Yet more ImmutableMap#of removal

Did some refactoring of PathTrie along the way to remove warnings. Added a
simple toString to it to make it easier to debug.

core/src/main/java/org/elasticsearch/cluster/block/ClusterBlocks.java

@@ -24,6 +24,7 @@ import com.google.common.collect.ImmutableMap;
 import org.elasticsearch.cluster.AbstractDiffable;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaDataIndexStateService;
+import org.elasticsearch.common.collect.ImmutableOpenMap;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.rest.RestStatus;
@@ -68,7 +69,7 @@ public class ClusterBlocks extends AbstractDiffable<ClusterBlocks> {
                     .filter(containsLevel)
                     .collect(toSet()));
 
-            ImmutableMap.Builder<String, Set<ClusterBlock>> indicesBuilder = ImmutableMap.builder();
+            ImmutableOpenMap.Builder<String, Set<ClusterBlock>> indicesBuilder = ImmutableOpenMap.builder();
             for (Map.Entry<String, Set<ClusterBlock>> entry : indicesBlocks.entrySet()) {
                 indicesBuilder.put(entry.getKey(), unmodifiableSet(entry.getValue().stream()
                         .filter(containsLevel)
@@ -91,7 +92,7 @@ public class ClusterBlocks extends AbstractDiffable<ClusterBlocks> {
         return levelHolders[level.id()].global();
     }
 
-    public Map<String, Set<ClusterBlock>> indices(ClusterBlockLevel level) {
+    public ImmutableOpenMap<String, Set<ClusterBlock>> indices(ClusterBlockLevel level) {
         return levelHolders[level.id()].indices();
     }
 
@@ -238,12 +239,12 @@ public class ClusterBlocks extends AbstractDiffable<ClusterBlocks> {
 
     static class ImmutableLevelHolder {
 
-        static final ImmutableLevelHolder EMPTY = new ImmutableLevelHolder(emptySet(), ImmutableMap.of());
+        static final ImmutableLevelHolder EMPTY = new ImmutableLevelHolder(emptySet(), ImmutableOpenMap.of());
 
         private final Set<ClusterBlock> global;
-        private final ImmutableMap<String, Set<ClusterBlock>> indices;
+        private final ImmutableOpenMap<String, Set<ClusterBlock>> indices;
 
-        ImmutableLevelHolder(Set<ClusterBlock> global, ImmutableMap<String, Set<ClusterBlock>> indices) {
+        ImmutableLevelHolder(Set<ClusterBlock> global, ImmutableOpenMap<String, Set<ClusterBlock>> indices) {
             this.global = global;
             this.indices = indices;
         }
@@ -252,7 +253,7 @@ public class ClusterBlocks extends AbstractDiffable<ClusterBlocks> {
             return global;
         }
 
-        public ImmutableMap<String, Set<ClusterBlock>> indices() {
+        public ImmutableOpenMap<String, Set<ClusterBlock>> indices() {
             return indices;
         }
     }

core/src/main/java/org/elasticsearch/cluster/routing/RoutingTableValidation.java

@@ -19,7 +19,6 @@
 
 package org.elasticsearch.cluster.routing;
 
-import com.google.common.collect.ImmutableMap;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Streamable;
@@ -31,6 +30,8 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import static java.util.Collections.emptyMap;
+
 /**
  * Encapsulates the result of a routing table validation and provides access to
  * validation failures.
@@ -72,7 +73,7 @@ public class RoutingTableValidation implements Streamable {
 
     public Map<String, List<String>> indicesFailures() {
         if (indicesFailures == null) {
-            return ImmutableMap.of();
+            return emptyMap();
         }
         return indicesFailures;
     }
@@ -128,7 +129,7 @@ public class RoutingTableValidation implements Streamable {
         }
         size = in.readVInt();
         if (size == 0) {
-            indicesFailures = ImmutableMap.of();
+            indicesFailures = emptyMap();
         } else {
             indicesFailures = new HashMap<>();
             for (int i = 0; i < size; i++) {

core/src/main/java/org/elasticsearch/common/Table.java

@@ -19,13 +19,13 @@
 
 package org.elasticsearch.common;
 
