实战Spring Boot 2.0系列(五) - Listener, Servlet和Filter, Controller和Interceptor

忘是亡心i 2022-04-11 14:57 147阅读 0赞

# 前言 #

用户认证授权、日志记录 `MDC`、编码解码、`UA` 检查、多端对应等都需要通过 **拦截请求** 来进行处理。这时就需要 `Servlet`、`Filter`、`Listener`、`Interceptor` 这几种组件。而把非 `Spring Boot` 项目转换成 `Spring Boot` 项目，需要沿用以前的这些代码，所以有必要了解这它们的 **用法** 和 **生命周期**。

![12738336-c2cfde6a2db164a4][]

image

# 正文 #

## 1. 几种组件介绍 ##

### 1.1. 监听器Listener ###

`Listener` 可以监听 `web` 服务器中某一个 **事件操作**，并触发注册的 **回调函数**。通俗的语言就是在 `application`，`session`，`request` 三个对象 **创建/消亡** 或者 **增删改** 属性时，自动执行代码的功能组件。

### 1.2. Servlet ###

`Servlet` 是一种运行 **服务器端** 的 `java` 应用程序，具有 **独立于平台和协议** 的特性，并且可以动态的生成 `web` 页面，它工作在 **客户端请求** 与 **服务器响应** 的中间层。

### 1.3. 过滤器Filter ###

`Filter` 对 **用户请求** 进行 **预处理**，接着将请求交给 `Servlet` 进行 **处理** 并 **生成响应**，最后 `Filter` 再对 **服务器响应** 进行 **后处理**。`Filter` 是可以复用的代码片段，常用来转换 `HTTP` **请求**、**响应** 和 **头信息**。`Filter` 不像 `Servlet`，它不能产生 **响应**，而是只 **修改** 对某一资源的 **请求** 或者 **响应**。

### 1.4. 拦截器Interceptor ###

类似 **面向切面编程** 中的 **切面** 和 **通知**，我们通过 **动态代理** 对一个 `service()` 方法添加 **通知** 进行功能增强。比如说在方法执行前进行 **初始化处理**，在方法执行后进行 **后置处理**。**拦截器** 的思想和 `AOP` 类似，区别就是 **拦截器** 只能对 `Controller` 的 `HTTP` 请求进行拦截。

## 2. 过滤器 VS 拦截器 ##

### 2.1. 两者的区别 ###

1.  `Filter` 是基于 **函数回调**的，而 `Interceptor` 则是基于 `Java` **反射** 和 **动态代理**。
2.  `Filter` 依赖于 `Servlet` 容器，而 `Interceptor` 不依赖于 `Servlet` 容器。
3.  `Filter` 对几乎 **所有的请求** 起作用，而 `Interceptor` 只对 `Controller` 对请求起作用。

### 2.2. 执行顺序 ###

对于自定义 `Servlet` 对请求分发流程：

1.  `Filter` 过滤请求处理；
2.  `Servlet` 处理请求；
3.  `Filter` 过滤响应处理。

对于自定义 `Controller` 的请求分发流程：

1.  `Filter` 过滤请求处理；
2.  `Interceptor` 拦截请求处理；
3.  对应的 `HandlerAdapter` 处理请求；
4.  `Interceptor` 拦截响应处理；
5.  `Interceptor` 的最终处理；
6.  `Filter` 过滤响应处理。

## 3. 环境准备 ##

### 配置gradle依赖 ###

利用 `Spring Initializer` 创建一个 `gradle` 项目 `spring-boot-web-async-task`，创建时添加相关依赖。得到的初始 `build.gradle` 如下：

buildscript {
        ext {
            springBootVersion = '2.0.3.RELEASE'
        }
        repositories {
            mavenCentral()
        }
        dependencies {
            classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
        }
    }
    
    apply plugin: 'java'
    apply plugin: 'eclipse'
    apply plugin: 'org.springframework.boot'
    apply plugin: 'io.spring.dependency-management'
    
    group = 'io.ostenant.springboot.sample'
    version = '0.0.1-SNAPSHOT'
    sourceCompatibility = 1.8
    
    repositories {
        mavenCentral()
    }
    
    
    dependencies {
        compile('org.springframework.boot:spring-boot-starter-web')
        testCompile('org.springframework.boot:spring-boot-starter-test')
    }

