diff --git a/qa/restart-upgrade/src/test/java/org/opensearch/knn/bwc/IndexingIT.java b/qa/restart-upgrade/src/test/java/org/opensearch/knn/bwc/IndexingIT.java
index 7437cf0c1..c8d0cac93 100644
--- a/qa/restart-upgrade/src/test/java/org/opensearch/knn/bwc/IndexingIT.java
+++ b/qa/restart-upgrade/src/test/java/org/opensearch/knn/bwc/IndexingIT.java
@@ -5,7 +5,6 @@
 
 package org.opensearch.knn.bwc;
 
-import org.opensearch.common.Strings;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.knn.index.SpaceType;
 
@@ -96,21 +95,20 @@ public void testKNNIndexCustomMethodFieldMapping() throws Exception {
     // test null parameters
     public void testNullParametersOnUpgrade() throws Exception {
         if (isRunningAgainstOldCluster()) {
-            String mapping = Strings.toString(
-                XContentFactory.jsonBuilder()
-                    .startObject()
-                    .startObject(PROPERTIES)
-                    .startObject(TEST_FIELD)
-                    .field(VECTOR_TYPE, KNN_VECTOR)
-                    .field(DIMENSION, String.valueOf(DIMENSIONS))
-                    .startObject(KNN_METHOD)
-                    .field(NAME, METHOD_HNSW)
-                    .field(PARAMETERS, (String) null)
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-            );
+            String mapping = XContentFactory.jsonBuilder()
+                .startObject()
+                .startObject(PROPERTIES)
+                .startObject(TEST_FIELD)
+                .field(VECTOR_TYPE, KNN_VECTOR)
+                .field(DIMENSION, String.valueOf(DIMENSIONS))
+                .startObject(KNN_METHOD)
+                .field(NAME, METHOD_HNSW)
+                .field(PARAMETERS, (String) null)
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .toString();
 
             createKnnIndex(testIndex, getKNNDefaultIndexSettings(), mapping);
         } else {
@@ -121,21 +119,20 @@ public void testNullParametersOnUpgrade() throws Exception {
     // test empty parameters
     public void testEmptyParametersOnUpgrade() throws Exception {
         if (isRunningAgainstOldCluster()) {
-            String mapping = Strings.toString(
-                XContentFactory.jsonBuilder()
-                    .startObject()
-                    .startObject(PROPERTIES)
-                    .startObject(TEST_FIELD)
-                    .field(VECTOR_TYPE, KNN_VECTOR)
-                    .field(DIMENSION, String.valueOf(DIMENSIONS))
-                    .startObject(KNN_METHOD)
-                    .field(NAME, METHOD_HNSW)
-                    .field(PARAMETERS, "")
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-            );
+            String mapping = XContentFactory.jsonBuilder()
+                .startObject()
+                .startObject(PROPERTIES)
+                .startObject(TEST_FIELD)
+                .field(VECTOR_TYPE, KNN_VECTOR)
+                .field(DIMENSION, String.valueOf(DIMENSIONS))
+                .startObject(KNN_METHOD)
+                .field(NAME, METHOD_HNSW)
+                .field(PARAMETERS, "")
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .toString();
 
             createKnnIndex(testIndex, getKNNDefaultIndexSettings(), mapping);
         } else {
@@ -146,20 +143,19 @@ public void testEmptyParametersOnUpgrade() throws Exception {
     // test no parameters
     public void testNoParametersOnUpgrade() throws Exception {
         if (isRunningAgainstOldCluster()) {
-            String mapping = Strings.toString(
-                XContentFactory.jsonBuilder()
-                    .startObject()
-                    .startObject(PROPERTIES)
-                    .startObject(TEST_FIELD)
-                    .field(VECTOR_TYPE, KNN_VECTOR)
-                    .field(DIMENSION, String.valueOf(DIMENSIONS))
-                    .startObject(KNN_METHOD)
-                    .field(NAME, METHOD_HNSW)
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-            );
+            String mapping = XContentFactory.jsonBuilder()
+                .startObject()
+                .startObject(PROPERTIES)
+                .startObject(TEST_FIELD)
+                .field(VECTOR_TYPE, KNN_VECTOR)
+                .field(DIMENSION, String.valueOf(DIMENSIONS))
+                .startObject(KNN_METHOD)
+                .field(NAME, METHOD_HNSW)
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .toString();
 
             createKnnIndex(testIndex, getKNNDefaultIndexSettings(), mapping);
         } else {
diff --git a/qa/restart-upgrade/src/test/java/org/opensearch/knn/bwc/ModelIT.java b/qa/restart-upgrade/src/test/java/org/opensearch/knn/bwc/ModelIT.java
index 473802ca8..0324822f7 100644
--- a/qa/restart-upgrade/src/test/java/org/opensearch/knn/bwc/ModelIT.java
+++ b/qa/restart-upgrade/src/test/java/org/opensearch/knn/bwc/ModelIT.java
@@ -11,7 +11,6 @@
 import org.opensearch.client.Request;
 import org.opensearch.client.Response;
 import org.opensearch.client.ResponseException;
-import org.opensearch.common.Strings;
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.core.xcontent.XContentParser;
@@ -245,17 +244,16 @@ public void trainKNNModelDefault(String modelId, String trainingIndexName, Strin
 
