SpringMVC简单实现@RequestMapping_from action map request.getservletpath spring-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_53990507/article/details/124792363

web结构图如下

第一步搭建一个普通的web项目

第二步写一个注解

package cn.zzj.anno;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

@Target({METHOD,TYPE,FIELD})//类，方法对象
@Retention(RUNTIME) // 表示注解在字节码文件（硬盘，内存）都存在
@Documented//一直保留到 运行期间
public @interface ReqMapping {
    String value();//参数，并不是方法
}

第三步创建一个Servlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <servlet>
        <servlet-name>MyServlet</servlet-name>
        <servlet-class>cn.zzj.servlet.MyServlet</servlet-class>
        <init-param>
            <param-name>namespace</param-name>
            <param-value>cn.zzj.controller</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>MyServlet</servlet-name>
        <url-pattern>*.do</url-pattern>
    </servlet-mapping>
</web-app>

MyServlet

1.在inti初始化方法里面操作包扫描

2..反射获取类对象，方法，实例化

3.存放到HashMap里面

package cn.zzj.servlet;

import cn.zzj.anno.ReqMapping;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

public class MyServlet extends HttpServlet {
    Map<String, Method> mapUrlMethod = new HashMap<>();//用来存放注解，方法
    Map<String, Object> mapUrlObject = new HashMap<>();//用来存放方法，实例化的对象
    public MyServlet(){
        System.out.println("调用了一次");
    }
    @Override //初始化，只会执行一次
    public void init(ServletConfig config) throws ServletException {
        //super.init(config);
        String path = config.getInitParameter("namespace");//cn.zzj.controller
        System.out.println("init=" + path);//打印一下是不是拿到了

        String path2 = path.replace(".","/");//把路径替换成计算机能读懂的路径
        System.out.println("计算机能读懂的包："+ path2);//打印看看

        File f2 = new File(MyServlet.class.getResource("/").getPath());//拿到当前的电脑路径

        System.out.println("电脑路径为：" + f2);
        path2 = f2.toString() + "/" + path2;//把字节路径跟已经转成计算机能读懂的扫描的包路径加起来
        //根据包名称，可以找到字节码所在的位置

        System.out.println("总路径："+path2);
        File f = new File(path2);//拿到文件所有列表
        String [] list = f.list();
        //打印
        for (String s : list){
            System.out.println("拿到文件中的各个包：" + s);
        }
        String[] list2 = new String[list.length];//获取当前扫描包的配置文件
        for (int i = 0;i<list.length;i++){
            list2[i] = path + "." + list[i].replace(".class","");//进行拼接拿到路径，替换掉class
        }
        //打印
        for (String s : list2){
            System.out.println("打印新的数组" + s);
        }
        for (int i = 0; i < list2.length; i++) {
            try {
                Class<?> c = Class.forName(list2[i]);//获取类对象
                Method[] mm = c.getDeclaredMethods();//获取方法
                Object obj = c.newInstance();//类对象实例化对象
                System.out.println(obj);
                for (Method m : mm) {
                    System.out.println(m);//获取方法对象
                    ReqMapping an = m.getAnnotation(ReqMapping.class);//获取方法的注解
                    ReqMapping cn = c.getAnnotation(ReqMapping.class);//获取类对象的注解
                    if (an == null) continue;//没有注解的方法就跳过
                    System.out.println(cn.value() + an.value());//类对象注解和方法注解合并
                    mapUrlMethod.put(cn.value() + an.value(), m);//用 HashMap 方法存放起来注解队形的方法
                    mapUrlObject.put(cn.value() + an.value(), obj);//用 HashMap 方法存放方法，对象
                }
            } catch (Exception e) {
                System.out.println(e);
            }
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request,response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String action = request.getServletPath();
        System.out.println("请求动作：" + request.getServletPath());
        Method m = mapUrlMethod.get(action);//根据注解的名称，获取方法对象
        System.out.println(m);
        if (m == null) {
            response.getWriter().println(request.getServletPath()+"404。。。");
//            System.out.println("404");
            return;
        }
        //获取方法实例的对象
        Object obj = mapUrlObject.get(action);
        if (obj == null) {
            response.getWriter().println(request.getServletPath()+"404。。。");
//            System.out.println("404");
            return;
        }
        try {
            m.invoke(obj,request,response);
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

第四步编写一个控制类

package cn.zzj.controller;


import cn.zzj.anno.ReqMapping;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@ReqMapping("/book")
public class BookController {

    @ReqMapping("/add.do")
    public void add(HttpServletRequest request, HttpServletResponse response) throws Exception {
        System.out.println("我是Book add="+request);
        System.out.println("我是Book add="+response);
        //页面输出
        response.getWriter().write("Book add这是书本的添加");
    }

    @ReqMapping("/del.do")
    public void del(HttpServletRequest request,HttpServletResponse response) throws Exception{
        System.out.println("Book del="+request);
        System.out.println("Book del="+response);
        response.getWriter().write("Book del");
    }
}