### 配置启动入口类 ###

配置一个 `Spring Boot` 启动入口类，这里需要配置两个注解。

*  @ServletComponentScan: 允许 `Spring Boot` 扫描和装载当前 **包路径** 和 **子路径** 下配置的 `Servlet`。
 *  @EnableWvc: 允许 `Spring Boot` 配置 `Spring MVC` 相关自定义的属性，比如：拦截器、资源处理器、消息转换器等。

@EnableWebMvc
    @ServletComponentScan
    @SpringBootApplication
    public class Application {
        public static void main(String[] args) {
            SpringApplication.run(Application.class, args);
        }
    }

## 4. 配置监听器Listener ##

配置一个 `ServletContext` 监听器，使用 `@WebListener` 标示即可。在 `Servlet` 容器 **初始化** 过程中，`contextInitialized()` 方法会被调用，在容器 **销毁** 时会调用 `contextDestroyed()`。

@WebListener
    public class IndexServletContextListener implements ServletContextListener {
        private static final Logger LOGGER = LoggerFactory.getLogger(IndexServletContextListener.class);
        public static final String INITIAL_CONTENT = "Content created in servlet Context";
    
        @Override
        public void contextInitialized(ServletContextEvent sce) {
            LOGGER.info("Start to initialize servlet context");
            ServletContext servletContext = sce.getServletContext();
            servletContext.setAttribute("content", INITIAL_CONTENT);
        }
    
        @Override
        public void contextDestroyed(ServletContextEvent sce) {
            LOGGER.info("Destroy servlet context");
        }
    }

这里在容器初始化时，往 `ServletContext` 上下文设置了参数名称为 `INITIAL_CONTENT`，可以全局直接访问。

## 5. 配置Servlet ##

配置 `IndexHttpServlet`，重写 `HttpServlet` 的 `doGet()` 方法，直接输出 `IndexHttpServlet` 定义的 **初始化参数** 和在 `IndexServletContextListener` 设置的 `ServletContext` 上下文参数。

@WebServlet(name = "IndexHttpServlet",
            displayName = "indexHttpServlet",
            urlPatterns = {"/index/IndexHttpServlet"},
            initParams = {
                    @WebInitParam(name = "createdBy", value = "Icarus"),
                    @WebInitParam(name = "createdOn", value = "2018-06-20")
            }
    )
    public class IndexHttpServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp)
                throws IOException {
            resp.getWriter().println(format("Created by %s", getInitParameter("createdBy")));
            resp.getWriter().println(format("Created on %s", getInitParameter("createdOn")));
            resp.getWriter().println(format("Servlet context param: %s",
                    req.getServletContext().getAttribute("content")));
        }
    }

配置 `@WebServlet` 注解用于注册这个 `Servlet`，`@WebServlet` 注解的 **各个参数** 分别对应 `web.xml` 中的配置：

<servlet-mapping>  
        <servlet-name>IndexHttpServlet</servlet-name>
        <url-pattern>/index/IndexHttpServlet</url-pattern>
    </servlet-mapping>
    <servlet>  
        <servlet-name>IndexHttpServlet</servlet-name>  
        <servlet-class>io.ostenant.springboot.sample.servlet.IndexHttpServlet</servlet-class>
        <init-param>
            <param-name>createdBy</param-name>
            <param-value>Icarus</param-value>
        </init-param>
        <init-param>
            <param-name>createdOn</param-name>
            <param-value>2018-06-20</param-value>
        </init-param>
    </servlet>

## 6. 配置过滤器Filter ##

一个 `Servlet` 请求可以经由多个 `Filter` 进行过滤，最终由 `Servlet` 处理并响应客户端。这里配置两个过滤器示例：

FirstIndexFilter.java

@WebFilter(filterName = "firstIndexFilter",
            displayName = "firstIndexFilter",
            urlPatterns = {"/index/*"},
            initParams = @WebInitParam(
                    name = "firstIndexFilterInitParam",
                    value = "io.ostenant.springboot.sample.filter.FirstIndexFilter")
    )
    public class FirstIndexFilter implements Filter {
        private static final Logger LOGGER = LoggerFactory.getLogger(FirstIndexFilter.class);
    
