[Servlet/Tomcat] HttpServletRequest#getHeader(headerNameWithIgnoreCase)（獲取header時不區分大小寫）

1 故事背景

• 最近項目上有個業務需求，翻譯成技術需求，即：將request.headers中的幾個header入參轉換成request.body(pageRequest)中的內置參數。

爲便於靈活配置，header 參數名稱是動態可配置的（存放於nacos配置中心），比如：sysCode、Accept-Language

• 技術實現，主要就 springmvc的org.springframework.web.bind.WebDataBinder ，並結合 javax.servlet.http.HttpServletRequest，實現將header中的指定參數轉發至request.body(pageRequest).params中

核心代碼如下：

@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) {
        //判斷是否啓用本特性
        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);

        //獲取被綁定對象----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 -> {
            //獲取目標header參數值，並轉發至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);
        });
    }

    // ...
}

• 那麼，我寫這篇博客的目的是什麼呢？
• 你有沒有這麼一個疑惑：request.getHeader(headerName)，這個基於Tomcat.catalina實現的方法，是否區分headerName的大小寫？

如果不區分大小寫，那還好辦；如果區分大小寫，就尷尬了————我將需要將Accept-Language的每一種字母大小寫的可能性都要一一進行配置！
經過源碼分析，答案是：request.getHeader(headerName)不區分大小寫！
感興趣的朋友，可以進入第2章節，一起看看源碼

2 源碼分析

• springmvc: 5.2.15.RELEASE
• springboot: 2.3.12.RELEASE
• tomcat-embed: 9.0.46 (springboot內嵌的tomcat)
• 調試工具: 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

特別說明：org.apache.catalina.connector.Request#getHeader 其實現了接口：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 參考文獻

無