[SPARK-48320][CORE][DOCS] Add structured logging guide to the scala and java doc

common/utils/src/main/java/org/apache/spark/internal/SparkLogger.java

@@ -28,6 +28,49 @@
 import org.slf4j.Logger;
 // checkstyle.on: RegexpSinglelineJava
 
+// checkstyle.off: RegexpSinglelineJava
+/**
+ * Guidelines for the Structured Logging Framework - Java Logging
+ * <p>
+ *
+ * Use the `org.apache.spark.internal.SparkLoggerFactory` to get the logger instance in Java code:
+ * Getting Logger Instance:
+ *   Instead of using `org.slf4j.LoggerFactory`, use `org.apache.spark.internal.SparkLoggerFactory`
+ *   to ensure structured logging.
+ * <p>
+ *
+ * import org.apache.spark.internal.SparkLogger;
+ * import org.apache.spark.internal.SparkLoggerFactory;
+ * private static final SparkLogger logger = SparkLoggerFactory.getLogger(JavaUtils.class);
+ * <p>
+ *
+ * Logging Messages with Variables:
+ *   When logging messages with variables, wrap all the variables with `MDC`s and they will be
+ *   automatically added to the Mapped Diagnostic Context (MDC).
+ * <p>
+ *
+ * import org.apache.spark.internal.LogKeys;
+ * import org.apache.spark.internal.MDC;
+ * logger.error("Unable to delete file for partition {}", MDC.of(LogKeys.PARTITION_ID$.MODULE$, i));
+ * <p>
+ *
+ * Constant String Messages:
+ *   For logging constant string messages, use the standard logging methods.
+ * <p>
+ *
+ * logger.error("Failed to abort the writer after failing to write map output.", e);
+ * <p>
+ *
+ * If you want to output logs in `java code` through the structured log framework,
+ * you can define `custom LogKey` and use it in `java` code as follows:
+ * <p>
+ *
+ * // To add a `custom LogKey`, implement `LogKey`
+ * public static class CUSTOM_LOG_KEY implements LogKey { }
+ * import org.apache.spark.internal.MDC;
+ * logger.error("Unable to delete key {} for cache", MDC.of(CUSTOM_LOG_KEY, "key"));
+ */
+// checkstyle.on: RegexpSinglelineJava
 public class SparkLogger {
 
   private static final MessageFactory MESSAGE_FACTORY = ParameterizedMessageFactory.INSTANCE;

common/utils/src/main/scala/org/apache/spark/internal/LogKey.scala

@@ -20,9 +20,37 @@ import java.util.Locale
 
 /**
  * All structured logging `keys` used in `MDC` must be extends `LogKey`
+ * <p>
+ *
+ * `LogKey`s serve as identifiers for mapped diagnostic contexts (MDC) within logs.
+ * Follow these guidelines when adding a new LogKey:
+ * <ul>
+ *   <li>
+ *     Define all structured logging keys in `LogKey.scala`, and sort them alphabetically for
+ *     ease of search.
+ *   </li>
+ *   <li>
+ *     Use `UPPER_SNAKE_CASE` for key names.
+ *   </li>
+ *   <li>
+ *     Key names should be both simple and broad, yet include specific identifiers like `STAGE_ID`,
+ *     `TASK_ID`, and `JOB_ID` when needed for clarity. For instance, use `MAX_ATTEMPTS` as a
+ *     general key instead of creating separate keys for each scenario such as
+ *     `EXECUTOR_STATE_SYNC_MAX_ATTEMPTS` and `MAX_TASK_FAILURES`.
+ *     This balances simplicity with the detail needed for effective logging.
+ *   </li>
+ *   <li>
+ *     Use abbreviations in names if they are widely understood,
+ *     such as `APP_ID` for APPLICATION_ID, and `K8S` for KUBERNETES.
+ *   </li>
+ *   <li>
+ *     For time-related keys, use milliseconds as the unit of time.
+ *   </li>
+ * </ul>
  */
 trait LogKey {
-  val name: String = this.toString.toLowerCase(Locale.ROOT)
+  private lazy val _name: String = getClass.getSimpleName.stripSuffix("$").toLowerCase(Locale.ROOT)
+  def name: String = _name
 }
 
 /**

common/utils/src/main/scala/org/apache/spark/internal/Logging.scala

@@ -29,6 +29,44 @@ import org.slf4j.{Logger, LoggerFactory}
 import org.apache.spark.internal.Logging.SparkShellLoggingFilter
 import org.apache.spark.util.SparkClassUtils
 