        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            LOGGER.info("Register a new filter {}", filterConfig.getFilterName());
        }
    
        @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
                throws IOException, ServletException {
            LOGGER.info("FirstIndexFilter pre filter the request");
            String filter = request.getParameter("filter1");
            if (isEmpty(filter)) {
                response.getWriter().println("Filtered by firstIndexFilter, " +
                        "please set request parameter \"filter1\"");
                return;
            }
            chain.doFilter(request, response);
            LOGGER.info("FirstIndexFilter post filter the response");
        }
    
        @Override
        public void destroy() {
            LOGGER.info("Destroy filter {}", getClass().getName());
        }
    }

以上 `@WebFilter` 相关的配置属性，对应于 `web.xml` 的配置如下：

<filter-mapping>
        <filter-name>firstIndexFilter</filter-name>
        <filter-class>io.ostenant.springboot.sample.filter.FirstIndexFilter</filter-class>
        <url-pattern>/index/*</url-pattern>
        <init-param>
            <param-name>firstIndexFilterInitParam</param-name>
            <param-value>io.ostenant.springboot.sample.filter.FirstIndexFilter</param-value>
        </init-param>
    </filter-mapping>

配置 `FirstIndexFilter`，使用 `@WebFilter` 注解进行标示。当 `FirstIndexFilter` 初始化时，会执行 `init()` 方法。每次请求路径匹配 `urlPatterns` 配置的路径时，就会进入 `doFilter()` 方法进行具体的 **请求** 和 **响应过滤**。

当 `HTTP` 请求携带 `filter1` 参数时，请求会被放行；否则，直接 **过滤中断**，结束请求处理。

SecondIndexFilter.java

@WebFilter(filterName = "secondIndexFilter",
            displayName = "secondIndexFilter",
            urlPatterns = {"/index/*"},
            initParams = @WebInitParam(
                    name = "secondIndexFilterInitParam",
                    value = "io.ostenant.springboot.sample.filter.SecondIndexFilter")
    )
    public class SecondIndexFilter implements Filter {
        private static final Logger LOGGER = LoggerFactory.getLogger(SecondIndexFilter.class);
    
        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            LOGGER.info("Register a new filter {}", filterConfig.getFilterName());
        }
    
        @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
                throws IOException, ServletException {
            LOGGER.info("SecondIndexFilter pre filter the request");
            String filter = request.getParameter("filter2");
            if (isEmpty(filter)) {
                response.getWriter().println("Filtered by firstIndexFilter, " +
                        "please set request parameter \"filter2\"");
                return;
            }
            chain.doFilter(request, response);
            LOGGER.info("SecondIndexFilter post filter the response");
    
        }
    
        @Override
        public void destroy() {
            LOGGER.info("Destroy filter {}", getClass().getName());
        }
    }

以上 `@WebFilter` 相关的配置属性，对应于 `web.xml` 的配置如下：

<filter-mapping>
        <filter-name>secondIndexFilter</filter-name>
        <filter-class>io.ostenant.springboot.sample.filter.SecondIndexFilter</filter-class>
        <url-pattern>/index/*</url-pattern>
        <init-param>
            <param-name>secondIndexFilterInitParam</param-name>
            <param-value>io.ostenant.springboot.sample.filter.SecondIndexFilter</param-value>
        </init-param>
    </filter-mapping>

配置 `SecondIndexFilter`，使用 `@WebFilter` 注解进行标示。当 `SecondIndexFilter` 初始化时，会执行 `init()` 方法。每次请求路径匹配 `urlPatterns` 配置的路径时，就会进入 `doFilter()` 方法进行具体的 **请求** 和 **响应过滤**。

