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DataStax Astra DB Serverless Documentation

    • Overview
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      • Grant a user access
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        • Connecting custom DNS
      • Connecting Change Data Capture (CDC)
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      • Phase 1: Deploy ZDM Proxy and connect client applications
        • Set up the ZDM Automation with ZDM Utility
        • Deploy the ZDM Proxy and monitoring
          • Configure Transport Layer Security
        • Connect client applications to ZDM Proxy
        • Manage your ZDM Proxy instances
      • Phase 2: Migrate and validate data
      • Phase 3: Enable asynchronous dual reads
      • Phase 4: Change read routing to Target
      • Phase 5: Connect client applications directly to Target
      • Additional resources
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    • Managing
      • Managing your organization
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      • Managing your database
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      • Managing with DevOps API
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    • Developing with Stargate APIs
      • Develop with REST
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        • Develop with GraphQL (CQL-first)
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      • Develop with gRPC
        • gRPC Rust client
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    • Stargate QuickStarts
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      • DevOps REST API v2
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  • DataStax Astra DB Serverless Documentation
  • Java developing

Java developing

Generating gRPC code stubs

To see a guide how the Java code is compiled from the proto files see the gRPC setup project dependencies. To update the protobuf files being used, add the new files to the top level proto directory and then run make proto from the root of the project.

More notes on the asynchronous use of the gRPC API

Up to this point, we were using the blocking version of the generated stub. We can also interact with the Stargate API using the async version of the stub. To do so, we need to pass the StreamObserver that will be called asynchronously when the results are available.

Every StreamObserver needs to implement 3 methods: onNext(), onError() and onComplete(). For example:

StreamObserver<QueryOuterClass.Response> streamObserver = new StreamObserver<QueryOuterClass.Response>() {
           @Override
           public void onNext(QueryOuterClass.Response response) {
               try {
                   System.out.println("response:" + response.getResultSet());
               } catch (InvalidProtocolBufferException e) {
                   throw new RuntimeException(e);
               }
           }
           @Override
           public void onError(Throwable throwable) {
               System.out.println("Error: " + throwable);
           }
           @Override
           public void onCompleted() {
               // close resources, finish processing
               System.out.println("completed");
           }
       };

Please note that this is a very simplified version only for demonstration purposes and should not be used on production.

Once we have the Observer, we can pass it to the executeQuery method on the async stub:

stub.executeQuery(QueryOuterClass.Query
  .newBuilder()
  .setCql("SELECT k, v FROM ks.test")
  .build(), streamObserver);

This query will return immediately because it is non-blocking. If your program (or test) is progressing to the end, you may not be able to see the results. Your program may exit before the data arrives. After some time, when the data arrives, the streamObserver will be called.

The output of our program will look like this:

response:columns {
  type {
    basic: VARCHAR
  }
  name: "k"
}
columns {
  type {
    basic: INT
  }
  name: "v"
}
rows {
  values {
    string: "a"
  }
  values {
    int: 1
  }
}

completed

Please note, that at the end we have a completed emitted. This is called by the onCompleted method.

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