How do we obtain the Google App Engine safe-URL key in Java for a different appId and namespace? -


when need application without namespace can use following code:

final key mykey = keyfactory.createkey(kind, id); final string safeurlkey = keyfactory.keytostring(mykey);

unfortunately when need different appid or namespace don't find way in java.

in python example can use following code:

new_key = db.key.from_path(entity, id, _app=application_id, namespace=namespace) return str(new_key)

but in java doesn't seem available.

any idea on how can this?

the app engine sdk indeed try prohibit this, evidenced lack of public classes/methods can handle app ids , namespaces. in python discouraged underscore prefix on _app keyword argument. because app engine apps meant well-contained within project.

it possible use reflection workaround these barriers, only on standard java 8 runtime (which in beta). standard java 7 runtime prohibits reflecting non-accessible methods. (if you're using app engine flex suspect you'll ok too, although haven't tested that.)

if using java 8 or willing switch, able create keys arbitrary app ids/namespaces following:

key createkey(string appid, string namespace, string kind, long id) {   try {     class<?> appnsclazz = class.forname("com.google.appengine.api.datastore.appidnamespace");     constructor<?> constructor = appnsclazz.getconstructor(string.class, string.class);     constructor.setaccessible(true);      constructor<key> keyfactory = key.class.getdeclaredconstructor(string.class,        key.class, long.class, string.class, appnsclazz);     keyfactory.setaccessible(true);      object appns = constructor.newinstance(appid, namespace);     return keyfactory.newinstance(kind, /* parent key */ null, id, /* name */ null, appns);   } catch (classnotfoundexception | nosuchmethodexception |             invocationtargetexception | instantiationexception |             illegalaccessexception e) {     throw new runtimeexception(e);   } }

if running code cache constructor instances, , appns instance if possible avoid performance overhead of reflection.

please note code not work on standard java 7 runtime.


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