手写简易SpringMVC

古城微笑少年丶 2024-04-18 11:23 47阅读 0赞

# 手写简易SpringMVC #

--------------------

> 手写系列框架代码基于普通Maven构建，因此在手写SpringMVC的过程中，需要手动的集成Tomcat容器
> 
> 必备知识：  
> Servlet相关理解和使用，Maven，Java 反射，Java自定义注解

## 配置Web类型结构 ##

`结构如图所示：`

![在这里插入图片描述][20190906003328937.png]  
注意 要设置 webapp为web moudle -> IDEA 有蓝色小圈圈为准，resource 配置为资源文件

## 配置Web.xml，配置Artifacts，配置文件 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgzNDQ2NA_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgzNDQ2NA_size_16_color_FFFFFF_t_70 1]

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
    
        <servlet>
            <servlet-name>KerwinCodes</servlet-name>
            <servlet-class>com.mycode.servlet.MyDispatcherServlet</servlet-class>
            <init-param>
                <param-name>contextConfigLocation</param-name>
                <param-value>application.properties</param-value>
            </init-param>
            <load-on-startup>1</load-on-startup>
        </servlet>
    
        <servlet-mapping>
            <servlet-name>KerwinCodes</servlet-name>
            <url-pattern>/*</url-pattern>
        </servlet-mapping>
    </web-app>

// 配置包扫描的路径
    scanPackage=com.mycode

## 编码阶段 ##

1.  第一步毋庸置疑，我们需要创建必要的注解，如MyController,MyRequestMapping等等

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface MyController { 
    
        String value() default "";
    }
    
    @Target({ ElementType.TYPE,ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface MyRequestMapping { 
    
        String value() default "";
    }
    
    @Target(ElementType.PARAMETER)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface MyRequestParam { 
    
        String value();
    }

1.  需要思考我们如何才能实现SpringMVC

A.参考真正的SpringMVC， 它是基于Spring的基础上，因此我们需要自行实现IOC容器
    B.想要实现IOC容易，管理Bean，我们就需要根据包扫描的路径进行全项目扫描
    C.全项目扫描后，利用反射，同时根据注解判断是否是Bean，然后注入到Map容器中即可
    
    D.遍历容器，获取存储的Bean中的方法，配合RequestMapping注解，得到 url - method映射，同时得到 url - object映射，存储到新的Map集合总，便于后续反射调用
    
    E.页面请求时候，判断request.url 映射的到底是哪一个bean，哪一个方法 同时获取方法的参数，解析request的参数，即可匹配路径调用方法
    
    F.万事俱备，到底如何运行？
    Servlet -> init方法，doGet方法，doPost方法  实质就是Servlet生命周期中初始化和真正执行策略的方法，我们只需要重写方法，然后让doGet，doPost 都调用我们的方法即可

1.  核心代码如下：

package com.mycode.servlet;
    
    import com.mycode.annotation.MyController;
    import com.mycode.annotation.MyRequestMapping;
    
    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.*;
    import java.lang.reflect.Member;
    import java.lang.reflect.Method;
    import java.net.URL;
    import java.util.*;
    
    /** * ****************************** * author： 柯贤铭 * createTime: 2019/9/5 11:53 * description: MyDispatcherServlet * version: V1.0 * ****************************** */
    public class MyDispatcherServlet extends HttpServlet{ 
    
        /** 配置信息 **/
        private Properties properties = new Properties();
    
        /** 所有类的Class地址 **/
        private List<String> classNames = new ArrayList<>();
    
        /** Bean容器 **/
        private Map<String, Object> iocFactory = new HashMap<>();
    
        /** HandlerMapping - 方法**/
        private Map<String, Method> handleMapping = new HashMap<>();
    
        /** HandlerMapping - 对象**/
        private Map<String, Object> controllers = new HashMap<>();
    
        @Override
        public void init(ServletConfig config) throws ServletException { 
    
            // 1.加载配置文件
            doLoadConfig(config.getInitParameter("contextConfigLocation"));
    
            // 2.初始化所有相关联的类,扫描用户设定的包下面所有的类
            doScanner(properties.getProperty("scanPackage"));
    
            // 3.拿到扫描到的类,通过反射机制,实例化,并且放到ioc容器中(k-v beanName-bean)
            doInstance();
    
            // 4.初始化HandlerMapping(将url和method对应上)
            initHandlerMapping();
        }
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
            this.doPost(req,resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
            try { 
                doDispatch(req, resp);
            } catch (Exception e) { 
                e.printStackTrace();
            }
        }
    
        // 加载配置文件索取包扫描路径
        private void doLoadConfig (String fileUrl)  { 
            try { 
                properties.load(this.getClass().getClassLoader().getResourceAsStream(fileUrl));
            } catch (IOException e) { 
                e.printStackTrace();
            }
        }
    
