679 lines
21 KiB
Markdown
679 lines
21 KiB
Markdown
# 精尽 Spring MVC 源码分析 —— HandlerMapping 组件（二）之 HandlerInterceptor
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# 1. 概述
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本文，我们来分享 Spring MVC 的拦截器，可能是大家最最最熟悉的组件。如果胖友没有实现过自定义的 Spring MVC 的拦截器，那可能有丢丢遗憾。所以，在看这篇文章之余，胖友也可以自己去尝试写一个 Spring MVC 的拦截器。
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# 2. HandlerInterceptor
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`org.springframework.web.servlet.HandlerInterceptor` ，处理器拦截器接口。代码如下：
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```
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// HandlerInterceptor.java
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public interface HandlerInterceptor {
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/**
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* 拦截处理器，在 {@link HandlerAdapter#handle(HttpServletRequest, HttpServletResponse, Object)} 执行之前
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*/
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default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
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throws Exception {
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return true;
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}
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/**
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* 拦截处理器，在 {@link HandlerAdapter#handle(HttpServletRequest, HttpServletResponse, Object)} 执行成功之后
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*/
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default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
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@Nullable ModelAndView modelAndView) throws Exception {
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}
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/**
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* 拦截处理器，在 {@link HandlerAdapter} 执行完之后，无论成功还是失败
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*
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* 并且，只有 {@link #preHandle(HttpServletRequest, HttpServletResponse, Object)} 执行成功之后，才会被执行
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*/
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default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
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@Nullable Exception ex) throws Exception {
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}
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}
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```
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一共有三个方法，胖友看看方法上的注释。
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# 3. HandlerExecutionChain
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`org.springframework.web.servlet.HandlerExecutionChain` ，处理器执行链。
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## 3.1 构造方法
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```
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// HandlerExecutionChain.java
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/**
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* 处理器
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*/
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private final Object handler;
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/**
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* 拦截器数组
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*/
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@Nullable
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private HandlerInterceptor[] interceptors;
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/**
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* 拦截器数组。
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*
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* 在实际使用时，会调用 {@link #getInterceptors()} 方法，初始化到 {@link #interceptors} 中
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*/
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@Nullable
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private List<HandlerInterceptor> interceptorList;
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/**
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* 已执行 {@link HandlerInterceptor#preHandle(HttpServletRequest, HttpServletResponse, Object)} 的位置
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*
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* 主要用于实现 {@link #applyPostHandle(HttpServletRequest, HttpServletResponse, ModelAndView)} 的逻辑
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*/
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private int interceptorIndex = -1;
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/**
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* Create a new HandlerExecutionChain.
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* @param handler the handler object to execute
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*/
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public HandlerExecutionChain(Object handler) {
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this(handler, (HandlerInterceptor[]) null);
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}
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/**
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* Create a new HandlerExecutionChain.
