利用反射机制，将表跟BEAN对象关联的原理

理解了这一点，就能明白如HIBERNATE等ORM框架的一些实现思路了

 

package joeho.blog.jdbc;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import joeho.blog.jdbc.domain.User;

public class ORMTest {

 /**
  * @param args
  * @throws Exception
  * @throws InvocationTargetException
  * @throws IllegalAccessException
  * @throws SQLException
  */
 public static void main(String[] args) throws SQLException,
   IllegalAccessException, InvocationTargetException, Exception {
  User user = (User) getObject(
    "select id as Id, name as Name, birthday as Birthday, money as Money  from user where id=1",
    User.class);
  System.out.println(user);

  Bean b = (Bean) getObject(
    "select id as Id, name as Name, birthday as Birthday, money as Money from user where id=1",
    Bean.class);
  System.out.println(b);
 }

 static List<Object> getObjects(String sql, Class clazz)
   throws SQLException, Exception, IllegalAccessException,
   InvocationTargetException {
  Connection conn = null;
  PreparedStatement ps = null;
  ResultSet rs = null;
  try {
   conn = JdbcUtils.getConnection();
   ps = conn.prepareStatement(sql);
   rs = ps.executeQuery();
   String[] colNames = getColNames(rs);

   List<Object> objects = new ArrayList<Object>();
   Method[] ms = clazz.getMethods();
   while (rs.next()) {
    Object object = clazz.newInstance();
    for (int i = 0; i < colNames.length; i++) {
     String colName = colNames[i];
     String methodName = "set" + colName;
      }
     for (Method m : ms) {
      if (methodName.equals(m.getName())) {
       m.invoke(object, rs.getObject(colName));
       break;
      }
     }
     objects.add(object);
    }
   }
   return objects;
  } finally {
   JdbcUtils.free(rs, ps, conn);
  }
 }

 private static String[] getColNames(ResultSet rs) throws SQLException {
  ResultSetMetaData rsmd = rs.getMetaData();
  int count = rsmd.getColumnCount();
  String[] colNames = new String[count];
  for (int i = 1; i <= count; i++) {
   colNames[i - 1] = rsmd.getColumnLabel(i);
  }
  return colNames;
 }

 

 static Object getObject(String sql, Class clazz) throws SQLException,
   Exception, IllegalAccessException, InvocationTargetException {
  Connection conn = null;
  PreparedStatement ps = null;
  ResultSet rs = null;
  try {
   conn = JdbcUtils.getConnection();
   ps = conn.prepareStatement(sql);
   rs = ps.executeQuery();
   String[] colNames = getColNames(rs);//得到所有列名

   Object object = null;
   Method[] ms = clazz.getMethods();//BEAN对象的方法名
   if (rs.next()) {
    object = clazz.newInstance();
    for (int i = 0; i < colNames.length; i++) {
     String colName = colNames[i];
     String methodName = "set" + colName;
   }
     for (Method m : ms) {
      if (methodName.equals(m.getName())) {//判断方法名跟列名是否相等
       m.invoke(object, rs.getObject(colName));//注入BEAN对象
       break;
      }
     }
    }
   }
   return object;
  } finally {
   JdbcUtils.free(rs, ps, conn);
  }
 }
}