     // mapping to create index from model
     public String modelIndexMapping(String fieldName, String modelId) throws IOException {
-        return Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject(PROPERTIES)
-                .startObject(fieldName)
-                .field(VECTOR_TYPE, KNN_VECTOR)
-                .field(MODEL_ID, modelId)
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        return XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject(PROPERTIES)
+            .startObject(fieldName)
+            .field(VECTOR_TYPE, KNN_VECTOR)
+            .field(MODEL_ID, modelId)
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
     }
 
     private ModelMetadata getModelMetadata() {
diff --git a/src/main/java/org/opensearch/knn/index/mapper/MethodFieldMapper.java b/src/main/java/org/opensearch/knn/index/mapper/MethodFieldMapper.java
index 42c12a5db..1db710bad 100644
--- a/src/main/java/org/opensearch/knn/index/mapper/MethodFieldMapper.java
+++ b/src/main/java/org/opensearch/knn/index/mapper/MethodFieldMapper.java
@@ -7,7 +7,6 @@
 
 import org.apache.lucene.document.FieldType;
 import org.opensearch.common.Explicit;
-import org.opensearch.common.Strings;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.knn.index.KNNMethodContext;
 import org.opensearch.knn.index.util.KNNEngine;
@@ -50,7 +49,7 @@ public class MethodFieldMapper extends KNNVectorFieldMapper {
         try {
             this.fieldType.putAttribute(
                 PARAMETERS,
-                Strings.toString(XContentFactory.jsonBuilder().map(knnEngine.getMethodAsMap(knnMethodContext)))
+                XContentFactory.jsonBuilder().map(knnEngine.getMethodAsMap(knnMethodContext)).toString()
             );
         } catch (IOException ioe) {
             throw new RuntimeException(String.format("Unable to create KNNVectorFieldMapper: %s", ioe));
diff --git a/src/test/java/org/opensearch/knn/index/FaissIT.java b/src/test/java/org/opensearch/knn/index/FaissIT.java
index c275790d5..2d4dc8053 100644
--- a/src/test/java/org/opensearch/knn/index/FaissIT.java
+++ b/src/test/java/org/opensearch/knn/index/FaissIT.java
@@ -21,7 +21,6 @@
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.index.query.QueryBuilders;
 import org.opensearch.knn.KNNRestTestCase;
-import org.opensearch.common.Strings;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.knn.KNNResult;
 import org.opensearch.knn.TestUtils;
@@ -98,7 +97,7 @@ public void testEndToEnd_fromMethod() throws Exception {
             .endObject();
 
         Map<String, Object> mappingMap = xContentBuilderToMap(builder);
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
 
         createKnnIndex(indexName, mapping);
         assertEquals(new TreeMap<>(mappingMap), new TreeMap<>(getIndexMappingAsMap(indexName)));
@@ -175,7 +174,7 @@ public void testDocUpdate() throws IOException {
             .endObject()
             .endObject();
 
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
         createKnnIndex(indexName, mapping);
 
         Float[] vector = { 6.0f, 6.0f };
@@ -211,7 +210,7 @@ public void testDocDeletion() throws IOException {
             .endObject()
             .endObject();
 
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
         createKnnIndex(indexName, mapping);
 
         Float[] vector = { 6.0f, 6.0f };
@@ -255,17 +254,16 @@ public void testKNNQuery_withModelDifferentCombination_thenSuccess() {
         // Create knn index from model
         String fieldName = "test-field-name";
         String indexName = "test-index-name";
-        String indexMapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(fieldName)
-                .field("type", "knn_vector")
-                .field(MODEL_ID, modelId)
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        String indexMapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(fieldName)
+            .field("type", "knn_vector")
+            .field(MODEL_ID, modelId)
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
 
         createKnnIndex(indexName, getKNNDefaultIndexSettings(), indexMapping);
 
@@ -389,7 +387,7 @@ protected void setupKNNIndexForFilterQuery() throws Exception {
             .endObject()
             .endObject()
             .endObject();
-        final String mapping = Strings.toString(builder);
+        final String mapping = builder.toString();
 
         createKnnIndex(INDEX_NAME, mapping);
 
diff --git a/src/test/java/org/opensearch/knn/index/KNNCreateIndexFromModelTests.java b/src/test/java/org/opensearch/knn/index/KNNCreateIndexFromModelTests.java
index e0b2c05cf..3a4746158 100644
--- a/src/test/java/org/opensearch/knn/index/KNNCreateIndexFromModelTests.java
+++ b/src/test/java/org/opensearch/knn/index/KNNCreateIndexFromModelTests.java
@@ -14,7 +14,6 @@
 import com.google.common.collect.ImmutableMap;
 import org.opensearch.action.ActionListener;
 import org.opensearch.action.admin.indices.create.CreateIndexRequestBuilder;
-import org.opensearch.common.Strings;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.knn.KNNSingleNodeTestCase;
@@ -75,17 +74,16 @@ public void testCreateIndexFromModel() throws IOException, InterruptedException
         String indexName = "test-index";
         String fieldName = "test-field";
 
-        final String mapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(fieldName)
-                .field("type", "knn_vector")
-                .field("model_id", modelId)
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        final String mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(fieldName)
+            .field("type", "knn_vector")
+            .field("model_id", modelId)
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
 
         modelDao.put(model, ActionListener.wrap(indexResponse -> {
             CreateIndexRequestBuilder createIndexRequestBuilder = client().admin()
diff --git a/src/test/java/org/opensearch/knn/index/LuceneEngineIT.java b/src/test/java/org/opensearch/knn/index/LuceneEngineIT.java
index 594daeaeb..562765e0c 100644
--- a/src/test/java/org/opensearch/knn/index/LuceneEngineIT.java
+++ b/src/test/java/org/opensearch/knn/index/LuceneEngineIT.java
@@ -16,7 +16,6 @@
 import org.opensearch.client.Request;
 import org.opensearch.client.Response;
 import org.opensearch.client.ResponseException;
-import org.opensearch.common.Strings;
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.index.query.QueryBuilders;
@@ -101,7 +100,7 @@ public void testQuery_innerProduct_notSupported() throws Exception {
             .endObject()
             .endObject();
 
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
 
         createIndex(INDEX_NAME, getKNNDefaultIndexSettings());
 
@@ -179,7 +178,7 @@ public void testQuery_multipleEngines() throws Exception {
             .endObject()
             .endObject()
             .endObject();
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
         createKnnIndex(INDEX_NAME, mapping);
 
         for (int i = 0; i < TEST_INDEX_VECTORS.length; i++) {
@@ -219,7 +218,7 @@ public void testAddDoc() throws Exception {
             .endObject();
 
