Return List instead of an array from settings (#26903)

Today we return a `String[]` that requires copying values for every
access. Yet, we already store the setting as a list so we can also directly
return the unmodifiable list directly. This makes list / array access in settings
a much cheaper operation especially if lists are large.

core/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/AwarenessAllocationDecider.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.cluster.routing.allocation.decider;
 
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import com.carrotsearch.hppc.ObjectIntHashMap;
@@ -85,7 +86,7 @@ public class AwarenessAllocationDecider extends AllocationDecider {
 
     private volatile String[] awarenessAttributes;
 
-    private volatile Map<String, String[]> forcedAwarenessAttributes;
+    private volatile Map<String, List<String>> forcedAwarenessAttributes;
 
     public AwarenessAllocationDecider(Settings settings, ClusterSettings clusterSettings) {
         super(settings);
@@ -97,11 +98,11 @@ public AwarenessAllocationDecider(Settings settings, ClusterSettings clusterSett
     }
 
     private void setForcedAwarenessAttributes(Settings forceSettings) {
-        Map<String, String[]> forcedAwarenessAttributes = new HashMap<>();
+        Map<String, List<String>> forcedAwarenessAttributes = new HashMap<>();
         Map<String, Settings> forceGroups = forceSettings.getAsGroups();
         for (Map.Entry<String, Settings> entry : forceGroups.entrySet()) {
-            String[] aValues = entry.getValue().getAsArray("values");
-            if (aValues.length > 0) {
+            List<String> aValues = entry.getValue().getAsList("values");
+            if (aValues.size() > 0) {
                 forcedAwarenessAttributes.put(entry.getKey(), aValues);
             }
         }
@@ -169,7 +170,7 @@ private Decision underCapacity(ShardRouting shardRouting, RoutingNode node, Rout
             }
 
             int numberOfAttributes = nodesPerAttribute.size();
-            String[] fullValues = forcedAwarenessAttributes.get(awarenessAttribute);
+            List<String> fullValues = forcedAwarenessAttributes.get(awarenessAttribute);
             if (fullValues != null) {
                 for (String fullValue : fullValues) {
                     if (!shardPerAttribute.containsKey(fullValue)) {

core/src/main/java/org/elasticsearch/common/settings/Setting.java

@@ -804,14 +804,14 @@ private static class ListSetting<T> extends Setting<List<T>> {
 
         private ListSetting(String key, Function<Settings, List<String>> defaultStringValue, Function<String, List<T>> parser,
                             Property... properties) {
-            super(new ListKey(key), (s) -> Setting.arrayToParsableString(defaultStringValue.apply(s).toArray(Strings.EMPTY_ARRAY)), parser,
+            super(new ListKey(key), (s) -> Setting.arrayToParsableString(defaultStringValue.apply(s)), parser,
                 properties);
             this.defaultStringValue = defaultStringValue;
         }
 
         @Override
         public String getRaw(Settings settings) {
-            String[] array = settings.getAsArray(getKey(), null);
+            List<String> array = settings.getAsList(getKey(), null);
             return array == null ? defaultValue.apply(settings) : arrayToParsableString(array);
         }
 
@@ -823,11 +823,11 @@ boolean hasComplexMatcher() {
         @Override
         public void diff(Settings.Builder builder, Settings source, Settings defaultSettings) {
             if (exists(source) == false) {
-                String[] asArray = defaultSettings.getAsArray(getKey(), null);
-                if (asArray == null) {
-                    builder.putArray(getKey(), defaultStringValue.apply(defaultSettings));
+                List<String> asList = defaultSettings.getAsList(getKey(), null);
+                if (asList == null) {
+                    builder.putList(getKey(), defaultStringValue.apply(defaultSettings));
                 } else {
-                    builder.putArray(getKey(), asArray);
+                    builder.putList(getKey(), asList);
                 }
             }
         }
@@ -1087,7 +1087,7 @@ private static List<String> parseableStringToList(String parsableString) {
         }
     }
 
