2023-9-6 笔记反射

2023-12-11 03:28:01
开发
71

反射
1.读取正在运行类的方法和属性
1.Class对象
Class c=Class. forName("co.goho.yuanyu.pojo.Student");
Class co=Student.class;
Class c1=student.getClass();
c.getConstructors();
c.getMethods();
c.getFields();
c.getDeclaredMethods();


        //获得Student类的class对象
       
            Class c = Class.forName("cn.goho.yuanyu.pojo.Student");

            //获得Sudent类的所有的公开方法，返回一个方法数组
            Method[] methods = c.getMethods();
            for (Method m : methods) {
                System.out.println(m.getName());
            }
            //获得Student类的构造方法
            Constructor[] constructors = c.getConstructors();
            for (Constructor ctt : constructors) {
                System.out.println(ctt.getName());
            }

            //获得Student类的公有成员变量
            Field[] fields = c.getFields();
            for (Field field : fields) {
                System.out.println(field.getName());
            }


            //获得Student类的所有成员变量
            Field[] fields1 = c.getDeclaredFields();
            for (Field field : fields1) {
                System.out.println(field.getName());
            }

获得名称为a，参数为int的方法
Method m=c.getMethod("a",int.class)
获得指定构造方法
Constructor ctt=c.getConstructor(int.class,String.class,float.class);
调用构造函数创建对象
c.newInstance(4,"张三",38.9f);

 //使用class对象获得构造方法，并且使用构造方法创建对象
            Constructor ctt0 = c.getConstructor();
            Object o0 = ctt0.newInstance();
            System.out.println(o0);

            //调用有参构造,获得指定构造方法
            Constructor ctt2 = c.getConstructor(int.class, String.class, float.class);
            Object o1 = ctt2.newInstance(1, "张三", 2.3f);
            System.out.println(o1);

            //获得名称为a，参数为int的方法
            //o0对象中只有初始化属性，显示3，“李四”，200
            //找到对象的三个set
            Method a = c.getMethod("a", int.class);
            Method b = c.getMethod("b", String.class);
            Method d = c.getMethod("c", float.class);

            a.invoke(o0, 3);
            b.invoke(o0, "李四");
            d.invoke(o0, 200f);
            System.out.println(o0);

1.步骤，创建动态web项目
2.创建RegisterServlet(urlPattern="/register")继承HttpServlet，重写doGet和doPost,
所有请求交给doGet方法处理
3.修改index.jsp文件，添加一个表单。注册User (Stirng username,String
password,String realname,String tel)
4.创建Userservlet处理所有的和账号密码相关的请求
/user?method=register
5.在UserServlet先读取到mehtod的值，知道用户的意图
6.使用反射在当前类中找到对应的方法处理该请求
7.提取公共类

RegisterServlet类

@WebServlet(urlPatterns = "/register")
public class RegisterServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
      String username=req.getParameter("username");
      String password=req.getParameter("password");
      String realname=req.getParameter("realname");
      String tel=req.getParameter("tel");
        System.out.println(username);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       this.doGet(req,resp);
    }
}

UserServlet类

@WebServlet(urlPatterns = "/user")
//注册 /user?method=register
//登录 /user?method=login
//退出 /user?method=logout
//读取到method参数的值，就可以指定用户的意图
public class UserServlet extends BaseServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
   //先读取method
        String m=req.getParameter("method");
        //根据m来找到对应的方法
        if(m!=null){
            try {
                //通过用户传送过来的method参数找到对应的方法
                Method method=this.getClass().getDeclaredMethod(m,HttpServletRequest.class);
                method.invoke(this,req,resp);
            } catch (NoSuchMethodException e) {
                throw new RuntimeException(e);
            } catch (InvocationTargetException e) {
                throw new RuntimeException(e);
            } catch (IllegalAccessException e) {
                throw new RuntimeException(e);
            }
        }

    }
    public void register(HttpServletRequest req,HttpServletResponse resp){
      Map<String,String[]>parameterMap=req.getParameterMap();
        Set<String>set=parameterMap.keySet();
        Iterator<String>it=set.iterator();
        while ((it.hasNext())){
            System.out.println(it.next());
        }
    }
    public void showUser(HttpServletRequest req,HttpServletResponse resp){
        List<String>strings=new ArrayList<>();
        strings.add("张三李四");
        strings.add("123");
        strings.add("9527");
        req.setAttribute("strings",strings);
        try {
            req.getRequestDispatcher("show.jsp").forward(req,resp);
        } catch (ServletException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

index.jsp


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>注册</title>
    <style>
        div input{
            text-align: center;
        }
    </style>
</head>
<body>
<form method="post" action="${pageContext.request.contextPath}/user?method=register">
    <div><input type="text" name="username" placeholder="账号"></div>
    <div><input type="text" name="password" placeholder="密码"></div>
    <div><input type="text" name="realname" placeholder="姓名"></div>
    <div><input type="text" name="tel" placeholder="电话"></div>
    <div><input type="submit" value="注册"></div>




</form>
</body>
</html>

前端servlet问题的解决方案
1.继承BaseServlet
2.servlet.service
3.不在设置单独请求映射，在请求中添加方法参数，根据方法参数，找到对应的函数处理请求
4.反射，通过函数的名称和函数的参数类型找到方法，并且invoke该方法
5.继承，当一个类继承BaseServlet之后，BaseServlet中的共有方法就直接可以被子类调用

BaseServlet类

public class BaseServlet extends HttpServlet {


    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //先读取method
        String m=req.getParameter("method");
        //根据m来找到对应的方法
        if(m!=null){
            try {
                //通过用户传送过来的method参数找到对应的方法
                Method method=this.getClass().getDeclaredMethod(m,HttpServletRequest.class);
                method.invoke(this,req,resp);
            } catch (NoSuchMethodException e) {
                throw new RuntimeException(e);
            } catch (InvocationTargetException e) {
                throw new RuntimeException(e);
            } catch (IllegalAccessException e) {
                throw new RuntimeException(e);
            }
        }

    }
    public void register(HttpServletRequest req,HttpServletResponse resp){
        Map<String,String[]> parameterMap=req.getParameterMap();
        Set<String> set=parameterMap.keySet();
        Iterator<String> it=set.iterator();
        while ((it.hasNext())){
            System.out.println(it.next());
        }
    }
    public void showUser(HttpServletRequest req,HttpServletResponse resp){
        List<String> strings=new ArrayList<>();
        strings.add("张三李四");
        strings.add("123");
        strings.add("9527");
        req.setAttribute("strings",strings);
        try {
            req.getRequestDispatcher("show.jsp").forward(req,resp);
        } catch (ServletException e) {
            throw new RuntimeException(e);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

原文地址:https://blog.csdn.net/weixin_63379018/article/details/132722555 本文来自互联网用户投稿，该文观点仅代表作者本人，不代表本站立场。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如若转载，请注明出处：https://www.suanlizi.com/kf/1733931593409630208.html 如若内容造成侵权/违法违规/事实不符，请联系《酸梨子》网邮箱：1419361763@qq.com进行投诉反馈，一经查实，立即删除！

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