marked all of the OutputWriter implementations with a marker interface, for documentation

src/main/java/org/jmxtrans/embedded/output/ConsoleWriter.java

@@ -44,6 +44,7 @@
  *
  * @author <a href="mailto:[email protected]">Cyrille Le Clerc</a>
  */
+@ExplicitEpoch
 public class ConsoleWriter extends AbstractOutputWriter implements OutputWriter {
 
     /**

src/main/java/org/jmxtrans/embedded/output/CopperEggWriter.java

@@ -96,6 +96,7 @@
  * CopperEggWriter.java was derived from LibratoWriter.java 
  * @author <a href="mailto:[email protected]">Scott Johnson</a>
  */
+@ExplicitEpoch
 public class CopperEggWriter extends AbstractOutputWriter implements OutputWriter {
     public static final String METRIC_TYPE_GAUGE = "gauge";
     public static final String METRIC_TYPE_COUNTER = "counter";

src/main/java/org/jmxtrans/embedded/output/CsvWriter.java

@@ -55,6 +55,7 @@
  * @author <a href="mailto:[email protected]">Ryan Larson</a>
  *
  */
+@ExplicitEpoch
 public class CsvWriter extends AbstractOutputWriter implements OutputWriter {
 
     private final Logger logger = LoggerFactory.getLogger(getClass());

src/main/java/org/jmxtrans/embedded/output/ExplicitEpoch.java

@@ -0,0 +1,13 @@
+package org.jmxtrans.embedded.output;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * It's the contrary of ImplicitEpoch
+ *
+ * @see ImplicitEpoch
+ */
+@Retention(RetentionPolicy.SOURCE)
+@interface ExplicitEpoch {
+}

src/main/java/org/jmxtrans/embedded/output/GraphiteHttpWriter.java

@@ -56,6 +56,7 @@
  *
  * @author <a href="mailto:[email protected]">Simon Mazas</a>
  */
+@ExplicitEpoch
 public class GraphiteHttpWriter extends AbstractOutputWriter implements OutputWriter {
 
     public static final String DEFAULT_NAME_PREFIX = "servers.#hostname#.";

src/main/java/org/jmxtrans/embedded/output/GraphitePickleWriter.java

@@ -61,6 +61,7 @@
  *
  * @author <a href="mailto:[email protected]">Cyrille Le Clerc</a>
  */
+@ExplicitEpoch
 public class GraphitePickleWriter extends AbstractOutputWriter implements OutputWriter {
 
     public static final int DEFAULT_GRAPHITE_SERVER_PORT = 2004;

src/main/java/org/jmxtrans/embedded/output/GraphiteWriter.java

@@ -58,6 +58,7 @@
  * @author <a href="mailto:[email protected]">Cyrille Le Clerc</a>
  * @author <a href="mailto:[email protected]">Patrick Brühlmann</a>
  */
+@ExplicitEpoch
 public class GraphiteWriter extends AbstractOutputWriter implements OutputWriter {
 
     public static final int DEFAULT_GRAPHITE_SERVER_PORT = 2003;

src/main/java/org/jmxtrans/embedded/output/ImplicitEpoch.java

@@ -0,0 +1,17 @@
+package org.jmxtrans.embedded.output;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * Indicates that the OutputWriter is not exporting the time (epoch) at which the metric was collected.
+ * This is generally implied by the protocol being used to transport the metric.
+ * In this case, it's the server who's receiving the data that will set the metric epoch to the time it received it.
+ * <p/>
+ * The support for explicit epoch may be important when the export is happening a while after it was collected.
+ * OutputWriters implementing ImplicitEpoch will need to be exported sooner after the collection, and retry on error may not be appropriate.
+ * OutputWriters implementing ExplicitEpoch will support export delayed from collection, and retry on error will be remain accurate.
+ */
+@Retention(RetentionPolicy.SOURCE)
+@interface ImplicitEpoch {
+}

src/main/java/org/jmxtrans/embedded/output/LibratoWriter.java

@@ -74,6 +74,7 @@
  *
  * @author <a href="mailto:[email protected]">Cyrille Le Clerc</a>
  */
+@ExplicitEpoch
 public class LibratoWriter extends AbstractOutputWriter implements OutputWriter {
 
     public static final String METRIC_TYPE_GAUGE = "gauge";

src/main/java/org/jmxtrans/embedded/output/NoOpWriter.java

@@ -39,6 +39,7 @@
  *
  * @author <a href="mailto:[email protected]">Cyrille Le Clerc</a>
  */
+@ExplicitEpoch
 public class NoOpWriter extends AbstractOutputWriter {
 
     static class NullWriter extends Writer {

src/main/java/org/jmxtrans/embedded/output/Slf4jWriter.java

@@ -47,6 +47,7 @@
  *
  * @author <a href="mailto:[email protected]">Cyrille Le Clerc</a>
  */
+@ExplicitEpoch
 public class Slf4jWriter extends AbstractOutputWriter {
 
     private Logger logger = LoggerFactory.getLogger(getClass());

src/main/java/org/jmxtrans/embedded/output/StackdriverWriter.java

@@ -70,6 +70,7 @@
  * 
  * @author <a href="mailto:[email protected]">Eric Kilby</a>
  */
+@ExplicitEpoch
 public class StackdriverWriter extends AbstractOutputWriter implements OutputWriter {
 
 	public static final int STACKDRIVER_PROTOCOL_VERSION = 1;

src/main/java/org/jmxtrans/embedded/output/StatsDWriter.java

@@ -21,6 +21,7 @@
  * @author <a href="mailto:[email protected]">Cyrille Le Clerc</a>
  * @since 1.0.15
  */
+@ImplicitEpoch
 public class StatsDWriter extends AbstractOutputWriter implements OutputWriter {
 
     public final static String SETTING_BUFFER_SIZE = "bufferSize";