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State management sample

This sample illustrates the capabilities provided by Dapr Java SDK for state management. For further information about state management please refer to this link

Pre-requisites

Checking out the code

Clone this repository:

git clone https://github.com/dapr/java-sdk.git
cd java-sdk

Then build the Maven project:

# make sure you are in the `java-sdk` directory.
mvn install

Then change into the examples directory:

cd examples

Initialize Dapr

Run dapr init to initialize Dapr in Self-Hosted Mode if it's not already initialized.

Run MongoDB

docker compose -f ./src/main/java/io/dapr/examples/state/docker-compose-single-mongo.yml up -d

Running the StateClient

This example uses the Java SDK Dapr client in order to save, retrieve and delete a state, in this case, an instance of a class. Multiple state stores are supported since Dapr 0.4. See the code snippet bellow:

public class StateClient {
  ///...
  private static final String STATE_STORE_NAME = "statestore";

  private static final String FIRST_KEY_NAME = "myKey";

  private static final String SECOND_KEY_NAME = "myKey2";
  ///...
  public static void main(String[] args) throws Exception {
      try (DaprClient client = new DaprClientBuilder().build()) {
        System.out.println("Waiting for Dapr sidecar ...");
        client.waitForSidecar(10000).block();
        System.out.println("Dapr sidecar is ready.");

        String message = args.length == 0 ? " " : args[0];
  
        MyClass myClass = new MyClass();
        myClass.message = message;
        MyClass secondState = new MyClass();
        secondState.message = "test message";
  
        client.saveState(STATE_STORE_NAME, FIRST_KEY_NAME, myClass).block();
        System.out.println("Saving class with message: " + message);
  
        Mono<State<MyClass>> retrievedMessageMono = client.getState(STATE_STORE_NAME, FIRST_KEY_NAME, MyClass.class);
        System.out.println("Retrieved class message from state: " + (retrievedMessageMono.block().getValue()).message);
  
        System.out.println("Updating previous state and adding another state 'test state'... ");
        myClass.message = message + " updated";
        System.out.println("Saving updated class with message: " + myClass.message);
  
        // execute transaction
        List<TransactionalStateOperation<?>> operationList = new ArrayList<>();
        operationList.add(new TransactionalStateOperation<>(TransactionalStateOperation.OperationType.UPSERT,
            new State<>(FIRST_KEY_NAME, myClass, "")));
        operationList.add(new TransactionalStateOperation<>(TransactionalStateOperation.OperationType.UPSERT,
            new State<>(SECOND_KEY_NAME, secondState, "")));
  
        client.executeStateTransaction(STATE_STORE_NAME, operationList).block();
  
        // get multiple states
        Mono<List<State<MyClass>>> retrievedMessagesMono = client.getStates(STATE_STORE_NAME,
            Arrays.asList(FIRST_KEY_NAME, SECOND_KEY_NAME), MyClass.class);
        System.out.println("Retrieved messages using bulk get:");
        retrievedMessagesMono.block().forEach(System.out::println);
  
        System.out.println("Deleting states...");

        System.out.println("Verify delete key request is aborted if an etag different from stored is passed.");
        // delete state API
        try {
          client.deleteState(STATE_STORE_NAME, FIRST_KEY_NAME, "100", null).block();
        } catch (DaprException ex) {
          if (ex.getErrorCode().equals(Status.Code.ABORTED.toString())) {
            // Expected error due to etag mismatch.
            System.out.println(String.format("Expected failure. %s ", ex.getMessage()));
          } else {
            System.out.println("Unexpected exception.");
            throw ex;
          }
        }

        System.out.println("Trying to delete again with correct etag.");
        String storedEtag = client.getState(STATE_STORE_NAME, FIRST_KEY_NAME, MyClass.class).block().getEtag();
        client.deleteState(STATE_STORE_NAME, FIRST_KEY_NAME, storedEtag, null).block();
  
        // Delete operation using transaction API
        operationList.clear();
        operationList.add(new TransactionalStateOperation<>(TransactionalStateOperation.OperationType.DELETE,
            new State<>(SECOND_KEY_NAME)));
        client.executeStateTransaction(STATE_STORE_NAME, operationList).block();
  
        Mono<List<State<MyClass>>> retrievedDeletedMessageMono = client.getStates(STATE_STORE_NAME,
            Arrays.asList(FIRST_KEY_NAME, SECOND_KEY_NAME), MyClass.class);
        System.out.println("Trying to retrieve deleted states: ");
        retrievedDeletedMessageMono.block().forEach(System.out::println);
  
        // This is an example, so for simplicity we are just exiting here.
        // Normally a dapr app would be a web service and not exit main.
        System.out.println("Done");
      }
    }
}

The code uses the DaprClient created by the DaprClientBuilder. Notice that this builder uses default settings. Internally, it is using DefaultObjectSerializer for two properties: objectSerializer is for Dapr's sent and received objects, and stateSerializer is for objects to be persisted.

This example performs multiple operations:

  • client.waitForSidecar(...) for waiting until Dapr sidecar is ready.
  • client.saveState(...) for persisting an instance of MyClass.
  • client.getState(...) operation in order to retrieve back the persisted state using the same key.
  • client.executeStateTransaction(...) operation in order to update existing state and add new state.
  • client.getBulkState(...) operation in order to retrieve back the persisted states using the same keys.
  • client.deleteState(...) operation to remove one of the persisted states. An example of etag mismatch error is if something other than the current etag is added to request.
  • client.executeStateTransaction(...) operation in order to remove the other persisted state.

Finally, the code tries to retrieve the deleted states, which should not be found.

The Dapr client is also within a try-with-resource block to properly close the client at the end.

Running the example

Run this example with the following command:

dapr run --resources-path ./components/state --app-id state-example -- java -jar target/dapr-java-sdk-examples-exec.jar io.dapr.examples.state.StateClient 'my message'

Once running, the StateClient should print the output as follows:

== APP == Waiting for Dapr sidecar ...
== APP == Dapr sidecar is ready.
== APP == Saving class with message: my message
== APP == Retrieved class message from state: my message
== APP == Updating previous state and adding another state 'test state'... 
== APP == Saving updated class with message: my message updated
== APP == Retrieved messages using bulk get:
== APP == StateKeyValue{key='myKey', value=my message updated, etag='2', metadata={'{}'}, error='null', options={'null'}}
== APP == StateKeyValue{key='myKey2', value=test message, etag='1', metadata={'{}'}, error='null', options={'null'}}
== APP == Deleting states...
== APP == Verify delete key request is aborted if an etag different from stored is passed.
== APP == Expected failure. ABORTED: failed deleting state with key myKey: possible etag mismatch. error from state store: ERR Error running script (call to f_9b5da7354cb61e2ca9faff50f6c43b81c73c0b94): @user_script:1: user_script:1: failed to delete Tailmad-Fang||myKey 
== APP == Trying to delete again with correct etag.
== APP == Trying to retrieve deleted states: 
== APP == StateKeyValue{key='myKey', value=null, etag='null', metadata={'{}'}, error='null', options={'null'}}
== APP == StateKeyValue{key='myKey2', value=null, etag='null', metadata={'{}'}, error='null', options={'null'}}
== APP == Done

Cleanup

To close the app either press CTRL+C or run

dapr stop --app-id state-example

Then, stop MongoDB container.

docker compose -f ./src/main/java/io/dapr/examples/state/docker-compose-single-mongo.yml down