+per #16541 java docs for persistence query

akka-docs/rst/java/code/docs/persistence/query/MyEventsByTagJavaPublisher.java

@@ -0,0 +1,112 @@
+/*
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+
+package docs.persistence.query;
+
+import akka.actor.Cancellable;
+import akka.japi.Pair;
+import akka.japi.pf.ReceiveBuilder;
+import akka.persistence.PersistentRepr;
+import akka.serialization.Serialization;
+import akka.serialization.SerializationExtension;
+import akka.stream.actor.AbstractActorPublisher;
+import scala.Int;
+
+import akka.actor.Props;
+import akka.persistence.query.EventEnvelope;
+import akka.stream.actor.ActorPublisherMessage.Cancel;
+
+import scala.concurrent.duration.FiniteDuration;
+
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.util.ArrayList;
+import java.util.List;
+
+import static java.util.stream.Collectors.toList;
+
+//#events-by-tag-publisher
+class MyEventsByTagJavaPublisher extends AbstractActorPublisher<EventEnvelope> {
+  private final Serialization serialization =
+    SerializationExtension.get(context().system());
+
+  private final Connection connection;
+
+  private final String tag;
+
+  private final String CONTINUE = "CONTINUE";
+  private final int LIMIT = 1000;
+  private long currentOffset;
+  private List<EventEnvelope> buf = new ArrayList<>();
+
+  private Cancellable continueTask;
+
+  public MyEventsByTagJavaPublisher(Connection connection, String tag, Long offset, FiniteDuration refreshInterval) {
+    this.connection = connection;
+    this.tag = tag;
+    this.currentOffset = offset;
+
+    this.continueTask = context().system().scheduler().schedule(refreshInterval, refreshInterval, self(), CONTINUE, context().dispatcher(), self());
+    receive(ReceiveBuilder
+      .matchEquals(CONTINUE, (in) -> {
+        query();
+        deliverBuf();
+      })
+      .match(Cancel.class, (in) -> {
+        context().stop(self());
+      })
+      .build());
+  }
+
+  public static Props props(Connection conn, String tag, Long offset, FiniteDuration refreshInterval) {
+    return Props.create(() -> new MyEventsByTagJavaPublisher(conn, tag, offset, refreshInterval));
+  }
+
+  @Override
+  public void postStop() {
+    continueTask.cancel();
+  }
+
+  private void query() {
+    if (buf.isEmpty()) {
+      try {
+        PreparedStatement s = connection.prepareStatement(
+          "SELECT id, persistent_repr " +
+            "FROM journal WHERE tag = ? AND id >= ? " +
+            "ORDER BY id LIMIT ?");
+
+        s.setString(1, tag);
+        s.setLong(2, currentOffset);
+        s.setLong(3, LIMIT);
+        final ResultSet rs = s.executeQuery();
+
+        final List<Pair<Long, byte[]>> res = new ArrayList<>(LIMIT);
+        while (rs.next())
+          res.add(Pair.create(rs.getLong(1), rs.getBytes(2)));
+
+        if (!res.isEmpty()) {
+          currentOffset = res.get(res.size() - 1).first();
+        }
+
+        buf = res.stream().map(in -> {
+          final Long id = in.first();
+          final byte[] bytes = in.second();
+
+          final PersistentRepr p = serialization.deserialize(bytes, PersistentRepr.class).get();
+
+          return new EventEnvelope(id, p.persistenceId(), p.sequenceNr(), p.payload());
+        }).collect(toList());
+      } catch(Exception e) {
+          onErrorThenStop(e);
+      }
+    }
+  }
+
+  private void deliverBuf() {
+    while (totalDemand() > 0 && !buf.isEmpty())
+      onNext(buf.remove(0));
+  }
+}
+//#events-by-tag-publisher