Java学习笔记与实践分享

package com.gfxy.util; import java.lang.reflect.Field; import java.lang.reflect.InvocationTargetException; 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.text.SimpleDateFormat; import java.util.ArrayList; import java.util.Date; import java.util.List; public class JDBCUtil { public static String url = "jdbc:mysql://localhost:3306/blogdb?serverTimezone=UTC&useSSL=false&characterEncoding=utf8"; public static String dbusername = "root"; public static String dbpassword = "123456"; public static Connection conn =null; public static PreparedStatement ps = null; public static ResultSet resultSet = null; // 静态代码块加载驱动， 驱动只在JDBCUtil类加载的时候执行一次 static { try { System.out.println("MySql 驱动被加载...."); //1.加载驱动 Class.forName("com.mysql.cj.jdbc.Driver"); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public static Connection getConnection() { Connection conn = null; try { conn = DriverManager.getConnection(url,dbusername,dbpassword); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } return conn; } // 增删改 public static int update(String sql,Object[] args) { // 获取连接 Connection conn =getConnection(); PreparedStatement ps = null; int res = 0; try { //准备sql ps = conn.prepareStatement(sql); // update user set eamil=?,tel=? where id=?; for(int n = 1; n<args.length+1;n++) { ps.setObject(n, args[n-1]); } System.out.println(ps.toString()); res=ps.executeUpdate(); return res; } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); return 0; }finally { // 关闭资源 closeResource(ps,conn); } } /** * 查询 * @param sql * @param args * @return */ // 最好返回一个 list public static ResultSet select(String sql,Object[] args){ // 获取连接 conn =getConnection(); try { //准备sql ps = conn.prepareStatement(sql); // update user set eamil=?,tel=? where id=?; if(args != null) { for(int n = 1; n<args.length+1;n++) { ps.setObject(n, args[n-1]); } } System.out.println(ps.toString()); resultSet=ps.executeQuery(); return resultSet; } catch (SQLException e) { e.printStackTrace(); return null; }finally { // 关闭资源 //CloseDbResource.closeResource(res,ps,conn); } } public static List<Object> selectList(String sql,Object[] args,String classname){ // 获取连接 conn =getConnection(); try { //准备sql ps = conn.prepareStatement(sql); if(args != null) { for(int n = 1; n<args.length+1;n++) { ps.setObject(n, args[n-1]); } } System.out.println(ps.toString()); resultSet=ps.executeQuery(); //ResultSetMetaData data = resultSet.getMetaData(); //int n = data.getColumnCount(); //data. List<Object> list = new ArrayList<Object>(); while(resultSet.next()) { // 获取类的字节码 Class clazz = null; try { clazz = Class.forName(classname); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); }//User Object obj = null; try { obj = clazz.getConstructor().newInstance(); } catch (Exception e) { e.printStackTrace(); } Field[] fields = clazz.getDeclaredFields();//获取User类中的所有属性 for(int i = 0; i<fields.length;i++) { try { fields[i].setAccessible(true); // 给obj的fields[i]属性赋值 fields[i].set(obj, resultSet.getObject(fields[i].getName().toLowerCase())); } catch (IllegalArgumentException | IllegalAccessException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println(fields[i].getName()); } list.add(obj); } return list; } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); return null; }finally { // 关闭资源 closeResource(resultSet,ps,conn); } } public static void closeResource(AutoCloseable ...ac) { for(int i = 0; i<ac.length;i++) { if(ac[i] !=null) { try { ac[i].close(); } catch (Exception e) { e.printStackTrace(); } } } } }