昨晚撸了一个简易版的 Spring MVC 框架

protected void initStrategies(ApplicationContext context) {
  //用于处理上传请求。处理方法是将普通的request包装成MultipartHttpServletRequest，后者可以直接调用getFile方法获取File.
  initMultipartResolver(context);
  //SpringMVC主要有两个地方用到了Locale：一是ViewResolver视图解析的时候；二是用到国际化资源或者主题的时候。
  initLocaleResolver(context); 
  //用于解析主题。SpringMVC中一个主题对应一个properties文件，里面存放着跟当前主题相关的所有资源、
  //如图片、css样式等。SpringMVC的主题也支持国际化， 
  initThemeResolver(context);
  //用来查找Handler的。
  initHandlerMappings(context);
  //从名字上看，它就是一个适配器。Servlet需要的处理方法的结构却是固定的，都是以request和response为参数的方法。
  //如何让固定的Servlet处理方法调用灵活的Handler来进行处理呢？这就是HandlerAdapter要做的事情
  initHandlerAdapters(context);
  //其它组件都是用来干活的。在干活的过程中难免会出现问题，出问题后怎么办呢？
  //这就需要有一个专门的角色对异常情况进行处理，在SpringMVC中就是HandlerExceptionResolver。
  initHandlerExceptionResolvers(context);
  //有的Handler处理完后并没有设置View也没有设置ViewName，这时就需要从request获取ViewName了，
  //如何从request中获取ViewName就是RequestToViewNameTranslator要做的事情了。
  initRequestToViewNameTranslator(context);
  //ViewResolver用来将String类型的视图名和Locale解析为View类型的视图。
  //View是用来渲染页面的，也就是将程序返回的参数填入模板里，生成html（也可能是其它类型）文件。
  initViewResolvers(context);
  //用来管理FlashMap的，FlashMap主要用在redirect重定向中传递参数。
  initFlashMapManager(context); 
}

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0modelVersion>
  <groupId>com.liughgroupId>
  <artifactId>liughMVCartifactId>
  <version>0.0.1-SNAPSHOTversion>
  <packaging>warpackaging>
  
  <properties>
    <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
    <maven.compiler.source>1.8maven.compiler.source>
    <maven.compiler.target>1.8maven.compiler.target>
    <java.version>1.8java.version>
  properties>
  
  <dependencies>
       <dependency>
         <groupId>javax.servletgroupId> 
       <artifactId>javax.servlet-apiartifactId> 
       <version>3.0.1version> 
       <scope>providedscope>
    dependency>
    dependencies>
project>

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>MySpringMVCservlet-name>
    <servlet-class>com.liugh.servlet.MyDispatcherServletservlet-class>
    <init-param>
      <param-name>contextConfigLocationparam-name>
      <param-value>application.propertiesparam-value>
    init-param>
    <load-on-startup>1load-on-startup>
  servlet>
  <servlet-mapping>
    <servlet-name>MySpringMVCservlet-name>
    <url-pattern>/*url-pattern>
  servlet-mapping>web-app>

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyController {
  /**
     * 表示给controller注册别名
     * @return
     */
    String value() default "";

}

@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 "";

}

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface MyRequestParam {
  /**
     * 表示参数的别名，必填
     * @return
     */
    String value();

}

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) 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            //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]=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);
    try {
      //用Properties文件加载文件里的内容
      properties.load(resourceAsStream);
    } catch (IOException e) {
      e.printStackTrace();
    }finally {
      //关流
      if(null!=resourceAsStream){
        try {
          resourceAsStream.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }
    
  }
  
  private void doScanner(String packageName) {
    //把所有的.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 {
        //把类搞出来,反射来实例化(只有加@MyController需要实例化)
        Class clazz =Class.forName(className);
         if(clazz.isAnnotationPresent(MyController.class)){
          ioc.put(toLowerFirstWord(clazz.getSimpleName()),clazz.newInstance());
        }else{
          continue;
        }
        
        
      } catch (Exception e) {
        e.printStackTrace();
        continue;
      }
    }
  }


  private void initHandlerMapping(){
    if(ioc.isEmpty()){
      return;
    }
    try {
      for (Entry<String, Object> entry: ioc.entrySet()) {
        Classextends 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);
  }
  
    
}

@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();
        }
    }
}

来源：my.oschina.net/liughDevelop/blog/1622646