Dependencies

Guava version bumped to 20. It is not possible to use older versions of Guava with this version of gRPC. If this proves difficult to handle, please file an issue
netty: Netty version bumped to 4.1.22-Final. netty-tcnative 2.0.7.Final is still compatible

API changes

core: ManagedChannelBuilder.usePlaintext(boolean) is now deprecated. Use usePlaintext(void) instead, which is equivalent to usePlaintext(true). usePlaintext(false) was almost always a bug, but is still available by specifying NegotiationType.PLAINTEXT_UPGRADE to NettyChannelBuilder
bazel: grpc-java's Bazel workspace name was renamed to io_grpc_grpc_java. This was done to make the name more unique, since Bazel is now enforcing that users use the same name as in our workspace

core: Added ManagedChannel.enterIdle(). It gracefully shuts down any existing connections. This can have multiple uses, but is most immediately useful to allows smooth network interface changes on Android (#3688 #4179)
core: Added toString() to MethodDescriptor and ServiceDescriptor (#4013)
inprocess: Added InProcessServerBuilder.generateName(). This is a convenience for making a name instead of manually with UUID or similar
okhttp: Support for Conscrypt security provider. This allows you to include Conscrypt with your app and not depend on the OS nor Google Play Services Dynamic Security Provider for TLS support
inprocess: Added InProcessChannelBuilder.scheduledExecutorService(exec) to override the default timer executor used by gRPC
okhttp: Added OkHttpChannelBuilder.scheduledExecutorService(exec) to override the default timer executor used by gRPC
protobuf: Added StatusProto.fromStatusAndTrailers() to convert to a com.google.rpc.Status directly from a io.grpc.Status (instead of a Status*Exception)
alts: Added ALTS transport for Google Cloud Platform usage. It is similar to mutually authenticated TLS but with different protocol and trust model. ALTS is currently only available for whitelisted projects
cronet: Added API to apply TrafficStats tag and UID to Cronet GRPC channels (#4208)

core: ManagedChannel will now log when orphaned without proper shutdown (#4093)
core: Use exponential backoff for name resolution. After a NameResolver calls onError(), the channel will now automatically call refresh() after a delay. This replaced the hard-coded 60-second retry timer in the DNS name resolver. (#4105)
core: Added an internal panic mode for ManagedChannel. If the channel notices an internal uncaught exception it will attempt to put the channel into a permanent TRANSIENT_FAILURE state instead of hanging (#4023)
core: Servers that send too many or too few responses for a unary call will now properly see ServerCall.Listener.onCancel() called instead of onComplete(). The client will now see a cancellation instead of an explicit status message (#3819)
grpclb: Enter fallback mode immediately when balancer and all backend connections are lost (#4007)

Reduce false positive results of grpc/grpc-java-api-checker
core: Close InputStream returned by Marshallers for outgoing messages (#3419)
core: Fixed channel.getState(true) will not reconnect (#4170)
netty: Include more details for closure of unknown reason
netty: Client sends rst stream when server half-closes. This fixes a memory leak when server closes before client half closes (#4275)
netty: Fixed ProxySelector with Netty. This should finally enable the use of forward proxies that require authentication. Users should be able to migrate from GRPC_PROXY_EXP to -Dhttps.proxyHost at this time (#4137)
okhttp: Fixed HPACK reader bug. This resolves an incompatibility with nginx (#4277)