-import com.google.common.collect.ImmutableMap;
-
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import static java.util.Collections.emptyMap;
+
 /**
  */
 public class Table {
@@ -115,7 +115,7 @@ public class Table {
         Map<String, String> mAttr;
         if (attributes.length() == 0) {
             if (inHeaders) {
-                mAttr = ImmutableMap.of();
+                mAttr = emptyMap();
             } else {
                 // get the attributes of the header cell we are going to add to
                 mAttr = headers.get(currentCells.size()).attr;

core/src/main/java/org/elasticsearch/common/path/PathTrie.java

@@ -19,14 +19,15 @@
 
 package org.elasticsearch.common.path;
 
-import com.google.common.collect.ImmutableMap;
 import org.elasticsearch.common.Strings;
 
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
-import static org.elasticsearch.common.collect.MapBuilder.newMapBuilder;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.unmodifiableMap;
 
 /**
  *
@@ -45,7 +46,7 @@ public class PathTrie<T> {
     };
 
     private final Decoder decoder;
-    private final TrieNode<T> root;
+    private final TrieNode root;
     private final char separator;
     private T rootValue;
 
@@ -60,10 +61,10 @@ public class PathTrie<T> {
     public PathTrie(char separator, String wildcard, Decoder decoder) {
         this.decoder = decoder;
         this.separator = separator;
-        root = new TrieNode<>(new String(new char[]{separator}), null, null, wildcard);
+        root = new TrieNode(new String(new char[]{separator}), null, wildcard);
     }
 
-    public class TrieNode<T> {
+    public class TrieNode {
         private transient String key;
         private transient T value;
         private boolean isWildcard;
@@ -71,17 +72,14 @@ public class PathTrie<T> {
 
         private transient String namedWildcard;
 
-        private ImmutableMap<String, TrieNode<T>> children;
+        private Map<String, TrieNode> children;
 
-        private final TrieNode parent;
+        public TrieNode(String key, T value, String wildcard) {
-
-        public TrieNode(String key, T value, TrieNode parent, String wildcard) {
             this.key = key;
             this.wildcard = wildcard;
             this.isWildcard = (key.equals(wildcard));
-            this.parent = parent;
             this.value = value;
-            this.children = ImmutableMap.of();
+            this.children = emptyMap();
             if (isNamedWildcard(key)) {
                 namedWildcard = key.substring(key.indexOf('{') + 1, key.indexOf('}'));
             } else {
@@ -98,8 +96,14 @@ public class PathTrie<T> {
             return isWildcard;
         }
 
-        public synchronized void addChild(TrieNode<T> child) {
+        public synchronized void addChild(TrieNode child) {
-            children = newMapBuilder(children).put(child.key, child).immutableMap();
+            addInnerChild(child.key, child);
+        }
+
+        private void addInnerChild(String key, TrieNode child) {
+            Map<String, TrieNode> newChildren = new HashMap<>(children);
+            newChildren.put(key, child);
+            children = unmodifiableMap(newChildren);
         }
 
         public TrieNode getChild(String key) {
@@ -115,14 +119,11 @@ public class PathTrie<T> {
             if (isNamedWildcard(token)) {
                 key = wildcard;
             }
-            TrieNode<T> node = children.get(key);
+            TrieNode node = children.get(key);
             if (node == null) {
-                if (index == (path.length - 1)) {
+                T nodeValue = index == path.length - 1 ? value : null;
-                    node = new TrieNode<>(token, value, this, wildcard);
+                node = new TrieNode(token, nodeValue, wildcard);
-                } else {
+                addInnerChild(key, node);
-                    node = new TrieNode<>(token, null, this, wildcard);
-                }
-                children = newMapBuilder(children).put(key, node).immutableMap();
             } else {
                 if (isNamedWildcard(token)) {
                     node.updateKeyWithNamedWildcard(token);
@@ -158,7 +159,7 @@ public class PathTrie<T> {
                 return null;
 
             String token = path[index];
-            TrieNode<T> node = children.get(token);
+            TrieNode node = children.get(token);
             boolean usedWildcard;
             if (node == null) {
                 node = children.get(wildcard);
@@ -195,11 +196,16 @@ public class PathTrie<T> {
             return res;
         }
 
