Hibernate之ORM功能模块实现-优快云博客

本文介绍了一个简单的ORM框架实现过程，包括连接数据库、插入、删除、更新及查询操作，并通过Java反射机制动态生成SQL语句。

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Hibernate的ORM功能，简而言之就是用户传一个任意对象进去，然后系统自动生成相应的SQL语句并执行

因此，实现一个简易的ORM模块并不难，关键就在于对JAVA反射机制的使用和SQL语句的拼凑

基本思路是：

· 根据传入的Object来得到数据库的表名

· 得到属性名和对应的值

· 将所得信息进行整合，拼凑一条SQL语句

代码：

1. 定义两个测试用的POJO类（省略get和set方法）

public class UserInfo {
	
	private int id;
	private String userName;
	private String userPwd;
	private int userAge;

}

public class Article {
	private int id;
    private String title;
    private String author;
    private String content;
    
}

2. 然后写个数据库的连接静态类

import java.sql.Connection;
import java.sql.DriverManager;

public class DBConnector {

	public static Connection conn;
	
	public static boolean buildConn(){
		try{
	    	Class.forName("com.mysql.jdbc.Driver");
	    	String url = "jdbc:mysql://localhost:3306/test";
	    	conn = DriverManager.getConnection(url,"root","password");
	    	return true;
	    }catch(Exception e){
	    	e.printStackTrace();
	    }
		return false;
	}
}

3. 接下来是主体部分了

import java.lang.reflect.Method;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;

import cn.netjava.dao.DBConnector;
import cn.netjava.pojo.Article;
import cn.netjava.pojo.UserInfo;

public class ORMmodel {

	/**
	 * 插入数据
	 * @param obj 需要保存的对象
	 * @return 保存是否成功
	 */
	public boolean insert(Object obj){
		String sql = "insert into ";
		//得到表名
		String tableName = obj.getClass().getName();
		sql = sql + tableName.substring(tableName.lastIndexOf(".")+1) + "(";
		//得到properties和values
		Method[] methods = obj.getClass().getMethods();
		ArrayList<String> properties = getProperties(methods);
		ArrayList<Object> values = getValues(methods,obj);
		//拼接sql语句
		String sql1 = "";
		String sql2 = ") value (";
		for(int i=0;i<properties.size();i++){
			String property = properties.get(i);
			Object value = values.get(i);
			if(property.equals("Id")){//插入时id属性不需要处理，跳过
				continue;
			}
			sql1 += property + ",";
			sql2 += "'" + value + "',";
		}
		sql += sql1.substring(0,sql1.length()-1) + sql2.substring(0,sql2.length()-1) + ")";
		try{
			Statement state = DBConnector.conn.createStatement();
			state.executeUpdate(sql);
			return true;
			
		}catch(Exception e){
			e.printStackTrace();
		}
		return false;
	}
	/**
	 * 删除对象
	 * @param obj
	 * @return
	 */
	public boolean delete(Object obj){
		String sql = "delete from ";
		//得到表名
		String tableName = obj.getClass().getName();
		sql = sql + tableName.substring(tableName.lastIndexOf(".")+1) + " where ";
		//得到properties和values
		Method[] methods = obj.getClass().getMethods();
		ArrayList<String> properties = getProperties(methods);
		ArrayList<Object> values = getValues(methods,obj);
		//拼接sql语句
		for(int i=0;i<properties.size();i++){
			String property = properties.get(i);
			Object value = values.get(i);
			