当 `HTTP` 请求携带 `filter2` 参数时，请求会被放行；否则，直接 **过滤中断**，结束请求处理。

来看看 `doFilter()` 最核心的三个参数：

*  ServletRequest: 未到达 `Servlet` 的 `HTTP` 请求；
 *  ServletResponse: 由 `Servlet` 处理并生成的 `HTTP` 响应；
 *  FilterChain: **过滤器链** 对象，可以按顺序注册多个 **过滤器**。

FilterChain.doFilter(request, response);

> **解释：** 一个 **过滤器链** 对象可以按顺序注册多个 **过滤器**。符合当前过滤器过滤条件，即请求 **过滤成功** 直接放行，则交由下一个 **过滤器** 进行处理。所有请求过滤完成以后，由 `IndexHttpServlet` 处理并生成 **响应**，然后在 **过滤器链** 以相反的方向对 **响应** 进行后置过滤处理。

### 配置控制器Controller ###

配置 `IndexController`，用于测试 `/index/IndexController` 路径是否会被 `Filter` 过滤和 `Interceptor` 拦截，并验证两者的先后顺序。

@RestController
    @RequestMapping("index")
    public class IndexController {
        @GetMapping("IndexController")
        public String index() throws Exception {
            return "IndexController";
        }
    }

## 7. 配置拦截器Interceptor ##

拦截器 `Interceptor` 只对 `Handler` 生效。`Spring MVC` 会为 `Controller` 中的每个 **请求方法** 实例化为一个 `Handler`对象，由 `HandlerMapping` 对象路由请求到具体的 `Handler`，然后由 `HandlerAdapter` 通过反射进行请求 **处理** 和 **响应**，这中间就穿插着 **拦截处理**。

#### 编写拦截器 ####

为了区分日志，下面同样对 `IndexController` 配置两个拦截器类：

FirstIndexInterceptor.java

public class FirstIndexInterceptor implements HandlerInterceptor {
        private static final Logger LOGGER = LoggerFactory.getLogger(FirstIndexInterceptor.class);
    
        @Override
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
            LOGGER.info("FirstIndexInterceptor pre intercepted the request");
            String interceptor = request.getParameter("interceptor1");
            if (isEmpty(interceptor)) {
                response.getWriter().println("Filtered by FirstIndexFilter, " +
                        "please set request parameter \"interceptor1\"");
                return false;
            }
            return true;
        }
    
        @Override
        public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
            LOGGER.info("FirstIndexInterceptor post intercepted the response");
        }
    
        @Override
        public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
            LOGGER.info("FirstIndexInterceptor do something after request completed");
        }
    }

SecondIndexInterceptor.java

public class SecondIndexInterceptor implements HandlerInterceptor {
        private static final Logger LOGGER = LoggerFactory.getLogger(SecondIndexInterceptor.class);
    
        @Override
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
            LOGGER.info("SecondIndexInterceptor pre intercepted the request");
            String interceptor = request.getParameter("interceptor2");
            if (isEmpty(interceptor)) {
                response.getWriter().println("Filtered by SecondIndexInterceptor, " +
                        "please set request parameter \"interceptor2\"");
                return false;
            }
            return true;
        }
    
        @Override
        public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
            LOGGER.info("SecondIndexInterceptor post intercepted the response");
        }
    
        @Override
        public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
            LOGGER.info("SecondIndexInterceptor do something after request completed");
        }
    }

#### 配置拦截器 ####

在 `Spring Boot` 中 **配置拦截器** 很简单，只需要实现 `WebMvcConfigurer` 接口，在 `addInterceptors()` 方法中通过 `InterceptorRegistry` 添加 **拦截器** 和 **匹配路径** 即可。

@Configuration
    public class WebConfiguration implements WebMvcConfigurer {
        private static final Logger LOGGER = LoggerFactory.getLogger(WebConfiguration.class);
    
        @Override
        public void addInterceptors(InterceptorRegistry registry) {
            registry.addInterceptor(new FirstIndexInterceptor()).addPathPatterns("/index/**");
            registry.addInterceptor(new SecondIndexInterceptor()).addPathPatterns("/index/**");
            LOGGER.info("Register FirstIndexInterceptor and SecondIndexInterceptor onto InterceptorRegistry");
        }
    }