+/**
+ * Guidelines for the Structured Logging Framework - Scala Logging
+ * <p>
+ *
+ * Use the `org.apache.spark.internal.Logging` trait for logging in Scala code:
+ * Logging Messages with Variables:
+ *   When logging a message with variables, wrap all the variables with `MDC`s and they will be
+ *   automatically added to the Mapped Diagnostic Context (MDC).
+ * This allows for structured logging and better log analysis.
+ * <p>
+ *
+ * logInfo(log"Trying to recover app: ${MDC(LogKeys.APP_ID, app.id)}")
+ * <p>
+ *
+ * Constant String Messages:
+ *   If you are logging a constant string message, use the log methods that accept a constant
+ *   string.
+ * <p>
+ *
+ * logInfo("StateStore stopped")
+ * <p>
+ *
+ * Exceptions:
+ *   To ensure logs are compatible with Spark SQL and log analysis tools, avoid
+ *   `Exception.printStackTrace()`. Use `logError`, `logWarning`, and `logInfo` methods from
+ *   the `Logging` trait to log exceptions, maintaining structured and parsable logs.
+ * <p>
+ *
+ * If you want to output logs in `scala code` through the structured log framework,
+ * you can define `custom LogKey` and use it in `scala` code as follows:
+ * <p>
+ *
+ * // To add a `custom LogKey`, implement `LogKey`
+ * case object CUSTOM_LOG_KEY extends LogKey
+ * import org.apache.spark.internal.MDC;
+ * logInfo(log"${MDC(CUSTOM_LOG_KEY, "key")}")
+ */
+
 /**
  * Mapped Diagnostic Context (MDC) that will be used in log messages.
  * The values of the MDC will be inline in the log message, while the key-value pairs will be

common/utils/src/test/java/org/apache/spark/util/PatternSparkLoggerSuite.java

@@ -84,7 +84,12 @@ String expectedPatternForMsgWithMDCValueIsNull(Level level) {
   }
 
   @Override
-  String expectedPatternForExternalSystemCustomLogKey(Level level) {
-    return toRegexPattern(level, ".*<level> <className>: External system custom log message.\n");
+  String expectedPatternForScalaCustomLogKey(Level level) {
+    return toRegexPattern(level, ".*<level> <className>: Scala custom log message.\n");
+  }
+
+  @Override
+  String expectedPatternForJavaCustomLogKey(Level level) {
+    return toRegexPattern(level, ".*<level> <className>: Java custom log message.\n");
   }
 }

common/utils/src/test/java/org/apache/spark/util/SparkLoggerSuiteBase.java

@@ -26,9 +26,10 @@
 import org.apache.logging.log4j.Level;
 import org.junit.jupiter.api.Test;
 
-import org.apache.spark.internal.SparkLogger;
+import org.apache.spark.internal.LogKey;
 import org.apache.spark.internal.LogKeys;
 import org.apache.spark.internal.MDC;
+import org.apache.spark.internal.SparkLogger;
 
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -68,8 +69,11 @@ private String basicMsg() {
 
   private final MDC executorIDMDCValueIsNull = MDC.of(LogKeys.EXECUTOR_ID$.MODULE$, null);
 
-  private final MDC externalSystemCustomLog =
-    MDC.of(CustomLogKeys.CUSTOM_LOG_KEY$.MODULE$, "External system custom log message.");
+  private final MDC scalaCustomLogMDC =
+    MDC.of(CustomLogKeys.CUSTOM_LOG_KEY$.MODULE$, "Scala custom log message.");
+
+  private final MDC javaCustomLogMDC =
+    MDC.of(JavaCustomLogKeys.CUSTOM_LOG_KEY, "Java custom log message.");
 
   // test for basic message (without any mdc)
   abstract String expectedPatternForBasicMsg(Level level);
@@ -89,8 +93,11 @@ private String basicMsg() {
   // test for message (with mdc - the value is null)
   abstract String expectedPatternForMsgWithMDCValueIsNull(Level level);
 
-  // test for external system custom LogKey
-  abstract String expectedPatternForExternalSystemCustomLogKey(Level level);
+  // test for scala custom LogKey
+  abstract String expectedPatternForScalaCustomLogKey(Level level);
+
+  // test for java custom LogKey
+  abstract String expectedPatternForJavaCustomLogKey(Level level);
 
