静态代码块加载properties配置文件，注册驱动
静态方法创建连接
静态方法关闭，一个方法关connection,statement，另一个方法多关一个resultSet
package com.aistart.tech.until;import java.io.IOException;
import java.sql.*;
import java.util.Properties;public class JDBCUtil {public static final Properties info = new Properties();static {try {info.load(JDBCUtil.class.getClassLoader().getResourceAsStream("com/aistart/tech/config/jdbc.properties"));Class.forName(info.getProperty("driver"));} catch (ClassNotFoundException e) {throw new RuntimeException(e);} catch (IOException e) {throw new RuntimeException(e);}}public static Connection getConnection() throws SQLException {//获取配置中的urlString url = info.getProperty("url");//获取用户和密码String user = info.getProperty("user");String password = info.getProperty("password");Connection connection = null;if (connection==null){connection = DriverManager.getConnection(url,user,password);}return connection;}public static void closeAll(Connection connection, Statement statement){if (statement != null) {try {statement.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (connection != null) {try {connection.close();} catch (SQLException e) {throw new RuntimeException(e);}}}public static void closeAll(Connection connection, Statement statement, ResultSet resultSet){if (resultSet != null) {try {resultSet.close();} catch (SQLException e) {throw new RuntimeException(e);}}closeAll(connection,statement);}}创建Map，键代表字段别名
把id传入占位符中执行sql
获取元数据的列数，根据列数循环获取每列的别名及相应的值，put到Map中
//根据id获取一行内容
public Map<String, Object> getEmpInfoById(int id) {Map<String, Object> map = new HashMap<>();Connection connection =null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = JDBCUtil.getConnection();preparedStatement = connection.prepareStatement("select e.last_name as emp_name,job_title from employees e left join jobs j on e.job_id = j.job_id\n" +"where employee_id =? ");preparedStatement.setInt(1,id);resultSet= preparedStatement.executeQuery();//获取结果的列信息,元数据ResultSetMetaData metaData = resultSet.getMetaData();//获取总共有几列int columnCount = metaData.getColumnCount();if (resultSet.next()){for (int i = 1; i <= columnCount ; i++) {//是对应数据库表中原本的列名String columnName = metaData.getColumnName(i);//返回的table中名字(如果取别名,拿到就是别名)String columnLabel = metaData.getColumnLabel(i);map.put(columnLabel,resultSet.getString(columnLabel));
// map.put()}return map;}} catch (SQLException e) {throw new RuntimeException(e);}finally {JDBCUtil.closeAll(connection,preparedStatement,resultSet);}return null;}@Testpublic void empTest(){Map<String, Object> empInfoById = iEmpDao.getEmpInfoById(100);System.out.println(empInfoById.get("emp_name"));System.out.println(empInfoById.values());}
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