-    private static String arrayToParsableString(String[] array) {
+    private static String arrayToParsableString(List<String> array) {
         try {
             XContentBuilder builder = XContentBuilder.builder(XContentType.JSON.xContent());
             builder.startArray();

core/src/main/java/org/elasticsearch/common/settings/Settings.java

@@ -396,48 +396,48 @@ public SizeValue getAsSize(String setting, SizeValue defaultValue) throws Settin
     }
 
     /**
-     * The values associated with a setting key as an array.
+     * The values associated with a setting key as an immutable list.
      * <p>
      * It will also automatically load a comma separated list under the settingPrefix and merge with
      * the numbered format.
      *
-     * @param key The setting prefix to load the array by
-     * @return The setting array values
+     * @param key The setting key to load the list by
+     * @return The setting list values
      */
-    public String[] getAsArray(String key) throws SettingsException {
-        return getAsArray(key, Strings.EMPTY_ARRAY, true);
+    public List<String> getAsList(String key) throws SettingsException {
+        return getAsList(key, Collections.emptyList());
     }
 
     /**
-     * The values associated with a setting key as an array.
+     * The values associated with a setting key as an immutable list.
      * <p>
      * If commaDelimited is true, it will automatically load a comma separated list under the settingPrefix and merge with
      * the numbered format.
      *
-     * @param key The setting key to load the array by
-     * @return The setting array values
+     * @param key The setting key to load the list by
+     * @return The setting list values
      */
-    public String[] getAsArray(String key, String[] defaultArray) throws SettingsException {
-        return getAsArray(key, defaultArray, true);
+    public List<String> getAsList(String key, List<String> defaultValue) throws SettingsException {
+        return getAsList(key, defaultValue, true);
     }
 
     /**
-     * The values associated with a setting key as an array.
+     * The values associated with a setting key as an immutable list.
      * <p>
      * It will also automatically load a comma separated list under the settingPrefix and merge with
      * the numbered format.
      *
-     * @param key  The setting key to load the array by
-     * @param defaultArray   The default array to use if no value is specified
+     * @param key  The setting key to load the list by
+     * @param defaultValue   The default value to use if no value is specified
      * @param commaDelimited Whether to try to parse a string as a comma-delimited value
-     * @return The setting array values
+     * @return The setting list values
      */
-    public String[] getAsArray(String key, String[] defaultArray, Boolean commaDelimited) throws SettingsException {
+    public List<String> getAsList(String key, List<String> defaultValue, Boolean commaDelimited) throws SettingsException {
         List<String> result = new ArrayList<>();
         final Object valueFromPrefix = settings.get(key);
         if (valueFromPrefix != null) {
             if (valueFromPrefix instanceof List) {
-                result =  ((List<String>) valueFromPrefix);
+                return ((List<String>) valueFromPrefix); // it's already unmodifiable since the builder puts it as a such
             } else if (commaDelimited) {
                 String[] strings = Strings.splitStringByCommaToArray(get(key));
                 if (strings.length > 0) {
@@ -451,9 +451,9 @@ public String[] getAsArray(String key, String[] defaultArray, Boolean commaDelim
         }
 
         if (result.isEmpty()) {
-            return defaultArray;
+            return defaultValue;
         }
-        return result.toArray(new String[result.size()]);
+        return Collections.unmodifiableList(result);
     }
 
 
@@ -582,7 +582,7 @@ public static Settings readSettingsFromStream(StreamInput in) throws IOException
                 if (value == null) {
                     builder.putNull(key);
                 } else if (value instanceof List) {
-                    builder.putArray(key, (List<String>) value);
+                    builder.putList(key, (List<String>) value);
                 } else {
                     builder.put(key, value.toString());
                 }
@@ -709,7 +709,7 @@ private static void fromXContent(XContentParser parser, StringBuilder keyBuilder
                 }
                 String key = keyBuilder.toString();
                 validateValue(key, list, builder, parser, allowNullValues);
-                builder.putArray(key, list);
+                builder.putList(key, list);
             } else if (parser.currentToken() == XContentParser.Token.VALUE_NULL) {
                 String key = keyBuilder.toString();
                 validateValue(key, null, builder, parser, allowNullValues);
@@ -928,7 +928,7 @@ public Builder copy(String key, String sourceKey, Settings source) {
             }
             final Object value = source.settings.get(sourceKey);
             if (value instanceof List) {
-                return putArray(key, (List)value);
+                return putList(key, (List)value);
             } else if (value == null) {
                 return putNull(key);
             } else {
@@ -1052,8 +1052,8 @@ public Builder put(String setting, long value, ByteSizeUnit sizeUnit) {
          * @param values  The values
          * @return The builder
          */
-        public Builder putArray(String setting, String... values) {
-            return putArray(setting, Arrays.asList(values));
+        public Builder putList(String setting, String... values) {
+            return putList(setting, Arrays.asList(values));
         }
 
