Spring HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE并不总是设置

Question

好奇,如果有人可以分享一些关于为什么HttpServletRequest可能没有从Spring Framework设置特定属性的反馈.我们正在使用HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE键入的属性.(https://docs.spring.io/spring-framework/docs/4.3.4.RELEASE/javadoc-api/org/springframework/web/servlet/HandlerMapping.html)

调用链后,示例代码位于OncePerRequestFilter.doFilterInternal()内.

protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain)
    throws ServletException, IOException {
    String path = (new UrlPathHelper()).getPathWithinApplication(request);
    chain.doFilter(request, response);
    String scrubbedPath = scrubPath(request, path);
}

private String scrubPath(HttpServletRequest request, String path) {
    String message = "Response Metric Info";
    String scrubbedPath = path;
    Object bestMatchingPattern = request.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE);
    if (bestMatchingPattern != null) {
        //This changes path from .../collection/{alias} to ../collection/alias
        scrubbedPath = fixSpecialCharacters(bestMatchingPattern.toString());
    } else {
        // this is temporary to help with understanding why we get multiple metric names for the same path
        message = "BEST_MATCHING_PATTERN_ATTRIBUTE null";
    }

    logHandlerInfo(message, request, path);

    return scrubbedPath;
}

// temp helper method to understand why some metrics are being formatted differently for the same path
// causing multiple metrics for the same path
private void logHandlerInfo(String message, HttpServletRequest request, String path) {
    final String LINE_SEPARATOR = System.lineSeparator();
    StringBuilder metricInfoBuilder = new StringBuilder();
    metricInfoBuilder.append(message);
    metricInfoBuilder.append(LINE_SEPARATOR).append(String.format("Input Path=%s", path));
    metricInfoBuilder.append(LINE_SEPARATOR).append(String.format("HandlerMapping.Path=%s", request.getAttribute(HandlerMapping.PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE)));
    metricInfoBuilder.append(LINE_SEPARATOR).append(String.format("HandlerMapping.Best=%s", request.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE)));
    metricInfoBuilder.append(LINE_SEPARATOR).append(String.format("HandlerMapping.Introspect=%s", request.getAttribute(HandlerMapping.INTROSPECT_TYPE_LEVEL_MAPPING)));
    metricInfoBuilder.append(LINE_SEPARATOR).append(String.format("HandlerMapping.UriTemplate=%s", request.getAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE)));
    metricInfoBuilder.append(LINE_SEPARATOR).append(String.format("HandlerMapping.Matrix=%s", request.getAttribute(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE)));
    metricInfoBuilder.append(LINE_SEPARATOR).append(String.format("HandlerMapping.MediaTypes=%s", request.getAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE)));
    log.info(metricInfoBuilder.toString());
}

这是示例日志.

2018-10-08 20:51:58:300 [qtp1346560976-53746897] []  INFO  c.e.m.e.metrics.MetricsFilter - Response Metric Info
Input Path=/v1/group/test/collection/test-dev/status
HandlerMapping.Path=/v1/group/test/collection/test-dev/status
HandlerMapping.Best=/v1/group/{groupAlias}/collection/{alias}/status
HandlerMapping.Introspect=null
HandlerMapping.UriTemplate={groupAlias=test, alias=test-dev}

2018-10-08 20:46:57:745 [qtp1346560976-53746897] []  INFO  c.e.m.e.metrics.MetricsFilter - BEST_MATCHING_PATTERN_ATTRIBUTE null
Input Path=/v1/group/test/collection/test-dev/status
HandlerMapping.Path=null
HandlerMapping.Best=null
HandlerMapping.Introspect=null
HandlerMapping.UriTemplate=null

Answer 1

这些属性由 HandlerMapping 设置，该 HandlerMapping 为请求找到匹配的处理程序。正如 Javadoc 所示，并非所有 HandlerMapping 实现都需要这样做，但 AbstractUrlHandlerMapping 和 RequestMappingInfoHandlerMapping 需要这样做，其中涵盖了内置实现。

对于缺失的属性，它们要么不添加，要么稍后删除，这两种情况似乎都不太可能。为了进一步调试，我建议首先找出哪个 HandlerMapping 用于特定请求，例如将 org.springframework.web 的日志级别设置为 DEBUG。这将告诉您映射是否支持添加这些属性。如果它是上述其中之一的子类，那么应该添加它们。

您还可以在代码中找到设置属性的位置并放置断点以查看会发生什么。假设您发现属性确实被添加，那么您可以调试以查看它们是否由于某种原因被删除。