用Java实现简单的 O/R Mapping 模拟

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程序运行条件：MySQL数据库

请自行配置数据库信息，在session.java中进行配置。

本例子使用的数据库语句。

create database hibernate;create table _student(_id int primary key, _name varchar(20), _age int);

文件结构：

两个包：com.test.model Student.java

com.test.testSession.java Test.java

Student.java

package com.test.model;public class Student {

<span style="white-space:pre"></span>//简单的student类private int id; private String name;private int age;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}

Session.java

package com.test.test;import java.lang.reflect.Method;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.util.HashMap;import java.util.Map;import com.test.model.Student;public class Session {String tableName="_student";Map<String ,String > cfs = new HashMap<String ,String>();String[] methodNames ;public Session() {cfs.put("_id","id");cfs.put("_name", "name");cfs.put("_age","age");methodNames = new String[cfs.size()];}public void save(Student s) throws Exception {// TODO Auto-generated method stubString sql = createSQL();Class.forName("com.mysql.jdbc.Driver");Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/hibernate","root","zhaohui");PreparedStatement ps = conn.prepareStatement(sql);for(int i =0 ;i<methodNames.length;i++) {Method m = s.getClass().getMethod( methodNames[i] );<span style="white-space:pre"></span>//利用反射机制调用student的getXXX方法取得其值，然后使用ps对数据库进行赋值Class r =  m.getReturnType();<span style="white-space:pre"></span>//这里用到了反射，不了解请自行百度。System.out.println(m.getName() + "|" + r.getName() );if( r.getName().equals("java.lang.String")){<span style="white-space:pre"></span>//根据插入值类型的不同调用不同的set方法，如setString setIntString returnValue = (String)m.invoke(s);ps.setString( i+1 , returnValue  );}if( r.getName().equals("int")){Integer returnValue = (Integer) m.invoke(s);ps.setInt( i+1 , returnValue  );}} ps.executeUpdate();ps.close();conn.close();}private String createSQL() {// 生成插入语句"insert into _student (_id,_name ,_age) values (?,?,?)"String str1 = "";int index = 0;for(String s : cfs.keySet()){String v = cfs.get(s);v = Character.toUpperCase(v.charAt(0)) + v.substring(1);methodNames[index] = "get" + v;System.out.println("methodNames["+index +"]:"+methodNames[index]);str1 += s + ",";index++;}str1 = str1.substring(0,str1.length()-1);System.out.println(str1);String str2 = "";for(int i =0;i<cfs.size();i++){str2 +="?,";}str2 = str2.substring(0,str2.length()-1);System.out.println(str2);String sql = "insert into " + tableName + "(" +str1 + ")" +  " values ( "+ str2 +  ")";System.out.println(sql);return sql;}}

test.java

package com.test.test;import com.test.model.Student;public class Test {public static void main(String[] args) throws Exception {Student s = new Student();s.setId(3);s.setAge(21);s.setName("tom");Session session = new Session();session.save(s);//session.close();}}

注意运行程序时不要忘了往程序中导入JDBC 的jar包

本例子出自马士兵Java视频中hibernate框架的片段

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