最简单的ORM

1.准备数据库

drop database if exists orm_test;

create database if not exists orm_test character set gbk;

use orm_test;

create table person_table
(
    id int auto_increment primary key,
    name varchar(255) not null,
    age int,
    height int,
    weight float
);

insert into person_table values(null, 'zhangsan', 21, 175, 60);
insert into person_table values(null, 'lisi', 30, 180, 70);
insert into person_table values(null, 'wangwu', 21, 178, 59);
insert into person_table values(null, 'leeyohn', 21, 176, 60);
insert into person_table values(null, 'yun', 22, 168, 50);
insert into person_table values(null, 'zhaoliu', 21, 170, 80);
insert into person_table values(null, 'king', 25, 168, 68);

 

2.编写实体类

public class Person { private int id; private String name; private int age; private int height; private float weight; //无参数构造器 public Person() { } //初始化全部属性的构造器 public Person(int id, String name, int age, int height , float weight) { this.id = id; this.name = name; this.age = age; this.height = height; this.weight = weight; } //id属性的setter和getter方法 public void setId(int id) { this.id = id; } public int getId() { return id; } //name属性的setter和getter方法 public void setName(String name) { this.name = name; } public String getName() { return name; } //age属性的setter和getter方法 public void setAge(int age) { this.age = age; } public int getAge() { return age; } //height属性的setter和getter方法 public void setHeight(int height) { this.height = height; } public int getHeight() { return height; } //weight属性的setter和getter方法 public void setWeight(float weight) { this.weight = weight; } public float getWeight() { return weight; } public String toString() { return "name=" + name + " age=" + age + " height=" + height + " weight=" + weight; } }

 

 

SimpleORM.java

 

import java.lang.reflect.*; import java.sql.*; /* * Copyright 2009-2012 the original author or authors. * Description: * <br/>网站: <a href="http://www.crazyit.org" mce_href="http://www.crazyit.org">疯狂Java联盟</a> * <br/>Program Name: SimpleORM.java * <br/>Project Name: * <br/>Date: 2010-2-11 * @author : leeyohn * @e-mail : leeyohn@hotmail.com * @QQ : 1417515725 * @version : 1.0 */ public class SimpleORM { private Connection conn; private PreparedStatement pstmt; private ResultSet rs; private void getConnection() throws Exception { if (conn == null) { Class.forName("com.mysql.jdbc.Driver"); conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/orm_test", "root", "12345"); } } public Object get(String table, int id, Class<?> clazz) throws Exception { getConnection(); pstmt = conn.prepareStatement("select * from " + table + " where id=?"); pstmt.setInt(1, id); ResultSet rs = pstmt.executeQuery(); if (rs.next()) { Object target = clazz.newInstance(); Method[] methods = clazz.getDeclaredMethods(); //获取结果集元数据 ResultSetMetaData meta = pstmt.getMetaData(); //获取表中列数 int cols = meta.getColumnCount(); for (int i = 0; i < cols; i++) { String colName = meta.getColumnName(i + 1); for (int j = 0; j < methods.length; j++) { //是否匹配setter方法 if (methods[j].getName().equalsIgnoreCase("set" + colName)) { methods[j].invoke(target, rs.getObject(i + 1)); } } } return target; } return null; } public void closeRs() throws Exception { if (rs != null) { rs.close(); } if (pstmt != null) { pstmt.close(); } if (conn != null) { conn.close(); } } public static void main(String[] args) throws Exception { SimpleORM orm = new SimpleORM(); Person p = (Person)orm.get("person_table", 1, Person.class); System.out.println(p); orm.closeRs(); } }