手写一个SpringMVC框架(转)

一：梳理SpringMVC的设计思路

　　本文只实现本身的@Controller、@RequestMapping、@RequestParam注解起做用，其他SpringMVC功能读者能够尝试本身实现。　html

一、读取配置

　　SpringMVC本质上是一个Servlet,这个 Servlet 继承自 HttpServlet。FrameworkServlet负责初始化SpringMVC的容器，并将Spring容器设置为父容器。由于本文只是实现SpringMVC，对于Spring容器不作过多讲解。java

　　为了读取web.xml中的配置，咱们用到ServletConfig这个类，它表明当前Servlet在web.xml中的配置信息。经过web.xml中加载咱们本身写的MyDispatcherServlet和读取配置文件。web

二、初始化阶段

加载配置文件app
扫描用户配置包下面全部的类框架
拿到扫描到的类，经过反射机制，实例化。而且放到ioc容器中(Map的键值对 beanName-bean) beanName默认是首字母小写jsp
初始化HandlerMapping，这里其实就是把url和method对应起来放在一个k-v的Map中,在运行阶段取出ide

三、运行阶段　

　　每一次请求将会调用doGet或doPost方法，因此统一运行阶段都放在doDispatch方法里处理，它会根据url请求去HandlerMapping中匹配到对应的Method，而后利用反射机制调用Controller中的url对应的方法，并获得结果返回。按顺序包括如下功能：测试

异常的拦截this
获取请求传入的参数并处理参数url
经过初始化好的handlerMapping中拿出url对应的方法名，反射调用

2、实现本身的SpringMVC框架

　　工程文件及目录：

用到javax.servlet.jar

web.xml:

<?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" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>web01</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
    <servlet>
           <servlet-name>MySpringMVC</servlet-name>
           <servlet-class>com.gdut.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>MySpringMVC</servlet-name>
           <url-pattern>/*</url-pattern>
     </servlet-mapping>
</web-app>

application.properties文件中只是配置要扫描的包到SpringMVC容器中。application.properties文件内容为：

建立本身的Controller注解，它只能标注在类上面：

package com.gdut.annotation; import java.lang.annotation.Documented; 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) @Documented public @interface MyController { /** * 表示给controller注册别名 * @return
        */ String value() default ""; }

RequestMapping注解，能够在类和方法上：

package com.gdut.annotation; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; @Target({ElementType.TYPE,ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface MyRequestMapping { /** * 表示访问该方法的url * @return
    */ String value() default ""; }

RequestParam注解,只能注解在参数上

package com.gdut.annotation; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; @Target(ElementType.PARAMETER) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface MyRequestParam { /** * 表示参数的别名，必填 * @return
    */ String value(); }

而后建立MyDispatcherServlet这个类，去继承HttpServlet，重写init方法、doGet、doPost方法，以及加上咱们第二步分析时要实现的功能：

