I am trying to generate java client library for my existing web application, but each time a select \"generate cloud endpoint client library\" the eclipse shows progress dia
You should be able to find out at least a little bit more information about the error in generating the library by looking at the Eclipse error log. However, I'm guessing the error is something generic like a 503
error from the service that generates the library.
The most common reason for those types of errors is that you're using an incompatible type in your entity class. Using the command line tool won't help in this case.
However, there are some cases where the command line tool has succeeded when GPE has failed. To generate the library without GPE run the following from the root of your application:
$SDK/bin/endpoints.sh get-java-client-lib helloworld.endpoint.HelloWorldEndpoint
Replace helloworld.endpoint.HelloWorldEndpoint
with the space-delimited name(s) of your Endpoint class(es).