-        private void put(Map<String, String> params, TrieNode<T> node, String value) {
+        private void put(Map<String, String> params, TrieNode node, String value) {
             if (params != null && node.isNamedWildcard()) {
                 params.put(node.namedWildcard(), value);
             }
         }
+
+        @Override
+        public String toString() {
+            return key;
+        }
     }
 
     public void insert(String path, T value) {

core/src/main/java/org/elasticsearch/gateway/DanglingIndicesState.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.gateway;
 
 import com.google.common.collect.ImmutableMap;
+
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.common.component.AbstractComponent;
@@ -34,6 +35,8 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Set;
 
+import static java.util.Collections.emptyMap;
+
 /**
  * The dangling indices state is responsible for finding new dangling indices (indices that have
  * their state written on disk, but don't exists in the metadata of the cluster), and importing
@@ -107,7 +110,7 @@ public class DanglingIndicesState extends AbstractComponent {
             indices = nodeEnv.findAllIndices();
         } catch (Throwable e) {
             logger.warn("failed to list dangling indices", e);
-            return ImmutableMap.of();
+            return emptyMap();
         }
 
         Map<String, IndexMetaData>  newIndices = new HashMap<>();

core/src/main/java/org/elasticsearch/index/IndexService.java

@@ -20,11 +20,11 @@
 package org.elasticsearch.index;
 
 import com.google.common.collect.ImmutableMap;
+
 import org.apache.lucene.util.Accountable;
 import org.apache.lucene.util.IOUtils;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
-import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.Strings;
@@ -74,6 +74,7 @@ import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import static java.util.Collections.emptyMap;
 import static org.elasticsearch.common.collect.MapBuilder.newMapBuilder;
 
 /**
@@ -110,7 +111,7 @@ public class IndexService extends AbstractIndexComponent implements IndexCompone
     private final NodeEnvironment nodeEnv;
     private final IndicesService indicesServices;
 
-    private volatile ImmutableMap<Integer, IndexShardInjectorPair> shards = ImmutableMap.of();
+    private volatile Map<Integer, IndexShardInjectorPair> shards = emptyMap();
 
     private static class IndexShardInjectorPair {
         private final IndexShard indexShard;

core/src/main/java/org/elasticsearch/index/get/GetResult.java

@@ -19,7 +19,6 @@
 
 package org.elasticsearch.index.get;
 
-import com.google.common.collect.ImmutableMap;
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.compress.CompressorFactory;
@@ -40,6 +39,7 @@ import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 
+import static java.util.Collections.emptyMap;
 import static org.elasticsearch.index.get.GetField.readGetField;
 
 /**
@@ -68,7 +68,7 @@ public class GetResult implements Streamable, Iterable<GetField>, ToXContent {
         this.source = source;
         this.fields = fields;
         if (this.fields == null) {
-            this.fields = ImmutableMap.of();
+            this.fields = emptyMap();
         }
     }
 
@@ -286,7 +286,7 @@ public class GetResult implements Streamable, Iterable<GetField>, ToXContent {
             }
             int size = in.readVInt();
             if (size == 0) {
-                fields = ImmutableMap.of();
+                fields = emptyMap();
             } else {
                 fields = new HashMap<>(size);
                 for (int i = 0; i < size; i++) {

core/src/main/java/org/elasticsearch/index/mapper/MapperService.java

@@ -20,7 +20,6 @@
 package org.elasticsearch.index.mapper;
 
 import com.carrotsearch.hppc.ObjectHashSet;
-import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterators;
 
 import org.apache.lucene.analysis.Analyzer;
@@ -64,6 +63,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
@@ -73,7 +73,9 @@ import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.function.Function;
 
+import static java.util.Collections.emptyMap;
 import static java.util.Collections.emptySet;
+import static java.util.Collections.unmodifiableMap;
 import static java.util.Collections.unmodifiableSet;
 import static org.elasticsearch.common.collect.MapBuilder.newMapBuilder;
 
@@ -98,7 +100,7 @@ public class MapperService extends AbstractIndexComponent implements Closeable {
     private volatile String defaultMappingSource;
     private volatile String defaultPercolatorMappingSource;
 
-    private volatile Map<String, DocumentMapper> mappers = ImmutableMap.of();
+    private volatile Map<String, DocumentMapper> mappers = emptyMap();
 
     // A lock for mappings: modifications (put mapping) need to be performed
     // under the write lock and read operations (document parsing) need to be
@@ -118,7 +120,7 @@ public class MapperService extends AbstractIndexComponent implements Closeable {
 
     private final List<DocumentTypeListener> typeListeners = new CopyOnWriteArrayList<>();
 