   @Test
   public void testBasicMsgLogger() {
@@ -142,8 +149,6 @@ public void testLoggerWithMDC() {
     Runnable errorFn = () -> logger().error(msgWithMDC, executorIDMDC);
     Runnable warnFn = () -> logger().warn(msgWithMDC, executorIDMDC);
     Runnable infoFn = () -> logger().info(msgWithMDC, executorIDMDC);
-    Runnable debugFn = () -> logger().debug(msgWithMDC, executorIDMDC);
-    Runnable traceFn = () -> logger().trace(msgWithMDC, executorIDMDC);
     List.of(
         Pair.of(Level.ERROR, errorFn),
         Pair.of(Level.WARN, warnFn),
@@ -213,20 +218,46 @@ public void testLoggerWithMDCValueIsNull() {
   }
 
   @Test
-  public void testLoggerWithExternalSystemCustomLogKey() {
-    Runnable errorFn = () -> logger().error("{}", externalSystemCustomLog);
-    Runnable warnFn = () -> logger().warn("{}", externalSystemCustomLog);
-    Runnable infoFn = () -> logger().info("{}", externalSystemCustomLog);
+  public void testLoggerWithScalaCustomLogKey() {
+    Runnable errorFn = () -> logger().error("{}", scalaCustomLogMDC);
+    Runnable warnFn = () -> logger().warn("{}", scalaCustomLogMDC);
+    Runnable infoFn = () -> logger().info("{}", scalaCustomLogMDC);
+    List.of(
+        Pair.of(Level.ERROR, errorFn),
+        Pair.of(Level.WARN, warnFn),
+        Pair.of(Level.INFO, infoFn)).forEach(pair -> {
+      try {
+        assertTrue(captureLogOutput(pair.getRight()).matches(
+          expectedPatternForScalaCustomLogKey(pair.getLeft())));
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
+    });
+  }
+
+  @Test
+  public void testLoggerWithJavaCustomLogKey() {
+    Runnable errorFn = () -> logger().error("{}", javaCustomLogMDC);
+    Runnable warnFn = () -> logger().warn("{}", javaCustomLogMDC);
+    Runnable infoFn = () -> logger().info("{}", javaCustomLogMDC);
     List.of(
         Pair.of(Level.ERROR, errorFn),
         Pair.of(Level.WARN, warnFn),
         Pair.of(Level.INFO, infoFn)).forEach(pair -> {
       try {
         assertTrue(captureLogOutput(pair.getRight()).matches(
-          expectedPatternForExternalSystemCustomLogKey(pair.getLeft())));
+          expectedPatternForJavaCustomLogKey(pair.getLeft())));
       } catch (IOException e) {
         throw new RuntimeException(e);
       }
     });
   }
 }
+
+class JavaCustomLogKeys {
+  // Custom `LogKey` must be `implements LogKey`
+  public static class CUSTOM_LOG_KEY implements LogKey { }
+
+  // Singleton
+  public static final CUSTOM_LOG_KEY CUSTOM_LOG_KEY = new CUSTOM_LOG_KEY();
+}

common/utils/src/test/java/org/apache/spark/util/StructuredSparkLoggerSuite.java

@@ -149,14 +149,28 @@ String expectedPatternForMsgWithMDCValueIsNull(Level level) {
   }
 
   @Override
-  String expectedPatternForExternalSystemCustomLogKey(Level level) {
+  String expectedPatternForScalaCustomLogKey(Level level) {
     return compactAndToRegexPattern(level, """
       {
         "ts": "<timestamp>",
         "level": "<level>",
-        "msg": "External system custom log message.",
+        "msg": "Scala custom log message.",
         "context": {
-          "custom_log_key": "External system custom log message."
+          "custom_log_key": "Scala custom log message."
+        },
+        "logger": "<className>"
+      }""");
+  }
+
+  @Override
+  String expectedPatternForJavaCustomLogKey(Level level) {
+    return compactAndToRegexPattern(level, """
+      {
+        "ts": "<timestamp>",
+        "level": "<level>",
+        "msg": "Java custom log message.",
+        "context": {
+          "custom_log_key": "Java custom log message."
         },
         "logger": "<className>"
       }""");

common/utils/src/test/scala/org/apache/spark/util/PatternLoggingSuite.scala

@@ -47,8 +47,8 @@ class PatternLoggingSuite extends LoggingSuiteBase with BeforeAndAfterAll {
   override def expectedPatternForMsgWithMDCAndException(level: Level): String =
     s""".*$level $className: Error in executor 1.\njava.lang.RuntimeException: OOM\n[\\s\\S]*"""
 
-  override def expectedPatternForExternalSystemCustomLogKey(level: Level): String = {
-    s""".*$level $className: External system custom log message.\n"""
+  override def expectedPatternForCustomLogKey(level: Level): String = {
+    s""".*$level $className: Custom log message.\n"""
   }
 
   override def verifyMsgWithConcat(level: Level, logOutput: String): Unit = {