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* @param handler the handler object to execute
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* @param interceptors the array of interceptors to apply
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* (in the given order) before the handler itself executes
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*/
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public HandlerExecutionChain(Object handler, @Nullable HandlerInterceptor... interceptors) {
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if (handler instanceof HandlerExecutionChain) {
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HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
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this.handler = originalChain.getHandler();
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// 初始化到 interceptorList 中
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this.interceptorList = new ArrayList<>();
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CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList); // 逻辑比较简单，就是将前者添加到后者中，即添加到 interceptorList 中
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CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList); // 逻辑比较简单，就是将前者添加到后者中，即添加到 interceptorList 中
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} else {
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this.handler = handler;
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this.interceptors = interceptors;
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}
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}
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```
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## 3.2 addInterceptor
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`#addInterceptor(HandlerInterceptor interceptor)` 方法，添加拦截器到 `interceptorList` 中。代码如下：
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```
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// HandlerExecutionChain.java
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public void addInterceptor(HandlerInterceptor interceptor) {
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initInterceptorList().add(interceptor);
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}
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```
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- 首先，会调用 `#initInterceptorList()` 方法，保证 `interceptorList` 已初始化。代码如下：
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```
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// HandlerExecutionChain.java
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private List<HandlerInterceptor> initInterceptorList() {
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// 如果 interceptorList 为空，则初始化为 ArrayList
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if (this.interceptorList == null) {
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this.interceptorList = new ArrayList<>();
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// 如果 interceptors 非空，则添加到 interceptorList 中
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if (this.interceptors != null) {
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// An interceptor array specified through the constructor
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CollectionUtils.mergeArrayIntoCollection(this.interceptors, this.interceptorList);
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}
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}
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// 置空 interceptors
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this.interceptors = null;
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// 返回 interceptorList
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return this.interceptorList;
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}
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```
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- 虽然代码有点长，但是逻辑很简单。实际上，我们将 `interceptorList` 是 `interceptors` 的**配置**。
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- 然后，添加 `interceptor` 到 `interceptorList` 中。
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------
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`#addInterceptor(HandlerInterceptor interceptor)` 方法，添加拦截器们到 `interceptorList` 中。代码如下：
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```
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// HandlerExecutionChain.java
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public void addInterceptors(HandlerInterceptor... interceptors) {
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if (!ObjectUtils.isEmpty(interceptors)) {
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CollectionUtils.mergeArrayIntoCollection(interceptors, initInterceptorList());
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}
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}
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```
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## 3.3 getInterceptors
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`#getInterceptors()` 方法，获得 `interceptors` 数组。代码如下：
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```
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// HandlerExecutionChain.java
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@Nullable
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public HandlerInterceptor[] getInterceptors() {
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// 将 interceptorList 初始化到 interceptors 中
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if (this.interceptors == null && this.interceptorList != null) {
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this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[0]);
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}
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// 返回 interceptors 数组
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return this.interceptors;
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}
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```
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## 3.4 applyPreHandle
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`#applyPreHandle(HttpServletRequest request, HttpServletResponse response)` 方法，应用拦截器的前置处理。代码如下：
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```
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// HandlerExecutionChain.java
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/**
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* 应用拦截器的前置处理
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*
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* Apply preHandle methods of registered interceptors.
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* @return {@code true} if the execution chain should proceed with the
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* next interceptor or the handler itself. Else, DispatcherServlet assumes
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* that this interceptor has already dealt with the response itself.
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*/
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boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
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// <1> 获得拦截器数组
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HandlerInterceptor[] interceptors = getInterceptors();
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if (!ObjectUtils.isEmpty(interceptors)) {
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// <2> 遍历拦截器数组
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for (int i = 0; i < interceptors.length; i++) {
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HandlerInterceptor interceptor = interceptors[i];
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// <3> 前置处理
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if (!interceptor.preHandle(request, response, this.handler)) {
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// <3.1> 触发已完成处理
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triggerAfterCompletion(request, response, null);
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// 返回 false ，前置处理失败
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return false;
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}
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// <3.2> 标记 interceptorIndex 位置
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this.interceptorIndex = i;
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}
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}
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// <4> 返回 true ，前置处理成功
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return true;
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}
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```
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- `<1>` 处，调用 `#getInterceptors()` 方法，获得拦截器数组。即，[「3.3 getInterceptors」](https://svip.iocoder.cn/Spring-MVC/HandlerMapping-2-HandlerInterceptor/#) 处的逻辑。
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- `<2>` 处，遍历拦截器数组，逐个调用。
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- ```
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<3>
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```
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处，调用
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```
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HandlerInterceptor#preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
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```
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方法，执行拦截器的前置处理。如果成功，则返回
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```
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true
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```
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，否则返回
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```
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false
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```
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。
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- ```
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<3.1>
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```
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处，执行失败，则调用
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```
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#triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
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```
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方法，触发已完成处理。详细解析，见
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「3.5 triggerAfterCompletion」
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。注意，此处不是触发当前拦截器的已完成逻辑，而是触发
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```
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[0, interceptorIndex)
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```
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这几个拦截器已完成的逻辑(
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不包括
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当前这个拦截器 )，并且是按照
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倒序
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执行的。
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- 返回 `false` ，因为有拦截器执行失败。
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- `<3.2>` 处，标记 `interceptorIndex` 位置。
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- `<4>` 处，返回 `true` ，如果全部拦截器执行成功。
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## 3.5 triggerAfterCompletion
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`#triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)` 方法，触发拦截器的已完成处理。代码如下：
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```
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// HandlerExecutionChain.java
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/**
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* Trigger afterCompletion callbacks on the mapped HandlerInterceptors.
