[Servlet/Tomcat] HttpServletRequest#getHeader(headerNameWithIgnoreCase)（获取header时不区分大小写）

1 故事背景

• 最近项目上有个业务需求，翻译成技术需求，即：将request.headers中的几个header入参转换成request.body(pageRequest)中的内置参数。

为便于灵活配置，header 参数名称是动态可配置的（存放于nacos配置中心），比如：sysCode、Accept-Language

• 技术实现，主要就 springmvc的org.springframework.web.bind.WebDataBinder ，并结合 javax.servlet.http.HttpServletRequest，实现将header中的指定参数转发至request.body(pageRequest).params中

核心代码如下：

@RestController("cn.johnnyzen.bd.dataservice.biz.dataservice.controller.v2.CommonSearchController") @Validated @Api(tags = "DATA2API Controller # V2") public class CommonSearchController implements DataServiceOpenApi {          // ...      @Autowired     private ServiceConfig serviceConfig;      // ...      @InitBinder     public void forwardedHeadersToParamsDataBinder(WebDataBinder binder, HttpServletRequest request) {         //判断是否启用本特性         ForwardedHeaders forwardedHeaders = serviceConfig.getForwardedHeaders();         if(ObjectUtils.isEmpty(forwardedHeaders) || forwardedHeaders.getEnable().equals(Boolean.FALSE)){             logger.warn("Fail to forward headers to body's params because that `service-config.forwardedHeaders` be empty or not enabled!");             return ;         }         logger.info("Start to forward request's headers to request body params with `service-config.forwardedHeaders`,config data as follows : n{}", forwardedHeaders);          //获取被绑定对象----PageRequest         PageRequest<Map<String,Object>> pageRequest = (PageRequest<Map<String, Object>>) binder.getTarget();         if(ObjectUtils.isEmpty(pageRequest) || ObjectUtils.isEmpty(pageRequest.getParams())){             logger.error("`request.body(pageRequest)` or `request.body(pageRequest).params` is empty!");             return;         }         Map<String,Object> dynamicParams = pageRequest.getParams();          List<ForwardHeaderToParamConfig> forwardHeaderToParamConfigList = forwardedHeaders.getHeaders();         forwardHeaderToParamConfigList.stream().forEach(forwardedHeaderConfig -> {             //获取目标header参数值，并转发至params中             String headerName = forwardedHeaderConfig.getHeader();             String headerValue = request.getHeader( forwardedHeaderConfig.getHeader() );             String paramName = forwardedHeaderConfig.getParam();             logger.debug("headerName:{}, headerValue:{}, paramName:{}", headerName, headerValue, paramName);             dynamicParams.put(paramName, headerValue);         });     }      // ... } 

• 那么，我写这篇博客的目的是什么呢？
• 你有没有这么一个疑惑：request.getHeader(headerName)，这个基于Tomcat.catalina实现的方法，是否区分headerName的大小写？

如果不区分大小写，那还好办；如果区分大小写，就尴尬了————我将需要将Accept-Language的每一种字母大小写的可能性都要一一进行配置！
经过源码分析，答案是：request.getHeader(headerName)不区分大小写！
感兴趣的朋友，可以进入第2章节，一起看看源码

2 源码分析

• springmvc: 5.2.15.RELEASE
• springboot: 2.3.12.RELEASE
• tomcat-embed: 9.0.46 (springboot内嵌的tomcat)
• 调试工具: IDEA

Step1 javax.servlet.http.HttpServletRequest : request.getHeader("Accept-Language")

import javax.servlet.http.HttpServletRequest;  //... request.getHeader("Accept-Language") //... 

Step2 javax.servlet.http.HttpServletRequest#getHeader

javax.servlet.http.HttpServletRequest#getHeader 

Step3 org.apache.catalina.connector.Request#getHeader

特别说明：org.apache.catalina.connector.Request#getHeader 其实现了接口：javax.servlet.http.HttpServletRequest#getHeader

org.apache.catalina.connector.Request#getHeader 

Step4 org.apache.coyote.Request#getHeader

org.apache.coyote.Request#getHeader 

Step5 org.apache.tomcat.util.http.MimeHeaders#getHeader

org.apache.tomcat.util.http.MimeHeaders#getHeader 

Step6 org.apache.tomcat.util.http.MimeHeaders#getValue(java.lang.String)

org.apache.tomcat.util.http.MimeHeaders#getValue(java.lang.String) 

X 参考文献

无