public String getRequestHeaderFieldValue(String fieldName) {
        Assert.isNotNull(fieldName);
        return requestHeader.getFieldValue(fieldName);
    }
public String getRequestHeaderFieldValue(String fieldName) {
        Assert.isNotNull(fieldName);
        return requestHeader.getFieldValue(fieldName);
    }
public String getRequestHeaderFieldValue ( String fieldName ) { Assert . isNotNull ( fieldName ) ; return requestHeader . getFieldValue ( fieldName ) ; }
Returns the request header value associated with the given field name,
or <code>null</code> if there is no such field name.

@param fieldName the request header field name
@return the request header value associated with the given field name
@see #setRequestHeaderField(String, String)
Returns the request header value associated with the given field name or <code > null< / code > if there is no such field name .