1.Annotation

在JDK5之后，增加Annotation注解的基本语法，通过注解可以省略XML的配置信息，简化代码的编写形式。在Annotation中，如果想要自定义，可以通过如下语法：

@Target(ElementType.xxxx)
@Retention(RetentionPolicy.xxxx)
public @interface 注解名 {

}

Target：对应的是当前的注解能够定义在那个位置。

ElementType.Type -- 类之前
ElementType.Field --字段之前（domain中）
ElementType.Method --方法之前

Retention：在什么场景下起作用。

RetentionPolicy.CLASS - 定义类时
RetentionPolicy.SOURCE - 编写代码时
RetentionPolicy.RUNTIME --运行时（最常用）

1.1代码编写

根据当前自定义MVC框架的一个需求，我们定义了两个Annotation:

@Controller

package annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Controller {
}

@RequestMapping

package annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface RequestMapping {
//在使用RequestMapping的时候可以携带参数value，default为默认值。
    String value() default "";
}

1.2工具类

将所有包含了@Controller类进行遍历

package util;

import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.net.URL;
import java.net.URLDecoder;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;

/**
 * 获得包下面的所有的以.class结尾的java文件
 */
public class ClassScanner {
    /**
     * 获得包下面的所有的class
     */
    public static List<Class<?>> getClassFromPackage(String packageName) {
        List<Class<?>> clazzs = new ArrayList<>();
        //是否循环搜索子包
        boolean recursive = true;
        //包名对应的路径名称
        String packageDirName = packageName.replace(".", "/");
        //从当前正在运行的线程中，加载类加载器，通过给定的包名，找到所有该包下的类
        Enumeration<URL> dirs;
        try {
//currentThread()方法返回正在被执行的线程的信息。currenThread()和this的区别（currentThread()方法返回的是当前正在被执行的线程，而this是自定义线程对象。）
//Thread.currentThread().getContextClassLoader()方法返回当前正在运行的线程的上下文，如果没有，则默认返回父线程的上下文。
//getResource():getResource接受一个字符串参数，如果以”/”开头，就在classpath根目录下找（不会递归查找子目录），如果不以”/”开头，就在调用getResource的字节码对象所在目录下找（同样不会递归查找子目录）。
            dirs = Thread.currentThread().getContextClassLoader().getResources(packageDirName);
            while (dirs.hasMoreElements()) {
                URL url = dirs.nextElement();
                String protocol = url.getProtocol();
//getProtocol: 返回指定 URL 的协议。如:url=https:// www.geeksforgeeks.org;url.getProtocol()返回https
                if ("file".equals(protocol)) {
                    String filePath = URLDecoder.decode(url.getFile(), "UTF-8");
                    findClassInPackageByFile(packageName, filePath, recursive, clazzs);
                }
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return clazzs;
    }

    /**
     * 在package对应的路径下找到所有的class
     */
    public static void findClassInPackageByFile(String packageName, String filePath, final boolean recursive, List<Class<?>> clazzs) {
        File dir = new File(filePath);
        if (!dir.exists() || !dir.isDirectory()) {
            return;
        }
        File[] dirFiles = dir.listFiles(new FileFilter() {

            public boolean accept(File file) {
                boolean acceptDir = recursive && file.isDirectory();// 接受dir目录
                boolean acceptClass = file.getName().endsWith("class");// 接受class文件
                return acceptDir || acceptClass;
            }
        });
        for (File file : dirFiles) {
            if (file.isDirectory()) {
                findClassInPackageByFile(packageName + "." + file.getName(), file.getAbsolutePath(), recursive, clazzs);
            } else {
                String className = file.getName().substring(0, file.getName().length() - 6);
                try {
                    clazzs.add(Thread.currentThread().getContextClassLoader().loadClass(packageName + "." + className));
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

1.3监听器

ClassLoaderContextListener:

package listener;

import annotation.Controller;
import annotation.RequestMapping;
import util.ClassScanner;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.lang.reflect.Method;
import java.util.List;

public class ClassLoaderContextListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        initClassLoader() ;
    }

    private void initClassLoader(){
        List<Class<?>> classList = ClassScanner.getClassFromPackage("controller");

        for (Class clazz : classList){
            //如果当前类上存在Controller.class，就要获取方法
            if (clazz.isAnnotationPresent(Controller.class)){
                //Java反射
                Method[] methods = clazz.getMethods();
                //遍历当前包含了controller注解的所有方法
                for (Method method : methods){
                    //判断方法上是否添加了RequestMapping注解
                    if (method.isAnnotationPresent(RequestMapping.class)){
                        //获取到包含了RequestMapping注解的value值
                        String urlPath = method.getAnnotation(RequestMapping.class).value();
                        //将值作为键，将方法作为值，存储在map集合中
                        WebApplicationContext.methodMap.put(urlPath,method);
                    }
                }
            }
        }
    }
}

