• 自己实现简单版SpringMVC


    SpringMVC的主要作用是:从http请求中得到一个url字符串和对应的请求参数,根据该字符串找到Controller中的一个方法,利用反射执行该方法,将结果返回给前端

    1,初始化

      将url请求路径和controller中的方法一一对应

      将url请求路径和object一一对应, 反射调用方法时要传入object和方法入参

    2,执行请求

      获取http请求路径和参数,找到对应的方法,执行该方法后返回给前端

    ================================================================================================================================

    包扫描是怎么实现的

    递归指定路径的目录(class文件在项目中也是放在某个目录当中的),找出所有的全局限定类名,利用反射生成该类的实例,判断该类是否有特定的注解修饰,比如说@MyController,有注解修饰的就将实例放入Map中

    一,web.xml文件

    <?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"  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>MVC</servlet-name>
        <servlet-class>com.irish.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>MVC</servlet-name>
        <url-pattern>/*</url-pattern>
      </servlet-mapping>
    </web-app>

    二,DispathcherServlet

    public class MyDispatcherServlet extends HttpServlet{
    
        private static final long serialVersionUID = 1L;
    
        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
        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();
            System.out.println("requestUri:"+url);
            System.out.println("contextPath:"+contextPath);
            url=url.replace(contextPath, "").replaceAll("/+", "/");
            System.out.println("url:"+url);
            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();
            //获取方法的参数列表的注解值,顺序和长度与parameterTypes相同,
            String [] paramNames = getMethodParameterNamesByAnnotation(method);
            
            //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,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")){
                    String theParamName = paramNames[i];
                    for (Entry<String, String[]> param : parameterMap.entrySet()) {
                            if(param.getKey().equals(theParamName)) {
                                 String value =Arrays.toString(param.getValue()).replaceAll("\[|\]", "").replaceAll(",\s", ",");
                                 //[abc, ed]  替换为  abc,ed
                                 paramValues[i]=value;
                                 System.out.println(theParamName  + " : "+value);
                            } 
                    }
                }
            }  
            //利用反射机制来调用
            try {
                method.invoke(this.controllerMap.get(url), paramValues);
            } catch (Exception e) {
                e.printStackTrace();
            }
            
        }
    
        
        /**
         * 
         * 按照方法参数的顺序获取注解的值,没有注解的参数对应的位置为空
         */
        public static String[] getMethodParameterNamesByAnnotation(Method method) {
            Annotation[][] parameterAnnotations = method.getParameterAnnotations();
            if (parameterAnnotations == null || parameterAnnotations.length == 0) {
                return null;
            }
            String[] parameterNames = new String[parameterAnnotations.length];
            int i = 0;
            for (Annotation[] parameterAnnotation : parameterAnnotations) {
                if(parameterAnnotation.length == 0 ) {
                      parameterNames[i++] = null;
                }
                for (Annotation annotation : parameterAnnotation) {
                    if (annotation instanceof MyRequestParam) {
                        MyRequestParam param = (MyRequestParam) annotation;
                        parameterNames[i++] = param.value();
                    }
                }
            }
            return parameterNames;
        }
    
        
        @Override
        public void init(ServletConfig config) throws ServletException {
    
            //1.加载配置文件,将classpath路径下的application.properties文件加载到内存
            //config.getInitParameter("contextConfigLocation") 获取的是Servlet的配置参数
            doLoadConfig(config.getInitParameter("contextConfigLocation"));
    
            //2.将指定路径下的全局限定类名添加到classNames集合当中
            doScanner(properties.getProperty("scanPackage"));
    
            //3.通过反射实例化标注了MyController注解的类,并且放到ioc容器中
            doInstance();
    
            //4.初始化url和Method的对应关系,url和Object的对应关系
            initHandlerMapping();
    
        }
        
        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()) {
                    Class<? extends Object> clazz = entry.getValue().getClass();
                    if(!clazz.isAnnotationPresent(MyController.class)){
                        continue;
                    }
                    //拼url时,是controller头部的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();
            }
    
        }
    
        /**
         * 字符串首字母小写
         */
        private String toLowerFirstWord(String name){
            char[] charArray = name.toCharArray();
            charArray[0] += 32;
            return String.valueOf(charArray);
        }
        
        
    }

    三,自定义注解

    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface MyController {
        /**
         * 表示给controller注册别名
         * @return
         */
        String value() default "";
    
    }
    @Target({ElementType.TYPE,ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface MyRequestMapping {
        /**
         * 表示访问该方法的url
         * @return
         */
        String value() default "";
    
    }
    @Target(ElementType.PARAMETER)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface MyRequestParam {
        /**
         * 表示参数的别名,必填
         * @return
         */
        String value();
    
    }

    四,controller

    @MyController
    @MyRequestMapping("/test")
    public class TestController {
    
        @MyRequestMapping("/doTest")
        public void test1(HttpServletRequest request, HttpServletResponse response,
                @MyRequestParam("param1") String param1 , @MyRequestParam("param2") String param2  ){
            System.out.println("param1 = "+ param1);
            System.out.println("param2 = "+ param2);
            try {
                response.getWriter().write( "doTest method success! param1:"+param1 + " , param2:"+ param2);
            } 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();
            }
        }
    }

    五,application.properties

    scanPackage=com.irish.controller

    六,pom.xml

    <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>4.0.0</modelVersion>
      <groupId>com.irish</groupId>
      <artifactId>mySpringMVC</artifactId>
      <version>0.0.1-SNAPSHOT</version>
      <packaging>war</packaging>
      
         <properties>
            <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
            <maven.compiler.source>1.8</maven.compiler.source>
            <maven.compiler.target>1.8</maven.compiler.target>
            <java.version>1.8</java.version>
        </properties>
    
        <dependencies>
             <dependency>
               <groupId>javax.servlet</groupId> 
               <artifactId>javax.servlet-api</artifactId> 
               <version>3.0.1</version> 
               <scope>provided</scope>
            </dependency>
        </dependencies>
      
    </project>

    七,测试

     项目结构

     github地址    https://github.com/jake1263/MySpringMVC

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  • 原文地址:https://www.cnblogs.com/moris5013/p/11010113.html
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