if(rs != null){   // 关闭记录集   try{   rs.close() ;   }catch(SQLException e){   e.printStackTrace() ;   }   }   if(stmt != null){   // 关闭声明   try{   stmt.close() ;   }catch(SQLException e){   e.printStackTrace() ;   }   }   if(conn != null){  // 关闭连接对象   try{   conn.close() ;   }catch(SQLException e){   e.printStackTrace() ;   }   }

package com.jdbc.dbutils;import java.sql.Connection;
import java.sql.DriverManager;
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;public class JdbcUtils {/*** 数据库的用户名*/private final String USER = "root";/*** 数据库的密码*/private final String PASSWORD = "123456";/*** 数据库的驱动信息*/private final String DRIVER = "com.mysql.jdbc.Driver";/*** 访问数据库的地址*/private final String URL = "jdbc:mysql://localhost:3306/test";/*** 数据库的连接*/Connection connection;/*** sql语句的执行对象*/PreparedStatement preparedStatement;/*** 查询返回的结果集合*/ResultSet resultSet;public JdbcUtils() {try {Class.forName(DRIVER);System.out.println("注册驱动成功");} catch (ClassNotFoundException e) {e.printStackTrace();}}/*** 连接数据库* * @return 数据库的连接对象*/public Connection getConnection() {try {connection = DriverManager.getConnection(URL, USER, PASSWORD);} catch (SQLException e) {e.printStackTrace();}return connection;}/*** 完成对数据库的表的添加删除和修改的操作* * @param sql* @param params* @return* @throws SQLException*/public boolean updateByPrepareStatement(String sql, List<Object> params)throws SQLException {boolean flag = false;int result = -1;// 表示当用户执行添加删除和修改的时候所影响数据库的行数// 创建一个 PreparedStatement 对象来将参数化的 sql 语句发送到数据库。preparedStatement = connection.prepareStatement(sql);int index = 1;if (params != null && !params.isEmpty()) {for (Object object : params) {// 使用给定对象设置指定参数的值。index从1开始preparedStatement.setObject(index++, object);}}// 在此 PreparedStatement 对象中执行 SQL 语句，该语句必须是一个 SQL 数据操作语言语句，比如// INSERT、UPDATE 或 DELETE 语句result = preparedStatement.executeUpdate();flag = result > 0 ? true : false;return flag;}/*** 查询返回单条记录* * @param sql* @param params* @return* @throws SQLException*/public Map<String, Object> findSimpleResult(String sql, List<Object> params)throws SQLException {Map<String, Object> map = new HashMap<String, Object>();int index = 1;// 创建一个 PreparedStatement 对象来将参数化的 sql 语句发送到数据库。preparedStatement = connection.prepareStatement(sql);if (params != null && !params.isEmpty()) {for (Object object : params) {// 使用给定对象设置指定参数的值。index从1开始preparedStatement.setObject(index++, object);}}// 在此 PreparedStatement 对象中执行 SQL 查询，并返回该查询生成的 ResultSet 对象。resultSet = preparedStatement.executeQuery();// 获取此 ResultSet 对象的列的编号、类型和属性。ResultSetMetaData metaData = resultSet.getMetaData();int col_len = metaData.getColumnCount();while (resultSet.next()) {for (int i = 0; i < col_len; i++) {// sql数据库列的下标是从1开始的String col_name = metaData.getColumnName(i + 1);Object col_value = resultSet.getObject(col_name);if (col_value == null) {col_value = "";}map.put(col_name, col_value);}}return map;}public List<Map<String, Object>> findMoreResult(String sql,List<Object> params) throws SQLException {List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();int index = 1;// 创建一个 PreparedStatement 对象来将参数化的 sql 语句发送到数据库。preparedStatement = connection.prepareStatement(sql);if (params != null && !params.isEmpty()) {for (Object object : params) {// 使用给定对象设置指定参数的值。index从1开始preparedStatement.setObject(index++, object);}}// 在此 PreparedStatement 对象中执行 SQL 查询，并返回该查询生成的 ResultSet 对象。resultSet = preparedStatement.executeQuery();// 获取此 ResultSet 对象的列的编号、类型和属性。ResultSetMetaData metaData = resultSet.getMetaData();int col_len = metaData.getColumnCount();while (resultSet.next()) {Map<String, Object> map = new HashMap<String, Object>();for (int i = 0; i < col_len; i++) {// sql数据库列的下标是从1开始的String col_name = metaData.getColumnName(i + 1);Object col_value = resultSet.getObject(col_name);if (col_value == null) {col_value = "";}map.put(col_name, col_value);}list.add(map);}return list;}/*** 关闭数据库* * @throws SQLException*/public void releaseConn() throws SQLException {if (resultSet != null) {resultSet.close();}if (preparedStatement != null) {preparedStatement.close();}if (connection != null) {connection.close();}}static JdbcUtils jdbcUtils;public static void main(String[] args) throws SQLException {jdbcUtils = new JdbcUtils();jdbcUtils.getConnection();// insert();// update();// query();Morequery();}private static void query() throws SQLException {String sql = "select * from userinfo where pwd = ? ";List<Object> params = new ArrayList<Object>();params.add("123");Map<String, Object> map = jdbcUtils.findSimpleResult(sql, params);System.out.println(map);}private static void Morequery() throws SQLException {String sql = "select * from userinfo  ";List<Map<String, Object>> map = jdbcUtils.findMoreResult(sql, null);System.out.println(map);}/*** 更新数据库内容* * @throws SQLException*/private static void update() throws SQLException {String sql = "update userinfo set username =? where id=2";List<Object> params = new ArrayList<Object>();params.add("liumr");jdbcUtils.updateByPrepareStatement(sql, params);}/*** 增加数据* * @throws SQLException*/private static void insert() throws SQLException {String sql = "insert userinfo (username,pwd) values (?,?)";List<Object> params = new ArrayList<Object>();params.add("liugx");params.add("456");jdbcUtils.updateByPrepareStatement(sql, params);}}