Add logging abstraction with SLF4J backend

databricks-sdk-java/src/main/java/com/databricks/sdk/core/logging/Logger.java

@@ -0,0 +1,28 @@
+package com.databricks.sdk.core.logging;
+
+/**
+ * Logging contract used throughout the SDK.
+ *
+ * <p>Extend this class to provide a custom logging implementation, then register it via a custom
+ * {@link LoggerFactory} subclass and {@link LoggerFactory#setDefault}.
+ */
+public abstract class Logger {
+
+  public abstract boolean isDebugEnabled();
+
+  public abstract void debug(String msg);
+
+  public abstract void debug(String format, Object... args);
+
+  public abstract void info(String msg);
+
+  public abstract void info(String format, Object... args);
+
+  public abstract void warn(String msg);
+
+  public abstract void warn(String format, Object... args);
+
+  public abstract void error(String msg);
+
+  public abstract void error(String format, Object... args);
+}

databricks-sdk-java/src/main/java/com/databricks/sdk/core/logging/LoggerFactory.java

@@ -0,0 +1,52 @@
+package com.databricks.sdk.core.logging;
+
+/**
+ * Creates and configures {@link Logger} instances for the SDK.
+ *
+ * <p>By default, logging goes through SLF4J. Users can override the backend programmatically
+ * before creating any SDK client:
+ *
+ * <pre>{@code
+ * LoggerFactory.setDefault(myCustomFactory);
+ * WorkspaceClient ws = new WorkspaceClient();
+ * }</pre>
+ *
+ * <p>Extend this class to provide a fully custom logging backend.
+ */
+public abstract class LoggerFactory {
+
+  private static volatile LoggerFactory defaultFactory = Slf4jLoggerFactory.INSTANCE;
+
+  /** Returns a logger for the given class, using the current default factory. */
+  public static Logger getLogger(Class<?> type) {
+    return getDefault().newInstance(type);
+  }
+
+  /** Returns a logger with the given name, using the current default factory. */
+  public static Logger getLogger(String name) {
+    return getDefault().newInstance(name);
+  }
+
+  /**
+   * Overrides the logging backend used by the SDK.
+   *
+   * <p>Must be called before creating any SDK client or calling {@link #getLogger}. Loggers
+   * already obtained will not be affected by subsequent calls.
+   */
+  public static void setDefault(LoggerFactory factory) {
+    if (factory == null) {
+      throw new IllegalArgumentException("LoggerFactory must not be null");
+    }
+    defaultFactory = factory;
+  }
+
+  static LoggerFactory getDefault() {
+    return defaultFactory;
+  }
+
+  /** Creates a new logger for the given class. */
+  protected abstract Logger newInstance(Class<?> type);
+
+  /** Creates a new logger with the given name. */
+  protected abstract Logger newInstance(String name);
+}

databricks-sdk-java/src/main/java/com/databricks/sdk/core/logging/Slf4jLogger.java

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+package com.databricks.sdk.core.logging;
+
+/** Delegates all logging calls to an SLF4J {@code Logger}. */
+class Slf4jLogger extends Logger {
+
+  private final org.slf4j.Logger delegate;
+
+  private Slf4jLogger(org.slf4j.Logger delegate) {
+    this.delegate = delegate;
+  }
+
+  static Logger create(Class<?> type) {
+    return new Slf4jLogger(org.slf4j.LoggerFactory.getLogger(type));
+  }
+
+  static Logger create(String name) {
+    return new Slf4jLogger(org.slf4j.LoggerFactory.getLogger(name));
+  }
+
+  @Override
+  public boolean isDebugEnabled() {
+    return delegate.isDebugEnabled();
+  }
+
+  @Override
+  public void debug(String msg) {
+    delegate.debug(msg);
+  }
+
+  @Override
+  public void debug(String format, Object... args) {
+    delegate.debug(format, args);
+  }
+
+  @Override
+  public void info(String msg) {
+    delegate.info(msg);
+  }
+
+  @Override
+  public void info(String format, Object... args) {
+    delegate.info(format, args);
+  }
+
+  @Override
+  public void warn(String msg) {
+    delegate.warn(msg);
+  }
+
+  @Override
+  public void warn(String format, Object... args) {
+    delegate.warn(format, args);
+  }
+
+  @Override
+  public void error(String msg) {
+    delegate.error(msg);
+  }
+
+  @Override
+  public void error(String format, Object... args) {
+    delegate.error(format, args);
+  }
+}

databricks-sdk-java/src/main/java/com/databricks/sdk/core/logging/Slf4jLoggerFactory.java

@@ -0,0 +1,17 @@
+package com.databricks.sdk.core.logging;
+
+/** A {@link LoggerFactory} backed by SLF4J. This is the default. */
+public class Slf4jLoggerFactory extends LoggerFactory {
+
+  public static final Slf4jLoggerFactory INSTANCE = new Slf4jLoggerFactory();
+
+  @Override
+  protected Logger newInstance(Class<?> type) {
+    return Slf4jLogger.create(type);
+  }
+
+  @Override
+  protected Logger newInstance(String name) {
+    return Slf4jLogger.create(name);
+  }
+}

databricks-sdk-java/src/test/java/com/databricks/sdk/core/logging/LoggerFactoryTest.java

@@ -0,0 +1,33 @@
+package com.databricks.sdk.core.logging;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+public class LoggerFactoryTest {
+
+  @AfterEach
+  void resetFactory() {
+    LoggerFactory.setDefault(Slf4jLoggerFactory.INSTANCE);
+  }
+
+  @Test
+  void defaultFactoryIsSLF4J() {
+    Logger logger = LoggerFactory.getLogger(LoggerFactoryTest.class);
+    assertNotNull(logger);
+    logger.info("LoggerFactory defaultFactoryIsSLF4J test message");
+  }
+
+  @Test
+  void setDefaultRejectsNull() {
+    assertThrows(IllegalArgumentException.class, () -> LoggerFactory.setDefault(null));
+  }
+
+  @Test
+  void getLoggerByNameWorks() {
+    Logger logger = LoggerFactory.getLogger("com.example.Test");
+    assertNotNull(logger);
+    logger.info("getLoggerByNameWorks test message");
+  }
+}

databricks-sdk-java/src/test/java/com/databricks/sdk/core/logging/Slf4jLoggerTest.java

@@ -0,0 +1,31 @@
+package com.databricks.sdk.core.logging;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+public class Slf4jLoggerTest {
+
+  @Test
+  void createReturnsSlf4jLogger() {
+    Logger logger = Slf4jLogger.create(Slf4jLoggerTest.class);
+    assertNotNull(logger);
+    assertTrue(logger instanceof Slf4jLogger);
+  }
+
+  @Test
+  void slf4jLoggerOperations() {
+    Logger logger = Slf4jLogger.create(Slf4jLoggerTest.class);
+    logger.debug("debug");
+    logger.debug("debug {}", "arg");
+    logger.info("info");
+    logger.info("info {}", "arg");
+    logger.warn("warn");
+    logger.warn("warn {}", "arg");
+    logger.error("error");
+    logger.error("error {}", "arg");
+    logger.error("error {} failed", "op", new RuntimeException("cause"));
+    logger.isDebugEnabled();
+  }
+
+}