			if(property!=null&&value!=null){
				if(value instanceof Integer){              //如果属性类型为int而且
					int a = ((Integer) value).intValue();  //没被赋值时，默认是0，所以
					if(a==0){                              //此处对值为值为0的属性不做
						continue;                          //处理，跳过
					}                                      //（此处理只适用于不会出现值
				}                                          //为0的属性的对象，仅供测试）
				sql += property + "='" + value.toString() + "' and ";
			}
		}
		sql = sql.substring(0, sql.length()-5);
		try{
			Statement state = DBConnector.conn.createStatement();
			state.executeUpdate(sql);
			return true;
		}catch(Exception e){
			e.printStackTrace();
		}
		return false;
	}
	/**
	 * 修改对象
	 * @param obj
	 * @return
	 */
	public boolean update(Object obj){
		String sql = "update ";
		//得到表名
		String tableName = obj.getClass().getName();
		sql += tableName.substring(tableName.lastIndexOf(".")+1) + " set ";
		//得到properties和values
		Method[] methods = obj.getClass().getMethods();
		ArrayList<String> properties = getProperties(methods);
		ArrayList<Object> values = getValues(methods,obj);
		//拼接sql语句
		String id = null;
		for(int i=0;i<properties.size();i++){
			String property = properties.get(i);
			Object value = values.get(i);
			if(property.equals("Id")){
				id = value.toString();
				continue;
			}
			if(value instanceof Integer){
				int a = ((Integer) value).intValue();
				if(a==0){
					continue;
				}
			}
			sql += property + "='" + value.toString() + "',";
		}
		sql = sql.substring(0,sql.length()-1) + " where id='" + id + "'";
		try{
			Statement state = DBConnector.conn.createStatement();
			state.executeUpdate(sql);
			return true;
		}catch(Exception e){
			e.printStackTrace();
		}
		return false;
	}
	/**
	 * 查找所有包含指定属性的Object
	 * @param obj
	 * @return
	 */
	public ArrayList<Object> search(Object obj){
		ArrayList<Object> list = new ArrayList<Object>();
		String sql = "select * from ";
		//得到表名
		String tableName = obj.getClass().getName();
		sql += tableName.substring(tableName.lastIndexOf(".")+1) + " where ";
		//得到properties和values
		Method[] methods = obj.getClass().getMethods();
		ArrayList<String> properties = getProperties(methods);
		ArrayList<Object> values = getValues(methods,obj);
		//拼接sql语句
		for(int i=0;i<properties.size();i++){
			String property = properties.get(i);
			Object value = values.get(i);
			
			if(property!=null&&value!=null){
				if(value instanceof Integer){
					int a = ((Integer) value).intValue();
					if(a==0){
						continue;
					}
				}
				sql += property + "='" + value.toString() + "' and ";
			}
		}
		sql = sql.substring(0,sql.length()-5);
		try{
			Statement state = DBConnector.conn.createStatement();
			ResultSet set = state.executeQuery(sql);
			while(set.next()){
				if(tableName.substring(tableName.lastIndexOf(".")+1).equals("UserInfo")){
					UserInfo user = new UserInfo();
					user.setUserAge(set.getInt("userage"));
					user.setId(set.getInt("id"));
					user.setUserName(set.getString("username"));
					user.setUserPwd(set.getString("userpwd"));
					list.add(user);
				}
				if(tableName.substring(tableName.lastIndexOf(".")+1).equals("Article")){
					Article article = new Article();
					article.setAuthor(set.getString("author"));
					article.setId(set.getInt("id"));
					article.setContent(set.getString("content"));
					article.setTitle(set.getString("title"));
					list.add(article);
				}
			}
			return list;
		}catch(Exception e){
			e.printStackTrace();
		}
		return null;
	}
	/**
	 * 根据方法名得到属性名的List
	 * @param methods
	 * @return
	 */
	private ArrayList<String> getProperties(Method[] methods){
		ArrayList<String> properties = new ArrayList<String>();
		for(Method m : methods){
			String methodName = m.getName();
			if(methodName.startsWith("get")&&!methodName.equals("getClass")){
				String property = methodName.substring(3);
				properties.add(property);
			}
		}
		return properties;
	}
	/**
	 * 得到属性对应的value
	 * @param methods
	 * @param obj
	 * @return
	 */
	private ArrayList<Object> getValues(Method[] methods,Object obj){
		ArrayList<Object> values = new ArrayList<Object>();
		for(Method m : methods){
			String methodName = m.getName();
			if(methodName.startsWith("get")&&!methodName.equals("getClass")){
				try{
					Object value = m.invoke(obj, null);
					values.add(value);
				}catch(Exception e){
					e.printStackTrace();
				}
			}
		}
		return values;
	}
}

4. 最后再自己写个main函数测试下

特别说明：

·以上代码测试前需要准备好一个数据库并预先定义好userinfo和article表

·修改数据时id属性不能为0（未定义的话id也会默认为0滴）