Tablestore:Read data by using an iterator

Prerequisites

A client is initialized. For more information, see Initialize a Tablestore client.

Method description

public Iterator<Row> createRangeIterator(RangeIteratorParameter rangeIteratorParameter) throws TableStoreException, ClientException

Sample code

The following sample code demonstrates how to use an iterator to read data from the test_table table starting from the primary key value row1.

public static void createRangeIteratorExample(SyncClient client) {
    // Construct the iterative query condition.
    RangeIteratorParameter rangeIteratorParameter = new RangeIteratorParameter("test_table");
    // Specify the start primary key for the iterative query.
    PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
    primaryKeyBuilder.addPrimaryKeyColumn("id", PrimaryKeyValue.fromString("row1"));
    rangeIteratorParameter.setInclusiveStartPrimaryKey(primaryKeyBuilder.build());
    // Specify the end primary key for the iterative query. The result does not include the end primary key.
    primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
    primaryKeyBuilder.addPrimaryKeyColumn("id", PrimaryKeyValue.INF_MAX);
    rangeIteratorParameter.setExclusiveEndPrimaryKey(primaryKeyBuilder.build());
    // Specify the version to query.
    rangeIteratorParameter.setMaxVersions(1);

    // Call createRangeIterator to obtain the iterator.
    Iterator<Row> iterator = client.createRangeIterator(rangeIteratorParameter);
    while(iterator.hasNext()) {
        Row row = iterator.next();
        System.out.println(row);
    }
}

You can refer to the following sample code to configure parameters when you read data by using an iterator.

• Specify the direction in which data is read.

  // Specify that data is read in backward direction.
  rangeIteratorParameter.setDirection(Direction.BACKWARD);
  // Specify the start primary key for the iterative query. When you read data in backward direction, the start primary key must be larger than the end primary key.
  PrimaryKeyBuilder primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
  primaryKeyBuilder.addPrimaryKeyColumn("id", PrimaryKeyValue.INF_MAX);
  rangeIteratorParameter.setInclusiveStartPrimaryKey(primaryKeyBuilder.build());
  // Specify the end primary key for the iterative query. The result does not include the end primary key.
  primaryKeyBuilder = PrimaryKeyBuilder.createPrimaryKeyBuilder();
  primaryKeyBuilder.addPrimaryKeyColumn("id", PrimaryKeyValue.fromString("row1"));
  rangeIteratorParameter.setExclusiveEndPrimaryKey(primaryKeyBuilder.build());

• Specify the version range for the data to read. Only data within this range is returned.

  // Set the version range to query data from one day ago to the current time.
  rangeIteratorParameter.setTimeRange(new TimeRange(System.currentTimeMillis() - 86400*1000, System.currentTimeMillis()));

• Specify the maximum number of rows to read by using an iterator.

  rangeIteratorParameter.setMaxCount(20);

• Specify the buffer size.

  rangeIteratorParameter.setBufferSize(5);

• Specify the attribute columns to read.

  rangeIteratorParameter.addColumnsToGet("col2");

References

• Use the local transaction feature

• Read data whose primary key values are in the specified range

• Read multiple rows of data at the same time

• Read data concurrently by using TableStoreReader