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* Will just invoke afterCompletion for all interceptors whose preHandle invocation
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* has successfully completed and returned true.
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*/
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void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)
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throws Exception {
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// 获得拦截器数组
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HandlerInterceptor[] interceptors = getInterceptors();
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if (!ObjectUtils.isEmpty(interceptors)) {
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// 遍历拦截器数组
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for (int i = this.interceptorIndex; i >= 0; i--) { // 倒序！！！
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HandlerInterceptor interceptor = interceptors[i];
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try {
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// 已完成处理
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interceptor.afterCompletion(request, response, this.handler, ex);
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} catch (Throwable ex2) { // 注意，如果执行失败，仅仅会打印错误日志，不会结束循环
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logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
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}
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}
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}
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}
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```
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- 代码比较简单，正如上文所说。胖友自己瞅瞅，每一行的注释，都要仔细看。
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## 3.6 applyPostHandle
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`#applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv)` 方法，应用拦截器的后置处理。代码如下：
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```
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// HandlerExecutionChain.java
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void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
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throws Exception {
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// 获得拦截器数组
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HandlerInterceptor[] interceptors = getInterceptors();
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if (!ObjectUtils.isEmpty(interceptors)) {
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// 遍历拦截器数组
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for (int i = interceptors.length - 1; i >= 0; i--) { // 倒序
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HandlerInterceptor interceptor = interceptors[i];
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// 后置处理
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interceptor.postHandle(request, response, this.handler, mv);
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}
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}
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}
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```
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- 代码比较简单。胖友自己瞅瞅，每一行的注释，都要仔细看。
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## 3.7 applyAfterConcurrentHandlingStarted
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TODO 1003
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# 4. HandlerInterceptor 实现类
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HandlerInterceptor 的实现类，如下图所示：
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[](http://static.iocoder.cn/images/Spring/2022-03-04/01.png)类图
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比较多，本文我们只看几个重要的实现类。
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## 4.1 MappedInterceptor
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`org.springframework.web.servlet.handler.MappedInterceptor` ，实现 HandlerInterceptor 接口，支持地址匹配的 HandlerInterceptor 实现类。
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示例如下：
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```
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<mvc:interceptors>
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<mvc:interceptor>
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<mvc:mapping path="/interceptor/**" />
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<mvc:exclude-mapping path="/interceptor/b/*" />
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<bean class="com.elim.learn.spring.mvc.interceptor.MyInterceptor" />
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</mvc:interceptor>
