Writing a simple Kudu Java API Program

2015-10-01

This post is about using Apache Kudu service, via its Java API interface, in a Maven-based Java project.

Kudu ships with a Java client library that is ready to use via an Apache Maven build configuration.

The dependency to add in a pom.xml would be:

<dependency>
  <groupId>org.apache.kudu</groupId>
  <artifactId>kudu-client</artifactId>
  <version>1.0.0</version>
</dependency>

To start off, you will need to create a KuduClient object, like such:

KuduClient kuduClient =
  new KuduClientBuilder("kudu-master-hostname")
  .build();

To create a table, a schema needs to be built first, and then created via the client.

Lets say we have a simple schema for table users, with columns username with type (string, key) and age with type (8-bit signed int, value), then we can create it as shown below, utilising ColumnSchema and Schema objects via the previously created kuduClient object (above):

ColumnSchema usernameCol = new ColumnSchemaBuilder("username", Type.STRING)
  .key(true)
  .build();
ColumnSchema ageCol = new ColumnSchemaBuilder("age", Type.INT8)
  .build();

List<ColumnSchema> columns = new ArrayList<ColumnSchema>();
columns.add(usernameCol);
columns.add(ageCol);

Schema schema = new Schema(columns);
String tableName = "users";

if (!kuduClient.tableExists(tableName)) {
  client.createTable(tableName, schema);
}

Data work (such as inserts, updates or deletes) in Kudu are done over Sessions. The below shows how to insert a row after creating a Session and a KuduTable connection for the table users and applying an insert instruction through it:

KuduSession session = kuduClient.newSession();
KuduTable table = kuduClient.openTable(tableName);

Insert insert = table.newInsert();
insert.getRow().addString("username", "harshj");
insert.getRow().addInt("age", 25);

session.apply(insert);

Likewise, you can update existing rows:

Update update = table.newUpdate();
// Specify the key (unchanged)
update.getRow().addString("username", "harshj");
// Change age from value '25' previously written to '26'
update.getRow().addInt("age", 26);

session.apply(update);

Or even delete them by key (username column):

Delete delete = table.newDelete();
delete.getRow().addString("username", "harshj");

session.apply(delete);

Reading rows can be done via the KuduScanner class. The below example shows how to fetch only the key column data (all rows):

List<String> columnNames = new ArrayList<String>();
columnNames.add("username");

KuduScanner scanner = kuduClient.newScannerBuilder(tableName)
  .setProjectedColumnNames(columnNames)
  .build();

while (scanner.hasMoreRows()) {
  for (RowResult row : scanner.nextRows()) {
    System.out.println(row.getString("username"));
  }
}

Another fully runnable example can be found on Kudu’s kudu-examples repository.