Fluo 1.2.0 documentation  >>  Getting started  >>  Create Application

Once you have Fluo installed, you can create and run Fluo applications consisting of clients and observers. This documentation shows how to create a Fluo client and observer.

Fluo Maven Dependencies

For both clients and observers, you will need to include the following in your Maven pom:

<dependency>
  <groupId>org.apache.fluo</groupId>
  <artifactId>fluo-api</artifactId>
  <version>1.2.0</version>
</dependency>
<dependency>
  <groupId>org.apache.fluo</groupId>
  <artifactId>fluo-core</artifactId>
  <version>1.2.0</version>
  <scope>runtime</scope>
</dependency>

Fluo provides a classpath command to help users build a runtime classpath. This command along with the hadoop jar command is useful when writing scripts to run Fluo client code. These commands allow the scripts to use the versions of Hadoop, Accumulo, and Zookeeper installed on a cluster.

Creating a Fluo client

To create a FluoClient, you will need to provide it with a FluoConfiguration object that is configured to connect to your Fluo instance.

If you have access to the fluo-conn.properties file that was used to configure your Fluo instance, you can use it to build a FluoConfiguration object with all necessary properties:

FluoConfiguration config = new FluoConfiguration(new File("fluo-conn.properties"));
config.setApplicationName("myapp");

You can also create an empty FluoConfiguration object and set properties using Java:

FluoConfiguration config = new FluoConfiguration();
config.setInstanceZookeepers("localhost/fluo");
config.setApplicationName("myapp");

Once you have FluoConfiguration object, pass it to the newClient() method of FluoFactory to create a FluoClient:

try(FluoClient client = FluoFactory.newClient(config)){

  try (Transaction tx = client.newTransaction()) {
    // read and write some data
    tx.commit();
  }

  try (Snapshot snapshot = client.newSnapshot()) {
    //read some data
  }
}

It may help to reference the API javadocs while you are learning the Fluo API.

Creating a Fluo observer

To create an observer, follow these steps:

1. Create one or more classes that extend Observer like the example below. It is a good idea to use slf4j for any logging in observers as slf4j supports multiple logging implementations.

   public class InvertObserver implements Observer {
   
     @Override
     public void process(TransactionBase tx, Bytes row, Column col) throws Exception {
       // read value
       Bytes value = tx.get(row, col);
       // invert row and value
       tx.set(value, new Column("inv", "data"), row);
     }
   }
   

2. Create a class that implements ObserverProvider like the example below. The purpose of this class is associate a set Observers with columns that trigger the observers. The class can register multiple observers.

   class AppObserverProvider implements ObserverProvider {
     @Override
     public void provide(Registry reg, Context ctx) {
       //setup InvertObserver to be triggered when the column obs:data is modified
       reg.forColumn(new Column("obs", "data"), NotificationType.STRONG)
         .useObserver(new InvertObserver());
           
       //Observer is a Functional interface.  So Observers can be written as lambdas.
       reg.forColumn(new Column("new","data"), NotificationType.WEAK)
         .useObserver((tx,row,col) -> {
            Bytes combined = combineNewAndOld(tx,row);
            tx.set(row, new Column("current","data"), combined);
          });
     }
   }
   

3. Build a jar containing these classes. Put this jar and any other dependencies required for your application in a directory. Set fluo.observer.init.dir in fluo-app.properties to the path of this directory. When your application is initialized, these jars will be loaded to HDFS to make them accessible to all of your Fluo workers on the cluster.
4. Configure your Fluo application to use your observer provider by modifying the Application section of fluo-app.properties. Set fluo.observer.provider to the observer provider class name.
5. Initialize your Fluo application as described in the next section. During initialization Fluo will obtain the observed columns from the ObserverProvider and persist the columns in Zookeeper. These columns persisted in Zookeeper are used by transactions to know when to trigger observers.

Next Steps

Initialize your Fluo application before running it.