Hello World Java

Questo esempio di codice è un'applicazione "hello world" scritta in Java, utilizzando la libreria client di Cloud Bigtable per Java. L'esempio illustra come completare le seguenti attività:

  • Connetterti a un'istanza Cloud Bigtable.
  • Crea una nuova tabella.
  • Scrivi i dati nella tabella.
  • Rileggi i dati.
  • Elimina la tabella.

Esempio di esecuzione

Questo codice comunica con Cloud Bigtable utilizzando la libreria Google Cloud Bigtable nelle Librerie client di Google Cloud per Java.

Prima di iniziare, segui le istruzioni su GitHub di esempio per Google Cloud Platform.

Utilizzo della libreria client di Cloud con Bigtable

L'applicazione di esempio si connette a Bigtable e dimostra alcune operazioni semplici.

Connessione a Bigtable

Per iniziare, ti servono un client di dati da utilizzare per comunicare con la libreria client dell'API di dati e un client di amministrazione della tabella che utilizzi per comunicare con la libreria client dell'API di amministrazione.

Per prima cosa, crea un'istanza di un oggetto BigtableDataSettings che includa l'ID progetto e l'ID istanza che verranno utilizzati dall'applicazione hello world. Passa quindi le impostazioni al metodo BigtableDataClient.create() per creare il client di dati.

Analogamente, per il client di amministrazione, definisci innanzitutto le impostazioni creando un oggetto BigtableTableAdminSettings, quindi utilizza le impostazioni per creare un oggetto BigtableTableAdminClient.

Come best practice, quando utilizzi Bigtable, devi sempre creare un client una sola volta e riutilizzarlo in tutta l'applicazione.

samples/snippets/src/main/java/com/example/bigtable/HelloWorld.java 
// Creates the settings to configure a bigtable data client.
BigtableDataSettings settings =
    BigtableDataSettings.newBuilder().setProjectId(projectId).setInstanceId(instanceId).build();

// Creates a bigtable data client.
dataClient = BigtableDataClient.create(settings);

// Creates the settings to configure a bigtable table admin client.
BigtableTableAdminSettings adminSettings =
    BigtableTableAdminSettings.newBuilder()
        .setProjectId(projectId)
        .setInstanceId(instanceId)
        .build();

// Creates a bigtable table admin client.
adminClient = BigtableTableAdminClient.create(adminSettings);

Creazione di una tabella

Per creare una tabella, crea un oggetto CreateTableRequest e trasmettilo al metodo createTable() del client di amministrazione.

samples/snippets/src/main/java/com/example/bigtable/HelloWorld.java 
// Checks if table exists, creates table if does not exist.
if (!adminClient.exists(tableId)) {
  System.out.println("Creating table: " + tableId);
  CreateTableRequest createTableRequest =
      CreateTableRequest.of(tableId).addFamily(COLUMN_FAMILY);
  adminClient.createTable(createTableRequest);
  System.out.printf("Table %s created successfully%n", tableId);
}

Scrivere righe in una tabella

Crea un array di stringhe greetings[] contenente tre semplici saluti, da utilizzare come origine dati per scrivere nella tabella. Scorri l'array. In ogni iterazione del loop, crea un oggetto RowMutation e utilizza il metodo setCell() per aggiungere una voce alla modifica.

samples/snippets/src/main/java/com/example/bigtable/HelloWorld.java 
try {
  System.out.println("\nWriting some greetings to the table");
  String[] names = {"World", "Bigtable", "Java"};
  for (int i = 0; i < names.length; i++) {
    String greeting = "Hello " + names[i] + "!";
    RowMutation rowMutation =
        RowMutation.create(tableId, ROW_KEY_PREFIX + i)
            .setCell(COLUMN_FAMILY, COLUMN_QUALIFIER_NAME, names[i])
            .setCell(COLUMN_FAMILY, COLUMN_QUALIFIER_GREETING, greeting);
    dataClient.mutateRow(rowMutation);
    System.out.println(greeting);
  }
} catch (NotFoundException e) {
  System.err.println("Failed to write to non-existent table: " + e.getMessage());
}

