Fix sample and tidy up MetricWriter/GaugeWriter

The metric export configuration was still using the MetricWriter
interface where it should be using GaugeWriter

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/MetricExportAutoConfiguration.java

@@ -30,7 +30,7 @@ import org.springframework.boot.actuate.metrics.export.MetricExporters;
 import org.springframework.boot.actuate.metrics.reader.CompositeMetricReader;
 import org.springframework.boot.actuate.metrics.reader.MetricReader;
 import org.springframework.boot.actuate.metrics.statsd.StatsdMetricWriter;
-import org.springframework.boot.actuate.metrics.writer.MetricWriter;
+import org.springframework.boot.actuate.metrics.writer.GaugeWriter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
@@ -67,7 +67,7 @@ public class MetricExportAutoConfiguration {
 
 	@Autowired(required = false)
 	@ExportMetricWriter
-	private Map<String, MetricWriter> writers = Collections.emptyMap();
+	private Map<String, GaugeWriter> writers = Collections.emptyMap();
 
 	@Autowired(required = false)
 	private Map<String, Exporter> exporters = Collections.emptyMap();
@@ -75,7 +75,7 @@ public class MetricExportAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean(name = "metricWritersMetricExporter")
 	public SchedulingConfigurer metricWritersMetricExporter() {
-		Map<String, MetricWriter> writers = new HashMap<String, MetricWriter>();
+		Map<String, GaugeWriter> writers = new HashMap<String, GaugeWriter>();
 		MetricReader reader = this.endpointReader;
 		if (reader == null && !CollectionUtils.isEmpty(this.readers)) {
 			reader = new CompositeMetricReader(

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/export/MetricExporters.java

@@ -21,7 +21,7 @@ import java.util.Map;
 import java.util.Map.Entry;
 
 import org.springframework.boot.actuate.metrics.reader.MetricReader;
-import org.springframework.boot.actuate.metrics.writer.MetricWriter;
+import org.springframework.boot.actuate.metrics.writer.GaugeWriter;
 import org.springframework.scheduling.annotation.SchedulingConfigurer;
 import org.springframework.scheduling.config.IntervalTask;
 import org.springframework.scheduling.config.ScheduledTaskRegistrar;
@@ -36,7 +36,7 @@ public class MetricExporters implements SchedulingConfigurer {
 
 	private MetricReader reader;
 
-	private Map<String, MetricWriter> writers = new HashMap<String, MetricWriter>();
+	private Map<String, GaugeWriter> writers = new HashMap<String, GaugeWriter>();
 
 	private final MetricExportProperties properties;
 
@@ -50,7 +50,7 @@ public class MetricExporters implements SchedulingConfigurer {
 		this.reader = reader;
 	}
 
-	public void setWriters(Map<String, MetricWriter> writers) {
+	public void setWriters(Map<String, GaugeWriter> writers) {
 		this.writers.putAll(writers);
 	}
 
@@ -71,9 +71,9 @@ public class MetricExporters implements SchedulingConfigurer {
 				taskRegistrar.addFixedDelayTask(task);
 			}
 		}
-		for (Entry<String, MetricWriter> entry : this.writers.entrySet()) {
+		for (Entry<String, GaugeWriter> entry : this.writers.entrySet()) {
 			String name = entry.getKey();
-			MetricWriter writer = entry.getValue();
+			GaugeWriter writer = entry.getValue();
 			TriggerProperties trigger = this.properties.findTrigger(name);
 			if (trigger != null) {
 				MetricCopyExporter exporter = getExporter(writer, trigger);
@@ -86,7 +86,7 @@ public class MetricExporters implements SchedulingConfigurer {
 		}
 	}
 
-	private MetricCopyExporter getExporter(MetricWriter writer,
+	private MetricCopyExporter getExporter(GaugeWriter writer,
 			TriggerProperties trigger) {
 		MetricCopyExporter exporter = new MetricCopyExporter(this.reader, writer);
 		exporter.setIncludes(trigger.getIncludes());

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/export/MetricExportersTests.java

@@ -24,6 +24,7 @@ import org.junit.Test;
 import org.mockito.Mockito;
 
 import org.springframework.boot.actuate.metrics.reader.MetricReader;
+import org.springframework.boot.actuate.metrics.writer.GaugeWriter;
 import org.springframework.boot.actuate.metrics.writer.MetricWriter;
 import org.springframework.scheduling.config.ScheduledTaskRegistrar;
 
@@ -41,7 +42,7 @@ public class MetricExportersTests {
 
 	private MetricExportProperties export = new MetricExportProperties();
 
-	private Map<String, MetricWriter> writers = new LinkedHashMap<String, MetricWriter>();
+	private Map<String, GaugeWriter> writers = new LinkedHashMap<String, GaugeWriter>();
 
 	private MetricReader reader = Mockito.mock(MetricReader.class);
 

spring-boot-samples/spring-boot-sample-metrics-opentsdb/src/main/java/sample/metrics/opentsdb/SampleOpenTsdbExportApplication.java

@@ -21,7 +21,7 @@ import org.springframework.boot.actuate.autoconfigure.ExportMetricWriter;
 import org.springframework.boot.actuate.metrics.opentsdb.DefaultOpenTsdbNamingStrategy;
 import org.springframework.boot.actuate.metrics.opentsdb.OpenTsdbMetricWriter;
 import org.springframework.boot.actuate.metrics.opentsdb.OpenTsdbNamingStrategy;
-import org.springframework.boot.actuate.metrics.writer.MetricWriter;
+import org.springframework.boot.actuate.metrics.writer.GaugeWriter;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.context.annotation.Bean;
@@ -32,7 +32,7 @@ public class SampleOpenTsdbExportApplication {
 	@Bean
 	@ConfigurationProperties("metrics.export")
 	@ExportMetricWriter
-	public MetricWriter openTsdbMetricWriter() {
+	public GaugeWriter openTsdbMetricWriter() {
 		OpenTsdbMetricWriter writer = new OpenTsdbMetricWriter();
 		writer.setNamingStrategy(namingStrategy());
 		return writer;