[Java知识库]手写Spring框架（三）

这部分目标是MVC！

主要完成3个重要组件：
HandlerMapping:保存URL映射关系
HandlerAdapter：动态参数适配器
ViewResolvers：视图转换器，模板引擎

SpringMVC核心组件执行流程：


相对应的，用以下几个类来实现上述的功能：

初始化阶段

在DispatcherServlet这个类的init方法中，将mvc部分替换为initStrategies(context)：

并且调用初始化三个组件的方法。
分别完善这几个方法：

private void initViewResolvers(PigApplicationContext context) {
        //模板引擎的根路径
        String tempateRoot = context.getConfig().getProperty("templateRoot");
        String templateRootPath = this.getClass().getClassLoader().getResource(tempateRoot).getFile();

        File templateRootDir = new File(templateRootPath);
        for (File file : templateRootDir.listFiles()) {
            this.viewResolvers.add(new PIGViewResolver(tempateRoot));
        }
    }

    private void initHandlerAdapters(PigApplicationContext context) {
        for (PIGHandlerMapping handlerMapping : handlerMappings) {
            this.handlerAdapters.put(handlerMapping,new PIGHandlerAdapter());
        }
    }

    private void initHandlerMappings(PigApplicationContext context) {
        if(context.getBeanDefinitionCount() == 0){ return; }

        String [] beanNames = context.getBeanDefinitionNames();
        for (String beanName : beanNames) {
            Object instance = context.getBean(beanName);
            Class<?> clazz = instance.getClass();
            if(!clazz.isAnnotationPresent(PIGController.class)){ continue; }

            String baseUrl = "";
            if(clazz.isAnnotationPresent(PIGRequestMapping.class)){
                PIGRequestMapping requestMapping = clazz.getAnnotation(PIGRequestMapping.class);
                baseUrl = requestMapping.value();
            }

            //默认只获取public方法
            for (Method method : clazz.getMethods()) {
                if(!method.isAnnotationPresent(PIGRequestMapping.class)){continue;}
                PIGRequestMapping requestMapping = method.getAnnotation(PIGRequestMapping.class);
                //   //demo//query
                String regex = ("/" + baseUrl + "/" + requestMapping.value().replaceAll("\\*",".*")).replaceAll("/+","/");
                Pattern pattern = Pattern.compile(regex);
                handlerMappings.add(new PIGHandlerMapping(pattern,instance,method));
                System.out.println("Mapped " + regex + "," + method);

            }
        }
    }

全局变量：

    private List<PIGHandlerMapping> handlerMappings = new ArrayList<PIGHandlerMapping>();

    private Map<PIGHandlerMapping,PIGHandlerAdapter> handlerAdapters = new HashMap<PIGHandlerMapping, PIGHandlerAdapter>();

    private List<PIGViewResolver> viewResolvers = new ArrayList<PIGViewResolver>();

HandlerMapping与HandlerAdapter是一一对应的关系。

运行阶段

整体思路：

getHandler就是通过请求拿到URI，并与handlerMappings中存好的模板进行匹配：

    private PIGHandlerMapping getHandler(HttpServletRequest req) {
        String url = req.getRequestURI();
        String contextPath = req.getContextPath();
        url = url.replaceAll(contextPath,"").replaceAll("/+","/");

        for (PIGHandlerMapping handlerMapping : this.handlerMappings) {
            Matcher matcher = handlerMapping.getPattern().matcher(url);
            if(!matcher.matches()){continue;}
            return handlerMapping;
        }

        return null;
    }

HandlerAdapter

HandlerAdapter的handle方法负责反射调用具体方法。需要匹配参数，那么需要先保存好实参和形参列表。

形参列表：编译后就能拿到值

Map<String,Integer> paramIndexMapping = new HashMap<String, Integer>();

        //提取加了PIGRequestParam注解的参数的位置
        Annotation[][] pa = handler.getMethod().getParameterAnnotations();
        for (int i = 0; i < pa.length; i ++){
            for (Annotation a : pa[i]) {
                if(a instanceof PIGRequestParam){
                    String paramName = ((PIGRequestParam) a).value();
                    if(!"".equals(paramName.trim())){
                        paramIndexMapping.put(paramName,i);
                    }
                }
            }
        }

        //提取request和response的位置
        Class<?> [] paramTypes = handler.getMethod().getParameterTypes();
        for (int i = 0; i < paramTypes.length; i++) {
            Class<?> type = paramTypes[i];
            if(type == HttpServletRequest.class || type == HttpServletResponse.class){
                paramIndexMapping.put(type.getName(),i);
            }
        }

实参列表：要运行时才能拿到值

 Map<String,String[]> paramsMap = req.getParameterMap();
        //声明实参列表
        Object [] parameValues = new Object[paramTypes.length];
        for (Map.Entry<String,String[]> param : paramsMap.entrySet()) {
            String value = Arrays.toString(paramsMap.get(param.getKey()))
                    .replaceAll("\\[|\\]","")
                    .replaceAll("\\s","");
            if(!paramIndexMapping.containsKey(param.getKey())){continue;}

            int index = paramIndexMapping.get(param.getKey());
            parameValues[index] = caseStringVlaue(value,paramTypes[index]);
        }

        if(paramIndexMapping.containsKey(HttpServletRequest.class.getName())){
            int index = paramIndexMapping.get(HttpServletRequest.class.getName());
            parameValues[index] = req;
        }

        if(paramIndexMapping.containsKey(HttpServletResponse.class.getName())){
            int index = paramIndexMapping.get(HttpServletResponse.class.getName());
            parameValues[index] = resp;
        }

最后反射

总结：