Leggere una riga tramite la relativa chiave di riga

Utilizza il metodo readRow() del client di dati per leggere la prima riga che hai scritto.

samples/snippets/src/main/java/com/example/bigtable/HelloWorld.java 
try {
  System.out.println("\nReading a single row by row key");
  Row row = dataClient.readRow(tableId, ROW_KEY_PREFIX + 0);
  System.out.println("Row: " + row.getKey().toStringUtf8());
  for (RowCell cell : row.getCells()) {
    System.out.printf(
        "Family: %s    Qualifier: %s    Value: %s%n",
        cell.getFamily(), cell.getQualifier().toStringUtf8(), cell.getValue().toStringUtf8());
  }
  return row;
} catch (NotFoundException e) {
  System.err.println("Failed to read from a non-existent table: " + e.getMessage());
  return null;
}
try {
  System.out.println("\nReading specific cells by family and qualifier");
  Row row = dataClient.readRow(tableId, ROW_KEY_PREFIX + 0);
  System.out.println("Row: " + row.getKey().toStringUtf8());
  List<RowCell> cells = row.getCells(COLUMN_FAMILY, COLUMN_QUALIFIER_NAME);
  for (RowCell cell : cells) {
    System.out.printf(
        "Family: %s    Qualifier: %s    Value: %s%n",
        cell.getFamily(), cell.getQualifier().toStringUtf8(), cell.getValue().toStringUtf8());
  }
  return cells;
} catch (NotFoundException e) {
  System.err.println("Failed to read from a non-existent table: " + e.getMessage());
  return null;
}

Scansione di tutte le righe della tabella

Ora esegui la scansione dell'intera tabella. Crea un oggetto Query, passalo al metodo readRows() e assegna i risultati a un flusso di righe.

samples/snippets/src/main/java/com/example/bigtable/HelloWorld.java 
try {
  System.out.println("\nReading the entire table");
  Query query = Query.create(tableId);
  ServerStream<Row> rowStream = dataClient.readRows(query);
  List<Row> tableRows = new ArrayList<>();
  for (Row r : rowStream) {
    System.out.println("Row Key: " + r.getKey().toStringUtf8());
    tableRows.add(r);
    for (RowCell cell : r.getCells()) {
      System.out.printf(
          "Family: %s    Qualifier: %s    Value: %s%n",
          cell.getFamily(), cell.getQualifier().toStringUtf8(), cell.getValue().toStringUtf8());
    }
  }
  return tableRows;
} catch (NotFoundException e) {
  System.err.println("Failed to read a non-existent table: " + e.getMessage());
  return null;
}

Eliminazione di una tabella

Infine, elimina la tabella con il metodo deleteTable().

samples/snippets/src/main/java/com/example/bigtable/HelloWorld.java 
System.out.println("\nDeleting table: " + tableId);
try {
  adminClient.deleteTable(tableId);
  System.out.printf("Table %s deleted successfully%n", tableId);
} catch (NotFoundException e) {
  System.err.println("Failed to delete a non-existent table: " + e.getMessage());
}

Riepilogo

Ecco l'esempio di codice completo senza commenti.

samples/snippets/src/main/java/com/example/bigtable/HelloWorld.java 

package com.example.bigtable;

import static com.google.cloud.bigtable.data.v2.models.Filters.FILTERS;

import com.google.api.gax.rpc.NotFoundException;
import com.google.api.gax.rpc.ServerStream;
import com.google.cloud.bigtable.admin.v2.BigtableTableAdminClient;
import com.google.cloud.bigtable.admin.v2.BigtableTableAdminSettings;
import com.google.cloud.bigtable.admin.v2.models.CreateTableRequest;
import com.google.cloud.bigtable.data.v2.BigtableDataClient;
import com.google.cloud.bigtable.data.v2.BigtableDataSettings;
import com.google.cloud.bigtable.data.v2.models.Filters.Filter;
import com.google.cloud.bigtable.data.v2.models.Query;
import com.google.cloud.bigtable.data.v2.models.Row;
import com.google.cloud.bigtable.data.v2.models.RowCell;
import com.google.cloud.bigtable.data.v2.models.RowMutation;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Base64;
import java.util.List;