-    private volatile ImmutableMap<String, MappedFieldType> unmappedFieldTypes = ImmutableMap.of();
+    private volatile Map<String, MappedFieldType> unmappedFieldTypes = emptyMap();
 
     private volatile Set<String> parentTypes = emptySet();
 
@@ -538,24 +540,23 @@ public class MapperService extends AbstractIndexComponent implements Closeable {
      * Given a type (eg. long, string, ...), return an anonymous field mapper that can be used for search operations.
      */
     public MappedFieldType unmappedFieldType(String type) {
-        final ImmutableMap<String, MappedFieldType> unmappedFieldMappers = this.unmappedFieldTypes;
+        MappedFieldType fieldType = unmappedFieldTypes.get(type);
-        MappedFieldType fieldType = unmappedFieldMappers.get(type);
         if (fieldType == null) {
             final Mapper.TypeParser.ParserContext parserContext = documentMapperParser().parserContext(type);
             Mapper.TypeParser typeParser = parserContext.typeParser(type);
             if (typeParser == null) {
                 throw new IllegalArgumentException("No mapper found for type [" + type + "]");
             }
-            final Mapper.Builder<?, ?> builder = typeParser.parse("__anonymous_" + type, ImmutableMap.<String, Object>of(), parserContext);
+            final Mapper.Builder<?, ?> builder = typeParser.parse("__anonymous_" + type, emptyMap(), parserContext);
             final BuilderContext builderContext = new BuilderContext(indexSettings, new ContentPath(1));
             fieldType = ((FieldMapper)builder.build(builderContext)).fieldType();
 
             // There is no need to synchronize writes here. In the case of concurrent access, we could just
             // compute some mappers several times, which is not a big deal
-            this.unmappedFieldTypes = ImmutableMap.<String, MappedFieldType>builder()
+            Map<String, MappedFieldType> newUnmappedFieldTypes = new HashMap<>();
-                    .putAll(unmappedFieldMappers)
+            newUnmappedFieldTypes.putAll(unmappedFieldTypes);
-                    .put(type, fieldType)
+            newUnmappedFieldTypes.put(type, fieldType);
-                    .build();
+            unmappedFieldTypes = unmodifiableMap(newUnmappedFieldTypes);
         }
         return fieldType;
     }

core/src/main/java/org/elasticsearch/index/mapper/Mapping.java

@@ -22,7 +22,6 @@ package org.elasticsearch.index.mapper;
 import com.google.common.collect.ImmutableMap;
 
 import org.elasticsearch.Version;
-import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
@@ -34,6 +33,8 @@ import java.util.Comparator;
 import java.util.List;
 import java.util.Map;
 
+import static java.util.Collections.emptyMap;
+
 /**
  * Wrapper around everything that defines a mapping, without references to
  * utility classes like MapperService, ...
@@ -150,22 +151,11 @@ public final class Mapping implements ToXContent {
         return builder;
     }
 
-    /** Serialize to a {@link BytesReference}. */
-    public BytesReference toBytes() {
-        try {
-            XContentBuilder builder = XContentFactory.jsonBuilder().startObject();
-            toXContent(builder, new ToXContent.MapParams(ImmutableMap.<String, String>of()));
-            return builder.endObject().bytes();
-        } catch (IOException bogus) {
-            throw new AssertionError(bogus);
-        }
-    }
-
     @Override
     public String toString() {
         try {
             XContentBuilder builder = XContentFactory.jsonBuilder().startObject();
-            toXContent(builder, new ToXContent.MapParams(ImmutableMap.<String, String>of()));
+            toXContent(builder, new ToXContent.MapParams(emptyMap()));
             return builder.endObject().string();
         } catch (IOException bogus) {
             throw new AssertionError(bogus);

core/src/main/java/org/elasticsearch/index/snapshots/blobstore/BlobStoreIndexShardRepository.java

@@ -19,7 +19,11 @@
 
 package org.elasticsearch.index.snapshots.blobstore;
 
