Example: Java App Engine standard environment

This example is an App Engine application, written in Java, that writes some "hello world" greetings to a Bigtable table and reads them back. The application runs on Google Cloud in the App Engine standard environment. The application uses the Java 8 runtime. The code for this application is in the GitHub repository GoogleCloudPlatform/java-docs-samples, in the directory appengine-java8/bigtable.

Overview of the code sample

The code sample includes the following classes:

BigtableHelper

BigtableHelper provides a method to create a connection to Bigtable. It also caches the connection and provides a method that will retrieve the cached connection if it exists. Creating a connection is a relatively expensive operation, so as a best practice you should always create a single connection and reuse it.

public static void connect() throws IOException {  if (PROJECT_ID == null || INSTANCE_ID == null) {  if (sc != null) {  sc.log("environment variables BIGTABLE_PROJECT, and BIGTABLE_INSTANCE need to be defined.");  }  return;  }  connection = BigtableConfiguration.connect(PROJECT_ID, INSTANCE_ID); } /**  * Get the shared connection to Cloud Bigtable.  *  * @return the connection  */ public static Connection getConnection() {  if (connection == null) {  try {  connect();  } catch (IOException e) {  if (sc != null) {  sc.log("connect ", e);  }  }  }  if (connection == null) {  if (sc != null) {  sc.log("BigtableHelper-No Connection");  }  }  return connection; }

BigtableHelloWorld

BigtableHelloWorld is used to write a series of greetings to Bigtable, read the greetings, and then display them. The class gets a Bigtable connection from BigtableHelper, uses the connection to get a Table object, which lets you to read and write values, then uses the Table object to write to and read from the table.

 /**  * A minimal application that connects to Cloud Bigtable using the native HBase API and performs  * some basic operations.  */ public class BigtableHelloWorld {  // Refer to table metadata names by byte array in the HBase API  private static final byte[] TABLE_NAME = Bytes.toBytes("Hello-Bigtable");  private static final byte[] COLUMN_FAMILY_NAME = Bytes.toBytes("cf1");  private static final byte[] COLUMN_NAME = Bytes.toBytes("greeting");  // Write some friendly greetings to Cloud Bigtable  private static final String[] GREETINGS = {  "Hello World!", "Hello Cloud Bigtable!", "Hello HBase!"  };  /**  * Create a table -- first time only.  *  * @param connection to Bigtable  * @return the status  */  public static String create(Connection connection) {  try {  // The admin API lets us create, manage and delete tables  Admin admin = connection.getAdmin();  // Create a table with a single column family  HTableDescriptor descriptor = new HTableDescriptor(TableName.valueOf(TABLE_NAME));  descriptor.addFamily(new HColumnDescriptor(COLUMN_FAMILY_NAME));  admin.createTable(descriptor);  } catch (IOException e) {  return "Table exists.";  }  return "Create table " + Bytes.toString(TABLE_NAME);  }  /** Connects to Cloud Bigtable, runs some basic operations and prints the results. */  public static String doHelloWorld() {  StringBuilder result = new StringBuilder();  // Create the Bigtable connection, use try-with-resources to make sure it gets closed  Connection connection = BigtableHelper.getConnection();  result.append(create(connection));  result.append("<br><br>");  try (Table table = connection.getTable(TableName.valueOf(TABLE_NAME))) {  // Retrieve the table we just created so we can do some reads and writes  // Write some rows to the table  result.append("Write some greetings to the table<br>");  for (int i = 0; i < GREETINGS.length; i++) {  // Each row has a unique row key.  //  // Note: This example uses sequential numeric IDs for simplicity, but  // this can result in poor performance in a production application.  // Since rows are stored in sorted order by key, sequential keys can  // result in poor distribution of operations across nodes.  //  // For more information about how to design a Bigtable schema for the  // best performance, see the documentation:  //  // https://cloud.google.com/bigtable/docs/schema-design  String rowKey = "greeting" + i;  // Put a single row into the table. We could also pass a list of Puts to write a batch.  Put put = new Put(Bytes.toBytes(rowKey));  put.addColumn(COLUMN_FAMILY_NAME, COLUMN_NAME, Bytes.toBytes(GREETINGS[i]));  table.put(put);  }  // Get the first greeting by row key  String rowKey = "greeting0";  Result getResult = table.get(new Get(Bytes.toBytes(rowKey)));  String greeting = Bytes.toString(getResult.getValue(COLUMN_FAMILY_NAME, COLUMN_NAME));  result.append("Get a single greeting by row key<br>");  result.append(" ");  result.append(rowKey);  result.append("= ");  result.append(greeting);  result.append("<br>");  // Now scan across all rows.  Scan scan = new Scan();  result.append("Scan for all greetings:");  ResultScanner scanner = table.getScanner(scan);  for (Result row : scanner) {  byte[] valueBytes = row.getValue(COLUMN_FAMILY_NAME, COLUMN_NAME);  result.append(" ");  result.append(Bytes.toString(valueBytes));  result.append("<br>");  }  } catch (IOException e) {  result.append("Exception while running HelloWorld: " + e.getMessage() + "<br>");  result.append(e.toString());  return result.toString();  }  return result.toString();  } }