feat(bqjdbc): Per connection logs - Add PerConnectionFileHandler

java-bigquery/google-cloud-bigquery-jdbc/.gitignore

@@ -1,3 +1,3 @@
 drivers/**
 target-it/**
-*logs/**
+*logs**/**

java-bigquery/google-cloud-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryJdbcMdc.java

@@ -24,7 +24,7 @@
  * Allocates a dedicated, independent InheritableThreadLocal object per concrete BigQueryConnection
  * instance.
  */
-public class BigQueryJdbcMdc {
+class BigQueryJdbcMdc {
   private static final AtomicLong nextId = new AtomicLong(1);
   private static final ConcurrentHashMap<BigQueryConnection, InheritableThreadLocal<String>>
       instanceLocals = new ConcurrentHashMap<>();
@@ -35,7 +35,7 @@ public class BigQueryJdbcMdc {
   private static final InheritableThreadLocal<String> currentConnectionId =
       new InheritableThreadLocal<>();
 
-  public static void registerInstance(BigQueryConnection connection, String id) {
+  static void registerInstance(BigQueryConnection connection, String id) {
     if (connection != null) {
       String cleanId =
           instanceIds.computeIfAbsent(
@@ -56,12 +56,12 @@ public static void registerInstance(BigQueryConnection connection, String id) {
   /**
    * Returns the connection ID carried by any registered active connection on the current thread.
    */
-  public static String getConnectionId() {
+  static String getConnectionId() {
     return currentConnectionId.get();
   }
 
   /** Clears the connection ID context from all active connection contexts on the current thread. */
-  public static void removeInstance(BigQueryConnection connection) {
+  static void removeInstance(BigQueryConnection connection) {
     if (connection != null) {
       InheritableThreadLocal<String> local = instanceLocals.remove(connection);
       if (local != null) {
@@ -71,7 +71,7 @@ public static void removeInstance(BigQueryConnection connection) {
     }
   }
 
-  public static void clear() {
+  static void clear() {
     currentConnectionId.remove();
     for (InheritableThreadLocal<String> local : instanceLocals.values()) {
       local.remove();

java-bigquery/google-cloud-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/PerConnectionFileHandler.java

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed 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 com.google.cloud.bigquery.jdbc;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.logging.FileHandler;
+import java.util.logging.Handler;
+import java.util.logging.Level;
+import java.util.logging.LogRecord;
+
+/**
+ * Custom logging handler that dynamically creates and routes log records to per-connection specific
+ * log files using the connection ID retrieved from BigQueryJdbcMdc.
+ */
+class PerConnectionFileHandler extends Handler {
+  private final String baseLogPath;
+  private final Level level;
+  private final ConcurrentHashMap<String, FileHandler> handlers = new ConcurrentHashMap<>();
+  private FileHandler defaultHandler;
+
+  PerConnectionFileHandler(String baseLogPath, Level level) {
+    this.baseLogPath = baseLogPath;
+    this.level = level;
+
+    try {
+      if (!baseLogPath.isEmpty()) {
+        Path dir = Paths.get(baseLogPath);
+        if (!Files.exists(dir)) {
+          Files.createDirectories(dir);
+        }
+      }
+
+      String defaultPath = getLogFilePath("Jdbc-default");
+      this.defaultHandler = new FileHandler(defaultPath, 0, 1, true);
+      this.defaultHandler.setLevel(level);
+      this.defaultHandler.setFormatter(BigQueryJdbcRootLogger.getFormatter());
+    } catch (IOException e) {
+      System.err.println("Failed to initialize default log file: " + e.getMessage());
+    }
+  }
+
+  private String getLogFilePath(String id) {
+    String path = baseLogPath;
+    if (!path.isEmpty() && !path.endsWith("/")) {
+      path = path + "/";
+    }
+    return path + "BigQuery-" + id + ".log";
+  }
+
+  @Override
+  public void publish(LogRecord record) {
+    if (!isLoggable(record)) {
+      return;
+    }
+
+    String connectionId = BigQueryJdbcMdc.getConnectionId();
+    FileHandler handler = defaultHandler;
+
+    if (connectionId != null && !connectionId.isEmpty()) {
+      handler =
+          handlers.computeIfAbsent(
+              connectionId,
+              id -> {
+                try {
+                  String filePath = getLogFilePath(id);
+                  FileHandler fh = new FileHandler(filePath, 0, 1, true);
+                  fh.setLevel(level);
+                  fh.setFormatter(BigQueryJdbcRootLogger.getFormatter());
+                  return fh;
+                } catch (IOException e) {
+                  System.err.println(
+                      "Failed to create log file for connection " + id + ": " + e.getMessage());
+                  return defaultHandler;
+                }
+              });
+    }
+
+    if (handler != null) {
+      handler.publish(record);
+    }
+  }
+
+  @Override
+  public void flush() {
+    if (defaultHandler != null) {
+      defaultHandler.flush();
+    }
+    for (FileHandler h : handlers.values()) {
+      h.flush();
+    }
+  }
+
+  @Override
+  public void close() throws SecurityException {
+    if (defaultHandler != null) {
+      defaultHandler.close();
+    }
+    for (FileHandler h : handlers.values()) {
+      h.close();
+    }
+  }
+
+  public void closeHandler(String connectionId) {
+    if (connectionId != null) {
+      FileHandler handler = handlers.remove(connectionId);
+      if (handler != null) {
+        handler.close();
+      }
+    }
+  }
+}

