01-15', 'YJS'),
      (4, '李四2', '001', '1979-03-10', 'BK'),
      (5, '李四3', '003', '1995-08-16', 'YJS');

创建了一个名称为demo的数据库；并在库里创建了名称为T_TEACHER的教师表并向表中插入了数据

二、环境准备

1、添加依赖

<dependency>
    <groupId>org.mybatis.scripting</groupId>
    <artifactId>mybatis-velocity</artifactId>
    <version>2.1.0</version>
</dependency>

2、创建实体类

在cn.horse.demo下创建TeacherInfo、TeacherInfoQuery实体类：

TeacherInfo类：

package cn.horse.demo;

import java.time.LocalDate;

public class TeacherInfo {
    private Integer id;
    private String name;
    private String department;
    private LocalDate birth;
    private String degree;

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

    public Integer getId() {
        return id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setDepartment(String department) {
        this.department = department;
    }

    public String getDepartment() {
        return department;
    }

    public void setBirth(LocalDate birth) {
        this.birth = birth;
    }

    public LocalDate getBirth() {
        return birth;
    }

    public void setDegree(String degree) {
        this.degree = degree;
    }

    public String getDegree() {
        return degree;
    }

    @Override
    public String toString() {
        StringBuilder stringBuilder = new StringBuilder();
        stringBuilder.append("{ ");
        stringBuilder.append("id: ");
        stringBuilder.append(this.id);
        stringBuilder.append(", ");
        stringBuilder.append("name: ");
        stringBuilder.append(this.name);
        stringBuilder.append(", ");
        stringBuilder.append("department: ");
        stringBuilder.append(this.department);
        stringBuilder.append(", ");
        stringBuilder.append("birth: ");
        stringBuilder.append(this.birth);
        stringBuilder.append(", ");
        stringBuilder.append("degree: ");
        stringBuilder.append(this.degree);
        stringBuilder.append(" }");
        return stringBuilder.toString();
    }
}

TeacherInfoQuery类：

package cn.horse.demo;

public class TeacherInfoQuery {

    private String department;
    private String degree;

    public void setDepartment(String department) {
        this.department = department;
    }

    public String getDepartment() {
        return department;
    }

    public void setDegree(String degree) {
        this.degree = degree;
    }

    public String getDegree() {
        return degree;
    }
}

3、Mapper配置文件

在resources的目录下新建TeacherInfoMapper.xml配置文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="cn.horse.demo.TeacherInfoMapper">

</mapper>

4、动态语言配置

在resources下新建mybatis-config.xml配置文件，配置velocity默认的脚本语言，并引入TeacherInfoMapper.xml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>
    <settings>
        <setting name="logImpl" value="JDK_LOGGING"/>
        <setting name="defaultScriptingLanguage" value="org.mybatis.scripting.velocity.VelocityLanguageDriver"/>
    </settings>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="org.gjt.mm.mysql.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/demo?useUnicode=true&amp;useSSL=false&amp;characterEncoding=utf8"/>
                <property name="username" value="root"/>
                <property name="password" value="horse"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

其中<setting name="defaultScriptingLanguage" value="org.mybatis.scripting.velocity.VelocityLanguageDriver"/>用于配置velocity作为默认的动态语言

5、日志配置

在resources的目录下新建logging.properties配置文件

handlers=java.util.logging.ConsoleHandler
.level=INFO

cn.horse.demo.TeacherInfoMapper.level=FINER
java.util.logging.ConsoleHandler.level=ALL
java.util.logging.ConsoleHandler.formatter=java.util.logging.SimpleFormatter
java.util.logging.SimpleFormatter.format=%1$tY-%1$tm-%1$td %1$tT.%1$tL %4$s %3$s - %5$s%6$s%n

在cn.horse.demo下新建JdkLogConfig类：

JdkLogConfig类：

package cn.horse.demo;

import java.io.IOException;
import java.io.InputStream;
import java.util.logging.LogManager;

public class JdkLogConfig {

    public JdkLogConfig() {
        try {
            InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("logging.properties");
            LogManager.getLogManager().readConfiguration(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

6、会话工具类

在cn.horse.demo包下新建SqlSessionUtils工具类

package cn.horse.demo;

import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.InputStream;
import java.util.Objects;

public class SqlSessionUtils {

    private static final SqlSessionFactory sqlSessionFactory;
    static {
        // 读取mybatis配置文件
        InputStream inputStream = ClassLoader.getSystemClassLoader().getResourceAsStream("mybatis-config.xml");
        // 根据配置创建SqlSession工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder()
                .build(inputStream);
    }

    /**
     * 开启会话
     * @return
     */
    public static SqlSession openSession() {
        return sqlSessionFactory.openSession();
    }

    /**
     * 关闭会话
     * @param sqlSession
     */
    public static void closeSession(SqlSession sqlSession) {
        if(Objects.nonNull(sqlSession)) {
            sqlSession.close();
        }
    }
}