         Map<String, Object> mappingMap = xContentBuilderToMap(builder);
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
 
         createKnnIndex(INDEX_NAME, mapping);
         assertEquals(new TreeMap<>(mappingMap), new TreeMap<>(getIndexMappingAsMap(INDEX_NAME)));
@@ -305,7 +304,7 @@ public void testQuery_filterWithNonLuceneEngine() throws Exception {
             .endObject()
             .endObject();
 
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
         createKnnIndex(INDEX_NAME, mapping);
 
         addKnnDocWithAttributes(
@@ -371,7 +370,7 @@ private void createKnnIndexMappingWithLuceneEngine(int dimension, SpaceType spac
             .endObject()
             .endObject();
 
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
         createKnnIndex(INDEX_NAME, mapping);
     }
 
diff --git a/src/test/java/org/opensearch/knn/index/NmslibIT.java b/src/test/java/org/opensearch/knn/index/NmslibIT.java
index 7c6bce1a9..87bbe588f 100644
--- a/src/test/java/org/opensearch/knn/index/NmslibIT.java
+++ b/src/test/java/org/opensearch/knn/index/NmslibIT.java
@@ -19,7 +19,6 @@
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.knn.KNNRestTestCase;
 import org.opensearch.client.ResponseException;
-import org.opensearch.common.Strings;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.knn.KNNResult;
@@ -85,7 +84,7 @@ public void testEndToEnd() throws Exception {
             .endObject();
 
         Map<String, Object> mappingMap = xContentBuilderToMap(builder);
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
 
         createKnnIndex(indexName, mapping);
         assertEquals(new TreeMap<>(mappingMap), new TreeMap<>(getIndexMappingAsMap(indexName)));
@@ -187,25 +186,24 @@ public void testCreateIndexWithValidAlgoParams_mapping() {
             int efConstruction = 14;
             int m = 13;
 
-            String mapping = Strings.toString(
-                XContentFactory.jsonBuilder()
-                    .startObject()
-                    .startObject("properties")
-                    .startObject(FIELD_NAME)
-                    .field("type", "knn_vector")
-                    .field("dimension", 2)
-                    .startObject(KNNConstants.KNN_METHOD)
-                    .field(KNNConstants.METHOD_PARAMETER_SPACE_TYPE, spaceType)
-                    .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
-                    .startObject(KNNConstants.PARAMETERS)
-                    .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, efConstruction)
-                    .field(KNNConstants.METHOD_PARAMETER_M, m)
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-            );
+            String mapping = XContentFactory.jsonBuilder()
+                .startObject()
+                .startObject("properties")
+                .startObject(FIELD_NAME)
+                .field("type", "knn_vector")
+                .field("dimension", 2)
+                .startObject(KNNConstants.KNN_METHOD)
+                .field(KNNConstants.METHOD_PARAMETER_SPACE_TYPE, spaceType)
+                .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
+                .startObject(KNNConstants.PARAMETERS)
+                .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, efConstruction)
+                .field(KNNConstants.METHOD_PARAMETER_M, m)
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .toString();
 
             createKnnIndex(INDEX_NAME, settings, mapping);
 
@@ -243,25 +241,24 @@ public void testCreateIndexWithValidAlgoParams_mappingAndSettings() {
                 .put("index.knn.algo_param.ef_construction", efConstruction1)
                 .build();
 
-            String mapping = Strings.toString(
-                XContentFactory.jsonBuilder()
-                    .startObject()
-                    .startObject("properties")
-                    .startObject(FIELD_NAME)
-                    .field("type", "knn_vector")
-                    .field("dimension", 2)
-                    .startObject(KNNConstants.KNN_METHOD)
-                    .field(KNNConstants.METHOD_PARAMETER_SPACE_TYPE, spaceType1)
-                    .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
-                    .startObject(KNNConstants.PARAMETERS)
-                    .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, efConstruction1)
-                    .field(KNNConstants.METHOD_PARAMETER_M, m1)
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-            );
+            String mapping = XContentFactory.jsonBuilder()
+                .startObject()
+                .startObject("properties")
+                .startObject(FIELD_NAME)
+                .field("type", "knn_vector")
+                .field("dimension", 2)
+                .startObject(KNNConstants.KNN_METHOD)
+                .field(KNNConstants.METHOD_PARAMETER_SPACE_TYPE, spaceType1)
+                .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
+                .startObject(KNNConstants.PARAMETERS)
+                .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, efConstruction1)
+                .field(KNNConstants.METHOD_PARAMETER_M, m1)
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .toString();
 
             createKnnIndex(INDEX_NAME + "1", settings, mapping);
             Float[] vector = { 6.0f, 6.0f };
@@ -271,37 +268,36 @@ public void testCreateIndexWithValidAlgoParams_mappingAndSettings() {
             int efConstruction2 = 114;
             int m2 = 113;
 
-            mapping = Strings.toString(
-                XContentFactory.jsonBuilder()
-                    .startObject()
-                    .startObject("properties")
-                    .startObject(FIELD_NAME + "1")
-                    .field("type", "knn_vector")
-                    .field("dimension", 2)
-                    .startObject(KNNConstants.KNN_METHOD)
-                    .field(KNNConstants.METHOD_PARAMETER_SPACE_TYPE, spaceType1)
-                    .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
-                    .startObject(KNNConstants.PARAMETERS)
-                    .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, efConstruction1)
-                    .field(KNNConstants.METHOD_PARAMETER_M, m1)
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .startObject(FIELD_NAME + "2")
-                    .field("type", "knn_vector")
-                    .field("dimension", 2)
-                    .startObject(KNNConstants.KNN_METHOD)
-                    .field(KNNConstants.METHOD_PARAMETER_SPACE_TYPE, spaceType2)
-                    .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
-                    .startObject(KNNConstants.PARAMETERS)
-                    .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, efConstruction2)
-                    .field(KNNConstants.METHOD_PARAMETER_M, m2)
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-                    .endObject()
-            );
+            mapping = XContentFactory.jsonBuilder()
+                .startObject()
+                .startObject("properties")
+                .startObject(FIELD_NAME + "1")
+                .field("type", "knn_vector")
+                .field("dimension", 2)
+                .startObject(KNNConstants.KNN_METHOD)
+                .field(KNNConstants.METHOD_PARAMETER_SPACE_TYPE, spaceType1)
+                .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
+                .startObject(KNNConstants.PARAMETERS)
+                .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, efConstruction1)
+                .field(KNNConstants.METHOD_PARAMETER_M, m1)
+                .endObject()
+                .endObject()
+                .endObject()
+                .startObject(FIELD_NAME + "2")
+                .field("type", "knn_vector")
+                .field("dimension", 2)
+                .startObject(KNNConstants.KNN_METHOD)
+                .field(KNNConstants.METHOD_PARAMETER_SPACE_TYPE, spaceType2)
+                .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
+                .startObject(KNNConstants.PARAMETERS)
+                .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, efConstruction2)
+                .field(KNNConstants.METHOD_PARAMETER_M, m2)
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .endObject()
+                .toString();
 