WebApplicationContext:

package listener;

import javax.servlet.ServletContextListener;
import java.lang.reflect.Method;
import java.util.concurrent.ConcurrentHashMap;

public class WebApplicationContext {
    public static ConcurrentHashMap<String, Method> methodMap = new ConcurrentHashMap<>();

}

1.4解析用户的请求路径

package servlet;

import listener.WebApplicationContext;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class DispatcherServlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //步骤1:获取到用户请求的URL
        String urlPath = req.getServletPath();
        //根据URL获取到对应的method
        Method method = WebApplicationContext.methodMap.get(urlPath);

        if (method!=null){
            //步骤2：调用对应的method方法
            //如何找到对应的类
            Object instance = null;
            try {
                instance = method.getDeclaringClass().newInstance();
            } catch (InstantiationException e) {
                throw new RuntimeException(e);
            } catch (IllegalAccessException e) {
                throw new RuntimeException(e);
            }
            //如何传输参数，request,response
            try {
                method.invoke(instance,req,resp);
            } catch (IllegalAccessException e) {
                throw new RuntimeException(e);
            } catch (InvocationTargetException e) {
                throw new RuntimeException(e);
            }
        }else{
            resp.sendRedirect("failure.jsp");
        }
    }
}

1.5将上述项目打包jar

1.6使用

新建项目
需要在工程下建立com.csi.controller的包
在包中建立类，在该类上，添加@Controller的注解
建立类中的方法，根据需求，在适当的方法上添加@RequestMapping注解
在@RequestMapping注解中添加url请求的路径

1.6.1添加依赖

在pom.xml中添加依赖

添加依赖之后需要在web.xml中配置jar中的servlet和listener

注：servlet中的路径配置*.do，代表只要@RequestMapping()中的value参数是以.do结束的路径，就都可以匹配到。

1.6.2在domain包中写好product相关的字段

package domain;

import java.util.Set;

public class Product {
    private int id;
    private String name;
    private String description;
    private double price;
    private int stock;
    private int categoryLevel1Id;
    private int categoryLevel2Id;
    private int categoryLevel3Id;
    private String fileName;
    private int idDelete;
    private int brand_id;
    private Set<Comment> comments;
    private PageInfo<Comment> pageInfo;

    public PageInfo<Comment> getPageInfo() {
        return pageInfo;
    }

    public void setPageInfo(PageInfo<Comment> pageInfo) {
        this.pageInfo = pageInfo;
    }

    public Set<Comment> getComments() {
        return comments;
    }

    public void setComments(Set<Comment> comments) {
        this.comments = comments;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getStock() {
        return stock;
    }

    public void setStock(int stock) {
        this.stock = stock;
    }

    public int getCategoryLevel1Id() {
        return categoryLevel1Id;
    }

    public void setCategoryLevel1Id(int categoryLevel1Id) {
        this.categoryLevel1Id = categoryLevel1Id;
    }

    public int getCategoryLevel2Id() {
        return categoryLevel2Id;
    }

    public void setCategoryLevel2Id(int categoryLevel2Id) {
        this.categoryLevel2Id = categoryLevel2Id;
    }

    public int getCategoryLevel3Id() {
        return categoryLevel3Id;
    }

    public void setCategoryLevel3Id(int categoryLevel3Id) {
        this.categoryLevel3Id = categoryLevel3Id;
    }

    public String getFileName() {
        return fileName;
    }

    public void setFileName(String fileName) {
        this.fileName = fileName;
    }

    public int getIdDelete() {
        return idDelete;
    }

    public void setIdDelete(int idDelete) {
        this.idDelete = idDelete;
    }

    public int getBrand_id() {
        return brand_id;
    }

    public void setBrand_id(int brand_id) {
        this.brand_id = brand_id;
    }
}

1.6.3在dao中实现查询所有商品

public class ProductDaoImpl extends JDBCUtils implements ProductDao {
    @Override
    public List<Product> listByCategory4Index(int categoryId) throws SQLException {
        final String SQL = "SELECT * FROM easybuy_product WHERE categoryLevel1Id = ? limit 6";
        Connection connection = this.getConnection();
        PreparedStatement ps = connection.prepareStatement(SQL);
        ps.setInt(1,categoryId);
        ResultSet rs = ps.executeQuery();

