Hibernate的模拟实现

本例子是不使用Hibernate的jar包，单纯地使用java反射机制、JDBC模拟Hibernate的Session实现对象保存的功能。该程序体现了hibernate在于数据库交互过程中生成SQL语句，识别Getter,Setter方法向数据库插入数据的原理。

Student.java

package com.zenoh.bean;

public class Student {
	private int id ;
	private int age ;
	private String title ;
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	
}

 

 

DBUtil.java

package com.zenoh.db;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBUtil {
	private static Connection conn = null ;
	private static PreparedStatement ps = null ;
	private ResultSet rs = null ;
	
	public static Connection getConnection()
	{
		try {
			Class.forName("com.mysql.jdbc.Driver") ;
			conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/hibernate","root","root") ;
			
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}		
		return conn ;
	}
	
	public static PreparedStatement createStatement(String sql)
	{
		try {
			conn = getConnection() ;
			ps = conn.prepareStatement(sql) ;
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return ps ;
	}

	public static void close()
	{
		try {
			ps.close() ;
			conn.close() ;
		} catch (Exception e) {
			e.printStackTrace() ;
		}
	}
}

 

 

Session.java

 

package com.zenoh.session;

import java.lang.reflect.Method;
import java.sql.PreparedStatement;
import java.util.HashMap;
import java.util.Map;

import com.zenoh.bean.Student;
import com.zenoh.db.DBUtil;

public class Session {
	//先假定数据表名称
	String tableName = "_student" ;
	//保存数据库列名和类的属性名
	Map<String , String> map = new HashMap<String,String>() ;
	//类的属性方法名保存为字符串
	String[] methodNames ; 
	public void save(Student s) {
		PreparedStatement ps = null ;
		map.put("_id", "id") ;
		map.put("_age" , "age") ;
		map.put("_title", "title") ;
		
		methodNames = new String[map.size()] ;//根据map的大小创建属性方法的字符串的个数
		String sql = createSQL() ;//创建SQl语句
		 
		try {
			ps = DBUtil.createStatement(sql) ;
			for(int i=0; i<methodNames.length; i++){
				//利用Method的反射机制获取类的方法
				Method m = s.getClass().getMethod(methodNames[i]) ;
				//获得方法的返回值类型
				Class type = m.getReturnType() ;
				System.out.println(m.getClass() + " || " + m.getReturnType() );
				//根据返回值类型匹配，设置PreparedStatement的值
				if(type.getName().equals("java.lang.String")){
					String returnValue = (String)m.invoke(s) ;
					ps.setString(i+1,returnValue) ;
				}
				if(type.getName().equals("int")){
					Integer returnValue = (Integer)m.invoke(s) ;
					ps.setInt(i+1,returnValue) ;
				}
			}
			ps.executeUpdate() ;
		} catch (Exception e) {
			e.printStackTrace() ;
		}
	}

	private String createSQL() {
		String str1 = "" ;
		String str2 = "" ;
		int index = 0 ;
		for(String s : map.keySet()){
			String v = map.get(s) ;
			//构造方法名称
			methodNames[index] = "get" + Character.toUpperCase(v.charAt(0)) + v.substring(1) ;
			str1 += s + "," ;
			index++ ;
		}
		str1 = str1.substring(0,str1.length()-1) ;
		for(int i=0; i<map.size() ; i++){
			str2 += "?," ;
		}
		str2 = str2.substring(0, str2.length()-1) ;
		String sql = "insert into " + tableName + " (" + str1 + " ) values (" + str2 +")" ;
		
		return sql;
	}

}

 

 

测试类

package com.zenoh.test;

import com.zenoh.bean.Student;
import com.zenoh.session.Session;

public class SessionTest {
	public static void main(String args[])
	{
		Student s = new Student() ;
		s.setAge(20) ;
		s.setTitle("hello") ;
		Session session = new Session() ;
		session.save(s) ;
	}
}

 

 

SQl语句

create table _student(_id int primary key , _age int , _title  varchar(20))