java: Add convenient construction of rawPayload messages (#1544)

Part of svix/monorepo-private#9470.

java/lib/src/main/java/com/svix/Message.java

@@ -1,6 +1,9 @@
 package com.svix;
 
+import java.util.Collections;
+import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Map;
 
 import com.svix.exceptions.ApiException;
 import com.svix.internal.api.MessageApi;
@@ -16,18 +19,54 @@ public final class Message {
 		api = new MessageApi();
 	}
 
+	private static MessageIn messageInEmptyPayload() {
+		return new MessageIn()
+			.payload(Collections.emptyMap());
+	}
+
+	/**
+	 * Creates a MessageIn with the payload already being serialized.
+	 *
+	 * The payload is not normalized on the server (usually whitespace outside
+	 * of string literals, unnecessarily escaped characters in string and such
+	 * are fixed up by the server). The default Content-Type of application/json
+	 * is used. See the other overload if you want to send non-JSON payloads.
+	 *
+	 * @param payload Serialized message payload
+	 */
+	public static MessageIn messageInRaw(final String payload) {
+		return messageInEmptyPayload().transformationsParams(
+			Collections.singletonMap("rawPayload", payload)
+		);
+	}
+
+	/**
+	 * Creates a MessageIn with the payload already being serialized.
+	 *
+	 * This overload is intended for non-JSON payloads.
+	 *
+	 * @param payload Serialized message payload
+	 * @param contentType The value to use for the Content-Type header
+	 */
+	public static MessageIn messageInRaw(final String payload, final String contentType) {
+		HashMap<String, Object> trParam = new HashMap<>();
+		trParam.put("rawPayload", payload);
+		trParam.put("headers", Collections.singletonMap("content-type", contentType));
+		return messageInEmptyPayload().transformationsParams(trParam);
+	}
+
 	public ListResponseMessageOut list(final String appId, final MessageListOptions options) throws ApiException {
 		try {
 			return api.v1MessageList(
-					appId,
-					options.getLimit(),
-					options.getIterator(),
-					options.getChannel(),
-					options.getBefore(),
-					options.getAfter(),
-					options.getWithContent(),
-					options.getTag(),
-					new HashSet<>(options.getEventTypes())
+				appId,
+				options.getLimit(),
+				options.getIterator(),
+				options.getChannel(),
+				options.getBefore(),
+				options.getAfter(),
+				options.getWithContent(),
+				options.getTag(),
+				new HashSet<>(options.getEventTypes())
 			);
 		} catch (com.svix.internal.ApiException e) {
 			throw Utils.wrapInternalApiException(e);