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</mvc:interceptors>
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```
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- 每一个 `<mvc:interceptor />` 标签，将被解析成一个 MappedInterceptor Bean 对象。
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### 4.1.1 构造方法
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```
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// MappedInterceptor.java
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/**
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* 匹配的路径
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*/
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@Nullable
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private final String[] includePatterns;
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/**
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* 不匹配的路径
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*/
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@Nullable
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private final String[] excludePatterns;
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/**
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* 路径匹配器
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*/
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@Nullable
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private PathMatcher pathMatcher;
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/**
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* HandlerInterceptor 拦截器对象
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*/
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private final HandlerInterceptor interceptor;
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public MappedInterceptor(@Nullable String[] includePatterns, HandlerInterceptor interceptor) {
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this(includePatterns, null, interceptor);
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}
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public MappedInterceptor(@Nullable String[] includePatterns, @Nullable String[] excludePatterns,
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HandlerInterceptor interceptor) {
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this.includePatterns = includePatterns;
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this.excludePatterns = excludePatterns;
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this.interceptor = interceptor;
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}
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public MappedInterceptor(@Nullable String[] includePatterns, WebRequestInterceptor interceptor) {
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this(includePatterns, null, interceptor);
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}
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public MappedInterceptor(@Nullable String[] includePatterns, @Nullable String[] excludePatterns,
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WebRequestInterceptor interceptor) {
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this(includePatterns, excludePatterns, new WebRequestHandlerInterceptorAdapter(interceptor));
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}
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```
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- 属性比较简单，胖友自己瞅瞅。
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- `includePatterns` + `excludePatterns` + `pathMatcher` 属性，匹配路径。
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- `interceptor` 拦截器。
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### 4.1.2 matches
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`#matches(String lookupPath, PathMatcher pathMatcher)` 方法，判断路径是否匹配。代码如下：
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```
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// MappedInterceptor.java
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/**
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* Determine a match for the given lookup path.
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* @param lookupPath the current request path
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* @param pathMatcher a path matcher for path pattern matching
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* @return {@code true} if the interceptor applies to the given request path
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*/
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public boolean matches(String lookupPath, PathMatcher pathMatcher) {
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PathMatcher pathMatcherToUse = (this.pathMatcher != null ? this.pathMatcher : pathMatcher);
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// 先排重
