This project provides an implementation of EndpointsServlet with partial response support using "fields" parameter in Discovery-based APIs.

This feature used to be available in Cloud Endpoints v1, but was removed in v2.

It provides some additional features on top of partial responses:

• Validates the fields expression BEFORE calling backend methods, to avoid unnecessary work. This is disabled by default, enabled with "checkFieldsExpression=true" servlet init param
• Support for Json Pointer expressions if fields starts with a slash. This is disabled by default, enabled with "acceptJsonPointer=true" servlet init param

Some technical context:

• Antlr4 is used to generate the parser for the "fields" expression, and produces a tree describing the expression
• A similar structure is generated using Discovery files, so valid fields expression can be checked
• JSON "filtering" is implemented using the FilteringGeneratorDelegate feature from Jackson

To use this feature, just replace the declaration of com.google.api.server.spi.EndpointsServlet with com.aodocs.partialresponse.servlet.PartialResponseEndpointsServlet in your web.xml (or use annotations).