对应的 `Spring XML` 配置方式如下：

#### 原理剖析 ####

我们通过实现 `HandlerInterceptor` 接口来开发一个 **拦截器**，来看看 `HandlerInterceptor` 接口的三个重要的方法：

*  preHandle(): 在 `controller` 接收请求、处理 `request` 之前执行，返回值为 `boolean`，返回值为 `true` 时接着执行 `postHandle()` 和 `afterCompletion()` 方法；如果返回 `false` 则 **中断** 执行。
 *  postHandle(): 在 `controller` 处理请求之后， `ModelAndView` 处理前执行，可以对 **响应结果** 进行修改。
 *  afterCompletion(): 在 `DispatchServlet` 对本次请求处理完成，即生成 `ModelAndView` 之后执行。

下面简单的看一下 `Spring MVC` 中心调度器 `DispatcherServlet` 的 `doDispatch()` 方法的原理，重点关注 **拦截器** 的以上三个方法的执行顺序。

*  doDispatch(): `DispatchServlet` 处理请求分发的核心方法。

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;
        HandlerExecutionChain mappedHandler = null;
        boolean multipartRequestParsed = false;
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
        try {
            ModelAndView mv = null;
            Exception dispatchException = null;
            try {
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);
                // Determine handler for the current request.
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }
                // Determine handler adapter for the current request.
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
                // Process last-modified header, if supported by the handler.
                String method = request.getMethod();
                boolean isGet = "GET".equals(method);
                if (isGet || "HEAD".equals(method)) {
                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
                    if (logger.isDebugEnabled()) {
                        logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                    }
                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                        return;
                    }
                }
    
                // 1. 按从前往后的顺序调用各个拦截器preHandle()方法
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }
    
                // 2. HandlerAdapter开始真正的请求处理并生产响应视图对象
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    
                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }
    
                applyDefaultViewName(processedRequest, mv);
    
                // 3. 按照从后往前的顺序依次调用各个拦截器的postHandle()方法
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            } catch (Exception ex) {
                dispatchException = ex;
            } catch (Throwable err) {
                dispatchException = new NestedServletException("Handler dispatch failed", err);
            }
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        } catch (Exception ex) {
            // 4. 最终会调用拦截器的afterCompletion()方法
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        } catch (Throwable err) {
            // 4. 最终会调用拦截器的afterCompletion()方法
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new NestedServletException("Handler processing failed", err));
        } finally {
            if (asyncManager.isConcurrentHandlingStarted()) {
                if (mappedHandler != null) {
                    mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                }
            } else {
                if (multipartRequestParsed) {
                    cleanupMultipart(processedRequest);
                }
            }
        }
    }

> 上面注释的几个 `HandlerExecutionChain` 的方法: `applyPreHandle()`、`applyPostHandle()` 和 `triggerAfterCompletion()`。

*  applyPreHandle(): 按 **从前往后** 的顺序调用各个拦截器的 `preHandle()` 方法。任意一个 `HandlerInterceptor` 拦截返回 `false` ，则 `preHandle()` 返回 `false`，记录拦截器的位置 `interceptorIndex`，然后中断拦截处理，最终触发 `AfterCompletion()` 方法并返回 `false`。

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = 0; i < interceptors.length; i++) {
                HandlerInterceptor interceptor = interceptors[i];
                if (!interceptor.preHandle(request, response, this.handler)) {
                    triggerAfterCompletion(request, response, null);
                    return false;
                }
                this.interceptorIndex = i;
            }
        }
        return true;
    }

*  applyPostHandle(): 按照 **从后往前** 的顺序依次调用各个拦截器的 `postHandle()` 方法。只有当所有 `HandlerInterceptor` 的 `preHandle()` 方法返回 `true` 时，才有机会执行到 `applyPostHandle()` 方法。

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
            throws Exception {
        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = interceptors.length - 1; i >= 0; i--) {
                HandlerInterceptor interceptor = interceptors[i];
                interceptor.postHandle(request, response, this.handler, mv);
            }
        }
    }

