Mybatis的简单模仿实现

迷南。 2022-04-22 05:44 209阅读 0赞

通过网上的各种资源，结合自身，模仿出Mybatis的简单实现，下面是主要代码：项目是一个普通Java项目，只要导入数据库的Jar包就行（我使用的是Mysql） 其实也就是底层jdbc的实现，底层查询数据库基本就是通过给一个查询语句，使用原生的jdbc实现来查询出结果，其中主要的五个步骤是：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2ODI3OTU3_size_16_color_FFFFFF_t_70][]

不多说，直接上代码：

项目结构：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2ODI3OTU3_size_16_color_FFFFFF_t_70 1][]

package com.lyh;
    
    import java.io.Serializable;
    import java.util.Date;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 实体类
     * @create 2018-11-02 10:39
     * @since 1.7
     */
    public class User implements Serializable{
    
    
        private Long id;
    
        private String userName;
    
        private String userPassword;
    
        private Date gmt_create;
    
        private Date gmt_modified;
    
        private Integer is_status;
    
    
        public Long getId() {
            return id;
        }
    
        public void setId(Long id) {
            this.id = id;
        }
    
        public String getUserName() {
            return userName;
        }
    
        public void setUserName(String userName) {
            this.userName = userName;
        }
    
        public String getUserPassword() {
            return userPassword;
        }
    
        public void setUserPassword(String userPassword) {
            this.userPassword = userPassword;
        }
    
        public Date getGmt_create() {
            return gmt_create;
        }
    
        public void setGmt_create(Date gmt_create) {
            this.gmt_create = gmt_create;
        }
    
        public Date getGmt_modified() {
            return gmt_modified;
        }
    
        public void setGmt_modified(Date gmt_modified) {
            this.gmt_modified = gmt_modified;
        }
    
        public Integer getIs_status() {
            return is_status;
        }
    
        public void setIs_status(Integer is_status) {
            this.is_status = is_status;
        }
    
        @Override
        public String toString() {
            return "User{" +
                    "id=" + id +
                    ", userName='" + userName + '\'' +
                    ", userPassword='" + userPassword + '\'' +
                    ", gmt_create=" + gmt_create +
                    ", gmt_modified=" + gmt_modified +
                    ", is_status=" + is_status +
                    '}';
        }
    }

package com.lyh;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 执行器
     * @create 2018-11-02 9:49
     * @since 1.7
     */
    public interface MyExecutor {
        <T> T query(String statement);
    }

package com.lyh;
    
    import java.lang.reflect.Field;
    import java.sql.*;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 执行器的实现
     * @create 2018-11-02 9:51
     * @since 1.7
     */
    public class MyBaseExecutor implements MyExecutor {
        private static final String URL = "jdbc:mysql://localhost:3306/springboot";
        private static final String USER = "root";
        private static final String PASS = "";
    
    
        @Override
        public <T> T query(String statement) {
    
            Connection conn =null;
            PreparedStatement ps = null;
            ResultSet resultSet = null;
    
            try {
                Class.forName("com.mysql.jdbc.Driver");
                conn = DriverManager.getConnection(URL,USER,PASS);
                String sql = statement;
                ps = conn.prepareStatement(sql);
                resultSet = ps.executeQuery();
    
                Class<?> clazz = User.class;
                Object instance = null;
                if (resultSet.next()){
                    instance = clazz.newInstance();
                    //使用反射进行填充属性
                    Field[] fields = clazz.getDeclaredFields();
                    for (Field field : fields){
                        field.setAccessible(true);
                        field.set(instance,resultSet.getObject(field.getName()));
                    }
                }
                return (T) instance;
            }catch (Exception e) {
                e.printStackTrace();
                return null;
            }finally {
                if (resultSet != null) {
                    try {
                        resultSet.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
                if (ps != null) {
                    try {
                        ps.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
                if (conn != null) {
                    try {
                        conn.close();
                    } catch (SQLException e) {
                        e.printStackTrace();
                    }
                }
    
            }
        }
    }

package com.lyh;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 对类的描述
     * @create 2018-11-02 13:53
     * @since 1.7
     */
    public interface MySqlSession {
        <T> T selectOne(String param);
        <T> T getMapper(Class<T> clazz);
    }

package com.lyh;
    
    import java.lang.reflect.Proxy;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 对类的描述
     * @create 2018-11-02 13:56
     * @since 1.7
     */
    public class MyDefaultSqlSession implements MySqlSession {
    
        private MyExecutor myExecutor = new MyBaseExecutor();
        @Override
        public <T> T selectOne(String param) {
            return myExecutor.query(param);
        }
    
        @Override
        public <T> T getMapper(Class<T> clazz) {
            return (T) Proxy.newProxyInstance(clazz.getClassLoader(),new Class[]{clazz},new MyMapperProxy(this));
        }
    }

package com.lyh;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 对类的描述
     * @create 2018-11-02 11:12
     * @since 1.7
     */
    public interface UserMapper {
    
         // User findUserById(Integer id);
          void insert(User user);
          User findUserById(int id);
    }

package com.lyh;
    
    import java.util.HashMap;
    import java.util.Map;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 对类的描述
     * @create 2018-11-02 11:14
     * @since 1.7
     */
    public class UserMapperXML {
        //相当于xml的命名空间
        public static final String namespace = "com.lyh.UserMapper";
        //相当于select标签
        private static Map<String, String> methodSqlMap = new HashMap<>();
    
        static {
            methodSqlMap.put("findUserById", "select * from user where id = %s");
        }
        public static String getMethodSql(String method) {
            return methodSqlMap.get(method);
        }
    }

package com.lyh;
    
    import java.lang.reflect.InvocationHandler;
    import java.lang.reflect.Method;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 获取mapper，JDK的动态代理
     * @create 2018-11-02 14:01
     * @since 1.7
     */
    public class MyMapperProxy implements InvocationHandler{
        private MySqlSession sqlSession;
        public MyMapperProxy(){}
        public MyMapperProxy(MySqlSession sqlSession){
            this.sqlSession = sqlSession;
        }
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            String mapperClass = method.getDeclaringClass().getName();
            System.out.println("mapperClass"+mapperClass);
            if (UserMapperXML.namespace.equals(mapperClass)){
                String methodName = method.getName();
                String originsql = UserMapperXML.getMethodSql(methodName);
                String formatSql = String.format(originsql,String.valueOf(args[0]));
                return sqlSession.selectOne(formatSql);
            }
            return null;
        }
    }

package com.lyh;
    
    /**
     * @author 633805 LYH
     * @version V1.0
     * @description 首先根据命名空间，找出与mapper接口方法名相同的sql语句，然后交给sqlSession来执行。
     * @create 2018-11-02 14:15
     * @since 1.7
     */
    public class Test {
        public static void main(String[] args) {
            MySqlSession sqlSession = new MyDefaultSqlSession();
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            User user = userMapper.findUserById(1);
            System.out.println(user);
        }
    }

测试结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2ODI3OTU3_size_16_color_FFFFFF_t_70 2][]

下面是我的数据库表结构：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2ODI3OTU3_size_16_color_FFFFFF_t_70 3][]

参考：[https://www.jianshu.com/p/73ee8caddc68?open\_source=weibo\_search][https_www.jianshu.com_p_73ee8caddc68_open_source_weibo_search]

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[https_www.jianshu.com_p_73ee8caddc68_open_source_weibo_search]: https://www.jianshu.com/p/73ee8caddc68?open_source=weibo_search