Custom codecs¶

// cqlsh:ks> desc table test;
// CREATE TABLE ks.test (k int PRIMARY KEY, v text)...
ResultSet rs = session.execute("SELECT * FROM ks.test WHERE k = 1");
String v = rs.one().getString("v");

public class CqlIntToStringCodec implements TypeCodec<String> {

  @Override
  public GenericType<String> getJavaType() {
    return GenericType.STRING;
  }

  @Override
  public DataType getCqlType() {
    return DataTypes.INT;
  }

  @Override
  public ByteBuffer encode(String value, ProtocolVersion protocolVersion) {
    if (value == null) {
      return null;
    } else {
      int intValue = Integer.parseInt(value);
      return TypeCodecs.INT.encode(intValue, protocolVersion);
    }
  }

  @Override
  public String decode(ByteBuffer bytes, ProtocolVersion protocolVersion) {
    Integer intValue = TypeCodecs.INT.decode(bytes, protocolVersion);
    return intValue.toString();
  }

  @Override
  public String format(String value) {
    int intValue = Integer.parseInt(value);
    return TypeCodecs.INT.format(intValue);
  }

  @Override
  public String parse(String value) {
    Integer intValue = TypeCodecs.INT.parse(value);
    return intValue == null ? null : intValue.toString();
  }
}

enum WeekDay { MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY };
class Price {
  ... // a custom POJO that will be serialized as JSON
}

CqlSession session =
  CqlSession.builder()
    .addTypeCodecs(
      new CqlIntToStringCodec(),                  // user-created codec
      ExtraTypeCodecs.ZONED_TIMESTAMP_PERSISTED,  // tuple<timestamp,text> <-> ZonedDateTime
      ExtraTypeCodecs.BLOB_TO_ARRAY,              // blob <-> byte[]
      ExtraTypeCodecs.arrayOf(TypeCodecs.TEXT),   // list<text> <-> String[]
      ExtraTypeCodecs.enumNamesOf(WeekDay.class), // text <-> WeekDay
      ExtraTypeCodecs.json(Price.class),          // text <-> MyJsonPojo
      ExtraTypeCodecs.optionalOf(TypeCodecs.UUID) // uuid <-> Optional<UUID>
    )
    .build();

// The cast is required for backward compatibility reasons (registry mutability was introduced in
// 4.3.0). It is safe as long as you didn't write a custom registry implementation.
MutableCodecRegistry registry =
    (MutableCodecRegistry) session.getContext().getCodecRegistry();

registry.register(new CqlIntToStringCodec());

// cqlsh:ks> desc table test2;
// CREATE TABLE ks.test2 (k int PRIMARY KEY, v int)...
ResultSet rs = session.execute("SELECT * FROM ks.test2 WHERE k = 1");
String v = rs.one().getString("v"); // read a CQL int as a java.lang.String

PreparedStatement ps = session.prepare("INSERT INTO ks.test2 (k, v) VALUES (?, ?)");
session.execute(
    ps.boundStatementBuilder()
        .setInt("k", 2)
        .setString("v", "12") // write a java.lang.String as a CQL int
        .build());

// Assuming that ExtraTypeCodecs.ZONED_TIMESTAMP_PERSISTED was registered
// Assuming that ExtraTypeCodecs.BLOB_TO_ARRAY was registered
// Assuming that ExtraTypeCodecs.arrayOf(TypeCodecs.TEXT) was registered

// Reading
ZonedDateTime v1 = row.get("v1", ZonedDateTime.class); // assuming column is of type timestamp
byte[] v2        = row.get("v2", byte[].class);        // assuming column is of type blob
String[] v3      = row.get("v3", String[].class);      // assuming column is of type list<text>


// Writing
boundStatement.set("v1", v1, ZonedDateTime.class);
boundStatement.set("v2", v2, byte[].class);
boundStatement.set("v3", v3, String[].class);

// Assuming that TypeCodecs.enumNamesOf(WeekDay.class) was registered
// Assuming that TypeCodecs.json(Price.class) was registered

// Reading
WeekDay v1 = row.get("v1", WeekDay.class); // assuming column is of type text
Price v2   = row.get("v2", Price.class);   // assuming column is of type text

// Writing
boundStatement.set("v1", v1, WeekDay.class);
boundStatement.set("v2", v2, Price.class);

// Reading
String enumName = row.getString("v1");
String priceJson = row.getString("v2");

// Writing
boundStatement.setString("v1", enumName);
boundStatement.setString("v2", priceJson);

// Assuming that TypeCodecs.optionalOf(TypeCodecs.UUID) was registered

// Reading
Optional<UUID> opt = row.get("v", GenericType.optionalOf(UUID.class));