package com.gdut.servlet; import java.io.File; import java.io.IOException; import java.io.InputStream; import java.lang.reflect.Method; import java.net.URL; import java.util.ArrayList; import java.util.Arrays; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Map.Entry; import java.util.Properties; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.gdut.annotation.MyController; import com.gdut.annotation.MyRequestMapping; public class MyDispatcherServlet extends HttpServlet { private Properties properties = new Properties(); private List<String> classNames = new ArrayList<>(); private Map<String, Object> ioc = new HashMap<>(); private Map<String, Method> handlerMapping = new HashMap<>(); private Map<String, Object> controllerMap = new HashMap<>(); @Override public void init(ServletConfig config) throws ServletException { // 1.加载配置文件
        doLoadConfig(config.getInitParameter("contextConfigLocation")); // 2.初始化全部相关联的类,扫描用户设定的包下面全部的类
        doScanner(properties.getProperty("scanPackage")); // 3.拿到扫描到的类,经过反射机制,实例化,而且放到ioc容器中(k-v beanName-bean) beanName默认是首字母小写
 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 { // 处理请求
 doDispatch(req, resp); } catch (Exception e) { resp.getWriter().write("500!! Server Exception"); } } private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception { if (handlerMapping.isEmpty()) { return; } String url = req.getRequestURI(); String contextPath = req.getContextPath(); url = url.replace(contextPath, "").replaceAll("/+", "/"); if (!this.handlerMapping.containsKey(url)) { resp.getWriter().write("404 NOT FOUND!"); return; } Method method = this.handlerMapping.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 = req.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，作某些处理
            String requestParam = parameterTypes[i].getSimpleName(); if (requestParam.equals("HttpServletRequest")) { // 参数类型已明确，这边强转类型
                paramValues[i] = req; continue; } if (requestParam.equals("HttpServletResponse")) { paramValues[i] = resp; continue; } if (requestParam.equals("String")) { for (Entry<String, String[]> param : parameterMap.entrySet()) { String value = Arrays.toString(param.getValue()) .replaceAll("\\[|\\]", "").replaceAll(",\\s", ","); paramValues[i] = value; } } } // 利用反射机制来调用
        try { method.invoke(this.controllerMap.get(url), paramValues);// 第一个参数是method所对应的实例 // 在ioc容器中
        } catch (Exception e) { e.printStackTrace(); } } private void doLoadConfig(String location) { // 把web.xml中的contextConfigLocation对应value值的文件加载到流里面
        InputStream resourceAsStream = this.getClass().getClassLoader() .getResourceAsStream(location); // 用Properties文件加载文件里的内容
        try { properties.load(resourceAsStream); } catch (IOException e) { e.printStackTrace(); } finally { if (resourceAsStream != null) { try { resourceAsStream.close(); } catch (IOException e) { e.printStackTrace(); } } } } private void doScanner(String packageName) { // 把全部的.替换成/
        URL url = this.getClass().getClassLoader() .getResource("/" + packageName.replaceAll("\\.", "/")); File dir = new File(url.getFile()); for (File file : dir.listFiles()) { if (file.isDirectory()) { // 递归读取包
                doScanner(packageName + "." + file.getName()); } else { String className = packageName + "."
                        + file.getName().replace(".class", ""); classNames.add(className); } } } private void doInstance() { if (classNames.isEmpty()) { return; } for (String className : classNames) { try { Class<?> clazz = Class.forName(className); if (clazz.isAnnotationPresent(MyController.class)) { ioc.put(toLowerFirstWord(clazz.getSimpleName()), clazz.newInstance()); } } catch (Exception e) { e.printStackTrace(); } } } private void initHandlerMapping() { if (ioc.isEmpty()) { return; } try { for (Entry<String, Object> entry : ioc.entrySet()) { Class<? extends Object> clazz = entry.getValue().getClass(); if (!clazz.isAnnotationPresent(MyController.class)) { continue; } // 拼url时,是controller头的url拼上方法上的url
                String baseUrl = ""; if (clazz.isAnnotationPresent(MyRequestMapping.class)) { MyRequestMapping annotation = clazz .getAnnotation(MyRequestMapping.class); baseUrl = annotation.value(); } Method[] methods = clazz.getMethods(); for (Method method : methods) { if (!method.isAnnotationPresent(MyRequestMapping.class)) { continue; } MyRequestMapping annotation = method .getAnnotation(MyRequestMapping.class); String url = annotation.value(); url = (baseUrl + "/" + url).replaceAll("/+", "/"); handlerMapping.put(url, method); controllerMap.put(url, clazz.newInstance()); System.out.println(url + "," + method); } } } catch (Exception e) { e.printStackTrace(); } } /** * 把字符串的首字母小写 * * @param name * @return
     */
    private String toLowerFirstWord(String name) { char[] charArray = name.toCharArray(); charArray[0] += 32; return String.valueOf(charArray); } }

这里咱们就开发完了本身的SpringMVC，如今咱们测试一下：

package com.gdut.core; import java.io.IOException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.gdut.annotation.MyController; import com.gdut.annotation.MyRequestMapping; import com.gdut.annotation.MyRequestParam; @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(); } } }

访问http://localhost:8080/web01/test/doTest?param=liugh以下：

访问一个不存在的试试：

转自：https://www.cnblogs.com/java1024/p/8556519.html