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if (!ObjectUtils.isEmpty(this.excludePatterns)) {
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for (String pattern : this.excludePatterns) {
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if (pathMatcherToUse.match(pattern, lookupPath)) { // 匹配
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return false;
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}
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}
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}
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// 特殊，如果包含为空，则默认就是包含
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if (ObjectUtils.isEmpty(this.includePatterns)) {
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return true;
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}
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// 后包含
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for (String pattern : this.includePatterns) {
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if (pathMatcherToUse.match(pattern, lookupPath)) { // 匹配
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return true;
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}
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}
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return false;
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}
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```
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简单，胖友自己瞅瞅
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### 4.1.3 拦截方法实现
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```
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// MappedInterceptor.java
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@Override
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public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
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throws Exception {
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return this.interceptor.preHandle(request, response, handler);
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}
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@Override
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public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
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@Nullable ModelAndView modelAndView) throws Exception {
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this.interceptor.postHandle(request, response, handler, modelAndView);
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}
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@Override
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public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
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@Nullable Exception ex) throws Exception {
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this.interceptor.afterCompletion(request, response, handler, ex);
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}
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```
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直接调用拦截器对应的方法。
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## 4.2 其他
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TODO WebRequestInterceptor
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TODO ASYC
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TODO
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# 5. 拦截器配置
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在 Spring MVC 中，有多种方式，配置拦截器。那么对拦截器的配置是怎么解析和初始化的呢？下面，我们逐小节来解析。当然，本文暂时不会特别详细解析，而是交给胖友自己去研读。😝
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## 5.1 `<mvc:interceptors />` 标签
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实际上，我们已经看过 `<mvc:interceptors />` 的配置示例。那么，再来看一次，哈哈哈哈。
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```
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<mvc:interceptors>
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<mvc:interceptor>
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<mvc:mapping path="/interceptor/**" />
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<mvc:exclude-mapping path="/interceptor/b/*" />
|
||
<bean class="com.elim.learn.spring.mvc.interceptor.MyInterceptor" />
|
||
</mvc:interceptor>
|
||
</mvc:interceptors>
|
||
```
|
||
|
||
- 每一个 `<mvc:interceptor />` 标签，会被 `org.springframework.web.servlet.config.InterceptorsBeanDefinitionParser` 解析成 [「4.1 MappedInterceptor」](https://svip.iocoder.cn/Spring-MVC/HandlerMapping-2-HandlerInterceptor/#) 对象，注册到 Spring IOC 容器中。
|
||
|
||
- 在 AbstractHandlerMapping 的 `#detectMappedInterceptors(List<HandlerInterceptor> mappedInterceptors)` 方法中，会扫描 MappedInterceptor Bean 。代码如下：
|
||
|
||
```
|
||
// AbstractHandlerMapping.java
