[SPARK-53820] Introduce o.a.s.k8s.operator.utils.StringUtils

### What changes were proposed in this pull request?

This PR aims to introduce `org.apache.spark.k8s.operator.utils.StringUtils`.

### Why are the changes needed?

To reduce the dependency on `commons-lang3`.

**BEFORE**

```
$ git grep org.apache.commons.lang3 | grep -v test | grep -v checkstyle | wc -l
      11
```

**AFTER**

```
$ git grep org.apache.commons.lang3 | grep -v test | grep -v checkstyle | wc -l
       0
```

### Does this PR introduce _any_ user-facing change?

No behavior change.

### How was this patch tested?

Pass the CIs.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #370 from dongjoon-hyun/SPARK-53820.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

spark-operator-api/src/main/java/org/apache/spark/k8s/operator/utils/StringUtils.java

@@ -0,0 +1,73 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.spark.k8s.operator.utils;
+
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
+/** Utility class for string operations. */
+public final class StringUtils {
+  private StringUtils() {}
+
+  public static boolean isBlank(final String str) {
+    return str == null || str.isBlank();
+  }
+
+  public static boolean isNotBlank(final String str) {
+    return !isBlank(str);
+  }
+
+  public static boolean isEmpty(final String str) {
+    return str == null || str.length() == 0;
+  }
+
+  public static boolean isNotEmpty(final String str) {
+    return !isEmpty(str);
+  }
+
+  public static int ordinalIndexOf(final String str, final String substr, final int ordinal) {
+    if (str == null || substr == null || ordinal <= 0) {
+      return -1;
+    }
+    if (substr.isEmpty()) {
+      return 0;
+    }
+
+    int index = -1;
+    for (int i = 0; i < ordinal; i++) {
+      index = str.indexOf(substr, index + 1);
+      if (index == -1) {
+        return -1;
+      }
+    }
+    return index;
+  }
+
+  public static String getStackTrace(Throwable throwable) {
+    if (throwable == null) {
+      return "";
+    }
+
+    StringWriter sw = new StringWriter();
+    PrintWriter pw = new PrintWriter(sw);
+    throwable.printStackTrace(pw);
+    return sw.toString();
+  }
+}

spark-operator/src/main/java/org/apache/spark/k8s/operator/config/ConfigOption.java

@@ -27,9 +27,9 @@
 import lombok.RequiredArgsConstructor;
 import lombok.ToString;
 import lombok.extern.slf4j.Slf4j;
-import org.apache.commons.lang3.StringUtils;
 
 import org.apache.spark.k8s.operator.utils.ModelUtils;
+import org.apache.spark.k8s.operator.utils.StringUtils;
 
 /**
  * Config options for Spark Operator. Supports primitive and serialized JSON.

spark-operator/src/main/java/org/apache/spark/k8s/operator/config/SparkOperatorConfManager.java

@@ -27,7 +27,8 @@
 import java.util.Properties;
 
 import lombok.extern.slf4j.Slf4j;
-import org.apache.commons.lang3.StringUtils;
+
+import org.apache.spark.k8s.operator.utils.StringUtils;
 
 /**
  * Loads ConfigOption from properties file. In addition, loads hot properties override from config

spark-operator/src/main/java/org/apache/spark/k8s/operator/metrics/MetricsSystemFactory.java

@@ -24,9 +24,8 @@
 import java.util.Map;
 import java.util.Properties;
 
-import org.apache.commons.lang3.StringUtils;
-
 import org.apache.spark.k8s.operator.config.SparkOperatorConfManager;
+import org.apache.spark.k8s.operator.utils.StringUtils;
 
 /** Factory for MetricsSystem. */
 public final class MetricsSystemFactory {

spark-operator/src/main/java/org/apache/spark/k8s/operator/metrics/PrometheusPullModelHandler.java

@@ -40,9 +40,9 @@
 import jakarta.servlet.http.HttpServletRequest;
 import lombok.Getter;
 import lombok.extern.slf4j.Slf4j;
-import org.apache.commons.lang3.StringUtils;
 
 import org.apache.spark.k8s.operator.config.SparkOperatorConf;
+import org.apache.spark.k8s.operator.utils.StringUtils;
 import org.apache.spark.metrics.sink.PrometheusServlet;
 
 /** Serves as simple Prometheus sink (pull model), presenting metrics snapshot as HttpHandler. */

spark-operator/src/main/java/org/apache/spark/k8s/operator/reconciler/reconcilesteps/AppCleanUpStep.java

@@ -33,7 +33,6 @@
 import io.fabric8.kubernetes.client.KubernetesClient;
 import lombok.NoArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
-import org.apache.commons.lang3.StringUtils;
 
 import org.apache.spark.k8s.operator.SparkApplication;
 import org.apache.spark.k8s.operator.config.SparkOperatorConf;
@@ -48,6 +47,7 @@
 import org.apache.spark.k8s.operator.utils.ReconcilerUtils;
 import org.apache.spark.k8s.operator.utils.SparkAppStatusRecorder;
 import org.apache.spark.k8s.operator.utils.SparkAppStatusUtils;
+import org.apache.spark.k8s.operator.utils.StringUtils;
 
 /**
  * Cleanup all secondary resources when application is deleted, or at the end of each attempt.

spark-operator/src/main/java/org/apache/spark/k8s/operator/utils/ClassLoadingUtils.java

@@ -25,7 +25,6 @@
 import java.util.Set;
 
 import lombok.extern.slf4j.Slf4j;
-import org.apache.commons.lang3.StringUtils;
 
 import org.apache.spark.k8s.operator.listeners.BaseStatusListener;
 

spark-operator/src/main/java/org/apache/spark/k8s/operator/utils/SparkExceptionUtils.java

@@ -22,8 +22,6 @@
 import static java.net.HttpURLConnection.HTTP_CONFLICT;
 
 import io.fabric8.kubernetes.client.KubernetesClientException;
-import org.apache.commons.lang3.StringUtils;
-import org.apache.commons.lang3.exception.ExceptionUtils;
 
 /** Utility class for Spark exceptions. */
 public final class SparkExceptionUtils {
@@ -51,6 +49,6 @@ public static boolean isConflictForExistingResource(KubernetesClientException e)
    * @return A string containing the stack trace of the exception.
    */
   public static String buildGeneralErrorMessage(Exception e) {
-    return ExceptionUtils.getStackTrace(e);
+    return StringUtils.getStackTrace(e);
   }
 }

spark-operator/src/main/java/org/apache/spark/k8s/operator/utils/Utils.java

@@ -41,7 +41,6 @@
 import io.fabric8.kubernetes.api.model.HasMetadata;
 import io.javaoperatorsdk.operator.processing.event.ResourceID;
 import io.javaoperatorsdk.operator.processing.event.source.SecondaryToPrimaryMapper;
-import org.apache.commons.lang3.StringUtils;
 
 import org.apache.spark.k8s.operator.Constants;
 import org.apache.spark.k8s.operator.SparkApplication;

spark-operator/src/test/java/org/apache/spark/k8s/operator/config/SparkOperatorConfManagerTest.java

@@ -22,10 +22,11 @@
 import java.io.IOException;
 import java.util.Collections;
 
-import org.apache.commons.lang3.StringUtils;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
+import org.apache.spark.k8s.operator.utils.StringUtils;
+
 class SparkOperatorConfManagerTest {
   @Test
   void testLoadPropertiesFromInitFile() throws IOException {