Fix ElasticsearchVectorStore to parse similarity option correctly

 - Check for valid DenseVectorSimilarity by using DenseVectorSimilarity's jsonValue with SimilarityFunction string
 - Update elasticsearch image elasticsearch:8.18.1

Signed-off-by: Ilayaperumal Gopinathan <ilayaperumal.gopinathan@broadcom.com>

Author: ilayaperumalg

vector-stores/spring-ai-elasticsearch-store/src/main/java/org/springframework/ai/vectorstore/elasticsearch/ElasticsearchVectorStore.java

@@ -329,16 +329,26 @@ private void createIndexMapping() {
 		try {
 			this.elasticsearchClient.indices()
 				.create(cr -> cr.index(this.options.getIndexName())
-					.mappings(map -> map.properties(this.options.getEmbeddingFieldName(),
-							p -> p.denseVector(dv -> dv
-								.similarity(DenseVectorSimilarity.valueOf(this.options.getSimilarity().toString()))
-								.dims(this.options.getDimensions())))));
+					.mappings(
+							map -> map.properties(this.options.getEmbeddingFieldName(),
+									p -> p.denseVector(dv -> dv
+										.similarity(parseSimilarity(this.options.getSimilarity().toString()))
+										.dims(this.options.getDimensions())))));
 		}
 		catch (IOException e) {
 			throw new RuntimeException(e);
 		}
 	}
 
+	private DenseVectorSimilarity parseSimilarity(String similarity) {
+		for (DenseVectorSimilarity sim : DenseVectorSimilarity.values()) {
+			if (sim.jsonValue().equalsIgnoreCase(similarity)) {
+				return sim;
+			}
+		}
+		throw new IllegalArgumentException("Unsupported similarity: " + similarity);
+	}
+
 	@Override
 	public void afterPropertiesSet() {
 		if (!this.initializeSchema) {

vector-stores/spring-ai-elasticsearch-store/src/test/java/org/springframework/ai/vectorstore/elasticsearch/ElasticsearchImage.java

@@ -23,8 +23,7 @@
  */
 public final class ElasticsearchImage {
 
-	public static final DockerImageName DEFAULT_IMAGE = DockerImageName
-		.parse("docker.elastic.co/elasticsearch/elasticsearch:8.16.1");
+	public static final DockerImageName DEFAULT_IMAGE = DockerImageName.parse("elasticsearch:8.18.1");
 
 	private ElasticsearchImage() {