简单JDBC数据库数据查询工具类（模板模式+单例模式+回调）
  工作中经常需要开发一些小的工具以提高工作效率，最近写了一个数据库数据查询的工具类SimpleJDBCTemplate，估计apache commons上有更全面的，不过还是写了一个。
   文件包含：
       1、主类：SimpleJDBCTemplate 
       2、辅助类：ConnectionUtils 连接数据库
                  ResultSetHandler<T>  使用泛型定义处理结果集的接口

SimpleJdbcTemplate 源代码：
package com.cpit.work.util.database;

/*
 * 模板方法+回调（内部匿名类）的数据处理工具
 */
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class SimpleJdbcTemplate {
	public static <T> T query(String queryString, ResultSetHandler<T> rsHandler) {
		Connection connection = null;
		PreparedStatement stmt = null;
		try {
			connection = ConnectionUtils.getInstance().getConnectionion();   // get a db connection.
			stmt = connection.prepareStatement(queryString);
			ResultSet rs = stmt.executeQuery();
			return rsHandler.handle(rs);
		} catch (SQLException ex) {
			close(stmt);    // close the statement
			release(connection);    // release connection
			throw new RuntimeException("An sql exception occurred.", ex);    // rethrow a runtime exception
		} finally {
			close(stmt); // close the statement
			release(connection); // release connection
		}
	}

	private static void release(Connection conn) {
		try {
			if (conn != null) {
				conn.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}

	private static void close(Statement statement) {
		try {
			if (statement != null) {
				statement.close();
			}
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
}


ConnectionUtils 源代码：
package com.cpit.work.util.database;

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

public class ConnectionUtils {
	private final String ORACLE_DRIVER = "oracle.jdbc.driver.OracleDriver";

	private final String URL = "jdbc:oracle:thin:@***.***.***.***:1521:****";

	private final String USERNAME = "zj**";

	private final String PASSWORD = "zj**";
	
	private ConnectionUtils(){}
	
	private static class DataBaseHolder{
		private static final ConnectionUtils instance = new ConnectionUtils();
	}
	
	public static ConnectionUtils getInstance(){
		return DataBaseHolder.instance;
	}

	public Connection getConnectionion() {
		Connection conn = null;
		try {
			Class.forName(ORACLE_DRIVER);
			conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return conn;
	}

}


ResultSetHandler<T> 源代码：

package com.cpit.work.util.database;

import java.sql.ResultSet;

public interface ResultSetHandler<T> {
	public T handle(ResultSet rs);
}

使用代码：
Map<String,String> map = SimpleJdbcTemplate.query(sql, new ResultSetHandler<Map<String,String>>(){
			public Map<String,String> handle(ResultSet rs){
				Map<String,String> data = new HashMap<String,String>();
				try {
					while (rs.next()) {
						String key = rs.getString("key");
						String value = rs.getString("value");
						data.put(key, value);
					}
				} catch (SQLException e) {
					e.printStackTrace();
				} finally{
					if(rs !=null){
						try {
							rs.close();
						} catch (SQLException e) {
							e.printStackTrace();
						}
					}
				}
				return data;
			}
		});