logging: include ES logging front-end, wire to log4j back-end (elastic#373)

Author: yaauie

build.gradle

@@ -411,6 +411,7 @@ task importMinimalElasticsearch() {
             from(buildElasticsearchLocalDistro.lib) {
                 include jarPackageNamed("elasticsearch")
                 include jarPackageNamed("elasticsearch-core")
+                include jarPackageNamed("elasticsearch-logging")
                 include jarPackageNamed("elasticsearch-x-content")
                 include jarPackageNamed("elasticsearch-geo")
                 include jarPackageNamed("lucene-core")

src/main/java/co/elastic/logstash/filters/elasticintegration/EventProcessorBuilder.java

@@ -19,6 +19,7 @@
 import com.google.common.util.concurrent.Service;
 import com.google.common.util.concurrent.ServiceManager;
 import org.elasticsearch.client.RestClient;
+import org.elasticsearch.common.logging.LogConfigurator;
 import org.elasticsearch.logstashbridge.common.SettingsBridge;
 import org.elasticsearch.logstashbridge.core.IOUtilsBridge;
 import org.elasticsearch.logstashbridge.env.EnvironmentBridge;
@@ -49,6 +50,11 @@
 @SuppressWarnings("UnusedReturnValue")
 public class EventProcessorBuilder {
 
+    static {
+        // wires through to log4j under the hood
+        LogConfigurator.configureESLogging();
+    }
+
     static final Duration CACHE_MAXIMUM_AGE = Duration.ofHours(24);
     static final Duration CACHE_RELOAD_FREQUENCY = Duration.ofSeconds(60);