             createKnnIndex(INDEX_NAME + "2", settings, mapping);
             addKnnDoc(INDEX_NAME + "2", "1", FIELD_NAME, vector);
@@ -330,23 +326,22 @@ public void testInvalidIndexHnswAlgoParams_settings() {
     public void testInvalidIndexHnswAlgoParams_mapping() throws IOException {
         Settings settings = Settings.builder().put(getKNNDefaultIndexSettings()).build();
 
-        String mapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(FIELD_NAME)
-                .field("type", "knn_vector")
-                .field("dimension", 2)
-                .startObject(KNNConstants.KNN_METHOD)
-                .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
-                .startObject(KNNConstants.PARAMETERS)
-                .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, "-1")
-                .endObject()
-                .endObject()
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        String mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(FIELD_NAME)
+            .field("type", "knn_vector")
+            .field("dimension", 2)
+            .startObject(KNNConstants.KNN_METHOD)
+            .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
+            .startObject(KNNConstants.PARAMETERS)
+            .field(KNNConstants.METHOD_PARAMETER_EF_CONSTRUCTION, "-1")
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
 
         expectThrows(ResponseException.class, () -> createKnnIndex(INDEX_NAME, settings, mapping));
     }
@@ -354,23 +349,22 @@ public void testInvalidIndexHnswAlgoParams_mapping() throws IOException {
     public void testInvalidIndexHnswAlgoParams_mappingAndSettings() throws IOException {
         Settings settings = Settings.builder().put(getKNNDefaultIndexSettings()).put("index.knn.algo_param.m", "-1").build();
 
-        String mapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(FIELD_NAME)
-                .field("type", "knn_vector")
-                .field("dimension", 2)
-                .startObject(KNNConstants.KNN_METHOD)
-                .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
-                .startObject(KNNConstants.PARAMETERS)
-                .field(KNNConstants.METHOD_PARAMETER_M, "-1")
-                .endObject()
-                .endObject()
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        String mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(FIELD_NAME)
+            .field("type", "knn_vector")
+            .field("dimension", 2)
+            .startObject(KNNConstants.KNN_METHOD)
+            .field(KNNConstants.NAME, KNNConstants.METHOD_HNSW)
+            .startObject(KNNConstants.PARAMETERS)
+            .field(KNNConstants.METHOD_PARAMETER_M, "-1")
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
 
         expectThrows(ResponseException.class, () -> createKnnIndex(INDEX_NAME, settings, mapping));
     }
diff --git a/src/test/java/org/opensearch/knn/index/OpenSearchIT.java b/src/test/java/org/opensearch/knn/index/OpenSearchIT.java
index 95005a5cb..4130e2df5 100644
--- a/src/test/java/org/opensearch/knn/index/OpenSearchIT.java
+++ b/src/test/java/org/opensearch/knn/index/OpenSearchIT.java
@@ -20,7 +20,6 @@
 import org.opensearch.client.Request;
 import org.opensearch.client.Response;
 import org.opensearch.client.ResponseException;
-import org.opensearch.common.Strings;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.common.xcontent.XContentFactory;
@@ -108,7 +107,7 @@ public void testEndToEnd() throws Exception {
             .endObject();
 
         Map<String, Object> mappingMap = xContentBuilderToMap(builder);
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
         createKnnIndex(indexName, mapping);
         assertEquals(new TreeMap<>(mappingMap), new TreeMap<>(getIndexMappingAsMap(indexName)));
 
@@ -267,16 +266,15 @@ public void testIndexingVectorValidation_differentSizes() throws Exception {
     public void testVectorMappingValidation_noDimension() throws Exception {
         Settings settings = Settings.builder().put(getKNNDefaultIndexSettings()).build();
 
-        String mapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(FIELD_NAME)
-                .field("type", "knn_vector")
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        String mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(FIELD_NAME)
+            .field("type", "knn_vector")
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
 
         Exception ex = expectThrows(ResponseException.class, () -> createKnnIndex(INDEX_NAME, settings, mapping));
         assertThat(ex.getMessage(), containsString("Dimension value missing for vector: " + FIELD_NAME));
@@ -338,21 +336,20 @@ public void testVectorMappingValidation_multiFieldsDifferentDimension() throws E
 
         String f4 = FIELD_NAME + "-4";
         String f5 = FIELD_NAME + "-5";
-        String mapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(f4)
-                .field("type", "knn_vector")
-                .field("dimension", "4")
-                .endObject()
-                .startObject(f5)
-                .field("type", "knn_vector")
-                .field("dimension", "5")
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        String mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(f4)
+            .field("type", "knn_vector")
+            .field("dimension", "4")
+            .endObject()
+            .startObject(f5)
+            .field("type", "knn_vector")
+            .field("dimension", "5")
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
 
         createKnnIndex(INDEX_NAME, settings, mapping);
 
@@ -384,7 +381,7 @@ public void testExistsQuery() throws Exception {
         Request request = new Request("POST", "/" + INDEX_NAME + "/_doc/7?refresh=true");
 
