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)