         /**
@@ -1063,7 +1063,7 @@ public Builder putArray(String setting, String... values) {
          * @param values  The values
          * @return The builder
          */
-        public Builder putArray(String setting, List<String> values) {
+        public Builder putList(String setting, List<String> values) {
             remove(setting);
             map.put(setting, Collections.unmodifiableList(new ArrayList<>(values)));
             return this;

core/src/main/java/org/elasticsearch/env/Environment.java

@@ -153,7 +153,7 @@ public Environment(final Settings settings, final Path configPath) {
         Settings.Builder finalSettings = Settings.builder().put(settings);
         finalSettings.put(PATH_HOME_SETTING.getKey(), homeFile);
         if (PATH_DATA_SETTING.exists(settings)) {
-            finalSettings.putArray(PATH_DATA_SETTING.getKey(), dataPaths);
+            finalSettings.putList(PATH_DATA_SETTING.getKey(), dataPaths);
         }
         finalSettings.put(PATH_LOGS_SETTING.getKey(), logsFile.toString());
         this.settings = finalSettings.build();

core/src/main/java/org/elasticsearch/index/analysis/Analysis.java

@@ -71,7 +71,6 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.List;
@@ -110,10 +109,10 @@ public static CharArraySet parseStemExclusion(Settings settings, CharArraySet de
         if ("_none_".equals(value)) {
             return CharArraySet.EMPTY_SET;
         }
-        String[] stemExclusion = settings.getAsArray("stem_exclusion", null);
+        List<String> stemExclusion = settings.getAsList("stem_exclusion", null);
         if (stemExclusion != null) {
             // LUCENE 4 UPGRADE: Should be settings.getAsBoolean("stem_exclusion_case", false)?
-            return new CharArraySet(Arrays.asList(stemExclusion), false);
+            return new CharArraySet(stemExclusion, false);
         } else {
             return defaultStemExclusion;
         }
@@ -166,7 +165,7 @@ public static CharArraySet parseWords(Environment env, Settings settings, String
             if ("_none_".equals(value)) {
                 return CharArraySet.EMPTY_SET;
             } else {
-                return resolveNamedWords(Arrays.asList(settings.getAsArray(name)), namedWords, ignoreCase);
+                return resolveNamedWords(settings.getAsList(name), namedWords, ignoreCase);
             }
         }
         List<String> pathLoadedWords = getWordList(env, settings, name);
@@ -233,11 +232,11 @@ public static List<String> getWordList(Environment env, Settings settings, Strin
         String wordListPath = settings.get(settingPrefix + "_path", null);
 
         if (wordListPath == null) {
-            String[] explicitWordList = settings.getAsArray(settingPrefix, null);
+            List<String> explicitWordList = settings.getAsList(settingPrefix, null);
             if (explicitWordList == null) {
                 return null;
             } else {
-                return Arrays.asList(explicitWordList);
+                return explicitWordList;
             }
         }
 

core/src/main/java/org/elasticsearch/index/analysis/AnalysisRegistry.java

@@ -571,7 +571,7 @@ private void processAnalyzerFactory(DeprecationLogger deprecationLogger,
             // the setting is now removed but we only support it for loading indices created before v5.0
             deprecationLogger.deprecated("setting [{}] is only allowed on index [{}] because it was created before 5.x; " +
                 "analyzer aliases can no longer be created on new indices.", analyzerAliasKey, indexSettings.getIndex().getName());
-            Set<String> aliases = Sets.newHashSet(indexSettings.getSettings().getAsArray(analyzerAliasKey));
+            Set<String> aliases = Sets.newHashSet(indexSettings.getSettings().getAsList(analyzerAliasKey));
             for (String alias : aliases) {
                 if (analyzerAliases.putIfAbsent(alias, analyzer) != null) {
                     throw new IllegalStateException("alias [" + alias + "] is already used by [" + analyzerAliases.get(alias).name() + "]");

