MyBatis之Mapper动态代理

通过之前的学习,已经了解了MyBatis下传统三层模式如何运作了

现在会将以前的部分知识点与今天要学习的知识点进行对比学习

回顾:

• SQL映射文件的namespace随意命名
• SQL映射文件中的SQLID可以随意命名
• dao层操作数据库需要创建接口(UserDao)实现类(UserDaoImpl)对象
• 找寻SQL语句的方式,通过在SqlSession中指定参数:"nameSpace+SQLID"

Mapper动态代理:

• SQL映射文件的namespace必须和mapper接口的全限定类名保持一致
• mapper接口的接口方法名必须和xml中的SQL语句ID保持一致
• mapper接口的接口方法形参类型必须和SQL语句的输入参数类型保持一致
• mapper接口的接口方法返回类型必须和sql语句的resultType保持一致

下面会将之前的案例通过Mapper动态代理的方式翻新下!

一.案例展示

1.测试准备

①数据库mysql一枚

②database名为batistest且表名为user

③项目工程

2.代码展示(着重观察UserMapper.java和UserMapper.xml)

***pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.howie</groupId>
    <artifactId>mybatis_proxy</artifactId>
    <version>1.0-SNAPSHOT</version>
    
    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencies>
        <!--单元测试-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <!--log4j-->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
    </dependencies>
</project>

***bean.properties

UserService=com.howie.service.impl.UserServiceImpl

***db.properties

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/batistest?characterEncoding=utf-8
jdbc.username=root
jdbc.password=root

***User.java

package com.howie.pojo;

import java.util.Date;

/**
 * @Author weihuanwen
 * @Date 2019/8/9 9:54
 * @Version 1.0
 */
public class User {

    private Integer id;
    private String username;
    private Integer sex;
    private Date birthday;
    private String address;

    public Integer getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Integer getSex() {
        return sex;
    }

    public void setSex(Integer sex) {
        this.sex = sex;
    }

    public Date getBirthday() {
        return birthday;
    }

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

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

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

***BeanFactory.java

package com.howie.utils;


import org.apache.ibatis.session.SqlSession;

import java.lang.reflect.Constructor;
import java.util.ResourceBundle;

/**
 *  Bean工厂对象
 *  方法:
 *    传递接口,传递的是接口的class文件对象
 *    返回实现类的对象
 *
 *    泛型: 本身没有类型,未知的数据类型
 *    调用的时候,传递什么,就是什么类型
 */
public class BeanFactory {
    public static <T>T newInstance(Class<T> clazz){
        //获取传递的接口名
        String name = clazz.getSimpleName();
        //读取配置文件
        ResourceBundle resourceBundle = ResourceBundle.getBundle("bean");
        String className = resourceBundle.getString(name);
        //反射创建对象
        try {
            return (T)Class.forName(className).newInstance();
        }catch (Exception ex){
            ex.printStackTrace();
        }
        return null;
    }

    /**
     *  带参构造
     * @param clazz
     * @param sqlSession
     * @param <T>
     * @return
     */
    public static <T>T newInstance(Class<T> clazz, SqlSession sqlSession){
        //获取传递的接口名
        String name = clazz.getSimpleName();
        //读取配置文件
        ResourceBundle resourceBundle = ResourceBundle.getBundle("bean");
        String className = resourceBundle.getString(name);
        //获取带参构造函数
        try {
            Constructor constructor = Class.forName(className).getConstructor(SqlSession.class);
            Object[] params = {sqlSession};
            //反射创建对象
            return (T)constructor.newInstance(params);
        }catch (Exception ex){
            ex.printStackTrace();
        }
        return null;
    }
}

***SqlMapConfig.xml

<?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>

    <!--
        从外部文件db.properties读取数据库连接信息
    -->
    <properties resource="db.properties"/>

    <!--配置log4j日志-->
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>

    <!--批量起别名-->
    <typeAliases>
        <package name="com.howie.pojo"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--获取db文件中的数据-->
                <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>

    <mappers>
        <mapper resource="UserMapper.xml"/>
    </mappers>
</configuration>   

***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.howie.mapper.UserMapper">

    <!--
        1.根据用户名进行模糊查询
    -->
    <select id="queryUserByName" parameterType="string" resultType="User">
        SELECT
            *
        FROM
            `user`
        WHERE
            `username` LIKE #{username}
    </select>

    <!--
        2.添加用户,并返回新数据的主键ID
    -->
    <insert id="addUser" parameterType="User">
        <selectKey order="AFTER" resultType="int" keyProperty="id" keyColumn="id">
            select LAST_INSERT_ID()
        </selectKey>
        INSERT INTO `user` ( `username`, `sex`, `birthday`, `address` )
        VALUES
        ( #{username}, #{sex}, #{birthday}, #{address} )
    </insert>
    <!--
        3.删除指定用户的用户信息
    -->
    <delete id="delUser" parameterType="string">
        DELETE
        FROM
            `user`
        WHERE
            `username` = #{username}
    </delete>
    <!--
        4.更新指定用户的地址信息
    -->
    <update id="updateUser" parameterType="User">
        UPDATE `user`
        SET `address` = #{address}
        WHERE
            `username` = #{username}
    </update>
</mapper>

***UserMapper.java

package com.howie.mapper;

import com.howie.pojo.User;
import java.util.List;

/**
 * @Author weihuanwen
 * @Date 2019/8/9 10:03
 * @Version 1.0
 */
public interface UserMapper {