         XContentBuilder builder = XContentFactory.jsonBuilder().startObject().field("non-knn-field", "test").endObject();
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         Response response = client().performRequest(request);
         assertEquals(request.getEndpoint() + ": failed", RestStatus.CREATED, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
 
diff --git a/src/test/java/org/opensearch/knn/index/VectorDataTypeIT.java b/src/test/java/org/opensearch/knn/index/VectorDataTypeIT.java
index 17e33a17c..2c4f150c4 100644
--- a/src/test/java/org/opensearch/knn/index/VectorDataTypeIT.java
+++ b/src/test/java/org/opensearch/knn/index/VectorDataTypeIT.java
@@ -11,7 +11,6 @@
 import org.opensearch.client.Request;
 import org.opensearch.client.Response;
 import org.opensearch.client.ResponseException;
-import org.opensearch.common.Strings;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.core.xcontent.XContentBuilder;
@@ -274,7 +273,7 @@ public void testByteVectorDataTypeWithLegacyFieldMapperKnnIndexSetting() {
             .endObject()
             .endObject();
 
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
 
         ResponseException ex = expectThrows(ResponseException.class, () -> createKnnIndex(INDEX_NAME, mapping));
         assertTrue(
@@ -484,7 +483,7 @@ private void createKnnIndexMappingWithCustomEngine(int dimension, SpaceType spac
             .endObject()
             .endObject();
 
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
         createKnnIndex(INDEX_NAME, mapping);
     }
 
@@ -500,7 +499,7 @@ private void createKnnIndexMappingForScripting(int dimension, String vectorDataT
             .endObject()
             .endObject();
 
-        String mapping = Strings.toString(builder);
+        String mapping = builder.toString();
         createKnnIndex(INDEX_NAME, Settings.EMPTY, mapping);
     }
 
diff --git a/src/test/java/org/opensearch/knn/index/codec/KNN80Codec/KNN80DocValuesConsumerTests.java b/src/test/java/org/opensearch/knn/index/codec/KNN80Codec/KNN80DocValuesConsumerTests.java
index 8fa63a2e3..58f4b6e39 100644
--- a/src/test/java/org/opensearch/knn/index/codec/KNN80Codec/KNN80DocValuesConsumerTests.java
+++ b/src/test/java/org/opensearch/knn/index/codec/KNN80Codec/KNN80DocValuesConsumerTests.java
@@ -19,7 +19,6 @@
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import org.opensearch.cluster.service.ClusterService;
-import org.opensearch.common.Strings;
 import org.opensearch.common.settings.ClusterSettings;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.common.xcontent.XContentFactory;
@@ -162,7 +161,7 @@ public void testAddKNNBinaryField_fromScratch_nmslibCurrent() throws IOException
             new MethodComponentContext(METHOD_HNSW, ImmutableMap.of(METHOD_PARAMETER_M, 16, METHOD_PARAMETER_EF_CONSTRUCTION, 512))
         );
 
-        String parameterString = Strings.toString(XContentFactory.jsonBuilder().map(knnEngine.getMethodAsMap(knnMethodContext)));
+        String parameterString = XContentFactory.jsonBuilder().map(knnEngine.getMethodAsMap(knnMethodContext)).toString();
 
         FieldInfo[] fieldInfoArray = new FieldInfo[] {
             KNNCodecTestUtil.FieldInfoBuilder.builder(fieldName)
@@ -257,7 +256,7 @@ public void testAddKNNBinaryField_fromScratch_faissCurrent() throws IOException
             new MethodComponentContext(METHOD_HNSW, ImmutableMap.of(METHOD_PARAMETER_M, 16, METHOD_PARAMETER_EF_CONSTRUCTION, 512))
         );
 
-        String parameterString = Strings.toString(XContentFactory.jsonBuilder().map(knnEngine.getMethodAsMap(knnMethodContext)));
+        String parameterString = XContentFactory.jsonBuilder().map(knnEngine.getMethodAsMap(knnMethodContext)).toString();
 
         FieldInfo[] fieldInfoArray = new FieldInfo[] {
             KNNCodecTestUtil.FieldInfoBuilder.builder(fieldName)
diff --git a/src/test/java/org/opensearch/knn/plugin/action/RestKNNStatsHandlerIT.java b/src/test/java/org/opensearch/knn/plugin/action/RestKNNStatsHandlerIT.java
index e3b832e8c..411a51c3c 100644
--- a/src/test/java/org/opensearch/knn/plugin/action/RestKNNStatsHandlerIT.java
+++ b/src/test/java/org/opensearch/knn/plugin/action/RestKNNStatsHandlerIT.java
@@ -14,7 +14,6 @@
 import org.opensearch.client.Response;
 import org.opensearch.client.ResponseException;
 import org.opensearch.cluster.health.ClusterHealthStatus;
-import org.opensearch.common.Strings;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.common.unit.TimeValue;
 import org.opensearch.core.xcontent.XContentBuilder;
@@ -459,17 +458,16 @@ public void validateModelCreated(String modelId) throws Exception {
 
     // mapping to create index from model
     public String modelIndexMapping(String fieldName, String modelId) throws IOException {
-        return Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject(PROPERTIES)
-                .startObject(fieldName)
-                .field(VECTOR_TYPE, KNN_VECTOR)
-                .field(MODEL_ID, modelId)
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        return XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject(PROPERTIES)
+            .startObject(fieldName)
+            .field(VECTOR_TYPE, KNN_VECTOR)
+            .field(MODEL_ID, modelId)
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
     }
 
     @Override
diff --git a/src/test/java/org/opensearch/knn/plugin/script/KNNScriptScoringIT.java b/src/test/java/org/opensearch/knn/plugin/script/KNNScriptScoringIT.java
index 2b398245d..1ee7875c6 100644
--- a/src/test/java/org/opensearch/knn/plugin/script/KNNScriptScoringIT.java
+++ b/src/test/java/org/opensearch/knn/plugin/script/KNNScriptScoringIT.java
@@ -12,7 +12,6 @@
 import org.opensearch.client.Request;
 import org.opensearch.client.Response;
 import org.opensearch.client.ResponseException;
-import org.opensearch.common.Strings;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.core.xcontent.ToXContent;
 import org.opensearch.core.xcontent.XContentBuilder;
@@ -282,7 +281,7 @@ public void testKNNInvalidSourceScript() throws Exception {
         builder.endObject();
         Request request = new Request("POST", "/" + INDEX_NAME + "/_search");
 
