DAO以及获取自动生成主键值

package com.alibaba.sql;

import java.lang.reflect.InvocationTargetException;
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.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.commons.beanutils.BeanUtils;

public class DAO {
    public void update(String sql, Object...args){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        try{
            connection = JDBCTools.getConnection();
            preparedStatement = connection.prepareStatement(sql);
            for(int i = 0; i < args.length; i++){
                preparedStatement.setObject(i + 1, args[i]);
            }
            preparedStatement.executeUpdate();
        }catch (Exception e) {
            e.printStackTrace();
        }
        finally{
            JDBCTools.release(null, preparedStatement, connection);
        }
    }
    
    public <T> T get(Class<T> clazz, String sql, Object...args){
        List<T> list = getForList(clazz, sql, args);
        if(list != null){
            return list.get(0);
        }
        return null;
    }
    
    public <T> List<T> getForList(Class<T> clazz, String sql, Object...args){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        List<T> list = null;
        try{
            connection = JDBCTools.getConnection();
            preparedStatement = connection.prepareStatement(sql);
            for(int i = 0; i < args.length; i++){
                preparedStatement.setObject(i + 1, args[i]);
            }
            resultSet = preparedStatement.executeQuery();
            List<String> label = getLabel(resultSet);
            List<Map<String, Object>> values = getValues(resultSet, label);
            if(values.size() > 0){
                list = valueTolist(clazz, values);
            }
    }catch(Exception e){
        e.printStackTrace();
    }finally{
        JDBCTools.release(resultSet, preparedStatement, connection);
    }
        return list;
    }

    private <T> List<T> valueTolist(Class<T> clazz, List<Map<String, Object>> values) throws InstantiationException,
            IllegalAccessException, InvocationTargetException {
        List<T> list = new ArrayList<T>();
        for(Map<String, Object> map:values){
            T entity = clazz.newInstance();
            for(Map.Entry<String, Object> entry:map.entrySet()){
                String fieldName = entry.getKey();
                Object fieldValue = entry.getValue();
                BeanUtils.setProperty(entity, fieldName, fieldValue);
            }
            list.add(entity);
        }
        return list;
    }

    private List<Map<String, Object>> getValues(ResultSet resultSet,
            List<String> label) throws SQLException {
        List<Map<String, Object>> values = new ArrayList<Map<String, Object>>();
        while(resultSet.next()){
            Map<String, Object> map = new HashMap<String, Object>();
            for(int i = 0; i < label.size(); i++){
                String fieldName = label.get(i);
                Object fieldValue = resultSet.getObject(fieldName);
                map.put(fieldName, fieldValue);
            }
            values.add(map);
        }
        return values;
    }

    private List<String> getLabel(ResultSet resultSet) throws SQLException {
        ResultSetMetaData rsmd = resultSet.getMetaData();
        List<String> label = new ArrayList<String>();
        for(int i = 0; i< rsmd.getColumnCount(); i++){
            label.add(rsmd.getColumnLabel(i+1));
        }
        return label;
    }
    
    @SuppressWarnings("unchecked")
    public <E> E getForValue(String sql, Object...args){
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        E entity = null;
        try{
            connection = JDBCTools.getConnection();
            preparedStatement = connection.prepareStatement(sql);
            for(int i = 0; i < args.length; i++){
                preparedStatement.setObject(i + 1, args[i]);
            }
            resultSet = preparedStatement.executeQuery();
            if(resultSet.next()){
                entity = (E)resultSet.getObject(1);
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            JDBCTools.release(resultSet, preparedStatement, connection);
        }
        return entity;
    }
}