介绍 从浏览器发送出的请求，服务器的处理流程.
本文针对 springboot 应用。
总览
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| 浏览器请求 -> filter过滤器 -> Interceptor拦截器 -> ControllerAdvice -> Aspect 切片 -> Controller
浏览器请求 <- filter过滤器 <- Interceptor拦截器 <- ControllerAdvice <- Aspect 切片 <- Controller
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4种方式对比:
- Filter: Servlet 规定的组件。只能处理 ServletRequest 和 ServletResponse。
- Interceptor: Spring 自己实现的。不仅能处理 HttpServletRequest和HttpServletResponse，还能获取 对应的Controller方法 。
- ControllerAdvice: 通常用来做 统一异常处理
- Aspect: 自定义要切入的类或者方法。粒度最小。
filter过滤器
filter过滤器 属于 Servlet 规则中的组件。
最重要的方法是 doFilter()。
下面的代码简单展示了 ApplicationFilterChain 的处理过程。
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| public final class ApplicationFilterChain implements FilterChain {
public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException {
if (Globals.IS_SECURITY_ENABLED) {
} else {
this.internalDoFilter(request, response);
}
}
private void internalDoFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException {
if (this.pos < this.n) {
} else {
}
}
}
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流程为:
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| 浏览器 -> ApplicationFilterChain -> DispatcherServlet
浏览器 <- ApplicationFilterChain <- DispatcherServlet
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Interceptor 拦截器
Interceptor 拦截器是动态拦截Action调用的对象，它提供了一种机制可以使开发者在一个Action执行的前后执行一段代码，
也可以在一个Action执行前阻止其执行，同时也提供了一种可以提取Action中可重用部分代码的方式。
拦截器 的优点:
- 持有 HttpServletRequest
- 持有 HttpServletResponse
- 持有一个 handler: 包含了 Controller 实例、处理请求的方法和参数等信息
拦截器接口
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| public interface HandlerInterceptor {
default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
return true;
}
default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception {
}
default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception {
}
}
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spring 拦截器的生效代码在 DispatcherServlet 和 HandlerExecutionChain中:
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| public class DispatcherServlet extends FrameworkServlet {
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
try {
try {
try {
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
mappedHandler.applyPostHandle(processedRequest, response, mv);
} catch (Throwable var21) {
}
} catch (Throwable var23) {
}
} finally {
}
}
}
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| public class HandlerExecutionChain {
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = this.getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for(int i = 0; i < interceptors.length; this.interceptorIndex = i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
this.triggerAfterCompletion(request, response, (Exception)null);
return false;
}
}
}
return true;
}
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = this.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);
}
}
}
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) throws Exception {
HandlerInterceptor[] interceptors = this.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 var8) {
logger.error("HandlerInterceptor.afterCompletion threw exception", var8);
}
}
}
}
}
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流程为:
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| DispatcherServlet -> HandlerExecutionChain -> HandlerInterceptor
DispatcherServlet <- HandlerExecutionChain <- HandlerInterceptor
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ControllerAdvice
ControllerAdvice 是 controller的增强。可以 与 (ModelAttribute、InitBinder和 ExceptionHandler 配合)。
最常用的组合是 ControllerAdvice 和 ExceptionHandler。用于Controller 异常处理:
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| @ControllerAdvice
public class ControllerAdviceTest {
@ExceptionHandler(CustomException.class)
@ResponseStatus(value = HttpStatus.BAD_REQUEST)
public @ResponseBody
HashMap<String, Object> handleCustomException(Exception e) {
logger.error(e.getMessage(), e);
return genErrorMap(e);
}
}
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@ExceptionHandler 流程为:
请求来到 DispatcherServlet 中后，经过 具体的Controller 处理后，返回的结果如出现异常。 返回结果会依次经过 DispatcherServlet.processDispatchResult()和DispatcherServlet.processHandlerException()。
过程如下:
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| DispatcherServlet.processDispatchResult() -> DispatcherServlet.processHandlerException() -> HandlerExceptionResolver -> ExceptionHandlerExceptionResolver
DispatcherServlet.processDispatchResult() <- DispatcherServlet.processHandlerException() <- HandlerExceptionResolver <- ExceptionHandlerExceptionResolver
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HandlerExceptionResolver 的具体介绍自行查询。
aspect 切片
详见 面向切面编程。