Apache Calcite 快速入门指南

/**
 * Factory that creates a {@link CsvSchema}.
 *
 * <p>Allows a custom schema to be included in a <code><i>model</i>.json</code>
 * file.
 */
@SuppressWarnings("UnusedDeclaration")
public class CsvSchemaFactory implements SchemaFactory {
    /**
     * Public singleton, per factory contract.
     */
    public static final CsvSchemaFactory INSTANCE = new CsvSchemaFactory();
    
    private CsvSchemaFactory() {
    }
    
    @Override
    public Schema create(SchemaPlus parentSchema, String name, Map<String, Object> operand) {
        final String directory = (String) operand.get("directory");
        final File base = (File) operand.get(ModelHandler.ExtraOperand.BASE_DIRECTORY.camelName);
        File directoryFile = new File(directory);
        if (base != null && !directoryFile.isAbsolute()) {
            directoryFile = new File(base, directory);
        }
        String flavorName = (String) operand.get("flavor");
        CsvTable.Flavor flavor;
        if (flavorName == null) {
            flavor = CsvTable.Flavor.SCANNABLE;
        } else {
            flavor = CsvTable.Flavor.valueOf(flavorName.toUpperCase(Locale.ROOT));
        }
        return new CsvSchema(directoryFile, flavor);
    }
}

/**
 * Schema mapped onto a directory of CSV files. Each table in the schema
 * is a CSV file in that directory.
 */
public class CsvSchema extends AbstractSchema {
    private final File directoryFile;
    private final CsvTable.Flavor flavor;
    private Map<String, Table> tableMap;
    
    /**
     * Creates a CSV schema.
     *
     * @param directoryFile Directory that holds {@code .csv} files
     * @param flavor Whether to instantiate flavor tables that undergo
     * query optimization
     */
    public CsvSchema(File directoryFile, CsvTable.Flavor flavor) {
        super();
        this.directoryFile = directoryFile;
        this.flavor = flavor;
    }
    
    /**
     * Looks for a suffix on a string and returns
     * either the string with the suffix removed
     * or the original string.
     */
    private static String trim(String s, String suffix) {
        String trimmed = trimOrNull(s, suffix);
        return trimmed != null ? trimmed : s;
    }
    
    /**
     * Looks for a suffix on a string and returns
     * either the string with the suffix removed
     * or null.
     */
    private static String trimOrNull(String s, String suffix) {
        return s.endsWith(suffix) ? s.substring(0, s.length() - suffix.length()) : null;
    }
    
    @Override
    protected Map<String, Table> getTableMap() {
        if (tableMap == null) {
            tableMap = createTableMap();
        }
        return tableMap;
    }
    
    private Map<String, Table> createTableMap() {
        // Look for files in the directory ending in ".csv", ".csv.gz", ".json",
        // ".json.gz".
        final Source baseSource = Sources.of(directoryFile);
        File[] files = directoryFile.listFiles((dir, name) -> {
            final String nameSansGz = trim(name, ".gz");
            return nameSansGz.endsWith(".csv") || nameSansGz.endsWith(".json");
        });
        if (files == null) {
            System.out.println("directory " + directoryFile + " not found");
            files = new File[0];
        }
        // Build a map from table name to table; each file becomes a table.
        final ImmutableMap.Builder<String, Table> builder = ImmutableMap.builder();
        for (File file : files) {
            Source source = Sources.of(file);
            Source sourceSansGz = source.trim(".gz");
            final Source sourceSansJson = sourceSansGz.trimOrNull(".json");
            if (sourceSansJson != null) {
                final Table table = new JsonScannableTable(source);
                builder.put(sourceSansJson.relative(baseSource).path(), table);
            }
            final Source sourceSansCsv = sourceSansGz.trimOrNull(".csv");
            if (sourceSansCsv != null) {
                final Table table = createTable(source);
                builder.put(sourceSansCsv.relative(baseSource).path(), table);
            }
        }
        return builder.build();
    }
    
    /**
     * Creates different sub-type of table based on the "flavor" attribute.
     */
    private Table createTable(Source source) {
        switch (flavor) {
            case TRANSLATABLE:
                return new CsvTranslatableTable(source, null);
            case SCANNABLE:
                return new CsvScannableTable(source, null);
            case FILTERABLE:
                return new CsvFilterableTable(source, null);
            default:
                throw new AssertionError("Unknown flavor " + this.flavor);
        }
    }
}