Getting started with Google Cloud Datastore and Java/Protobuf
Setup
Before running through the steps below, make sure that:
- You have enabled Google Cloud Datastore API.
-
You have your
<dataset-id>(same identifier as your Google Cloud Project ID ). -
You are
connected
to a Compute Engine instance with both the
datastoreanduserinfo.emailscopes or have a<service-account>and the<path-to-private-key-file>. - You have a working Java environment with Maven (optional).
First,
download
and unzip the latest version of the
google-cloud-datastore
samples:
unzip google-cloud-datastore-1beta2-rev1-2.1.0.zip
If you are not connected to a Compute Engine instance, make sure to set the following environment variables to configure your credentials:
# ex: on a bash-like shell
export DATASTORE_SERVICE_ACCOUNT=<service-account>
export DATASTORE_PRIVATE_KEY_FILE=<path-to-private-key-file>
With Maven
Look at
google-cloud-datastore-1beta2-rev1-2.1.0/java/demos/pom.xml
to see how to configure a dependency to the
google-apis-service-datastore-protobuf
artifact:
<dependencies>
<dependency>
<groupId>com.google.apis</groupId>
<artifactId>google-api-services-datastore-protobuf</artifactId>
<version>v1beta2-rev1-2.1.0</version>
</dependency>
</dependencies>
Finally, run the
Adams
demo with your
<dataset-id>
as a parameter.
It will prompt for
the question
and validate your answer.
cd google-cloud-datastore-1beta2-rev1-2.1.0/java/demos
mvn package
mvn exec:java -Dexec.mainClass="com.google.api.services.datastore.demos.trivial.Adams" -Dexec.args="<dataset-id>"
Meaning of life?
> 11
Don't Panic!
Without Maven
- Download google-api-services-datastore-protobuf-java-v1beta2-rev1-2.1.0.zip
-
Run the following commands.
unzip google-api-services-datastore-protobuf-java-v1beta2-rev1-2.1.0.zip cd google-api-services-datastore-protobuf-java-v1beta2-rev1-2.1.0 java -jar google-api-services-datastore-protobuf-demos-all-deps-v1beta2-rev1-2.1.0.jar <dataset-id> Meaning of life? > 11 Don't Panic!
Study the code
The comments in the sample's source explain its behavior in detail:
package com.google.api.services.datastore.demos.trivial;
import com.google.api.services.datastore.DatastoreV1.*;
import com.google.api.services.datastore.client.Datastore;
import com.google.api.services.datastore.client.DatastoreException;
import com.google.api.services.datastore.client.DatastoreFactory;
import com.google.api.services.datastore.client.DatastoreHelper;
import com.google.protobuf.ByteString;
import java.io.IOException;
import java.security.GeneralSecurityException;
/**
* A trivial command-line application using the Datastore API.
*/
public class Adams {
public static void main(String[] args) {
if (args.length < 1) {
System.err.println("Usage: Adams <DATASET_ID>");
System.exit(1);
}
// Set the dataset from the command line parameters.
String datasetId = args[0];
Datastore datastore = null;
try {
// Setup the connection to Google Cloud Datastore and infer credentials
// from the environment.
datastore = DatastoreFactory.get().create(DatastoreHelper.getOptionsfromEnv()
.dataset(datasetId).build());
} catch (GeneralSecurityException exception) {
System.err.println("Security error connecting to the datastore: " + exception.getMessage());
System.exit(1);
} catch (IOException exception) {
System.err.println("I/O error connecting to the datastore: " + exception.getMessage());
System.exit(1);
}
try {
// Create an RPC request to begin a new transaction.
BeginTransactionRequest.Builder treq = BeginTransactionRequest.newBuilder();
// Execute the RPC synchronously.
BeginTransactionResponse tres = datastore.beginTransaction(treq.build());
// Get the transaction handle from the response.
ByteString tx = tres.getTransaction();
// Create an RPC request to get entities by key.
LookupRequest.Builder lreq = LookupRequest.newBuilder();
// Set the entity key with only one `path_element`: no parent.
Key.Builder key = Key.newBuilder().addPathElement(
Key.PathElement.newBuilder()
.setKind("Trivia")
.setName("hgtg"));
// Add one key to the lookup request.
lreq.addKey(key);
// Set the transaction, so we get a consistent snapshot of the
// entity at the time the transaction started.
lreq.getReadOptionsBuilder().setTransaction(tx);
// Execute the RPC and get the response.
LookupResponse lresp = datastore.lookup(lreq.build());
// Create an RPC request to commit the transaction.
CommitRequest.Builder creq = CommitRequest.newBuilder();
// Set the transaction to commit.
creq.setTransaction(tx);
Entity entity;
if (lresp.getFoundCount() > 0) {
entity = lresp.getFound(0).getEntity();
} else {
// If no entity was found, create a new one.
Entity.Builder entityBuilder = Entity.newBuilder();
// Set the entity key.
entityBuilder.setKey(key);
// Add two entity properties:
// - a utf-8 string: `question`
entityBuilder.addProperty(Property.newBuilder()
.setName("question")
.setValue(Value.newBuilder().setStringValue("Meaning of Life?")));
// - a 64bit integer: `answer`
entityBuilder.addProperty(Property.newBuilder()
.setName("answer")
.setValue(Value.newBuilder().setIntegerValue(42)));
// Build the entity.
entity = entityBuilder.build();
// Insert the entity in the commit request mutation.
creq.getMutationBuilder().addInsert(entity);
}
// Execute the Commit RPC synchronously and ignore the response.
// Apply the insert mutation if the entity was not found and close
// the transaction.
datastore.commit(creq.build());
// Get `question` property value.
String question = entity.getProperty(0).getValue().getStringValue();
// Get `answer` property value.
Long answer = entity.getProperty(1).getValue().getIntegerValue();
System.out.println(question);
String result = System.console().readLine("> ");
if (result.equals(answer.toString())) {
System.out.println("fascinating, extraordinary and, " +
"when you think hard about it, completely obvious.");
} else {
System.out.println("Don't Panic!");
}
} catch (DatastoreException exception) {
// Catch all Datastore rpc errors.
System.err.println("Error while doing datastore operation");
// Log the exception, the name of the method called and the error code.
System.err.println(String.format("DatastoreException(%s): %s %s",
exception.getMessage(),
exception.getMethodName(),
exception.getCode()));
System.exit(1);
}
}
}
With this example, you learned how to use the:
-
com.google.api.services.datastore.clientpackage to connect to the Datastore API. -
beginTransactionmethod to start a transaction. -
lookupmethod to retrieve entities by key from your dataset. -
commitmethod to send mutations to entities in your dataset and commit the transaction.
Now, you are now ready to learn more about the Key Datastore Concepts and look at the JAVA API reference and the Protocol Buffers service definition .