jsp补-java数据库连接、java反射机制

标签：statement   roo   password   cte   java   declared   lan   trace   close   

DB

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.*;
public class DB {
	private static String driver = "com.mysql.jdbc.Driver";//写死
	public static void main(String[] args) throws ClassNotFoundException, SQLException {
		Connection conn=null;
		Statement stmt=null;
		ResultSet rs=null;
		conn = getConnection();
		stmt=conn.createStatement();
		String sql = "select * from tb_user";
		rs = stmt.executeQuery(sql);//执行sql语句  结果保存在rs里
		while(rs.next()){//每次只访问一行  必须先调用next 因为如同指向空头节点 return true if the new current row is valid; false if there are no more rows
			System.out.println(rs.getString("name"));
		}
		 //  前面的链接和结果让前面的代码继续抛 main throws
		sql="insert into tb_user(name,email) values(‘jerry‘,‘123@123‘)";
		stmt.executeUpdate(sql);
		close(rs);// 是种资源。按顺序关闭 不能一起放一个try里不然抛出异常会导致后面close失败 所以要分别
		close(stmt);  //内部都可以捕获 异常 
		close(conn);
		//crud 

	}
	public static void close(Object toClose){
		//利用反射机制
		Class theClass=toClose.getClass();//得到参数的类
		try {
			Method close = theClass.getMethod("close");//找到这个类叫colse的方法
			close.invoke(toClose);//对某个对象做close方法
			//规律 改变方法属性时要用方法确定这些方法属性从属于哪个对象
		} catch (NoSuchMethodException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	/*
	public static void close(Connection conn) {
		try {
			conn.close();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	public static void close(Statement stmt) {
		try {
			stmt.close();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	public static void close(ResultSet rs) {
		try {
			rs.close();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}*/
	//总是要用到的代码   外面的也可以链接这个数据库
	public static Connection getConnection() throws ClassNotFoundException, SQLException {
		Connection conn;
		Class.forName(driver);
		String password="";
		String url="jdbc:mysql://localhost:3306/chat?useUnicode=true&characterEncoding=UTF-8";
		String user="root";
		conn = DriverManager.getConnection(url,user,password);
		return conn;
	}

}

Bank

import java.lang.reflect.Field;

public class Bank {
	private int money;
	
	public int getMoney() {
		return money;
	}
	public void setMoney(int money) {
		this.money = money;
	}

}

User

import java.lang.reflect.Field;

public class User {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Bank bank = new Bank();
		Class<? extends Bank> bankClass = bank.getClass();
		Field money;
		try {
			money = bankClass.getDeclaredField("money");
			money.setAccessible(true);//money原本是私有的 改变访问规则
			money.setInt(bank, 100);//应该修改字段的对象
			System.out.println(bank.getMoney());
		} catch (NoSuchFieldException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}//反射字段 属性名
		catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		
	}

}

jsp补-java数据库连接、java反射机制

标签：statement   roo   password   cte   java   declared   lan   trace   close   

原文地址：https://www.cnblogs.com/leefree/p/12747374.html