avoid unnecessary ArrayList creations; use Collections.singletonList …

prometheus-metrics-config/src/main/java/io/prometheus/metrics/config/ExporterFilterProperties.java

@@ -1,6 +1,5 @@
 package io.prometheus.metrics.config;
 
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
@@ -26,10 +25,10 @@ private ExporterFilterProperties(List<String> allowedNames, List<String> exclude
     }
 
     private ExporterFilterProperties(List<String> allowedNames, List<String> excludedNames, List<String> allowedPrefixes, List<String> excludedPrefixes, String prefix) {
-        this.allowedNames = allowedNames == null ? null : Collections.unmodifiableList(new ArrayList<>(allowedNames));
-        this.excludedNames = excludedNames == null ? null : Collections.unmodifiableList(new ArrayList<>(excludedNames));
-        this.allowedPrefixes = allowedPrefixes == null ? null : Collections.unmodifiableList(new ArrayList<>(allowedPrefixes));
-        this.excludedPrefixes = excludedPrefixes == null ? null : Collections.unmodifiableList(new ArrayList<>(excludedPrefixes));
+        this.allowedNames = allowedNames == null ? null : Collections.unmodifiableList(allowedNames);
+        this.excludedNames = excludedNames == null ? null : Collections.unmodifiableList(excludedNames);
+        this.allowedPrefixes = allowedPrefixes == null ? null : Collections.unmodifiableList(allowedPrefixes);
+        this.excludedPrefixes = excludedPrefixes == null ? null : Collections.unmodifiableList(excludedPrefixes);
         validate(prefix);
     }
 

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/registry/MetricNameFilter.java

@@ -1,8 +1,8 @@
 package io.prometheus.metrics.model.registry;
 
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.function.Predicate;
 
 import static java.util.Collections.unmodifiableCollection;
@@ -23,10 +23,10 @@ public class MetricNameFilter implements Predicate<String> {
     private final Collection<String> nameDoesNotStartWith;
 
     private MetricNameFilter(Collection<String> nameIsEqualTo, Collection<String> nameIsNotEqualTo, Collection<String> nameStartsWith, Collection<String> nameDoesNotStartWith) {
-        this.nameIsEqualTo = unmodifiableCollection(new ArrayList<>(nameIsEqualTo));
-        this.nameIsNotEqualTo = unmodifiableCollection(new ArrayList<>(nameIsNotEqualTo));
-        this.nameStartsWith = unmodifiableCollection(new ArrayList<>(nameStartsWith));
-        this.nameDoesNotStartWith = unmodifiableCollection(new ArrayList<>(nameDoesNotStartWith));
+        this.nameIsEqualTo = unmodifiableCollection(nameIsEqualTo);
+        this.nameIsNotEqualTo = unmodifiableCollection(nameIsNotEqualTo);
+        this.nameStartsWith = unmodifiableCollection(nameStartsWith);
+        this.nameDoesNotStartWith = unmodifiableCollection(nameDoesNotStartWith);
     }
 
     @Override
@@ -107,7 +107,8 @@ private Builder() {
          * @see #nameMustBeEqualTo(Collection)
          */
         public Builder nameMustBeEqualTo(String... names) {
-            return nameMustBeEqualTo(Arrays.asList(names));
+            Collections.addAll(nameEqualTo, names);
+            return this;
         }
 
         /**
@@ -132,7 +133,8 @@ public Builder nameMustBeEqualTo(Collection<String> names) {
          * @see #nameMustNotBeEqualTo(Collection)
          */
         public Builder nameMustNotBeEqualTo(String... names) {
-            return nameMustNotBeEqualTo(Arrays.asList(names));
+            Collections.addAll(nameNotEqualTo, names);
+            return this;
         }
 
         /**
@@ -155,7 +157,8 @@ public Builder nameMustNotBeEqualTo(Collection<String> names) {
          * @see #nameMustStartWith(Collection)
          */
         public Builder nameMustStartWith(String... prefixes) {
-            return nameMustStartWith(Arrays.asList(prefixes));
+            Collections.addAll(nameStartsWith, prefixes);
+            return this;
         }
 
         /**
@@ -174,7 +177,8 @@ public Builder nameMustStartWith(Collection<String> prefixes) {
          * @see #nameMustNotStartWith(Collection)
          */
         public Builder nameMustNotStartWith(String... prefixes) {
-            return nameMustNotStartWith(Arrays.asList(prefixes));
+            Collections.addAll(nameDoesNotStartWith, prefixes);
+            return this;
         }
 
         /**

simpleclient-archive/simpleclient_caffeine/src/main/java/io/prometheus/client/cache/caffeine/CacheMetricsCollector.java

@@ -99,7 +99,7 @@ public void clear(){
     @Override
     public List<MetricFamilySamples> collect() {
         List<MetricFamilySamples> mfs = new ArrayList<MetricFamilySamples>();
-        List<String> labelNames = Arrays.asList("cache");
+        List<String> labelNames = Collections.singletonList("cache");
 
         CounterMetricFamily cacheHitTotal = new CounterMetricFamily("caffeine_cache_hit_total",
                 "Cache hit totals", labelNames);
@@ -138,7 +138,7 @@ public List<MetricFamilySamples> collect() {
         mfs.add(cacheLoadSummary);
 
         for(Map.Entry<String, Cache> c: children.entrySet()) {
-            List<String> cacheName = Arrays.asList(c.getKey());
+            List<String> cacheName = Collections.singletonList(c.getKey());
             CacheStats stats = c.getValue().stats();
 
             try{

simpleclient-archive/simpleclient_dropwizard/src/main/java/io/prometheus/client/dropwizard/DropwizardExports.java

