presto-example-http/src/main/java/io/prestosql/plugin/example/ExampleMetadata.java/ExampleMetadata/getColumnHandles
class ExampleMetadata:    @Override
    public Map<String, ColumnHandle> getColumnHandles(ConnectorSession session, ConnectorTableHandle tableHandle)
    {
        ExampleTableHandle exampleTableHandle = (ExampleTableHandle) tableHandle;

        ExampleTable table = exampleClient.getTable(exampleTableHandle.getSchemaName(), exampleTableHandle.getTableName());
        if (table == null) {
            throw new TableNotFoundException(exampleTableHandle.toSchemaTableName());
        }

        ImmutableMap.Builder<String, ColumnHandle> columnHandles = ImmutableMap.builder();
        int index = 0;
        for (ColumnMetadata column : table.getColumnsMetadata()) {
            columnHandles.put(column.getName(), new ExampleColumnHandle(column.getName(), column.getType(), index));
            index++;
        }
        return columnHandles.build();
    }