public class HelloWorld {

  private static final String COLUMN_FAMILY = "cf1";
  private static final String COLUMN_QUALIFIER_GREETING = "greeting";
  private static final String COLUMN_QUALIFIER_NAME = "name";
  private static final String ROW_KEY_PREFIX = "rowKey";
  private final String projectId;
  private final String instanceId;
  private final String tableId;
  private final BigtableDataClient dataClient;
  private final BigtableTableAdminClient adminClient;

  public static void main(String[] args) throws Exception {

    if (args.length != 2) {
      System.out.println("Missing required project id or instance id");
      return;
    }
    String projectId = args[0];
    String instanceId = args[1];

    HelloWorld helloWorld = new HelloWorld(projectId, instanceId, "test-table");
    helloWorld.run();
  }

  public HelloWorld(String projectId, String instanceId, String tableId) throws IOException {
    this.tableId = tableId;
    this.projectId = projectId;
    this.instanceId = instanceId;

    BigtableDataSettings settings =
        BigtableDataSettings.newBuilder().setProjectId(projectId).setInstanceId(instanceId).build();

    dataClient = BigtableDataClient.create(settings);

    BigtableTableAdminSettings adminSettings =
        BigtableTableAdminSettings.newBuilder()
            .setProjectId(projectId)
            .setInstanceId(instanceId)
            .build();

    adminClient = BigtableTableAdminClient.create(adminSettings);
  }

  public void run() throws Exception {
    createTable();
    writeToTable();
    readSingleRow();
    readSpecificCells();
    readTable();
    filterLimitCellsPerCol(this.projectId, this.instanceId, tableId);
    deleteTable();
    close();
  }

  public void close() {
    dataClient.close();
    adminClient.close();
  }

  public void createTable() {
    if (!adminClient.exists(tableId)) {
      System.out.println("Creating table: " + tableId);
      CreateTableRequest createTableRequest =
          CreateTableRequest.of(tableId).addFamily(COLUMN_FAMILY);
      adminClient.createTable(createTableRequest);
      System.out.printf("Table %s created successfully%n", tableId);
    }
  }

  public void writeToTable() {
    try {
      System.out.println("\nWriting some greetings to the table");
      String[] names = {"World", "Bigtable", "Java"};
      for (int i = 0; i < names.length; i++) {
        String greeting = "Hello " + names[i] + "!";
        RowMutation rowMutation =
            RowMutation.create(tableId, ROW_KEY_PREFIX + i)
                .setCell(COLUMN_FAMILY, COLUMN_QUALIFIER_NAME, names[i])
                .setCell(COLUMN_FAMILY, COLUMN_QUALIFIER_GREETING, greeting);
        dataClient.mutateRow(rowMutation);
        System.out.println(greeting);
      }
    } catch (NotFoundException e) {
      System.err.println("Failed to write to non-existent table: " + e.getMessage());
    }
  }

  public Row readSingleRow() {
    try {
      System.out.println("\nReading a single row by row key");
      Row row = dataClient.readRow(tableId, ROW_KEY_PREFIX + 0);
      System.out.println("Row: " + row.getKey().toStringUtf8());
      for (RowCell cell : row.getCells()) {
        System.out.printf(
            "Family: %s    Qualifier: %s    Value: %s%n",
            cell.getFamily(), cell.getQualifier().toStringUtf8(), cell.getValue().toStringUtf8());
      }
      return row;
    } catch (NotFoundException e) {
      System.err.println("Failed to read from a non-existent table: " + e.getMessage());
      return null;
    }
  }