@@ -86,7 +86,7 @@ private static String getHelpMessage(String metricName, Metric metric) {
     MetricFamilySamples fromCounter(String dropwizardName, Counter counter) {
         MetricFamilySamples.Sample sample = sampleBuilder.createSample(dropwizardName, "", new ArrayList<String>(), new ArrayList<String>(),
                 new Long(counter.getCount()).doubleValue());
-        return new MetricFamilySamples(sample.name, Type.GAUGE, getHelpMessage(dropwizardName, counter), Arrays.asList(sample));
+        return new MetricFamilySamples(sample.name, Type.GAUGE, getHelpMessage(dropwizardName, counter), Collections.singletonList(sample));
     }
 
     /**
@@ -106,7 +106,7 @@ MetricFamilySamples fromGauge(String dropwizardName, Gauge gauge) {
         }
         MetricFamilySamples.Sample sample = sampleBuilder.createSample(dropwizardName, "",
                 new ArrayList<String>(), new ArrayList<String>(), value);
-        return new MetricFamilySamples(sample.name, Type.GAUGE, getHelpMessage(dropwizardName, gauge), Arrays.asList(sample));
+        return new MetricFamilySamples(sample.name, Type.GAUGE, getHelpMessage(dropwizardName, gauge), Collections.singletonList(sample));
     }
 
     /**
@@ -155,7 +155,7 @@ MetricFamilySamples fromMeter(String dropwizardName, Meter meter) {
                 new ArrayList<String>(),
                 meter.getCount());
         return new MetricFamilySamples(sample.name, Type.COUNTER, getHelpMessage(dropwizardName, meter),
-                        Arrays.asList(sample));
+                Collections.singletonList(sample));
     }
 
     @Override

simpleclient-archive/simpleclient_guava/src/main/java/io/prometheus/client/guava/cache/CacheMetricsCollector.java

@@ -86,7 +86,7 @@ public void clear(){
     @Override
     public List<MetricFamilySamples> collect() {
         List<MetricFamilySamples> mfs = new ArrayList<MetricFamilySamples>();
-        List<String> labelNames = Arrays.asList("cache");
+        List<String> labelNames = Collections.singletonList("cache");
 
         CounterMetricFamily cacheHitTotal = new CounterMetricFamily("guava_cache_hit_total",
                 "Cache hit totals", labelNames);
@@ -121,7 +121,7 @@ public List<MetricFamilySamples> collect() {
         mfs.add(cacheLoadSummary);
 
         for(Map.Entry<String, Cache> c: children.entrySet()) {
-            List<String> cacheName = Arrays.asList(c.getKey());
+            List<String> cacheName = Collections.singletonList(c.getKey());
             CacheStats stats = c.getValue().stats();
 
             cacheHitTotal.addMetric(cacheName, stats.hitCount());

simpleclient-archive/simpleclient_hibernate/src/main/java/io/prometheus/client/hibernate/HibernateStatisticsCollector.java

@@ -44,7 +44,7 @@ public class HibernateStatisticsCollector extends Collector {
 
   private static final List<String> LABEL_NAMES = Collections.singletonList("unit");
 
-  private static final List<String> LABEL_NAMES_PER_QUERY = Arrays.asList("unit", "query");
+  private static final List<String> LABEL_NAMES_PER_QUERY = Collections.unmodifiableList(Arrays.asList("unit", "query"));
 
   private final Map<String, SessionFactory> sessionFactories = new ConcurrentHashMap<String, SessionFactory>();
 
@@ -476,7 +476,7 @@ public double getValue(Statistics statistics) {
   private List<MetricFamilySamples> getPerQueryMetrics() {
     List<MetricFamilySamples> metrics = new ArrayList<MetricFamilySamples>();
 
-    metrics.addAll(Arrays.asList(
+    Collections.addAll(metrics,
 
         createCounterForQuery("hibernate_per_query_cache_hit_total",
                 "Global number of cache hits for query (getCacheHitCount)",
@@ -558,7 +558,7 @@ public double getValue(Statistics statistics, String query) {
               }
             }
         )
-    ));
+    );
 
     return metrics;
   }

simpleclient-archive/simpleclient_jetty/src/main/java/io/prometheus/client/jetty/JettyStatisticsCollector.java

@@ -32,7 +32,7 @@
  */
 public class JettyStatisticsCollector extends Collector {
   private final StatisticsHandler statisticsHandler;
-  private static final List<String> EMPTY_LIST = new ArrayList<String>();
+  private static final List<String> EMPTY_LIST = Collections.emptyList();
 
   public JettyStatisticsCollector(StatisticsHandler statisticsHandler) {
     this.statisticsHandler = statisticsHandler;

simpleclient-archive/simpleclient_servlet_common/src/main/java/io/prometheus/client/servlet/common/exporter/Exporter.java

@@ -87,7 +87,9 @@ private Set<String> parse(HttpServletRequestAdapter req) {
     if (includedParam == null) {
       return Collections.emptySet();
     } else {
-      return new HashSet<String>(Arrays.asList(includedParam));
+      Set<String> result = new HashSet<String>();
+      Collections.addAll(result, includedParam);
+      return result;
     }
   }