|
||
|
||
protected void detectMappedInterceptors(List<HandlerInterceptor> mappedInterceptors) {
|
||
// 扫描已注册的 MappedInterceptor 的 Bean 们，添加到 mappedInterceptors 中
|
||
// MappedInterceptor 会根据请求路径做匹配，是否进行拦截。
|
||
mappedInterceptors.addAll(
|
||
BeanFactoryUtils.beansOfTypeIncludingAncestors(
|
||
obtainApplicationContext(), MappedInterceptor.class, true, false).values());
|
||
}
|
||
```
|
||
|
||
所以，这种方式，胖友只要看看 **InterceptorsBeanDefinitionParser** 类即可。
|
||
|
||
当然，基于这样的思路，我们直接配置 MappedInterceptor 的 Bean 对象也是可以的，无论是通过 XML ，还是通过 `@Bean` 注解。
|
||
|
||
## 5.2 Java Config
|
||
|
||
在使用 Spring Boot 时，这是主流的方式。示例如下：
|
||
|
||
```
|
||
// SecurityInterceptor.java
|
||
|
||
@Component
|
||
public class SecurityInterceptor extends HandlerInterceptorAdapter {
|
||
|
||
// ... 省略无关代码
|
||
|
||
}
|
||
|
||
// MVCConfiguration.java
|
||
|
||
@EnableWebMvc
|
||
@Configuration
|
||
public class MVCConfiguration extends WebMvcConfigurerAdapter {
|
||
|
||
@Autowired
|
||
private SecurityInterceptor securityInterceptor;
|
||
|
||
@Override
|
||
public void addInterceptors(InterceptorRegistry registry) {
|
||
registry.addInterceptor(securityInterceptor);
|
||
}
|
||
|
||
}
|
||
```
|
||
|
||
- SecurityInterceptor 是拦截器，通过 `@Component` 注册到 Spring IOC 容器中。因为它是 HandlerInterceptorAdapter 的子类，而不是 MappedInterceptor 的子类，所以不会被 AbstractHandlerMapping 的 `#detectMappedInterceptors(List<HandlerInterceptor> mappedInterceptors)` 方法扫描到。
|
||
- 在 MVCConfiguration 的 `#addInterceptors(InterceptorRegistry registry)` 方法中，我们将 `securityInterceptor` 拦截器添加到 InterceptorRegistry 这个拦截器注册表中。
|
||
|
||
所以，这种方式，胖友可能要看的类是不少的，艿艿暂时没有细看。
|
||
|
||
- **InterceptorRegistry**
|
||
- **WebMvcConfigurerAdapter**
|
||
|
||
通过 WebMvcConfigurationSupport 的 `#getInterceptors()` 方法，获得拦截器们。代码如下：
|
||
|
||
```
|
||
// WebMvcConfigurationSupport.java
|
||
|
||
@Nullable
|
||
private List<Object> interceptors;
|
||
|
||
protected final Object[] getInterceptors() {
|
||
// 若 interceptors 未初始化，则进行初始化
|
||
if (this.interceptors == null) {
|
||
// 创建 InterceptorRegistry 对象
|
||
InterceptorRegistry registry = new InterceptorRegistry();
|
||
// 添加拦截器到 interceptors 中
|
||
addInterceptors(registry); // <x>
|
||
// 添加内置拦截器到 interceptors 中
|
||
registry.addInterceptor(new ConversionServiceExposingInterceptor(mvcConversionService()));
|
||
registry.addInterceptor(new ResourceUrlProviderExposingInterceptor(mvcResourceUrlProvider()));
|
||
// 初始化到 interceptors 属性
|
||
this.interceptors = registry.getInterceptors();
|
||
}
|
||
// 若 interceptors 已初始化，则直接返回
|
||
return this.interceptors.toArray();
|
||
}
|
||
```
|
||
|
||
- 代码虽然比较长，重点在 `<x>` 处，调用 `#addInterceptors(InterceptorRegistry registry)` 方法，添加拦截器到 `interceptors` 中。代码如下：
|
||
|
||
```
|
||
// WebMvcConfigurationSupport.java
|
||
|
||
protected void addInterceptors(InterceptorRegistry registry) {
|
||
}
|
||
```
|
||
|
||
- 这是一个空方法，可由子类来进行实现。
|
||
|
||
- 我们一起来看 DelegatingWebMvcConfiguration 对 `#addInterceptors(InterceptorRegistry registry)` 方法，从 WebMvcConfigurer 对象中，获得拦截器，并添加到 `registry` 中。代码如下：
|
||
|
||
```
|
||
// DelegatingWebMvcConfiguration.java
|
||
|
||
private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();
|
||
|
||
@Override
|
||
protected void addInterceptors(InterceptorRegistry registry) {
|
||
this.configurers.addInterceptors(registry);
|
||
}
|
||
|
||
// WebMvcConfigurerComposite.class
|
||
|
||
@Override
|
||
public void addInterceptors(InterceptorRegistry registry) {
|
||
for (WebMvcConfigurer delegate : this.delegates) {
|
||
delegate.addInterceptors(registry);
|
||
}
|
||
}
|
||
```
|
||
|
||
- 其中，我们在示例给的 MVCConfiguration ，其实就是一个 WebMvcConfigurer 对象。这样，我们自己实现的 MVCConfiguration 的 `#addInterceptors(InterceptorRegistry registry)` 方法，就会被调用列。
|
||
|
||
而通过这样的方式的方式配置拦截器，最终通过 AbstractMappingHandler 的 `#setInterceptors(Object... interceptors)` 方法，设置到 MappingHandler 中。代码如下：
|
||
|
||
```
|
||
// AbstractHandlerMapping.java
|
||
|
||
public void setInterceptors(Object... interceptors) {
|
||
this.interceptors.addAll(Arrays.asList(interceptors));
|
||
}
|
||
```
|
||
|
||
- 当然，具体哪些地方调用 AbstractMappingHandler 的 `#setInterceptors(Object... interceptors)` 方法，请使用 IDEA 的**搜索**下，哪些地方调用了 WebMvcConfigurationSupport 的 `#getInterceptors()` 方法。
|
||
|
||
> 艿艿：关于这个过程，可以搭建一个 Spring Boot 项目，然后配置一个自定义拦截器，进行调试。
|
||
|
||
# 666. 彩蛋
|
||
|
||
正如文头所说，如果没实现过 Spring MVC 自定义拦截器的胖友，赶紧先来一发。😈
|
||
|
||
参考和推荐如下文章：
|
||
|
||
- 丶Format [《Spring MVC 拦截器详解[附带源码分析\]》](https://www.cnblogs.com/fangjian0423/p/springMVC-interceptor.html)
|
||
- 郝佳 [《Spring 源码深度解析》](https://item.jd.com/11311737.html) 的 [「11.3 DispatcherServlet」](https://svip.iocoder.cn/Spring-MVC/HandlerMapping-2-HandlerInterceptor/#) 小节
|
||
- 韩路彪 [《看透 Spring MVC：源代码分析与实践》](https://item.jd.com/11807414.html) 的 [「第12章 HandlerMapping」](https://svip.iocoder.cn/Spring-MVC/HandlerMapping-2-HandlerInterceptor/#) 小节 |