-import org.apache.lucene.index.*;
+import org.apache.lucene.index.CorruptIndexException;
+import org.apache.lucene.index.IndexCommit;
+import org.apache.lucene.index.IndexFormatTooNewException;
+import org.apache.lucene.index.IndexFormatTooOldException;
+import org.apache.lucene.index.SegmentInfos;
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.store.IndexOutput;
@@ -47,7 +51,11 @@ import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.util.iterable.Iterables;
 import org.elasticsearch.index.IndexService;
 import org.elasticsearch.index.shard.ShardId;
-import org.elasticsearch.index.snapshots.*;
+import org.elasticsearch.index.snapshots.IndexShardRepository;
+import org.elasticsearch.index.snapshots.IndexShardRestoreFailedException;
+import org.elasticsearch.index.snapshots.IndexShardSnapshotException;
+import org.elasticsearch.index.snapshots.IndexShardSnapshotFailedException;
+import org.elasticsearch.index.snapshots.IndexShardSnapshotStatus;
 import org.elasticsearch.index.snapshots.blobstore.BlobStoreIndexShardSnapshot.FileInfo;
 import org.elasticsearch.index.store.Store;
 import org.elasticsearch.index.store.StoreFileMetaData;
@@ -63,8 +71,15 @@ import org.elasticsearch.repositories.blobstore.LegacyBlobStoreFormat;
 import java.io.FilterInputStream;
 import java.io.IOException;
 import java.io.InputStream;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.unmodifiableMap;
 import static org.elasticsearch.repositories.blobstore.BlobStoreRepository.testBlobPrefix;
 
 /**
@@ -808,7 +823,7 @@ public class BlobStoreIndexShardRepository extends AbstractComponent implements
                     snapshotMetaData.put(fileInfo.metadata().name(), fileInfo.metadata());
                     fileInfos.put(fileInfo.metadata().name(), fileInfo);
                 }
-                final Store.MetadataSnapshot sourceMetaData = new Store.MetadataSnapshot(snapshotMetaData, Collections.EMPTY_MAP, 0);
+                final Store.MetadataSnapshot sourceMetaData = new Store.MetadataSnapshot(unmodifiableMap(snapshotMetaData), emptyMap(), 0);
                 final Store.RecoveryDiff diff = sourceMetaData.recoveryDiff(recoveryTargetMetadata);
                 for (StoreFileMetaData md : diff.identical) {
                     FileInfo fileInfo = fileInfos.get(md.name());

core/src/main/java/org/elasticsearch/index/store/Store.java

@@ -20,13 +20,35 @@
 package org.elasticsearch.index.store;
 
 import com.google.common.collect.ImmutableMap;
+
 import org.apache.lucene.codecs.CodecUtil;
-import org.apache.lucene.index.*;
+import org.apache.lucene.index.CorruptIndexException;
-import org.apache.lucene.store.*;
+import org.apache.lucene.index.IndexCommit;
-import org.apache.lucene.util.*;
+import org.apache.lucene.index.IndexFileNames;
+import org.apache.lucene.index.IndexFormatTooNewException;
+import org.apache.lucene.index.IndexFormatTooOldException;
+import org.apache.lucene.index.IndexNotFoundException;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.SegmentCommitInfo;
+import org.apache.lucene.index.SegmentInfos;
+import org.apache.lucene.store.AlreadyClosedException;
+import org.apache.lucene.store.BufferedChecksum;
+import org.apache.lucene.store.ByteArrayDataInput;
+import org.apache.lucene.store.ChecksumIndexInput;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.FilterDirectory;
+import org.apache.lucene.store.IOContext;
+import org.apache.lucene.store.IndexInput;
+import org.apache.lucene.store.IndexOutput;
+import org.apache.lucene.store.Lock;
+import org.apache.lucene.store.SimpleFSDirectory;
+import org.apache.lucene.util.ArrayUtil;
+import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.BytesRefBuilder;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.Version;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.ExceptionsHelper;
-import org.apache.lucene.util.Version;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.collect.Tuple;
@@ -44,26 +66,38 @@ import org.elasticsearch.common.lucene.store.InputStreamIndexInput;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.util.Callback;
-import org.elasticsearch.common.util.iterable.Iterables;
 import org.elasticsearch.common.util.SingleObjectCache;
 import org.elasticsearch.common.util.concurrent.AbstractRefCounted;
 import org.elasticsearch.common.util.concurrent.RefCounted;
+import org.elasticsearch.common.util.iterable.Iterables;
 import org.elasticsearch.env.ShardLock;
 import org.elasticsearch.index.engine.Engine;
 import org.elasticsearch.index.settings.IndexSettings;
 import org.elasticsearch.index.shard.AbstractIndexShardComponent;
 import org.elasticsearch.index.shard.ShardId;
 
