For example, if you use the Images API to resize images, you can use the Capabilities API to detect when the Images API is unavailable and skip the resize:

import com.google.appengine.api.capabilities.*;

CapabilitiesService service =
    CapabilitiesServiceFactory.getCapabilitiesService();
CapabilityStatus status = service.getStatus(Capability.IMAGES).getStatus();

if (status == CapabilityStatus.DISABLED) {
    // Images API is not available.
}

You can separately query for the availability of Datastore reads and writes. The following sample shows how to detect the availability of Datastore writes and, during downtime, provide a message to users:

CapabilityStatus status =
    service.getStatus(Capability.DATASTORE_WRITE).getStatus();

if (status == CapabilityStatus.DISABLED) {
    // Datastore is in read-only mode.
}

Using the Capabilities API in Java

Each Capability is represented as a static constant on the Capability class (such as Capability.DATASTORE_WRITE ). Each Capability has a state, which you can retrieve from CapabilitiesService.getStatus(Capability) . Each state has a status, which is an enumeration reflecting a the availability of a capability: either ENABLED or DISABLED . See below for the list of services currently enabled in this API.

Supported capabilities

The API currently supports the following capabilities:

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