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         ResponseException ex = expectThrows(ResponseException.class, () -> client().performRequest(request));
         assertThat(EntityUtils.toString(ex.getResponse().getEntity()), containsString("Unknown script name Dummy_source"));
     }
@@ -415,16 +414,15 @@ public void testKNNScoreforNonVectorDocument() throws Exception {
     @SuppressWarnings("unchecked")
     public void testHammingScriptScore_Long() throws Exception {
         createIndex(INDEX_NAME, Settings.EMPTY);
-        String longMapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(FIELD_NAME)
-                .field("type", "long")
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        String longMapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(FIELD_NAME)
+            .field("type", "long")
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
         putMappingRequest(INDEX_NAME, longMapping);
 
         addDocWithNumericField(INDEX_NAME, "0", FIELD_NAME, 8L);
@@ -525,17 +523,16 @@ public void testHammingScriptScore_Long() throws Exception {
     @SuppressWarnings("unchecked")
     public void testHammingScriptScore_Base64() throws Exception {
         createIndex(INDEX_NAME, Settings.EMPTY);
-        String longMapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(FIELD_NAME)
-                .field("type", "binary")
-                .field("doc_values", true)
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        String longMapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(FIELD_NAME)
+            .field("type", "binary")
+            .field("doc_values", true)
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
         putMappingRequest(INDEX_NAME, longMapping);
 
         addDocWithBinaryField(INDEX_NAME, "0", FIELD_NAME, "AAAAAAAAAAk=");
diff --git a/src/test/java/org/opensearch/knn/plugin/script/PainlessScriptIT.java b/src/test/java/org/opensearch/knn/plugin/script/PainlessScriptIT.java
index f46ee9847..e2fd536f1 100644
--- a/src/test/java/org/opensearch/knn/plugin/script/PainlessScriptIT.java
+++ b/src/test/java/org/opensearch/knn/plugin/script/PainlessScriptIT.java
@@ -17,7 +17,6 @@
 import org.opensearch.client.Request;
 import org.opensearch.client.Response;
 import org.opensearch.client.ResponseException;
-import org.opensearch.common.Strings;
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.common.xcontent.XContentFactory;
 import org.opensearch.index.query.MatchAllQueryBuilder;
@@ -63,7 +62,7 @@ protected String createMapping(List<MappingProperty> properties) throws IOExcept
             builder.endObject();
         }
         xContentBuilder.endObject().endObject();
-        return Strings.toString(xContentBuilder);
+        return xContentBuilder.toString();
     }
 
     /*
diff --git a/src/test/java/org/opensearch/knn/plugin/transport/DeleteModelResponseTests.java b/src/test/java/org/opensearch/knn/plugin/transport/DeleteModelResponseTests.java
index 626068d13..fcb72795c 100644
--- a/src/test/java/org/opensearch/knn/plugin/transport/DeleteModelResponseTests.java
+++ b/src/test/java/org/opensearch/knn/plugin/transport/DeleteModelResponseTests.java
@@ -11,7 +11,6 @@
 
 package org.opensearch.knn.plugin.transport;
 
-import org.opensearch.common.Strings;
 import org.opensearch.common.io.stream.BytesStreamOutput;
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.common.xcontent.XContentFactory;
@@ -40,6 +39,6 @@ public void testXContentWithoutError() throws IOException {
         String expectedResponseString = "{\"model_id\":\"test-model\",\"result\":\"deleted\"}";
         XContentBuilder xContentBuilder = XContentFactory.jsonBuilder();
         deleteModelResponse.toXContent(xContentBuilder, null);
-        assertEquals(expectedResponseString, Strings.toString(xContentBuilder));
+        assertEquals(expectedResponseString, xContentBuilder.toString());
     }
 }
diff --git a/src/test/java/org/opensearch/knn/plugin/transport/GetModelResponseTests.java b/src/test/java/org/opensearch/knn/plugin/transport/GetModelResponseTests.java
index 1d69e02cb..56788840f 100644
--- a/src/test/java/org/opensearch/knn/plugin/transport/GetModelResponseTests.java
+++ b/src/test/java/org/opensearch/knn/plugin/transport/GetModelResponseTests.java
@@ -11,7 +11,6 @@
 
 package org.opensearch.knn.plugin.transport;
 
-import org.opensearch.common.Strings;
 import org.opensearch.common.io.stream.BytesStreamOutput;
 import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.common.xcontent.XContentFactory;
@@ -50,7 +49,7 @@ public void testXContent() throws IOException {
             "{\"model_id\":\"test-model\",\"model_blob\":\"aGVsbG8=\",\"state\":\"created\",\"timestamp\":\"2021-03-27 10:15:30 AM +05:30\",\"description\":\"test model\",\"error\":\"\",\"space_type\":\"l2\",\"dimension\":4,\"engine\":\"nmslib\"}";
         XContentBuilder xContentBuilder = XContentFactory.jsonBuilder();
         getModelResponse.toXContent(xContentBuilder, null);
-        assertEquals(expectedResponseString, Strings.toString(xContentBuilder));
+        assertEquals(expectedResponseString, xContentBuilder.toString());
     }
 
