手写一个简单的spring mvc解析器

     spring mvc的运行流程如下图所示

   在这里我们只实现基本功能，对流程做一定的简化。我们需要以下几个步骤：

      加载配置文件

      获取所有的class名称

      获取需要注入的实例

      缓存方法映射

      注入bean

  第一步，加载配置文件，首先在resource目录下新建application.properties文件，并创建自己的servlet，配置web.xml

application.properties文件

#设置扫描根目录，此处为了简化，直接使用properties文件
baseScanPackage=com.study.mvc

自定义的servlet

...

// DispatcherServlet类继承HttpServlet，并覆写doGet、doPost方法

public class DispatcherServlet extends HttpServlet { private static final String Context_CONFIG_LOCATON = "contextConfigLocation"; private Properties properties = new Properties(); 

    //缓存读取到的class
    private Set<String> classNames = new HashSet<>();

    //缓存className与class实例的对应关系
    private Map<String, Object> iocMap = new HashMap<>();

    //缓存url与controller的映射关系
    private Map<String, Object> controllerMap = new HashMap<>();

    //缓存url与其对应方法的映射关系
    private Map<String, Method> handMappingMap = new HashMap<>();

    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        String configPath = servletConfig.getInitParameter(Context_CONFIG_LOCATON);

        try {

            //加载配置文件
            doLoadConfig(configPath);

            //获取所有class名称
            String baseScanPackage = properties.getProperty("baseScanPackage");
            doLoadClassNames(baseScanPackage);

            //获取需要注入的实例
            doLoadIocMap();

            //方法映射
            doHandMapping();

            //注入bean
            doIoc();

        } catch (Exception e) {
            throw new RuntimeException(e);
        }


        super.init();
    }

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

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

    //实际调用的路由方法
    private void doDispatcher(HttpServletRequest req, HttpServletResponse resp) {
        String url = req.getRequestURI();
        System.out.println(url);
        Method method = handMappingMap.get(url);
        Object controller = controllerMap.get(url);
        try {

 
            Parameter[] parameters = method.getParameters();
            if (parameters != null && parameters.length > 0) {
                Object[] args = new Object[parameters.length];
                //根据requestParam封装参数
                for (int i = 0; i < parameters.length; i++) {
                    if (parameters[i].isAnnotationPresent(RequestParam.class)) {
                        RequestParam requestParam = parameters[i].getAnnotation(RequestParam.class);
                        args[i] = req.getParameter(requestParam.value());
                        continue;
                    }
                    args[i] = null;
                }
                method.invoke(controller, args);
            } else {

                method.invoke(controller);
            }

            resp.getWriter().print("success");

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

   ...
}

web.xml

<!DOCTYPE web-app PUBLIC
        "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
        "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
    <display-name>Archetype Created Web Application</display-name>


    <!--定义自己的servlet-->
    <servlet>
        <servlet-name>dispatcherServlet</servlet-name>
        <servlet-class>com.study.mvc.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>application.properties</param-value>
        </init-param>
    </servlet>

    <servlet-mapping>
        <servlet-name>dispatcherServlet</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>