模拟Hibernate框架的小demo

该程序为尚学堂马士兵老师讲解，模拟了hibernate的原理，主要应用了字符串拼接，反射知识。

step1,新建数据库

use jd;
create table _student(
_id int(11),
_nage varchar(20),
_age int(11));

step 2 student实体类，再次略过

step3,编写session类，模拟hibernate的实现原理。

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;

import com.bjsxt.hibernate.model.Student;

public class Session {
	static String tableName = "_Student";
	static Map<String, String> cfs = new HashMap<String, String>();
	static String[] methodNames;

	public Session() {
		cfs.put("_id", "id");
		cfs.put("_name", "name");
		cfs.put("_age", "age");
		methodNames = new String[cfs.size()];
	}

	public static void save(Student s) throws Exception {
		// TODO Auto-generated method stub
		int index = 0;
		String sql = createSql();

		try {
			Class.forName("com.mysql.jdbc.Driver");
			Connection conn = DriverManager.getConnection(
					"jdbc:mysql://localhost/jd", "root", "123456");
			PreparedStatement ps = conn.prepareStatement(sql);
				

			for (int i = 0; i < methodNames.length; i++) {
				Method m = s.getClass().getMethod(methodNames[i]);
				Class r = m.getReturnType();
				if (r.getName().equals("java.lang.String")) {
					String returnValue = (String) m.invoke(s);
					ps.setString(i + 1, returnValue);
					System.out.println(returnValue);
				}
				if (r.getName().equals("int")) {
					Integer returnValue = (Integer) m.invoke(s);
					ps.setInt(i + 1, returnValue);
					System.out.println(returnValue);
				}
				// System.out.println(m.getName()+","+m.getReturnType()+","+r.getName());
			}
			System.out.println(sql);
			ps.executeUpdate();	
			ps.close();
			conn.close();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}

	private static String createSql() {

		String str2 = "";
		String str1 = "";
		int index = 0;
		for (String s : cfs.keySet()) {//s为_id,_Age,_Name
			String v = cfs.get(s);
			v = Character.toUpperCase(v.charAt(0)) + v.substring(1);//Id,Name,Age
			//System.out.println(v+"涛");
			methodNames[index] = "get" + v; // str1+=s+",";//getId,getName,getAge
			//System.out.println(s);
			//System.out.println(methodNames[index]);
			str1 += s + ",";
			index++;
			System.out.println(str1);
		}
		str1 = str1.substring(0, str1.length() - 1);
		//System.out.println(str1);
		for (int i = 0; i < cfs.size(); i++) {

			if (i == cfs.size() - 1) {
				str2 += "?";
			} else {
				str2 += "?,";
			}

		}
		//System.out.println(str2);
		String sql = "insert into " + tableName + "(" + str1 + ")"
				+ " values (" + str2 + ")";
		System.out.println(sql+"createSql方法里面");
		return sql;
	}

}

step4，测试，

import com.bjsxt.hibernate.model.Student;
public class StudentTest {

	public static void main(String[] args) throws Exception {

		Student s = new Student();
		s.setId(10);
		s.setName("s1");
		s.setAge(1);		
		Session session = new Session();
		session.save(s);
	}
}