// Writing
boundStatement.set("v", opt, GenericType.optionalOf(UUID.class));

// Notice the '{}': this is an anonymous inner class
GenericType<Foo<Bar>> fooBarType = new GenericType<Foo<Bar>>(){};

Foo<Bar> v = row.get("v", fooBarType);

// Assuming that TypeCodecs.json(Price.class) was registered
// Assuming that each element of the list<text> column is a valid Json string

// Reading
List<Price> prices1 = row.getList("v", Price.class);
// alternative method using the generic get method with type token argument:
List<Price> prices2 = row.get("v", GenericType.listOf(Price.class));

// Writing
boundStatement.setList("v", prices1, Price.class);
// alternative method using the generic set method with type token argument:
boundStatement.set("v", prices2, GenericType.listOf(Price.class));

TypeCodec<String> defaultCodec = new CqlIntToStringCodec();
TypeCodec<String> specialCodec = ...; // a different implementation

CqlSession session =
    CqlSession.builder().addTypeCodecs(defaultCodec).build();

String s1 = row.getString("anIntColumn");         // int -> String, will decode with defaultCodec
String s2 = row.get("anIntColumn", specialCodec); // int -> String, will decode with specialCodec

public class CqlIntToStringCodec extends MappingCodec<Integer, String> {

  public CqlIntToStringCodec() {
    super(TypeCodecs.INT, GenericType.STRING);
  }

  @Nullable
  @Override
  protected String innerToOuter(@Nullable Integer value) {
    return value == null ? null : value.toString();
  }

  @Nullable
  @Override
  protected Integer outerToInner(@Nullable String value) {
    return value == null ? null : Integer.parseInt(value);
  }
}

public class Coordinates {
  public final int x;
  public final int y;
  public Coordinates(int x, int y) { this.x = x; this.y = y; }
}

public class CoordinatesCodec extends MappingCodec<UdtValue, Coordinates> {

  public CoordinatesCodec(@NonNull TypeCodec<UdtValue> innerCodec) {
    super(innerCodec, GenericType.of(Coordinates.class));
  }

  @NonNull @Override public UserDefinedType getCqlType() {
    return (UserDefinedType) super.getCqlType();
  }

  @Nullable @Override protected Coordinates innerToOuter(@Nullable UdtValue value) {
    return value == null ? null : new Coordinates(value.getInt("x"), value.getInt("y"));
  }

  @Nullable @Override protected UdtValue outerToInner(@Nullable Coordinates value) {
    return value == null ? null : getCqlType().newValue().setInt("x", value.x).setInt("y", value.y);
  }
}

CqlSession session = ...
CodecRegistry codecRegistry = session.getContext().getCodecRegistry();
// The target user-defined type
UserDefinedType coordinatesUdt =
    session
        .getMetadata()
        .getKeyspace("...")
        .flatMap(ks -> ks.getUserDefinedType("coordinates"))
        .orElseThrow(IllegalStateException::new);
// The "inner" codec that handles the conversions from CQL from/to UdtValue
TypeCodec<UdtValue> innerCodec = codecRegistry.codecFor(coordinatesUdt);
// The mapping codec that will handle the conversions from/to UdtValue and Coordinates
CoordinatesCodec coordinatesCodec = new CoordinatesCodec(innerCodec);
// Register the new codec
((MutableCodecRegistry) codecRegistry).register(coordinatesCodec);

BoundStatement stmt = ...;
stmt.set("coordinates", new Coordinates(10,20), Coordinates.class);

Row row = ...;
Coordinates coordinates = row.get("coordinates", Coordinates.class);

class Animal {}
class Cat extends Animal {}

BoundStatement bs = ...
bs.set(0, new Cat(), Animal.class); // works
bs.set(0, new Cat(),    Cat.class); // throws CodecNotFoundException

Row row = ...
Animal animal = row.get(0, Animal.class); // works
Cat    cat    = row.get(0,    Cat.class); // throws CodecNotFoundException

CodecRegistry getCodecRegistry = session.getContext().getCodecRegistry();

// Get the custom codec we registered earlier:
TypeCodec<String> cqlIntToString = codecRegistry.codecFor(DataTypes.INT, GenericType.STRING);

private static String formatRow(Row row) {
  StringBuilder result = new StringBuilder();
  for (int i = 0; i < row.size(); i++) {
    String name = row.getColumnDefinitions().get(i).getName().asCql(true);
    Object value = row.getObject(i);
    DataType cqlType = row.getType(i);
    
    // Find the best codec to format this CQL type: 
    TypeCodec<Object> codec = row.codecRegistry().codecFor(cqlType);

    if (i != 0) {
      result.append(", ");
    }
    result.append(name).append(" = ").append(codec.format(value));
  }
  return result.toString();
}