Basic lifecycle added

* LifeCycle interface added to some Core classes
* Operation API added to handle deferred setup tasks (#12)
* IndexTemplate failure doesn't prevent startup anymore

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/AsyncBatchDelivery.java

@@ -41,9 +41,14 @@ public class AsyncBatchDelivery implements BatchDelivery<String> {
 
     private static final Logger LOG = StatusLogger.getLogger();
 
+    private volatile State state = State.STOPPED;
+
     private final BatchOperations batchOperations;
     private final BatchEmitter batchEmitter;
 
+    private final IndexTemplate indexTemplate;
+    private final ClientObjectFactory<Object, Object> objectFactory;
+
     public AsyncBatchDelivery(int batchSize, int deliveryInterval, ClientObjectFactory objectFactory, FailoverPolicy failoverPolicy, IndexTemplate indexTemplate) {
         this.batchOperations = objectFactory.createBatchOperations();
         this.batchEmitter = createBatchEmitterServiceProvider()
@@ -52,9 +57,8 @@ public AsyncBatchDelivery(int batchSize, int deliveryInterval, ClientObjectFacto
                         deliveryInterval,
                         objectFactory,
                         failoverPolicy);
-        if (indexTemplate != null) {
-            objectFactory.execute(indexTemplate);
-        }
+        this.indexTemplate = indexTemplate;
+        this.objectFactory = objectFactory;
     }
 
     /**
@@ -149,4 +153,33 @@ public Builder withIndexTemplate(IndexTemplate indexTemplate) {
 
     }
 
+    // ==========
+    // LIFECYCLE
+    // ==========
+
+    @Override
+    public void start() {
+        if (indexTemplate != null) {
+            objectFactory.addOperation(() -> objectFactory.execute(indexTemplate));
+        }
+        batchEmitter.start();
+        state = State.STARTED;
+    }
+
+    @Override
+    public void stop() {
+        batchEmitter.stop();
+        state = State.STOPPED;
+    }
+
+    @Override
+    public boolean isStarted() {
+        return state == State.STARTED;
+    }
+
+    @Override
+    public boolean isStopped() {
+        return state == State.STOPPED;
+    }
+
 }

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/BatchDelivery.java

@@ -26,7 +26,7 @@
  *
  * @param <T> type of accepted items
  */
-public interface BatchDelivery<T> {
+public interface BatchDelivery<T> extends LifeCycle {
 
     String ELEMENT_TYPE = "batchDelivery";
 

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/BatchEmitter.java

@@ -27,7 +27,7 @@
  *
  * @param <T> type of accepted batch item
  */
-public interface BatchEmitter<T> {
+public interface BatchEmitter<T> extends LifeCycle {
 
     /**
      * @param batchItem batch item to be processed

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/BulkEmitter.java

@@ -35,6 +35,8 @@
  */
 public class BulkEmitter<BATCH_TYPE> implements BatchEmitter {
 
+    private volatile State state = State.STOPPED;
+
     private final AtomicInteger size = new AtomicInteger();
 
     private final int maxSize;
@@ -98,6 +100,30 @@ public void addListener(Function<BATCH_TYPE, Boolean> onReadyListener) {
         this.listener = onReadyListener;
     }
 
+    // ==========
+    // LIFECYCLE
+    // ==========
+
+    @Override
+    public void start() {
+        state = State.STARTED;
+    }
+
+    @Override
+    public void stop() {
+        state = State.STOPPED;
+    }
+
+    @Override
+    public boolean isStarted() {
+        return state == State.STARTED;
+    }
+
+    @Override
+    public boolean isStopped() {
+        return state == State.STOPPED;
+    }
+
     /*
      * Class used as monitor to increase lock visibility in profiling tools
      */

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/ClientObjectFactory.java

@@ -73,7 +73,17 @@ public interface ClientObjectFactory<CLIENT_TYPE, BATCH_TYPE> {
     /**
      * Updates target with index template
      * @param indexTemplate index template request
+     * @deprecated will be replaced by {@link #addOperation(Operation)} in future releases
      */
+    @Deprecated
     void execute(IndexTemplate indexTemplate);
 
+    /**
+     * Allows to add operation to be executed before next batch. Exact time of the execution depends on implementation of this factory.
+     *
+     * NOTE: {@code default} added for backwards compatibility. {@code default} will be removed future releases
+     * @param operation operation to be executed
+     */
+    default void addOperation(Operation operation) {}
+
 }

