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 statementrelease(connection); // release connectionthrow new RuntimeException("An sql exception occurred.", ex); // rethrow a runtime exception} finally {close(stmt); // close the statementrelease(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;}});