  public List<RowCell> readSpecificCells() {
    try {
      System.out.println("\nReading specific cells by family and qualifier");
      Row row = dataClient.readRow(tableId, ROW_KEY_PREFIX + 0);
      System.out.println("Row: " + row.getKey().toStringUtf8());
      List<RowCell> cells = row.getCells(COLUMN_FAMILY, COLUMN_QUALIFIER_NAME);
      for (RowCell cell : cells) {
        System.out.printf(
            "Family: %s    Qualifier: %s    Value: %s%n",
            cell.getFamily(), cell.getQualifier().toStringUtf8(), cell.getValue().toStringUtf8());
      }
      return cells;
    } catch (NotFoundException e) {
      System.err.println("Failed to read from a non-existent table: " + e.getMessage());
      return null;
    }
  }

  public List<Row> readTable() {
    try {
      System.out.println("\nReading the entire table");
      Query query = Query.create(tableId);
      ServerStream<Row> rowStream = dataClient.readRows(query);
      List<Row> tableRows = new ArrayList<>();
      for (Row r : rowStream) {
        System.out.println("Row Key: " + r.getKey().toStringUtf8());
        tableRows.add(r);
        for (RowCell cell : r.getCells()) {
          System.out.printf(
              "Family: %s    Qualifier: %s    Value: %s%n",
              cell.getFamily(), cell.getQualifier().toStringUtf8(), cell.getValue().toStringUtf8());
        }
      }
      return tableRows;
    } catch (NotFoundException e) {
      System.err.println("Failed to read a non-existent table: " + e.getMessage());
      return null;
    }
  }

  public static void filterLimitCellsPerCol(String projectId, String instanceId, String tableId) {
    Filter filter = FILTERS.limit().cellsPerColumn(1);
    readRowFilter(projectId, instanceId, tableId, filter);
    readFilter(projectId, instanceId, tableId, filter);
  }

  private static void readRowFilter(
      String projectId, String instanceId, String tableId, Filter filter) {
    try (BigtableDataClient dataClient = BigtableDataClient.create(projectId, instanceId)) {
      String rowKey =
          Base64.getEncoder().encodeToString("greeting0".getBytes(StandardCharsets.UTF_8));
      Row row = dataClient.readRow(tableId, rowKey, filter);
      printRow(row);
      System.out.println("Row filter completed.");
    } catch (IOException e) {
      System.out.println(
          "Unable to initialize service client, as a network error occurred: \n" + e);
    }
  }

  private static void readFilter(
      String projectId, String instanceId, String tableId, Filter filter) {
    try (BigtableDataClient dataClient = BigtableDataClient.create(projectId, instanceId)) {
      Query query = Query.create(tableId).filter(filter);
      ServerStream<Row> rows = dataClient.readRows(query);
      for (Row row : rows) {
        printRow(row);
      }
      System.out.println("Table filter completed.");
    } catch (IOException e) {
      System.out.println(
          "Unable to initialize service client, as a network error occurred: \n" + e);
    }
  }

  public void deleteTable() {
    System.out.println("\nDeleting table: " + tableId);
    try {
      adminClient.deleteTable(tableId);
      System.out.printf("Table %s deleted successfully%n", tableId);
    } catch (NotFoundException e) {
      System.err.println("Failed to delete a non-existent table: " + e.getMessage());
    }
  }

  private static void printRow(Row row) {
    if (row == null) {
      return;
    }
    System.out.printf("Reading data for %s%n", row.getKey().toStringUtf8());
    String colFamily = "";
    for (RowCell cell : row.getCells()) {
      if (!cell.getFamily().equals(colFamily)) {
        colFamily = cell.getFamily();
        System.out.printf("Column Family %s%n", colFamily);
      }
      String labels =
          cell.getLabels().size() == 0 ? "" : " [" + String.join(",", cell.getLabels()) + "]";
      System.out.printf(
          "\t%s: %s @%s%s%n",
          cell.getQualifier().toStringUtf8(),
          cell.getValue().toStringUtf8(),
          cell.getTimestamp(),
          labels);
    }
    System.out.println();
  }
}