HttpHeaders won't let me put/set "accept"

[elreydetodo]

The HttpHeaders class won't let me change the "accept" header with either the #put() or #set() methods. This seems to be because it's a special field with its own setter. I'm in a situation where I'm overriding a bunch of headers defined for me in a Map, so it's not at all convenient to be forced to call #setAccept() since I don't know for sure which of the things in that Map have their own special setters, and even if I did I'd have no easy way to convert a map key into a particular method name.

The problem lives in GenericData#put() and GenericData#set(). They both call .getClassInfo().getFieldInfo(keyName) to figure out if the thing being set is a special field on the object, and if so it tries to change the value of the field via reflection instead of putting it into the internal unknownFields map. This is all well and good, but I want to set just one accept header, and that field is a list of them. The result is that my attempt to set the header results in an exception:

java.lang.IllegalArgumentException: Can not set java.util.List field com.google.api.client.http.HttpHeaders.accept to java.lang.String
	at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
	at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
	at sun.reflect.UnsafeObjectFieldAccessorImpl.set(UnsafeObjectFieldAccessorImpl.java:81)
	at java.lang.reflect.Field.set(Field.java:764)
	at com.google.api.client.util.FieldInfo.setFieldValue(FieldInfo.java:245)
	at com.google.api.client.util.FieldInfo.setValue(FieldInfo.java:206)
	at com.google.api.client.util.GenericData.set(GenericData.java:125)
	at com.google.api.client.http.HttpHeaders.set(HttpHeaders.java:175)
<snip>

This is easily worked around for the purpose of HttpHeaders with this if statement:

// This FieldInfo nonsense is to deal with a bug in HttpHeaders.
FieldInfo fieldInfo = httpHeaders.getClassInfo().getFieldInfo(headerName);
if (fieldInfo != null) {
    httpHeaders.set(headerName, Lists.newArrayList(headerValue));
} else {
    httpHeaders.set(headerName, headerValue);
}

That won't work more generically however, because in the case of HttpHeaders all the fields are guaranteed to be lists (RFC 2616). I don't know what the more generic way to fix this is, but it's was pretty frustrating to me to have to deal with this.

[ipince]

+1

I ran into this as well, with the Authorization header. My use case is the same: I'm copying some headers over from a Map<String, String>.

Nowhere in the documentation does it say that some headers are "reserved" and cannot be overridden with the set() method.