@AccessesPartialKey
  static AesGcmKey createAesGcmKeyFromRandomness(
      AesGcmParameters parameters,
      InputStream stream,
      @Nullable Integer idRequirement,
      SecretKeyAccess access)
      throws GeneralSecurityException {
    validate(parameters);
    return AesGcmKey.builder()
        .setParameters(parameters)
        .setIdRequirement(idRequirement)
        .setKeyBytes(Util.readIntoSecretBytes(stream, parameters.getKeySizeBytes(), access))
        .build();
  }
This key manager generates new {@code AesGcmKey} keys and produces new instances of {@code
AesGcmJce}.
java_src/src/main/java/com/google/crypto/tink/aead/AesGcmKeyManager.java