Add Ordered Processing PTransform to Java SDK

sdks/java/extensions/ordered/build.gradle

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+/*
+ * 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.
+ */
+plugins { id 'org.apache.beam.module' }
+applyJavaNature(automaticModuleName: 'org.apache.beam.sdk.extensions.sorter')
+
+description = "Apache Beam :: SDKs :: Java :: Extensions :: Ordered"
+
+dependencies {
+    implementation project(path: ":sdks:java:core", configuration: "shadow")
+    implementation library.java.slf4j_api
+    implementation library.java.joda_time
+    implementation library.java.commons_lang3
+    implementation library.java.vendored_guava_32_1_2_jre
+    testImplementation library.java.junit
+    testImplementation library.java.hamcrest
+    testImplementation project(path: ':sdks:java:core')
+    testRuntimeOnly project(path: ":runners:direct-java", configuration: "shadow")
+}

sdks/java/extensions/ordered/src/main/java/org/apache/beam/sdk/extensions/ordered/EventExaminer.java

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+/*
+ * 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.
+ */
+package org.apache.beam.sdk.extensions.ordered;
+
+import java.io.Serializable;
+import org.checkerframework.checker.nullness.qual.NonNull;
+
+/**
+ * Classes extending this interface will be called by {@link OrderedEventProcessor} to examine every
+ * incoming event.
+ *
+ * @param <EventT>
+ * @param <StateT>
+ */
+public interface EventExaminer<EventT, StateT extends MutableState<EventT, ?>>
+    extends Serializable {
+
+  /**
+   * Is this event the first expected event for the given key and window?
+   *
+   * @param sequenceNumber the sequence number of the event as defined by the key of the input
+   *     PCollection to {@link OrderedEventProcessor}
+   * @param event being processed
+   * @return true if this is the initial sequence.
+   */
+  boolean isInitialEvent(long sequenceNumber, EventT event);
+
+  /**
+   * If the event was the first event in the sequence, create the state to hold the required data
+   * needed for processing. This data will be persisted.
+   *
+   * @param event the first event in the sequence.
+   * @return the state to persist.
+   */
+  @NonNull
+  StateT createStateOnInitialEvent(EventT event);
+
+  /**
+   * Is this event the last expected event for a given key and window?
+   *
+   * @param sequenceNumber of the event
+   * @param event being processed
+   * @return true if the last event. There are cases where it's impossible to know whether it's the
+   *     last event. False should be returned in those cases.
+   */
+  boolean isLastEvent(long sequenceNumber, EventT event);
+}

sdks/java/extensions/ordered/src/main/java/org/apache/beam/sdk/extensions/ordered/MutableState.java

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+/*
+ * 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.
+ */
+package org.apache.beam.sdk.extensions.ordered;
+
+import java.io.Serializable;
+
+/** Mutable state mutates when events apply to it. It is stored in a Beam state. */
+public interface MutableState<EventT, ResultT> extends Serializable {
+
+  /**
+   * The interface assumes that events will mutate the state without the possibility of throwing an
+   * error.
+   *
+   * @param event to be processed
+   * @throws Exception if a checked exception is thrown, the event will be output into {@link
+   *     OrderedEventProcessorResult#unprocessedEvents()} with
+   */
+  void mutate(EventT event) throws Exception;
+
+  /**
+   * This method is called after each state mutation.
+   *
+   * @return Result of the processing. Can be null if nothing needs to be output after this
+   *     mutation.
+   */
+  ResultT produceResult();
+}