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/ElasticsearchAppender.java

@@ -35,6 +35,7 @@
 import org.apache.logging.log4j.core.layout.AbstractLayout;
 import org.apache.logging.log4j.core.layout.AbstractStringLayout;
 
+
 /**
  * Plugin class responsible for delivery of incoming {@link LogEvent}(s) to {@link BatchDelivery} implementation.
  * <p>
@@ -51,8 +52,8 @@ public class ElasticsearchAppender extends AbstractAppender {
 
     public static final String PLUGIN_NAME = "Elasticsearch";
 
-    private IndexNameFormatter indexNameFormatter;
-    private final ItemAppender<LogEvent> itemAppender;
+    private final IndexNameFormatter indexNameFormatter;
+    private final ItemAppender itemAppender;
 
     protected ElasticsearchAppender(String name, Filter filter, AbstractLayout layout,
             boolean ignoreExceptions, BatchDelivery batchDelivery, boolean messageOnly, IndexNameFormatter indexNameFormatter) {
@@ -71,6 +72,18 @@ public void append(LogEvent event) {
         itemAppender.append(formattedIndexName, event);
     }
 
+    @Override
+    public void start() {
+        itemAppender.start();
+        super.start();
+    }
+
+    @Override
+    public void stop() {
+        itemAppender.stop();
+        super.stop();
+    }
+
     @PluginBuilderFactory
     public static Builder newBuilder() {
         return new Builder();

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/ItemAppender.java

@@ -25,7 +25,7 @@
  *
  * @param <T> log source type
  */
-public interface ItemAppender<T> {
+public interface ItemAppender<T> extends LifeCycle {
 
     void append(String formattedIndexName, T source);
 

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/ItemSourceAppender.java

@@ -29,6 +29,8 @@
  */
 public class ItemSourceAppender implements ItemAppender<LogEvent> {
 
+    private volatile State state = State.STOPPED;
+
     private final BatchDelivery batchDelivery;
     private final Function<LogEvent, ItemSource> serializer;
 
@@ -48,4 +50,28 @@ public final void append(String formattedIndexName, LogEvent event) {
         batchDelivery.add(formattedIndexName, serializer.apply(event));
     }
 
+    @Override
+    public void start() {
+        batchDelivery.start();
+        state = State.STARTED;
+    }
+
+    @Override
+    public void stop() {
+        if (batchDelivery.isStarted()) {
+            batchDelivery.stop();
+        }
+        state = State.STOPPED;
+    }
+
+    @Override
+    public boolean isStarted() {
+        return state == State.STARTED;
+    }
+
+    @Override
+    public boolean isStopped() {
+        return state == State.STOPPED;
+    }
+
 }

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/LifeCycle.java

@@ -0,0 +1,17 @@
+package org.appenders.log4j2.elasticsearch;
+
+public interface LifeCycle {
+
+    void start();
+
+    void stop();
+
+    boolean isStarted();
+
+    boolean isStopped();
+
+    enum State {
+        STARTED, STOPPED
+    }
+
+}

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/Operation.java

@@ -0,0 +1,7 @@
+package org.appenders.log4j2.elasticsearch;
+
+public interface Operation {
+
+    void execute() throws Exception;
+
+}

log4j2-elasticsearch-core/src/main/java/org/appenders/log4j2/elasticsearch/StringAppender.java

@@ -29,6 +29,8 @@
  */
 public class StringAppender implements ItemAppender<LogEvent> {
 
+    private volatile State state = State.STOPPED;
+
     private final BatchDelivery batchDelivery;
     private final Function<LogEvent, String> serializer;
 
@@ -48,4 +50,32 @@ public void append(String formattedIndexName, LogEvent logEvent) {
         batchDelivery.add(formattedIndexName, serializer.apply(logEvent));
     }
 
+    // ==========
+    // LIFECYCLE
+    // ==========
+
+    @Override
+    public void start() {
+        batchDelivery.start();
+        state = State.STARTED;
+    }
+
+    @Override
+    public void stop() {
+        if (batchDelivery.isStarted()) {
+            batchDelivery.stop();
+        }
+        state = State.STOPPED;
+    }
+
+    @Override
+    public boolean isStarted() {
+        return state == State.STARTED;
+    }
+
+    @Override
+    public boolean isStopped() {
+        return state == State.STOPPED;
+    }
+
 }