    /**
     * 1.根据用户名进行模糊查询->#{}取值
     * @param username
     * @return
     */
    List<User> queryUserByName(String username);

    /**
     * 2.添加用户并获取新数据主键
     * @param user
     */
    void addUser(User user);

    /**
     * 3.删除指定用户名的用户信息
     * @param username
     */
    void delUser(String username);
    /**
     * 4.更新用户地址信息
     * @param user
     */
    void updateUser(User user);
}

***UserService.java

package com.howie.service;

import com.howie.pojo.User;

import java.util.List;

/**
 * @Author weihuanwen
 * @Date 2019/8/9 10:56
 * @Version 1.0
 */
public interface UserService {

    /**
     * 1.根据用户名进行模糊查询->#{}取值
     * @param username
     * @return
     */
    List<User> queryUserByName1(String username);

    /**
     * 2.根据用户名进行模糊查询->${}取值
     * @param username
     * @return
     */
    List<User> queryUserByName2(String username);

    /**
     * 添加用户
     * @param user
     */
    void addUser(User user);

    /**
     * 删除指定用户名的用户信息
     * @param username
     */
    void delUser(String username);
    /**
     * 更新用户地址信息
     * @param user
     */
    void updateUser(User user);
}

***UserServiceImpl.java

package com.howie.service.impl;

import com.howie.mapper.UserMapper;
import com.howie.pojo.User;
import com.howie.service.UserService;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

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

/**
 * @Author weihuanwen
 * @Date 2019/8/9 10:56
 * @Version 1.0
 */
public class UserServiceImpl implements UserService {

    private static UserMapper userMapperImpl;

    static {
        try {
            SqlSessionFactoryBuilder ssfb = new SqlSessionFactoryBuilder();
            //加载SqlMapConfig.xml文件
            InputStream is = Resources.getResourceAsStream("SqlMapConfig.xml");
            SqlSessionFactory ssf = ssfb.build(is);
            SqlSession sqlSession = ssf.openSession();
            userMapperImpl = sqlSession.getMapper(UserMapper.class);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * 1.根据用户名进行模糊查询->#{}取值
     * @param username
     * @return
     */
    @Override
    public List<User> queryUserByName(String username){
        List<User> userList = userMapperImpl.queryUserByName(username);
        return userList;
    }

    /**
     * 2.添加用户并获取新数据主键
     * @param user
     */
    @Override
    public void addUser(User user) {
        userMapperImpl.addUser(user);
    }

    /**
     * 3.删除指定用户名的用户信息
     * @param username
     */
    @Override
    public void delUser(String username) {
        userMapperImpl.delUser(username);
    }
    /**
     * 4.更新用户地址信息
     * @param user
     */
    @Override
    public void updateUser(User user) {
        userMapperImpl.updateUser(user);
    }
}

***UserController.java

package com.howie.controller;

import com.howie.pojo.User;
import com.howie.service.UserService;
import com.howie.utils.BeanFactory;
import org.junit.Test;

import java.util.Date;
import java.util.List;

/**
 * @Author weihuanwen
 * @Date 2019/8/9 11:19
 * @Version 1.0
 */
public class UserController {

    private UserService userService = BeanFactory.newInstance(UserService.class);

    @Test
    public void test1(){
        List<User> userList = userService.queryUserByName("%张%");
        System.out.println(userList);
    }

    @Test
    public void test2(){
        User user = new User();
        user.setUsername("Jhon");
        user.setSex(2);
        user.setBirthday(new Date());
        user.setAddress("我是一匹来自北方的狼");
        userService.addUser(user);
        System.out.println("回显主键ID ::: "+user.getId());
    }

    @Test
    public void test3(){
        User user = new User();
        user.setUsername("Jhon");
        user.setAddress("一个遥远的地方");
        userService.updateUser(user);
    }
    @Test
    public void test4(){
        userService.delUser("Jhon");
    }
}

3.测试

①执行test1

**控制台输出:

[User{id=1, username='张三', sex=1, birthday=Tue Jul 10 00:00:00 CST 2018, address='北京'}]

②执行test2

**控制台输出:

回显主键ID ::: 7

**数据库表

③执行test3

**数据库表

④执行test4

**数据库表

二.总结

1.Mapper动态代理中是如何查找SQL语句的?

2.XML配置文件名称空间的省略写法

①将UserMapper.xml文件同UserMapper.java放置在相同的包体下,如下图:

②UserMapper.xml名称空间重新定义为:

<mapper namespace="com.howie.mapper.UserMapper">
    ....
    other code
    ....
</mapper>

③SqlMapConfig.xml重新修改配置

<mappers>
  <!--
     Mapper动态代理的第二种方式
     编译之后,配置文件XxxMapper.xml必须与XxxMapper接口文件在同一目录下
   -->
  <!--逐一完成配置文件注册-->
  <!--<mapper class="mapper.UserMapper" />-->
  <!--批量完成配置文件注册-->
  <package name="mapper" />
</mappers>

③原因:如果按照上面的包结构,UserMapper.xml和UserMapper.java在打包时会出现在同一个包mapper下

3.运行时常遇到的错误

java.lang.ExceptionInInitializerError

• 请检查SqlMapConfig.xml中关于sql配置文件UserMapper.xml注册时写的路径是否正确.一定要是全路径
• 请检查配置文件UserMapper.xml的名称空间是否正确,一定要是全路径