        //建立List对象
        List<Product> products = new ArrayList<>();
        while (rs.next()) {
            Product product = new Product();
            product.setId(rs.getInt("productId"));
            product.setName(rs.getString("name"));
            product.setPrice(rs.getDouble("price"));
            product.setFileName(rs.getString("fileName"));
            products.add(product);
        }
        this.release(rs,ps,connection);
        return products;
    }
}

1.6.4编写controller

package controller;

import annotation.Controller;
import annotation.RequestMapping;
import com.alibaba.fastjson.JSON;
import domain.Product;
import domain.Result;
import service.Impl.ProductServiceImpl;
import service.ProductService;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.SQLException;
import java.util.List;

@Controller
public class controller {

    @RequestMapping("/list.do")
    public void list(HttpServletRequest request,HttpServletResponse response) throws IOException, SQLException {
        response.setContentType("application/json;charset=utf-8");

        String categoryId = request.getParameter("categoryLevel1Id");
        int cate = 0;
        if (categoryId!=null){
            cate = Integer.parseInt(categoryId);
        }
        ProductService productService = new ProductServiceImpl();
        List<Product> list = productService.listByCategory4Index(cate);
        System.out.println(list.size());
        Result result = new Result();
        if (list.size()!=0){
            result.setCode(200);
            result.setMsg("success");
            result.setData(list);
        }else{
            result.setCode(400);
            result.setMsg("数据为空");
        }

        //转为JSON数据
        String s = JSON.toJSONString(result);
        PrintWriter out = response.getWriter();
        out.println(s);

    }

}

1.6.5JSP实现效果

此处演示了两种AJAX实现方式

<%--
  Created by IntelliJ IDEA.
  User: wyq
  Date: 2022/8/23
  Time: 21:28
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
    <!-- 最新版本的 Bootstrap 核心 CSS 文件 -->
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css"
          integrity="sha384-HSMxcRTRxnN+Bdg0JdbxYKrThecOKuH5zCYotlSAcp1+c8xmyTe9GYg1l9a69psu" crossorigin="anonymous">
    <script src="http://libs.baidu.com/jquery/1.11.3/jquery.min.js"></script>
    <!-- 最新的 Bootstrap 核心 JavaScript 文件 -->
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"
            integrity="sha384-aJ21OjlMXNL5UyIl/XNwTMqvzeRMZH2w8c5cRVpzpU8Y5bApTppSuUkhZXN0VxHd" crossorigin="anonymous">
    </script>
    <script src="http://libs.baidu.com/jquery/1.11.3/jquery.min.js"></script>

    <meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<div class="container">
    <div class="row">

    </div>
</div>
</body>
<script>
    $(function (){
       /*$.ajax({
           type:"get",
           url:"/list.do?categoryLevel1Id=742",
           dataType:"JSON",
           success:function (list){
               $.each(list,function (i,v){
                   var d = $("<div class='col-sm-6 col-md-4'>" +
                       "<div class='thumbnail' style='width: 300px'>" +
                       "<img src="+v.fileName+" alt='...'>" +
                       "<div class='caption'>" +
                       "<h3 style='color: red'>￥"+v.price+"</h3>" +
                       "<p><span style='color: red'>"+v.name+"</span>,"+v.description+"</p>" +
                       "<p style='color: darkgrey'><span style='color: blue'>2万+</span>条评论</p>" +
                       "<p style='color: darkgrey'>三星京东旗舰店</p>" +
                       "</div>" +
                       "</div>" +
                       "</div>");
                   $(".row").append(d);
               });
           },
           error:function (){
               alert("没有数据");
           }

       })*/
        $.get("/list.do?categoryLevel1Id=548",function (list){
            if (list.code==200){
                $(list.data).each(function (i,v){
                    var d = $("<div class='col-sm-6 col-md-4'>" +
                        "<div class='thumbnail' style='width: 300px'>" +
                        "<img src="+v.fileName+" alt='...'>" +
                        "<div class='caption'>" +
                        "<h3 style='color: red'>￥"+v.price+"</h3>" +
                        "<p><span style='color: red'>"+v.name+"</span>,"+v.description+"</p>" +
                        "<p style='color: darkgrey'><span style='color: blue'>2万+</span>条评论</p>" +
                        "<p style='color: darkgrey'>三星京东旗舰店</p>" +
                        "</div>" +
                        "</div>" +
                        "</div>");
                    $(".row").append(d);
                });
            }else{
                $(".row").html(list.msg);
            }
        })
    });
</script>
</html>

自定义的MVC框架