7、启动程序配置

package cn.horse.demo;

import org.apache.ibatis.session.SqlSession;

import java.util.List;

public class Main {
    public static void main(String[] args) {
        // 引入JDK日志配置
        System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");
    }

    private static void find(String statement, TeacherInfoQuery query) {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionUtils.openSession();
            List<TeacherInfo> teacherInfoList = sqlSession.selectList(statement, query);
            for (TeacherInfo teacherInfo: teacherInfoList) {
                System.out.println(teacherInfo);
            }
        } finally {
            SqlSessionUtils.closeSession(sqlSession);
        }
    }

    private static void insert(String statement, List<TeacherInfo> teacherInfoList) {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionUtils.openSession();
            sqlSession.insert(statement, teacherInfoList);
            sqlSession.commit();
        } finally {
            SqlSessionUtils.closeSession(sqlSession);
        }
    }

    private static void update(String statement, TeacherInfo teacherInfo) {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionUtils.openSession();
            sqlSession.update(statement, teacherInfo);
            sqlSession.commit();
        } finally {
            SqlSessionUtils.closeSession(sqlSession);
        }
    }

    private static void delete(String statement, List<Integer> idList) {
        SqlSession sqlSession = null;
        try {
            sqlSession = SqlSessionUtils.openSession();
            sqlSession.delete(statement, idList);
            sqlSession.commit();
        } finally {
            SqlSessionUtils.closeSession(sqlSession);
        }
    }
}

启动程序中，我们提供了新增、删除、修改、查询等方法，用于测试使用

三、查询数据

在TeacherInfoMapper.xml配置文件中新增findByQuery查询语句：

<select id="find" resultType="cn.horse.demo.TeacherInfo">
    SELECT
        ID,
        TEACHER_NAME name,
        DEPARTMENT,
        BIRTH,
        DEGREE
    FROM T_TEACHER
    #where()
        #if($_parameter.degree and '' != $_parameter.degree)
            AND DEGREE = @{_parameter.degree}
        #end
        #if($_parameter.department and '' != $_parameter.department)
            AND DEPARTMENT = @{_parameter.department}
        #end
    #end
</select>

#where()类似于<where>标签；

#if()类似于<if>标签，第一个标签代表的是degree不为null并且不为空字符串，第二个标签代表的是department不为null并且不为空字符串；

取参数值时使用

$_parameter.参数名

格式，例如：我们获取degree参数值时使用$_parameter.degree

预处理参数使用

@{_parameter.参数名}

格式，例如：我们预处理degree参数时使用@{_parameter.degree}

测试：

// 引入JDK日志配置
System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");

// 查询学历为本科的教师
TeacherInfoQuery query = new TeacherInfoQuery();
query.setDegree("BK");
find("cn.horse.demo.TeacherInfoMapper.find", query);

执行后的结果如下：

四、批量插入数据

在TeacherInfoMapper.xml配置文件中新增insert插入语句：

<insert id="insert">
    INSERT INTO T_TEACHER(ID, TEACHER_NAME, DEPARTMENT, BIRTH, DEGREE)
    #repeat($_parameter.list $teacherInfo "," "VALUES " "")
        (@{teacherInfo.id}, @{teacherInfo.name}, @{teacherInfo.department}, @{teacherInfo.birth}, @{teacherInfo.degree})
    #end
</insert>

#repeat类似于<foreach>标签，其格式为

#repeat(collection var separator open close)

#end

collection：数组或可迭代对象

var：数组中的元素或本次迭代的元素

separator：迭代之间的分隔符

open：指定开头的字符串

close：指定结尾的字符串

测试： 

// 引入JDK日志配置
System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");

List<TeacherInfo> teacherInfoList = new ArrayList<>();
TeacherInfo teacherInfo1 = new TeacherInfo();
teacherInfo1.setId(11);
teacherInfo1.setName("张三11");
teacherInfo1.setDepartment("001");
teacherInfo1.setBirth(LocalDate.of(1988, 5, 20));
teacherInfo1.setDegree("BK");
teacherInfoList.add(teacherInfo1);

TeacherInfo teacherInfo2 = new TeacherInfo();
teacherInfo2.setId(12);
teacherInfo2.setName("李四12");
teacherInfo2.setDepartment("003");
teacherInfo2.setBirth(LocalDate.of(1989, 8, 10));
teacherInfo2.setDegree("ZK");
teacherInfoList.add(teacherInfo2);
insert("cn.horse.demo.TeacherInfoMapper.insert", teacherInfoList);

执行的结果如下：

五、更新数据

在TeacherInfoMapper.xml配置文件中新增update更新语句：

<update id="update">
    UPDATE T_TEACHER
    #mset()
        #if($_parameter.name and '' != $_parameter.name)
            TEACHER_NAME = @{_parameter.name},
        #end
        #if($_parameter.department and '' != $_parameter.department)
            DEPARTMENT = @{_parameter.department},
        #end
        #if($_parameter.birth)
            BIRTH = @{_parameter.birth},
        #end
        #if($_parameter.degree and '' != $_parameter.degree)
            DEGREE = @{_parameter.degree},
        #end
    #end
    WHERE ID = @{_parameter.id}
</update>

#mset类似于<set>标签

测试： 

// 引入JDK日志配置
System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");

TeacherInfo teacherInfo = new TeacherInfo();
teacherInfo.setId(11);
teacherInfo.setName("张三22");
update("cn.horse.demo.TeacherInfoMapper.update", teacherInfo);

执行的结果如下：

六、批量删除数据

在TeacherInfoMapper.xml配置文件中新增delete删除语句：

<delete id="delete">
    DELETE FROM T_TEACHER
    WHERE ID IN
    #repeat($_parameter.list $id "," "(" ")")
        @{id}
    #end
</delete>

测试： 

// 引入JDK日志配置
System.setProperty("java.util.logging.config.class", "cn.horse.demo.JdkLogConfig");

delete("cn.horse.demo.TeacherInfoMapper.delete", Arrays.asList(11, 12));

执行的结果如下：