*  triggerAfterCompletion: `triggerAfterCompletion()` 只在 `preHandle()` 方法返回 `false` 和 **程序抛出异常** 时执行。在 `preHandle()` 方法中，通过 `interceptorIndex` 记录了返回 `false` 的 **拦截器索引**。一旦 `applyPreHandle()` 方法返回 `false`，则从当前返回 `false` 的拦截器 **从后往前** 的执行 `afterCompletion()` 方法。

void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)
            throws Exception {
        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = this.interceptorIndex; i >= 0; i--) {
                HandlerInterceptor interceptor = interceptors[i];
                try {
                    interceptor.afterCompletion(request, response, this.handler, ex);
                }
                catch (Throwable ex2) {
                    logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
                }
            }
        }
    }

## 8. 开始测试 ##

### 生命周期测试 ###

启动 `Spring Boot` 应用程序，观察启动时的程序日志，下面我按照 **顺序** 来分析启动过程中完成了哪些事情。

*  注册 `Spring MVC` 的 `dispatcherServlet` 和自定义的 `IndexHttpServlet`。

2018-06-23 09:39:55.400  INFO 12301 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Servlet dispatcherServlet mapped to [/]
    2018-06-23 09:39:55.404  INFO 12301 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Servlet IndexHttpServlet mapped to [/index/IndexHttpServlet]

> 注意: `dispatcherServlet` 的 `load-up-onstartup` 为 `1`，会优先于其他 `Servlet` 进行加载。

*  按照先后顺序，将所有的过滤器 `Filter` 对象与路径进行映射，其中 `characterEncodingFilter` 是 `Spring MVC` 自带的解决乱码的 `Filter`。

2018-06-23 09:39:55.408  INFO 12301 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
    2018-06-23 09:39:55.409  INFO 12301 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'firstIndexFilter' to urls: [/index/*]
    2018-06-23 09:39:55.409  INFO 12301 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'secondIndexFilter' to urls: [/index/*]

*  初始化 `IndexServletContextListener`，并执行 `contextInitialized()` 方法进行上下文初始化操作。

2018-06-23 09:39:55.429  INFO 12301 --- [ost-startStop-1] i.o.s.s.l.IndexServletContextListener    : Start to initialize servlet context

*  依次执行 `Filter` 的 `init()` 方法进行初始化处理。

2018-06-23 09:39:55.432  INFO 12301 --- [ost-startStop-1] i.o.s.sample.filter.SecondIndexFilter     : Register a new filter secondIndexFilter
    2018-06-23 09:39:55.434  INFO 12301 --- [ost-startStop-1] i.o.s.sample.filter.FirstIndexFilter      : Register a new filter firstIndexFilter

*  创建、初始化拦截器，并统一注册到 `InterceptorRegistry` 上。

2018-06-23 09:39:55.502  INFO 13150 --- [           main] i.o.s.s.interceptor.WebConfiguration     : Register FirstIndexInterceptor and SecondIndexInterceptor onto InterceptorRegistry

*  对 `IndexController` 进行处理，把 **请求** `URI` 和 **处理方法** 映射到 `HandlerMapping` 上并进行缓存。

2018-06-23 09:39:55.541  INFO 12301 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/index/IndexController],methods=[GET]}" onto public java.lang.String io.ostenant.springboot.sample.controller.IndexController.index() throws java.lang.Exception

关闭 `Spring Boot` 应用程序时，观察输出日志如下:

2018-06-23 10:07:03.294  INFO 12301 --- [ost-startStop-2] i.o.s.sample.filter.FirstIndexFilter     : Destroy filter io.ostenant.springboot.sample.filter.SecondIndexFilter
    2018-06-23 10:07:03.294  INFO 12301 --- [ost-startStop-2] i.o.s.sample.filter.FirstIndexFilter     : Destroy filter io.ostenant.springboot.sample.filter.FirstIndexFilter
    2018-06-23 10:07:03.294  INFO 12301 --- [ost-startStop-2] i.o.s.s.l.IndexServletContextListener    : Destroy servlet context

可以看到上面配置的过滤器的 `destroy()` 方法和 `IndexServletContextListener` 的 `contextDestroyed()` 方法都被调用了。