     public void testXContentWithNoModelBlob() throws IOException {
@@ -61,6 +60,6 @@ public void testXContentWithNoModelBlob() throws IOException {
             "{\"model_id\":\"test-model\",\"model_blob\":\"\",\"state\":\"failed\",\"timestamp\":\"2021-03-27 10:15:30 AM +05:30\",\"description\":\"test model\",\"error\":\"\",\"space_type\":\"l2\",\"dimension\":4,\"engine\":\"nmslib\"}";
         XContentBuilder xContentBuilder = XContentFactory.jsonBuilder();
         getModelResponse.toXContent(xContentBuilder, null);
-        assertEquals(expectedResponseString, Strings.toString(xContentBuilder));
+        assertEquals(expectedResponseString, xContentBuilder.toString());
     }
 }
diff --git a/src/test/resources/lang-painless/lang-painless-1.3.0-SNAPSHOT.zip b/src/test/resources/lang-painless/lang-painless-1.3.0-SNAPSHOT.zip
new file mode 100644
index 000000000..1ea8b8117
Binary files /dev/null and b/src/test/resources/lang-painless/lang-painless-1.3.0-SNAPSHOT.zip differ
diff --git a/src/testFixtures/java/org/opensearch/knn/KNNRestTestCase.java b/src/testFixtures/java/org/opensearch/knn/KNNRestTestCase.java
index b9d6a8ad3..9779dd94e 100644
--- a/src/testFixtures/java/org/opensearch/knn/KNNRestTestCase.java
+++ b/src/testFixtures/java/org/opensearch/knn/KNNRestTestCase.java
@@ -10,7 +10,6 @@
 import com.google.common.primitives.Floats;
 import org.apache.commons.lang.StringUtils;
 import org.apache.hc.core5.http.io.entity.EntityUtils;
-import org.opensearch.common.Strings;
 import org.opensearch.core.common.bytes.BytesReference;
 import org.opensearch.common.xcontent.XContentHelper;
 import org.opensearch.core.xcontent.DeprecationHandler;
@@ -165,17 +164,16 @@ protected void createKnnIndex(String index, Settings settings, String mapping) t
     }
 
     protected void createBasicKnnIndex(String index, String fieldName, int dimension) throws IOException {
-        String mapping = Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(fieldName)
-                .field("type", "knn_vector")
-                .field("dimension", Integer.toString(dimension))
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        String mapping = XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(fieldName)
+            .field("type", "knn_vector")
+            .field("dimension", Integer.toString(dimension))
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
 
         mapping = mapping.substring(1, mapping.length() - 1);
         createIndex(index, Settings.EMPTY, mapping);
@@ -194,7 +192,7 @@ protected Response searchKNNIndex(String index, KNNQueryBuilder knnQueryBuilder,
         request.addParameter("size", Integer.toString(resultSize));
         request.addParameter("explain", Boolean.toString(true));
         request.addParameter("search_type", "query_then_fetch");
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
 
         Response response = client().performRequest(request);
         assertEquals(request.getEndpoint() + ": failed", RestStatus.OK, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
@@ -215,7 +213,7 @@ protected Response searchExists(String index, ExistsQueryBuilder existsQueryBuil
         builder.endObject();
 
         request.addParameter("size", Integer.toString(resultSize));
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
 
         Response response = client().performRequest(request);
         assertEquals(request.getEndpoint() + ": failed", RestStatus.OK, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
@@ -304,38 +302,36 @@ protected void putMappingRequest(String index, String mapping) throws IOExceptio
      * Utility to create a Knn Index Mapping
      */
     protected String createKnnIndexMapping(String fieldName, Integer dimensions) throws IOException {
-        return Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(fieldName)
-                .field("type", "knn_vector")
-                .field("dimension", dimensions.toString())
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        return XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(fieldName)
+            .field("type", "knn_vector")
+            .field("dimension", dimensions.toString())
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
     }
 
     /**
      * Utility to create a Knn Index Mapping with specific algorithm and engine
      */
     protected String createKnnIndexMapping(String fieldName, Integer dimensions, String algoName, String knnEngine) throws IOException {
-        return Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject("properties")
-                .startObject(fieldName)
-                .field("type", "knn_vector")
-                .field("dimension", dimensions.toString())
-                .startObject("method")
-                .field("name", algoName)
-                .field("engine", knnEngine)
-                .endObject()
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        return XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject("properties")
+            .startObject(fieldName)
+            .field("type", "knn_vector")
+            .field("dimension", dimensions.toString())
+            .startObject("method")
+            .field("name", algoName)
+            .field("engine", knnEngine)
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
     }
 
     /**
@@ -354,7 +350,7 @@ protected String createKnnIndexMapping(List<String> fieldNames, List<Integer> di
         }
         xContentBuilder.endObject().endObject();
 
-        return Strings.toString(xContentBuilder);
+        return xContentBuilder.toString();
     }
 
     /**
@@ -416,7 +412,7 @@ protected void addKnnDoc(String index, String docId, String fieldName, Object[]
         Request request = new Request("POST", "/" + index + "/_doc/" + docId + "?refresh=true");
 
         XContentBuilder builder = XContentFactory.jsonBuilder().startObject().field(fieldName, vector).endObject();
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         client().performRequest(request);
 
         request = new Request("POST", "/" + index + "/_refresh");
@@ -436,7 +432,7 @@ protected void addKnnDoc(String index, String docId, List<String> fieldNames, Li
         }
         builder.endObject();
 
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         Response response = client().performRequest(request);
         assertEquals(request.getEndpoint() + ": failed", RestStatus.CREATED, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
     }
@@ -449,7 +445,7 @@ protected void addDocWithNumericField(String index, String docId, String fieldNa
 
         XContentBuilder builder = XContentFactory.jsonBuilder().startObject().field(fieldName, value).endObject();
 
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
 
         Response response = client().performRequest(request);
 
@@ -464,7 +460,7 @@ protected void addDocWithBinaryField(String index, String docId, String fieldNam
 
         XContentBuilder builder = XContentFactory.jsonBuilder().startObject().field(fieldName, base64String).endObject();
 
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
 
         Response response = client().performRequest(request);
 
@@ -479,7 +475,7 @@ protected void updateKnnDoc(String index, String docId, String fieldName, Object
 
         XContentBuilder builder = XContentFactory.jsonBuilder().startObject().field(fieldName, vector).endObject();
 
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
 
         Response response = client().performRequest(request);
         assertEquals(request.getEndpoint() + ": failed", RestStatus.OK, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
@@ -528,7 +524,7 @@ protected void updateClusterSettings(String settingKey, Object value) throws Exc
             .endObject()
             .endObject();
         Request request = new Request("PUT", "_cluster/settings");
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         Response response = client().performRequest(request);
         assertEquals(RestStatus.OK, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
     }
@@ -689,7 +685,7 @@ protected void addModelToSystemIndex(String modelId, ModelMetadata modelMetadata
             .field(MODEL_ERROR, modelMetadata.getError())
             .endObject();
 