        // 扫描目录下所有的类
        private void doScanner (String rootPath) throws ServletException { 
            URL url = this.getClass().getClassLoader().getResource( "/" + rootPath.replaceAll("\\.", "/"));
            File file = new File(Objects.requireNonNull(url).getFile());
            if (!file.isDirectory()) { 
                throw new ServletException("Base Package is wrong.");
            }
    
            for (File current : Objects.requireNonNull(file.listFiles())) { 
                if (current.isDirectory()) { 
                    doScanner(rootPath + "." + current.getName());
                } else { 
                    String className = rootPath + "." + current.getName().replace(".class", "");
                    classNames.add(className);
                }
            }
        }
    
        // 拿到所有的classNames 通过反射创建其对象 - 放入ioc容器中
        private void doInstance () { 
            if (classNames.isEmpty()) { 
                return;
            }
    
            try { 
                for (String className : classNames) { 
                    Class<?> clazz = Class.forName(className);
                    if (clazz.isAnnotationPresent(MyController.class)) { 
                        iocFactory.put(clazz.getSimpleName(), clazz.newInstance());
                    }
                }
            } catch (Exception e) { 
                e.printStackTrace();
            }
        }
    
        // 初始化HandlerMapping(将url和method对应上)
        private void initHandlerMapping () { 
            if (iocFactory.isEmpty()) { 
                return;
            }
    
            for (String key : iocFactory.keySet()) { 
                Class<? extends Object> clazz = iocFactory.get(key).getClass();
                if (!clazz.isAnnotationPresent(MyController.class)) { 
                    continue;
                }
    
                // 类 url
                MyRequestMapping annotation = clazz.getAnnotation(MyRequestMapping.class);
                String baseUrl = annotation.value();
    
                Method[] methods = clazz.getMethods();
                for (Method method : methods) { 
                    if (method.isAnnotationPresent(MyRequestMapping.class)) { 
                        String mappingUrl = method.getAnnotation(MyRequestMapping.class).value();
    
                        // 获取匹配方法及对象 方便之后通过反射调用
                        handleMapping.put(baseUrl + mappingUrl, method);
                        controllers.put(baseUrl + mappingUrl, iocFactory.get(key));
                    }
                }
            }
        }
    
        // 中央处理器
        private void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { 
            if (iocFactory.isEmpty() || handleMapping.isEmpty() || controllers.isEmpty()) { 
                return;
            }
    
            String url = request.getRequestURI();
    
            // 如果不存在url
            if (!handleMapping.containsKey(url)) { 
                response.getWriter().write("Do Not Get Url : 404 ERROR");
                return;
            }
    
            // HandleMapping 的方法
            Method method = handleMapping.get(url);
    
            // 获取方法的参数列表
            Class<?>[] parameterTypes = method.getParameterTypes();
    
            //获取请求的参数
            Map<String, String[]> parameterMap = request.getParameterMap();
    
            //保存参数值
            Object [] paramValues= new Object[parameterTypes.length];
    
            // 方法的参数列表
            for (int i = 0; i< parameterTypes.length; i++){ 
                //根据参数名称，做某些处理
                String requestParam = parameterTypes[i].getSimpleName();
    
                if (requestParam.equals("HttpServletRequest")){ 
                    //参数类型已明确，这边强转类型
                    paramValues[i] = request;
                    continue;
                }
                if (requestParam.equals("HttpServletResponse")){ 
                    paramValues[i] = response;
                    continue;
                }
                if(requestParam.equals("String")){ 
                    for (Map.Entry<String, String[]> param : parameterMap.entrySet()) { 
                        String value = Arrays.toString(param.getValue()).replaceAll("\\[|\\]", "").replaceAll(",\\s", ",");
                        paramValues[i] = value;
                    }
                }
            }
    
            method.invoke(controllers.get(url), paramValues);
        }
    }

1.  测试代码：

@MyController
    @MyRequestMapping("/test")
    public class TestController { 
    
        @MyRequestMapping("/doTest")
        public void test1 ( HttpServletRequest request, HttpServletResponse response,
                            @MyRequestParam("param") String param){ 
            System.out.println(param);
            try { 
                response.getWriter().write( "doTest method success! param:"+param);
            } catch (IOException e) { 
                e.printStackTrace();
            }
        }
    
        @MyRequestMapping("/doTest2")
        public void test2(HttpServletRequest request, HttpServletResponse response){ 
            try { 
                response.getWriter().println("doTest2 method success!");
            } catch (IOException e) { 
                e.printStackTrace();
            }
        }
    }

测试结果：

http://localhost:8080/ -> Do Not Get Url : 404 ERROR

http://localhost:8080/test/doTest2 -> doTest2 method success!

http://localhost:8080/test/doTest?param=asdasdad -> doTest method success! param:asdasdad

> 源码地址：https://github.com/kkzhilu/KerwinCodes code\_springmvc分支

[20190906003328937.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/506eb00773d240d9848d2fbde8b6b8d7.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgzNDQ2NA_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/0ab76dd701f74818b99126cf18a43546.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgzNDQ2NA_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/f5b1dddf3f8d4dba86e83194edcb1039.png