core/src/main/java/org/elasticsearch/index/analysis/CustomAnalyzerProvider.java

@@ -58,8 +58,8 @@ public void build(final Map<String, TokenizerFactory> tokenizers, final Map<Stri
             throw new IllegalArgumentException("Custom Analyzer [" + name() + "] failed to find tokenizer under name [" + tokenizerName + "]");
         }
 
-        String[] charFilterNames = analyzerSettings.getAsArray("char_filter");
-        List<CharFilterFactory> charFiltersList = new ArrayList<>(charFilterNames.length);
+        List<String> charFilterNames = analyzerSettings.getAsList("char_filter");
+        List<CharFilterFactory> charFiltersList = new ArrayList<>(charFilterNames.size());
         for (String charFilterName : charFilterNames) {
             CharFilterFactory charFilter = charFilters.get(charFilterName);
             if (charFilter == null) {
@@ -74,8 +74,8 @@ public void build(final Map<String, TokenizerFactory> tokenizers, final Map<Stri
 
         int offsetGap = analyzerSettings.getAsInt("offset_gap", -1);
 
-        String[] tokenFilterNames = analyzerSettings.getAsArray("filter");
-        List<TokenFilterFactory> tokenFilterList = new ArrayList<>(tokenFilterNames.length);
+        List<String> tokenFilterNames = analyzerSettings.getAsList("filter");
+        List<TokenFilterFactory> tokenFilterList = new ArrayList<>(tokenFilterNames.size());
         for (String tokenFilterName : tokenFilterNames) {
             TokenFilterFactory tokenFilter = tokenFilters.get(tokenFilterName);
             if (tokenFilter == null) {

core/src/main/java/org/elasticsearch/index/analysis/CustomNormalizerProvider.java

@@ -50,8 +50,8 @@ public void build(final TokenizerFactory keywordTokenizerFactory, final Map<Stri
             throw new IllegalArgumentException("Custom normalizer [" + name() + "] cannot configure a tokenizer");
         }
 
-        String[] charFilterNames = analyzerSettings.getAsArray("char_filter");
-        List<CharFilterFactory> charFiltersList = new ArrayList<>(charFilterNames.length);
+        List<String> charFilterNames = analyzerSettings.getAsList("char_filter");
+        List<CharFilterFactory> charFiltersList = new ArrayList<>(charFilterNames.size());
         for (String charFilterName : charFilterNames) {
             CharFilterFactory charFilter = charFilters.get(charFilterName);
             if (charFilter == null) {
@@ -66,8 +66,8 @@ public void build(final TokenizerFactory keywordTokenizerFactory, final Map<Stri
             charFiltersList.add(charFilter);
         }
 
-        String[] tokenFilterNames = analyzerSettings.getAsArray("filter");
-        List<TokenFilterFactory> tokenFilterList = new ArrayList<>(tokenFilterNames.length);
+        List<String> tokenFilterNames = analyzerSettings.getAsList("filter");
+        List<TokenFilterFactory> tokenFilterList = new ArrayList<>(tokenFilterNames.size());
         for (String tokenFilterName : tokenFilterNames) {
             TokenFilterFactory tokenFilter = tokenFilters.get(tokenFilterName);
             if (tokenFilter == null) {

core/src/main/java/org/elasticsearch/index/analysis/EdgeNGramTokenizerFactory.java