java-bigquery/google-cloud-bigquery-jdbc/src/test/java/com/google/cloud/bigquery/jdbc/PerConnectionFileHandlerTest.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed 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 com.google.cloud.bigquery.jdbc;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.logging.Level;
+import java.util.logging.LogRecord;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.mockito.Mockito;
+
+public class PerConnectionFileHandlerTest {
+
+  @TempDir
+  Path tempDir;
+
+  private PerConnectionFileHandler handler;
+  private BigQueryConnection mockConnection;
+
+  @BeforeEach
+  public void setUp() {
+    handler = new PerConnectionFileHandler(tempDir.toString(), Level.INFO);
+    mockConnection = Mockito.mock(BigQueryConnection.class);
+    BigQueryJdbcMdc.clear();
+  }
+
+  @AfterEach
+  public void tearDown() {
+    if (handler != null) {
+      handler.close();
+    }
+    BigQueryJdbcMdc.clear();
+  }
+
+  @Test
+  public void testInitialization() {
+    Path defaultLog = tempDir.resolve("BigQuery-Jdbc-default.log");
+    assertTrue(Files.exists(defaultLog));
+  }
+
+  @Test
+  public void testPublishDefault() throws IOException {
+    LogRecord record = new LogRecord(Level.INFO, "Test message default");
+    handler.publish(record);
+    handler.flush();
+
+    Path defaultLog = tempDir.resolve("BigQuery-Jdbc-default.log");
+    String content = new String(Files.readAllBytes(defaultLog));
+    assertTrue(content.contains("Test message default"));
+  }
+
+  @Test
+  public void testPublishConnectionSpecific() throws IOException {
+    BigQueryJdbcMdc.registerInstance(mockConnection, "123");
+
+    LogRecord record = new LogRecord(Level.INFO, "Test message connection 123");
+    handler.publish(record);
+    handler.flush();
+
+    Path connLog = tempDir.resolve("BigQuery-JdbcConnection-123.log");
+    assertTrue(Files.exists(connLog));
+    String content = new String(Files.readAllBytes(connLog));
+    assertTrue(content.contains("Test message connection 123"));
+  }
+
+  @Test
+  public void testCloseHandler() {
+    BigQueryJdbcMdc.registerInstance(mockConnection, "456");
+
+    LogRecord record = new LogRecord(Level.INFO, "Test message connection 456");
+    handler.publish(record);
+    handler.flush();
+
+    Path connLog = tempDir.resolve("BigQuery-JdbcConnection-456.log");
+    assertTrue(Files.exists(connLog));
+
+    handler.closeHandler("JdbcConnection-456");
+    assertTrue(Files.exists(connLog));
+  }
+}