import org.springframework.stereotype.Component; import org.springframework.web.servlet.HandlerInterceptor; import org.springframework.web.servlet.ModelAndView; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; @Component public class TestInterceptor implements HandlerInterceptor { @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { System.out.println("拦截器:执行 preHandle 方法。"); return true; } @Override public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { System.out.println("拦截器:执行 postHandle 方法。"); } @Override public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception { System.out.println("拦截器:执行 afterCompletion 方法。"); } }其中:
void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handle, Exception ex):会在整个请求结束之后再执行,也就是在 DispatcherServlet 渲染了对应的视图之后再执行。
import org.springframework.beans.factory.annotation.Autowired; import org.springframework.context.annotation.Configuration; import org.springframework.web.servlet.config.annotation.InterceptorRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurer; @Configuration public class AppConfig implements WebMvcConfigurer { // 堆代码 duidaima.com // 注入拦截器 @Autowired private TestInterceptor testInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(testInterceptor) // 添加拦截器 .addPathPatterns("/**"); // 拦截所有地址 .excludePathPatterns("/login"); // 放行接口 } }这样我们的拦截器就实现完了。
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { HttpServletRequest processedRequest = request; HandlerExecutionChain mappedHandler = null; boolean multipartRequestParsed = false; WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); try { try { ModelAndView mv = null; Object dispatchException = null; try { processedRequest = this.checkMultipart(request); multipartRequestParsed = processedRequest != request; mappedHandler = this.getHandler(processedRequest); if (mappedHandler == null) { this.noHandlerFound(processedRequest, response); return; } HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler()); String method = request.getMethod(); boolean isGet = HttpMethod.GET.matches(method); if (isGet || HttpMethod.HEAD.matches(method)) { long lastModified = ha.getLastModified(request, mappedHandler.getHandler()); if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) { return; } } // 调用预处理【重点】 if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // 执行 Controller 中的业务 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } this.applyDefaultViewName(processedRequest, mv); mappedHandler.applyPostHandle(processedRequest, response, mv); } catch (Exception var20) { dispatchException = var20; } catch (Throwable var21) { dispatchException = new NestedServletException("Handler dispatch failed", var21); } this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException); } catch (Exception var22) { this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22); } catch (Throwable var23) { this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23)); } } finally { if (asyncManager.isConcurrentHandlingStarted()) { if (mappedHandler != null) { mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response); } } else if (multipartRequestParsed) { this.cleanupMultipart(processedRequest); } } }从上述源码可以看出在开始执行 Controller 之前,会先调用 预处理方法 applyPreHandle,而 applyPreHandle 方法的实现源码如下:
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception { for(int i = 0; i < this.interceptorList.size(); this.interceptorIndex = i++) { // 获取项目中使用的拦截器 HandlerInterceptor HandlerInterceptor interceptor = (HandlerInterceptor)this.interceptorList.get(i); if (!interceptor.preHandle(request, response, this.handler)) { this.triggerAfterCompletion(request, response, (Exception)null); return false; } } return true; }从上述源码可以看出,在 applyPreHandle 中会获取所有的拦截器 HandlerInterceptor 并执行拦截器中的 preHandle 方法,这样就会咱们前面定义的拦截器对应上了,如下图所示:
使用难易程度不同:拦截器相对简单,通过实现接口即可使用。动态代理稍微复杂,需要了解动态代理的实现原理,然后通过相应的 api 实现。