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
 
         Response response = client().performRequest(request);
 
@@ -769,7 +765,7 @@ protected Request constructScriptedMetricAggregationSearchRequest(
         builder.endObject();
         String endpoint = String.format(Locale.getDefault(), "/%s/_search?size=0&filter_path=aggregations", INDEX_NAME);
         Request request = new Request("POST", endpoint);
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         return request;
     }
 
@@ -792,7 +788,7 @@ protected Request constructScriptScoreContextSearchRequest(
         builder.endObject();
         builder.endObject();
         Request request = new Request("POST", "/" + indexName + "/_search");
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         return request;
     }
 
@@ -808,7 +804,7 @@ protected Request constructKNNScriptQueryRequest(String indexName, QueryBuilder
         builder.endObject();
         builder.endObject();
         Request request = new Request("POST", "/" + indexName + "/_search");
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         return request;
     }
 
@@ -878,7 +874,7 @@ public float[][] getIndexVectorsFromIndex(String testIndex, String testField, in
         XContentBuilder builder = XContentFactory.jsonBuilder().startObject();
         builder.field("query", qb);
         builder.endObject();
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
 
         Response response = client().performRequest(request);
         assertEquals(request.getEndpoint() + ": failed", RestStatus.OK, RestStatus.fromCode(response.getStatusLine().getStatusCode()));
@@ -958,20 +954,19 @@ protected Settings createKNNIndexCustomLegacyFieldMappingSettings(SpaceType spac
     }
 
     public String createKNNIndexMethodFieldMapping(String fieldName, Integer dimensions) throws IOException {
-        return Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject(PROPERTIES)
-                .startObject(fieldName)
-                .field(VECTOR_TYPE, KNN_VECTOR)
-                .field(DIMENSION, dimensions.toString())
-                .startObject(KNN_METHOD)
-                .field(NAME, METHOD_HNSW)
-                .endObject()
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        return XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject(PROPERTIES)
+            .startObject(fieldName)
+            .field(VECTOR_TYPE, KNN_VECTOR)
+            .field(DIMENSION, dimensions.toString())
+            .startObject(KNN_METHOD)
+            .field(NAME, METHOD_HNSW)
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
     }
 
     public String createKNNIndexCustomMethodFieldMapping(
@@ -982,26 +977,25 @@ public String createKNNIndexCustomMethodFieldMapping(
         Integer m,
         Integer ef_construction
     ) throws IOException {
-        return Strings.toString(
-            XContentFactory.jsonBuilder()
-                .startObject()
-                .startObject(PROPERTIES)
-                .startObject(fieldName)
-                .field(VECTOR_TYPE, KNN_VECTOR)
-                .field(DIMENSION, dimensions.toString())
-                .startObject(KNN_METHOD)
-                .field(NAME, METHOD_HNSW)
-                .field(METHOD_PARAMETER_SPACE_TYPE, spaceType.getValue())
-                .field(KNN_ENGINE, engine)
-                .startObject(PARAMETERS)
-                .field(METHOD_PARAMETER_EF_CONSTRUCTION, ef_construction)
-                .field(METHOD_PARAMETER_M, m)
-                .endObject()
-                .endObject()
-                .endObject()
-                .endObject()
-                .endObject()
-        );
+        return XContentFactory.jsonBuilder()
+            .startObject()
+            .startObject(PROPERTIES)
+            .startObject(fieldName)
+            .field(VECTOR_TYPE, KNN_VECTOR)
+            .field(DIMENSION, dimensions.toString())
+            .startObject(KNN_METHOD)
+            .field(NAME, METHOD_HNSW)
+            .field(METHOD_PARAMETER_SPACE_TYPE, spaceType.getValue())
+            .field(KNN_ENGINE, engine)
+            .startObject(PARAMETERS)
+            .field(METHOD_PARAMETER_EF_CONSTRUCTION, ef_construction)
+            .field(METHOD_PARAMETER_M, m)
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject()
+            .endObject()
+            .toString();
     }
 
     // Default KNN script score settings
@@ -1114,7 +1108,7 @@ public Response trainModel(
         }
 
         Request request = new Request("POST", "/_plugins/_knn/models" + modelId + "/_train");
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         return client().performRequest(request);
     }
 
@@ -1331,7 +1325,7 @@ protected void addKnnDocWithAttributes(String docId, float[] vector, Map<String,
             builder.field(fieldName, fieldValues.get(fieldName));
         }
         builder.endObject();
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         client().performRequest(request);
 
         request = new Request("POST", "/" + INDEX_NAME + "/_refresh");
@@ -1353,7 +1347,7 @@ protected void addKnnDocWithAttributes(
             builder.field(fieldName, fieldValues.get(fieldName));
         }
         builder.endObject();
-        request.setJsonEntity(Strings.toString(builder));
+        request.setJsonEntity(builder.toString());
         client().performRequest(request);
 
         request = new Request("POST", "/" + indexName + "/_refresh");
diff --git a/src/testFixtures/java/org/opensearch/knn/ODFERestTestCase.java b/src/testFixtures/java/org/opensearch/knn/ODFERestTestCase.java
index 986a45e5e..0b951e5c3 100644
--- a/src/testFixtures/java/org/opensearch/knn/ODFERestTestCase.java
+++ b/src/testFixtures/java/org/opensearch/knn/ODFERestTestCase.java
@@ -39,7 +39,6 @@
 import org.opensearch.client.Response;
 import org.opensearch.client.RestClient;
 import org.opensearch.client.RestClientBuilder;
-import org.opensearch.common.Strings;
 import org.opensearch.common.io.PathUtils;
 import org.opensearch.common.settings.Settings;
 import org.opensearch.common.unit.TimeValue;
@@ -263,7 +262,7 @@ private void deleteAllDocs(final String indexName) throws IOException {
             .endObject()
             .endObject();
 
-        request.setJsonEntity(Strings.toString(matchAllDocsQuery));
+        request.setJsonEntity(matchAllDocsQuery.toString());
         adminClient().performRequest(request);
     }