### 访问控制测试 ###

#### Servlet测试 ####

访问 [http://localhost:8080/index/IndexHttpServlet][http_localhost_8080_index_IndexHttpServlet]，响应页面内容如下：

![12738336-8ad0240f5ccc1eac][]

image

访问 [http://localhost:8080/index/IndexHttpServlet?filter1=filter1][http_localhost_8080_index_IndexHttpServlet_filter1_filter1]，响应页面内容如下：

![12738336-eef06d7388053921][]

image

访问 [http://localhost:8080/index/IndexHttpServlet?filter1=filter1&filter2=filter2][http_localhost_8080_index_IndexHttpServlet_filter1_filter1_filter2_filter2]，响应页面内容如下：

![12738336-c7ad3b927c8a62b7][]

image

观察控制台输出日志，验证 **过滤器** 的过滤顺序正确。

2018-06-23 10:19:47.944  INFO 13150 --- [nio-8080-exec-1] i.o.s.sample.filter.FirstIndexFilter     : FirstIndexFilter pre filter the request
    2018-06-23 10:19:47.944  INFO 13150 --- [nio-8080-exec-1] i.o.s.sample.filter.SecondIndexFilter    : SecondIndexFilter pre filter the request
    2018-06-23 10:19:47.944  INFO 13150 --- [nio-8080-exec-1] i.o.s.sample.filter.SecondIndexFilter    : SecondIndexFilter post filter the response
    2018-06-23 10:19:47.944  INFO 13150 --- [nio-8080-exec-1] i.o.s.sample.filter.FirstIndexFilter     : FirstIndexFilter post filter the response

> **结论：** 自定义的 **过滤器** 对 `IndexHttpServlet` 生效， 而 **自定义** 的拦截器生效。

#### controller测试 ####

访问 [http://localhost:8080/index/IndexController][http_localhost_8080_index_IndexController]，响应页面内容如下：

![12738336-6c877b7db34adb36][]

image

访问 [http://localhost:8080/index/IndexController?filter1=filter1][http_localhost_8080_index_IndexController_filter1_filter1]，响应页面内容如下：

![12738336-5e78c292d04148a6][]

image

访问 [http://localhost:8080/index/IndexController?filter1=filter1&filter2=filter2][http_localhost_8080_index_IndexController_filter1_filter1_filter2_filter2]，响应页面内容如下：

![12738336-3ed795b9cfe045b7][]

image

访问 [http://localhost:8080/index/IndexController?filter1=filter1&filter2=filter2&interceptor1=interceptor1][http_localhost_8080_index_IndexController_filter1_filter1_filter2_filter2_interceptor1_interceptor1]，响应页面内容如下：

![12738336-baba2660370be5b9][]

image

访问 [http://localhost:8080/index/IndexController?filter1=filter1&filter2=filter2&interceptor1=interceptor1&interceptor2=interceptor2][http_localhost_8080_index_IndexController_filter1_filter1_filter2_filter2_interceptor1_interceptor1_interceptor2_interceptor2]，响应页面内容如下：

![12738336-69f443d388383ebd][]

image

2018-06-23 10:21:42.533  INFO 13150 --- [nio-8080-exec-4] i.o.s.sample.filter.FirstIndexFilter     : FirstIndexFilter pre filter the request
    2018-06-23 10:21:42.533  INFO 13150 --- [nio-8080-exec-4] i.o.s.sample.filter.SecondIndexFilter    : SecondIndexFilter pre filter the request
    2018-06-23 10:21:42.534  INFO 13150 --- [nio-8080-exec-4] i.o.s.s.i.FirstIndexInterceptor          : FirstIndexInterceptor pre intercepted the request
    2018-06-23 10:21:42.534  INFO 13150 --- [nio-8080-exec-4] i.o.s.s.i.SecondIndexInterceptor         : SecondIndexInterceptor pre intercepted the request
    2018-06-23 10:21:42.535  INFO 13150 --- [nio-8080-exec-4] i.o.s.s.i.SecondIndexInterceptor         : SecondIndexInterceptor post intercepted the response
    2018-06-23 10:21:42.535  INFO 13150 --- [nio-8080-exec-4] i.o.s.s.i.FirstIndexInterceptor          : FirstIndexInterceptor post intercepted the response
    2018-06-23 10:21:42.535  INFO 13150 --- [nio-8080-exec-4] i.o.s.s.i.SecondIndexInterceptor         : SecondIndexInterceptor do something after request completed
    2018-06-23 10:21:42.535  INFO 13150 --- [nio-8080-exec-4] i.o.s.s.i.FirstIndexInterceptor          : FirstIndexInterceptor do something after request completed
    2018-06-23 10:21:42.535  INFO 13150 --- [nio-8080-exec-4] i.o.s.sample.filter.SecondIndexFilter    : SecondIndexFilter post filter the response
    2018-06-23 10:21:42.535  INFO 13150 --- [nio-8080-exec-4] i.o.s.sample.filter.FirstIndexFilter     : FirstIndexFilter post filter the response