@@ -41,7 +41,7 @@ public EdgeNGramTokenizerFactory(IndexSettings indexSettings, Environment enviro
         super(indexSettings, name, settings);
         this.minGram = settings.getAsInt("min_gram", NGramTokenizer.DEFAULT_MIN_NGRAM_SIZE);
         this.maxGram = settings.getAsInt("max_gram", NGramTokenizer.DEFAULT_MAX_NGRAM_SIZE);
-        this.matcher = parseTokenChars(settings.getAsArray("token_chars"));
+        this.matcher = parseTokenChars(settings.getAsList("token_chars"));
     }
 
     @Override

core/src/main/java/org/elasticsearch/index/analysis/NGramTokenizerFactory.java

@@ -28,6 +28,7 @@
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 
@@ -65,8 +66,8 @@ public class NGramTokenizerFactory extends AbstractTokenizerFactory {
         MATCHERS = unmodifiableMap(matchers);
     }
 
-    static CharMatcher parseTokenChars(String[] characterClasses) {
-        if (characterClasses == null || characterClasses.length == 0) {
+    static CharMatcher parseTokenChars(List<String> characterClasses) {
+        if (characterClasses == null || characterClasses.isEmpty()) {
             return null;
         }
         CharMatcher.Builder builder = new CharMatcher.Builder();
@@ -85,7 +86,7 @@ public NGramTokenizerFactory(IndexSettings indexSettings, Environment environmen
         super(indexSettings, name, settings);
         this.minGram = settings.getAsInt("min_gram", NGramTokenizer.DEFAULT_MIN_NGRAM_SIZE);
         this.maxGram = settings.getAsInt("max_gram", NGramTokenizer.DEFAULT_MAX_NGRAM_SIZE);
-        this.matcher = parseTokenChars(settings.getAsArray("token_chars"));
+        this.matcher = parseTokenChars(settings.getAsList("token_chars"));
     }
 
     @Override

core/src/main/java/org/elasticsearch/index/analysis/SynonymTokenFilterFactory.java

@@ -91,7 +91,7 @@ public TokenStream create(TokenStream tokenStream) {
 
     protected Reader getRulesFromSettings(Environment env) {
         Reader rulesReader;
-        if (settings.getAsArray("synonyms", null) != null) {
+        if (settings.getAsList("synonyms", null) != null) {
             List<String> rulesList = Analysis.getWordList(env, settings, "synonyms");
             StringBuilder sb = new StringBuilder();
             for (String line : rulesList) {

core/src/test/java/org/elasticsearch/action/admin/indices/TransportAnalyzeActionTests.java

@@ -41,7 +41,6 @@
 import org.elasticsearch.indices.analysis.AnalysisModule.AnalysisProvider;
 import org.elasticsearch.indices.analysis.AnalysisModuleTests.AppendCharFilter;
 import org.elasticsearch.plugins.AnalysisPlugin;
-import static org.elasticsearch.plugins.AnalysisPlugin.requriesAnalysisSettings;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.IndexSettingsModule;
 
@@ -74,7 +73,7 @@ public void setUp() throws Exception {
                 .put("index.analysis.analyzer.custom_analyzer.tokenizer", "standard")
                 .put("index.analysis.analyzer.custom_analyzer.filter", "mock")
                 .put("index.analysis.normalizer.my_normalizer.type", "custom")
-                .putArray("index.analysis.normalizer.my_normalizer.filter", "lowercase").build();
+                .putList("index.analysis.normalizer.my_normalizer.filter", "lowercase").build();
         IndexSettings idxSettings = IndexSettingsModule.newIndexSettings("index", indexSettings);
         environment = new Environment(settings);
         AnalysisPlugin plugin = new AnalysisPlugin() {

core/src/test/java/org/elasticsearch/action/termvectors/AbstractTermVectorsTestCase.java

@@ -210,7 +210,7 @@ protected void createIndexBasedOnFieldSettings(String index, String alias, TestF
         Settings.Builder settings = Settings.builder()
                 .put(indexSettings())
                 .put("index.analysis.analyzer.tv_test.tokenizer", "standard")
-                .putArray("index.analysis.analyzer.tv_test.filter", "lowercase");
+                .putList("index.analysis.analyzer.tv_test.filter", "lowercase");
         assertAcked(prepareCreate(index).addMapping("type1", mappingBuilder).setSettings(settings).addAlias(new Alias(alias)));
     }