Add Java SDK

docs/spelling_wordlist.txt

@@ -1129,6 +1129,7 @@ opsgenie
 Optimise
 optimise
 optimizationObjective
+OptIn
 optionality
 ora
 oracledb

java-sdk/.editorconfig

@@ -0,0 +1,31 @@
+#
+# 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.
+
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+indent_style = space
+indent_size = 4
+
+[*.java]
+indent_size = 2
+
+[*.kt]
+indent_size = 2

java-sdk/.gitattributes

@@ -0,0 +1,11 @@
+#
+# https://help.github.com/articles/dealing-with-line-endings/
+#
+# Linux start script should use lf
+/gradlew        text eol=lf
+
+# These are Windows script files and should use crlf
+*.bat           text eol=crlf
+
+# Binary files should be left untouched
+*.jar           binary

java-sdk/.gitignore

@@ -0,0 +1,56 @@
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+.kotlin
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
+# Ignore Gradle build output directory
+build
+
+### Artifacts of airflow standalone command ###
+airflow.cfg
+airflow.db
+simple_auth_manager_passwords.json.generated
+logs/dag_id=*
+logs/dag_processor
+
+### Compatibility Test Results ###
+validation/serialization/serialized_java.json
+validation/serialization/serialized_python.json

java-sdk/README.md

@@ -0,0 +1,74 @@
+<!--
+ 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.
+ -->
+
+# Airflow Java SDK
+
+A **JVM** SDK for Apache Airflow. You can use any JVM-compatible language to write
+workflow bundles, and have Airflow consume the result.
+
+The SDK and execution-time logic is implemented in Kotlin.
+An example is bundled showing how the SDK can be used in Java.
+
+## Building
+
+```bash
+./gradlew build
+```
+
+## Technical Details
+
+The Java program is launched as a subprocess by the Airflow worker and communicates
+through TCP sockets. The Java program accepts flags `--comm` and `--logs` from the
+command line.
+
+The Java program "parses" DAGs on launch, and then connects to the specified TCP servers.
+The rest is similar to the standard Airflow:
+
+* DAG-parsing:
+  1. On connection, the parent immediately sends a DagParsingRequest through the socket.
+  2. The Java program sends back a DagParsingResult to the parent.
+  3. The Java program exits.
+* Execution:
+  1. On connection, the parent immediately sends a StartupDetails through the socket.
+  2. The Java program uses the information to find the relevant task to execute.
+  3. The task is run.
+  4. The Java program tells the parent to update the task's terminal state.
+  5. The Java program exits.
+
+Communication uses the same formats as the Python-based processes.
+
+## Serialization Validation
+
+Workflow:
+
+```bash
+# 1. Generate Java output (runs as part of normal test suite)
+# More specifically, the test `sdk/src/test/kotlin/org/apache/airflow/sdk/execution/SerializationCompatibilityTest.kt` generates the output file `validation/serialization/serialized_java.json`.
+./gradlew sdk:test
+
+# 2. Generate Python output (requires Airflow env)
+uv run validation/serialization/serialize_python.py \
+    validation/serialization/test_dags.yaml \
+    validation/serialization/serialized_python.json
+
+# 3. Compare
+uv run validation/serialization/compare.py \
+    validation/serialization/serialized_python.json \
+    validation/serialization/serialized_java.json
+```