> **结论：** 自定义的 **过滤器** 和 **拦截器** 对 **控制器** `Controller` 生效。而 **过滤器** 的优先级高于 **拦截器**。

# 小结 #

本文详细介绍了 `Listener`，`Servlet`，`Filter`，`Controller` 和 `Interceptor` 等 `Web` 多种组件的功能、方法、顺序、作用域和生命周期。给出了详细的示例代码，结合 **源码** 分析了流程，结合 **测试** 验证了结论。长篇大论，希望大家对 `Servlet` 组件和 `Spring MVC` 的框架组件有了更清晰的认识。

--------------------

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[12738336-c2cfde6a2db164a4]: https://upload-images.jianshu.io/upload_images/12738336-c2cfde6a2db164a4
[http_localhost_8080_index_IndexHttpServlet]: http://localhost:8080/index/IndexHttpServlet
[12738336-8ad0240f5ccc1eac]: https://upload-images.jianshu.io/upload_images/12738336-8ad0240f5ccc1eac
[http_localhost_8080_index_IndexHttpServlet_filter1_filter1]: http://localhost:8080/index/IndexHttpServlet?filter1=filter1
[12738336-eef06d7388053921]: https://upload-images.jianshu.io/upload_images/12738336-eef06d7388053921
[http_localhost_8080_index_IndexHttpServlet_filter1_filter1_filter2_filter2]: http://localhost:8080/index/IndexHttpServlet?filter1=filter1&filter2=filter2
[12738336-c7ad3b927c8a62b7]: https://upload-images.jianshu.io/upload_images/12738336-c7ad3b927c8a62b7
[http_localhost_8080_index_IndexController]: http://localhost:8080/index/IndexController
[12738336-6c877b7db34adb36]: https://upload-images.jianshu.io/upload_images/12738336-6c877b7db34adb36
[http_localhost_8080_index_IndexController_filter1_filter1]: http://localhost:8080/index/IndexController?filter1=filter1
[12738336-5e78c292d04148a6]: https://upload-images.jianshu.io/upload_images/12738336-5e78c292d04148a6
[http_localhost_8080_index_IndexController_filter1_filter1_filter2_filter2]: http://localhost:8080/index/IndexController?filter1=filter1&filter2=filter2
[12738336-3ed795b9cfe045b7]: https://upload-images.jianshu.io/upload_images/12738336-3ed795b9cfe045b7
[http_localhost_8080_index_IndexController_filter1_filter1_filter2_filter2_interceptor1_interceptor1]: http://localhost:8080/index/IndexController?filter1=filter1&filter2=filter2&interceptor1=interceptor1
[12738336-baba2660370be5b9]: https://upload-images.jianshu.io/upload_images/12738336-baba2660370be5b9
[http_localhost_8080_index_IndexController_filter1_filter1_filter2_filter2_interceptor1_interceptor1_interceptor2_interceptor2]: http://localhost:8080/index/IndexController?filter1=filter1&filter2=filter2&interceptor1=interceptor1&interceptor2=interceptor2
[12738336-69f443d388383ebd]: https://upload-images.jianshu.io/upload_images/12738336-69f443d388383ebd
[12738336-a0ed87c00830c7dd]: https://upload-images.jianshu.io/upload_images/12738336-a0ed87c00830c7dd