Add support for json-in-a-string serialization

Author: swallez

java-client/src/main/java/co/elastic/clients/json/JsonpDeserializer.java

@@ -24,6 +24,7 @@
 import jakarta.json.stream.JsonParser;
 import jakarta.json.stream.JsonParser.Event;
 
+import java.io.StringReader;
 import java.util.EnumSet;
 import java.util.List;
 import java.util.Map;
@@ -216,4 +217,27 @@ static <K extends JsonEnum, V> JsonpDeserializer<Map<K, V>> enumMapDeserializer(
     ) {
         return new JsonpDeserializerBase.EnumMapDeserializer<>(keyDeserializer, valueDeserializer);
     }
+
+    /**
+     * Creates a deserializer that will accept a value both as regular JSON and as JSON-in-a-string.
+     */
+    static <T> JsonpDeserializer<T> jsonString(JsonpDeserializer<T> valueDeserializer) {
+        EnumSet<Event> acceptedEvents = EnumSet.copyOf(valueDeserializer.acceptedEvents());
+        acceptedEvents.add(Event.VALUE_STRING);
+
+        EnumSet<Event> nativeEvents = EnumSet.copyOf(valueDeserializer.nativeEvents());
+        nativeEvents.add(Event.VALUE_STRING);
+
+        return new JsonpDeserializerBase<T>(acceptedEvents, nativeEvents) {
+            @Override
+            public T deserialize(JsonParser parser, JsonpMapper mapper, Event event) {
+                if (event == Event.VALUE_STRING) {
+                    JsonParser stringParser = mapper.jsonProvider().createParser(new StringReader(parser.getString()));
+                    return valueDeserializer.deserialize(stringParser, mapper);
+                } else {
+                    return valueDeserializer.deserialize(parser, mapper, event);
+                }
+            }
+        };
+    }
 }

java-client/src/main/java/co/elastic/clients/json/JsonpUtils.java

@@ -33,6 +33,7 @@
 
 import javax.annotation.Nullable;
 import java.io.StringReader;
+import java.io.StringWriter;
 import java.io.Writer;
 import java.util.AbstractMap;
 import java.util.Map;
@@ -328,6 +329,14 @@ public void close() {
         return dest;
     }
 
+    public static String toJsonString(JsonpSerializable value, JsonpMapper mapper) {
+        StringWriter writer = new StringWriter();
+        JsonGenerator generator = mapper.jsonProvider().createGenerator(writer);
+        value.serialize(generator, mapper);
+        generator.close();
+        return writer.toString();
+    }
+
     /**
      * Renders a <code>JsonpSerializable</code> as a string in a destination <code>StringBuilder</code>by serializing it to JSON.
      * Any object of an application-specific class in the object graph is rendered using that object's <code>toString()</code>