如何从Java Google Cloud Endpoint处理程序访问API Explorer的“字段”字段？

Question

I would like to allow clients of my endpoints to mask the fields that my web service will return. I've noticed that there is a "fields" field in the Google APIs Explorer that looks like it is meant for this feature. However, I cannot find any documentation on how I can access "fields" from my Java Endpoints handler methods in order to carry out the wishes of the client and return the reduced set of data. Is this a supported feature? If so, how do I leverage it?

Answer 1

As there is no documentation found regarding this fields parameter I have to speak from my own experiments.

In my understanding Google Cloud Endpoints dispatcher does that field masking automatically. Returned object from your API method is processed by Jackson JSON parser which returns only fields given in fields parameter. Your object's fields should appear in field editor also.

Below is image how that field editor appears in Drive API. Your own Endpoints APIs should produce likewise field editor and Jackson should parse only fields you have selected.

NOTES:

• Appengine devserver (localhost) shows that field editor too but somehow does not take selected fields in account when parsing to JSON.
• In some cases field editor allows you to select fields in nested objects, in some cases not. I have not found out the logic behind this behaviour.
• If using Hibernate (or some other similar framework) with lazy-fetched fields you will probably face "could not initialize proxy" -error. In those cases you have to open Hibernate session manually in Endpoints. One solution I found is to inherit com.google.api.server.spi.SystemServiceServlet class and open session in doPost -method. That method handles all requests sent to Endpoints. You should also annotate your entities with @JsonIgnoreProperties({"hibernateLazyInitializer", "handler"}) -annotation as Jackson will fail trying to parse those fields.

Answer 2

In the Cloud Endpoints Generated Client code, you will find that for each of the methods that you have exposed, there is a setFields method that you can set. Use that and it should return the specific fields only.