Affects: \ webmvc 5.3.3 first:
response.setHeader("Content-Type","application/json"); in Filter. after: ServletServerHttpResponse:getFirst() can't not get Header when headername is "Content-Type". because， when response.setHeader("Content-Type","application/json") ，tomcat response have not add Content-Type to header, it's only set contentType,so ServletServerHttpResponse:getFirst() can't not get Header when headername is "Content-Type"

tomcat setHeader code: @Override public void setHeader(String name, String value) {

    if (name == null || name.length() == 0 || value == null) {
        return;
    }

    if (isCommitted()) {
        return;
    }

    // Ignore any call from an included servlet
    if (included) {
        return;
    }

    char cc=name.charAt(0);
    if (cc=='C' || cc=='c') {
        if (checkSpecialHeader(name, value)) {
            return;
        }
    }

    getCoyoteResponse().setHeader(name, value);
}

issue fix code: if value is null from super.getFirst,then to servletResponse.getContentType();

         @Override
    @Nullable
    public String getFirst(String headerName) {
        if (headerName.equalsIgnoreCase(CONTENT_TYPE)) {
            // Content-Type is written as an override so check super first
            String value = super.getFirst(headerName);
            if (value == null) {
                value = servletResponse.getContentType();
            }

            return (value != null ? value : servletResponse.getHeader(headerName));
        }
        else {
            String value = servletResponse.getHeader(headerName);
            return (value != null ? value : super.getFirst(headerName));
        }
    }

Comment From: bclozel

Sorry for the late reply. Instead of suggesting a solution, can you provide a minimal application that we can take a look at?

Comment From: spring-projects-issues

If you would like us to look at this issue, please provide the requested information. If the information is not provided within the next 7 days this issue will be closed.

Comment From: spring-projects-issues

Closing due to lack of requested feedback. If you would like us to look at this issue, please provide the requested information and we will re-open the issue.