基于Spring JDBC 手写定制自己的ORM框架

说到ResultSet，对于有java开发经验的小伙伴自然是熟悉不过了。从ResultSet的取值大家都会，比如：

private static List select(String sql) {
       List result = new ArrayList<>();
       Connection con = null;          //连接对象
       PreparedStatement pstm = null;  //语句集
       ResultSet rs = null;            //结果集
       try {
           //1、加载驱动类
           Class.forName("com.mysql.jdbc.Driver");
           //2、建立连接
           con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/spring-db-demo","root","123456");
            //3、创建语句集
            pstm =  con.prepareStatement(sql);
            //4、执行语句集
            rs = pstm.executeQuery();
            while (rs.next()){
                //纯粹的硬编码
                Member instance = new Member();
                instance.setId(rs.getLong("id"));
                instance.setName(rs.getString("name"));
                instance.setAge(rs.getInt("age"));
                instance.setAddr(rs.getString("addr"));
                result.add(instance);
            }
            //5、获取结果集
        }catch (Exception e){
            e.printStackTrace();
        }
        //6、关闭结果集、关闭语句集、关闭连接
        finally {
            try {
                rs.close();
                pstm.close();
                con.close();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
        return result;
    }

这是我们之前没用框架的常规操作。但是随着业务和开发量的增加，我们可以发现在数据持久层这样的重复代码出现频次非常高。因此我们第一步想到的都是将非功能性代码和业务代码进行分离。大家首先想到的应该都是将封装数据的代码部分进行分离，类似如下代码：

private static List select(String sql) {
        List result = new ArrayList<>();
        Connection con = null;
        PreparedStatement pstm = null;
        ResultSet rs = null;
        try {
            //1、加载驱动类
            Class.forName("com.mysql.jdbc.Driver");
            //2、建立连接
            con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/spring-db-demo","root","123456");
            //3、创建语句集
            pstm =  con.prepareStatement(sql);
            //4、执行语句集
            rs = pstm.executeQuery();
            while (rs.next()){
                Member instance = mapperRow(rs,rs.getRow());
                result.add(instance);
            }
            //5、获取结果集
        }catch (Exception e){
            e.printStackTrace();
        }
        //6、关闭结果集、关闭语句集、关闭连接
        finally {
            try {
                rs.close();
                pstm.close();
                con.close();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
        return result;
    }

    private static Member mapperRow(ResultSet rs, int i) throws Exception {
        Member instance = new Member();
        instance.setId(rs.getLong("id"));
        instance.setName(rs.getString("name"));
        instance.setAge(rs.getInt("age"));
        instance.setAddr(rs.getString("addr"));
        return instance;
    }

但是在日常开发中，这样的代码逻辑重复率还是太高，上面的改造只能应用Member这个类，换一个类有需要重新封装，所以太过麻烦，这个时候我们不妨做出如下改进：

首先创建Member类：

@Entity
@Table(name = "t_member")
public class Member implements Serializable {
    @Id
    private Long id;
    private String name;
    private String addr;
    private Integer age;

    public Member() {
    }

    public Member(String name, String addr, Integer age) {
        this.name = name;
        this.addr = addr;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Member{" +
                "id=" + id +
                ", name='" + name + ''' +
                ", addr='" + addr + ''' +
                ", age=" + age +
                '}';
    }

    public Long getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getAddr() {
        return addr;
    }

    public void setAddr(String addr) {
        this.addr = addr;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }
}

对JDBC操作优化：

   public static void main(String[] args) {

        Member condition = new Member();
        condition.setName("TomCat");
        List result = select(condition);
        System.out.println(JSON.toJSONString(result,true));
    }

    public static List select(Object condition) {

        List