feat: add custom logging provider to support structured logging for SLF4J 1.x + Logback 1.2.x

.github/workflows/ci.yaml

@@ -228,6 +228,10 @@ jobs:
       - name: Install Maven modules
         run: |
           mvn install -B -ntp -DskipTests -Dclirr.skip -Dcheckstyle.skip
+      - name: Install logging module # this module is not part of root project.
+        run: |
+          mvn install -B -ntp -DskipTests -Dclirr.skip -Dcheckstyle.skip
+        working-directory: java-sdk-logging
       - name: Java Linter
         working-directory: java-showcase
         run: |

.github/workflows/java_sdk_logging.yaml

@@ -31,13 +31,28 @@ jobs:
       with:
         java-version: 8
         distribution: temurin
+    - run: echo "JAVA8_HOME=${JAVA_HOME}" >> $GITHUB_ENV
+    - uses: actions/setup-java@v4
+      with:
+        java-version: 17
+        distribution: temurin
     - name: Install parent module
       run: |
         mvn install -B -ntp -pl gapic-generator-java-pom-parent
-    - name: Unit Tests
+    - name: Install logging module
+      run: |
+        mvn install -B -ntp -Dcheckstyle.skip -Dfmt.skip
       working-directory: java-sdk-logging
+    - name: Unit Tests in Java 8
       run: |
-        mvn test -B -ntp -Dcheckstyle.skip -Dfmt.skip
+        set -x
+        export JAVA_HOME=$JAVA_HOME
+        export PATH=${JAVA_HOME}/bin:$PATH
+        mvn verify -B -ntp \
+          -Dcheckstyle.skip \
+          -Dfmt.skip \
+          -Djvm="${JAVA8_HOME}/bin/java"
+      working-directory: java-sdk-logging
   module-lint:
     runs-on: ubuntu-latest
     steps:
@@ -59,7 +74,7 @@ jobs:
     - uses: actions/checkout@v4
     - uses: actions/setup-java@v4
       with:
-        java-version: 11
+        java-version: 17
         distribution: temurin
     - name: Install parent module
       run: |
@@ -74,7 +89,7 @@ jobs:
     - uses: actions/checkout@v4
     - uses: actions/setup-java@v4
       with:
-        java-version: 11
+        java-version: 17
         distribution: temurin
     - name: Install parent module
       run: |

java-sdk-logging/logback-extension/pom.xml

@@ -14,6 +14,8 @@
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <logback.version>1.2.13</logback.version>
+    <!-- do not update this version as this is the last version support
+     SLF4J 1.x and logback 1.2.x -->
     <logstash.encoder.version>7.3</logstash.encoder.version>
   </properties>
 

java-sdk-logging/logback-extension/src/main/java/com/google/cloud/sdk/logging/SDKLoggingMdcJsonProvider.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google LLC nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.cloud.sdk.logging;
+
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import java.io.IOException;
+import java.util.Map;
+import net.logstash.logback.composite.loggingevent.MdcJsonProvider;
+
+public class SDKLoggingMdcJsonProvider extends MdcJsonProvider {
+
+  private final ObjectMapper objectMapper = new ObjectMapper();
+
+  @Override
+  public void writeTo(JsonGenerator generator, ILoggingEvent event) throws IOException {
+    Map<String, String> mdcProperties = event.getMDCPropertyMap();
+    if (mdcProperties == null || mdcProperties.isEmpty()) {
+      return;
+    }
+
+    boolean hasWrittenStart = false;
+    for (Map.Entry<String, String> entry : mdcProperties.entrySet()) {
+      String fieldName = entry.getKey();
+      String entryValueString = entry.getValue();
+      // an entry will be skipped if one of the scenario happens:
+      // 1. key or value is null
+      if (fieldName == null || entryValueString == null) {
+        continue;
+      }
+      // 2. includeMdcKeyNames is not empty and the key is not in the list
+      if (!getIncludeMdcKeyNames().isEmpty() && !getIncludeMdcKeyNames().contains(fieldName)) {
+        continue;
+      }
+      // 3. excludeMdcKeyNames is not empty and the key is in the list
+      if (!getExcludeMdcKeyNames().isEmpty() && getExcludeMdcKeyNames().contains(fieldName)) {
+        continue;
+      }
+
+      fieldName = getMdcKeyFieldNames().getOrDefault(entry.getKey(), fieldName);
+      if (!hasWrittenStart && getFieldName() != null) {
+        generator.writeObjectFieldStart(getFieldName());
+        hasWrittenStart = true;
+      }
+      generator.writeFieldName(fieldName);
+
+      try {
+        generator.writeTree(convertToTreeNode(entryValueString));
+      } catch (JsonProcessingException e) {
+        // in case of conversion exception, just use String
+        generator.writeObject(entryValueString);
+      }
+    }
+    if (hasWrittenStart) {
+      generator.writeEndObject();
+    }
+  }
+
+  private JsonNode convertToTreeNode(String jsonString) throws JsonProcessingException {
+    return objectMapper.readTree(jsonString);
+  }
+}