Added JsonSerializable interface

com.eclipsesource.json/src/main/java/com/eclipsesource/json/Json.java

@@ -153,9 +153,12 @@ public static JsonValue value(boolean value) {
   }
 
   /**
-   * Returns a JsonValue instance that represents the given object.
+   * Returns a JsonValue instance that represents the given object. If the object implements
+   * {@link JsonSerializable}, its {@link JsonSerializable#asJsonValue()} method is called and the
+   * result returned.
    * <p>
-   *  Converts null values to null literals and non-trivial objects to their string representation.
+   * Converts null values to null literals and non-trivial objects to their string representation.
+   *
    * @param object
    *          the object to get a JSON representation for
    * @return a JSON value that represents the given object

com.eclipsesource.json/src/main/java/com/eclipsesource/json/JsonBuilder.java

@@ -37,16 +37,20 @@
  */
 public class JsonBuilder {
   /**
-   * Creates a JsonValue from a Java object. Converts null values to null literals and non-trivial
-   * objects to their string representation.
-   *
-   * @param object The object to convert to json
+   * Creates a JsonValue from a Java object. If the object implements {@link JsonSerializable}, its
+   * {@link JsonSerializable#asJsonValue()} method is called and the result returned.
+   * <p>
+   * Converts null values to null literals and non-trivial objects to their string representation.
    *
+   * @param object
+   *          The object to convert to json
    * @return The Java object as {@link JsonValue}
    */
   public static JsonValue toJsonValue(final Object object) {
     if (object == null) {
       return Json.NULL;
+    } else if (object instanceof JsonSerializable) {
+      return ((JsonSerializable)object).asJsonValue();
     } else if (object instanceof Boolean) {
       return Json.value(((Boolean)object).booleanValue());
     } else if (object instanceof Byte) {

com.eclipsesource.json/src/main/java/com/eclipsesource/json/JsonSerializable.java

@@ -0,0 +1,35 @@
+/*******************************************************************************
+ * Copyright (c) 2017 EclipseSource.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ ******************************************************************************/
+package com.eclipsesource.json;
+
+/**
+ * Objects, which implement this interface, can be directly serialized as {@link JsonValue}.
+ */
+public interface JsonSerializable {
+
+  /**
+   * Serializes the object into a {@link JsonValue}
+   *
+   * @return The object as json representation
+   */
+  public JsonValue asJsonValue();
+}

com.eclipsesource.json/src/test/java/com/eclipsesource/json/JsonBuilder_Test.java

@@ -1,6 +1,7 @@
 package com.eclipsesource.json;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
 
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -110,6 +111,18 @@ public String toString() {
     assertEquals("\"toString\"", value.toString());
   }
 
+  @Test
+  public void callsAsJsonValueOfAJsonSerializeableObject() {
+    final JsonValue expected = Json.value(123);
+    JsonValue value = JsonBuilder.toJsonValue(new JsonSerializable() {
+
+      public JsonValue asJsonValue() {
+        return expected;
+      }
+    });
+    assertSame(expected, value);
+  }
+
   @Test
   public void convertsList() {
     List<Object> list = new ArrayList<Object>();