Extract function OptionalUtil.stream(Optional<T>)

Author: emlun

webauthn-server-attestation/src/main/java/com/yubico/fido/metadata/FidoMetadataService.java

@@ -637,8 +637,7 @@ public TrustRootsResult findTrustRoots(
         .trustRoots(
             findEntries(attestationCertificateChain, aaguid.map(AAGUID::new)).stream()
                 .map(MetadataBLOBPayloadEntry::getMetadataStatement)
-                .filter(Optional::isPresent)
-                .map(Optional::get)
+                .flatMap(OptionalUtil::stream)
                 .flatMap(
                     metadataStatement ->
                         metadataStatement.getAttestationRootCertificates().stream())

webauthn-server-demo/src/main/java/com/yubico/webauthn/attestation/YubicoJsonMetadataService.java

@@ -30,6 +30,7 @@
 import com.google.common.collect.Maps;
 import com.yubico.internal.util.CertificateParser;
 import com.yubico.internal.util.CollectionUtil;
+import com.yubico.internal.util.OptionalUtil;
 import com.yubico.webauthn.attestation.matcher.ExtensionMatcher;
 import com.yubico.webauthn.data.ByteArray;
 import java.security.cert.CertificateException;
@@ -124,8 +125,7 @@ public Optional<Attestation> findMetadata(X509Certificate attestationCertificate
                               .deviceProperties(deviceProps)
                               .build());
             })
-        .filter(Optional::isPresent)
-        .map(Optional::get)
+        .flatMap(OptionalUtil::stream)
         .findAny();
   }
 

yubico-util/src/main/java/com/yubico/internal/util/OptionalUtil.java

@@ -3,6 +3,8 @@
 import java.util.Optional;
 import java.util.function.BinaryOperator;
 import java.util.function.Supplier;
+import java.util.stream.Stream;
+import lombok.NonNull;
 import lombok.experimental.UtilityClass;
 
 /** Utilities for working with {@link Optional} values. */
@@ -21,6 +23,17 @@ public static <T> Optional<T> orElseOptional(Optional<T> primary, Supplier<Optio
     }
   }
 
+  /**
+   * Returns a sequential {@link Stream} with this {@link Optional} as its source.
+   *
+   * @param o the {@link Optional} to interpret as a {@link Stream}
+   * @return a sequential {@link Stream} containing the value of this {@link Optional} if present,
+   *     otherwise an empty {@link Stream}.
+   */
+  public static <T> Stream<T> stream(@NonNull Optional<T> o) {
+    return o.map(Stream::of).orElseGet(Stream::empty);
+  }
+
   /**
    * If both <code>a</code> and <code>b</code> are present, return <code>f(a, b)</code>.
    *