Add an Optional convenience method.

Author: io7m

com.io7m.dixmont.core/src/main/java/com/io7m/dixmont/core/DmJsonRestrictedDeserializerBuilderType.java

@@ -21,6 +21,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.Set;
 
 /**
@@ -88,6 +89,28 @@ default DmJsonRestrictedDeserializerBuilderType allowClasses(
     return this;
   }
 
+  /**
+   * Allow access to optionals of the given class.
+   *
+   * @param clazz The class
+   *
+   * @return this
+   *
+   * @since 3.0.0
+   */
+
+  default DmJsonRestrictedDeserializerBuilderType allowOptionalOfClass(
+    final Class<?> clazz)
+  {
+    return this.allowClass(clazz)
+      .allowClassName(
+        "%s<%s>".formatted(
+          Optional.class.getCanonicalName(),
+          clazz.getCanonicalName()
+        )
+      );
+  }
+
   /**
    * Allow access to lists of the given class.
    *

com.io7m.dixmont.tests/src/main/java/com/io7m/dixmont/tests/DmJsonRestrictedDeserializersTest.java

@@ -26,6 +26,7 @@
 
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.Set;
 
 import static com.io7m.dixmont.tests.EnumExample.ENUM_EXAMPLE_A;
@@ -257,6 +258,34 @@ public void testListIntAllowedConvenience()
     );
   }
 
+  @Test
+  public void testOptionalIntAllowedConvenience()
+    throws Exception
+  {
+    final var deserializers =
+      DmJsonRestrictedDeserializers.builder()
+        .allowOptionalOfClass(Integer.class)
+        .build();
+
+    final var simpleModule = new SimpleModule();
+    simpleModule.setDeserializers(deserializers);
+
+    final var builder = JsonMapper.builder();
+    builder.addModule(simpleModule);
+
+    final var mapper =
+      (ObjectMapper) builder.disable(FAIL_ON_UNKNOWN_PROPERTIES)
+        .build();
+
+    assertEquals(
+      Optional.of(Integer.valueOf(23)),
+      mapper.readValue(
+        "23", new TypeReference<Optional<Integer>>()
+        {
+        })
+    );
+  }
+
   @Test
   public void testMultiConvenience()
     throws Exception