-import java.io.*;
+import java.io.Closeable;
+import java.io.EOFException;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 import java.util.zip.Adler32;
 import java.util.zip.CRC32;
 import java.util.zip.Checksum;
 
+import static java.util.Collections.emptyMap;
+
 /**
  * A Store provides plain access to files written by an elasticsearch index shard. Each shard
  * has a dedicated store that is uses to access Lucene's Directory which represents the lowest level
@@ -734,7 +768,7 @@ public class Store extends AbstractIndexShardComponent implements Closeable, Ref
         private static final ESLogger logger = Loggers.getLogger(MetadataSnapshot.class);
         private static final Version FIRST_LUCENE_CHECKSUM_VERSION = Version.LUCENE_4_8;
 
-        private final ImmutableMap<String, StoreFileMetaData> metadata;
+        private final Map<String, StoreFileMetaData> metadata;
 
         public static final MetadataSnapshot EMPTY = new MetadataSnapshot();
 
@@ -743,16 +777,14 @@ public class Store extends AbstractIndexShardComponent implements Closeable, Ref
         private final long numDocs;
 
         public MetadataSnapshot(Map<String, StoreFileMetaData> metadata, Map<String, String> commitUserData, long numDocs) {
-            ImmutableMap.Builder<String, StoreFileMetaData> metaDataBuilder = ImmutableMap.builder();
+            this.metadata = metadata;
-            this.metadata = metaDataBuilder.putAll(metadata).build();
+            this.commitUserData = commitUserData;
-            ImmutableMap.Builder<String, String> commitUserDataBuilder = ImmutableMap.builder();
-            this.commitUserData = commitUserDataBuilder.putAll(commitUserData).build();
             this.numDocs = numDocs;
         }
 
         MetadataSnapshot() {
-            metadata = ImmutableMap.of();
+            metadata = emptyMap();
-            commitUserData = ImmutableMap.of();
+            commitUserData = emptyMap();
             numDocs = 0;
         }
 

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/PipelineAggregatorStreams.java

@@ -18,21 +18,22 @@
  */
 package org.elasticsearch.search.aggregations.pipeline;
 
-import com.google.common.collect.ImmutableMap;
-
 import org.elasticsearch.common.bytes.BytesReference;
-import org.elasticsearch.common.collect.MapBuilder;
 import org.elasticsearch.common.io.stream.StreamInput;
 
 import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.unmodifiableMap;
 
 /**
  * A registry for all the dedicated streams in the aggregation module. This is to support dynamic addAggregation that
  * know how to stream themselves.
  */
 public class PipelineAggregatorStreams {
-
+    private static Map<BytesReference, Stream> streams = emptyMap();
-    private static ImmutableMap<BytesReference, Stream> streams = ImmutableMap.of();
 
     /**
      * A stream that knows how to read an aggregation from the input.
@@ -48,11 +49,11 @@ public class PipelineAggregatorStreams {
      * @param types     The types associated with the streams
      */
     public static synchronized void registerStream(Stream stream, BytesReference... types) {
-        MapBuilder<BytesReference, Stream> uStreams = MapBuilder.newMapBuilder(streams);
+        Map<BytesReference, Stream> newStreams = new HashMap<>(streams);
         for (BytesReference type : types) {
-            uStreams.put(type, stream);
+            newStreams.put(type, stream);
         }
-        streams = uStreams.immutableMap();
+        streams = unmodifiableMap(newStreams);
     }
 
     /**

core/src/main/java/org/elasticsearch/search/dfs/DfsPhase.java

@@ -19,10 +19,10 @@
 
 package org.elasticsearch.search.dfs;
 
-import com.carrotsearch.hppc.ObjectObjectHashMap;
 import com.carrotsearch.hppc.ObjectHashSet;
+import com.carrotsearch.hppc.ObjectObjectHashMap;
 import com.carrotsearch.hppc.cursors.ObjectCursor;
-import com.google.common.collect.ImmutableMap;
+
 import org.apache.lucene.index.IndexReaderContext;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.index.TermContext;
@@ -39,6 +39,8 @@ import java.util.Collection;
 import java.util.Iterator;
 import java.util.Map;
 
+import static java.util.Collections.emptyMap;
+
 /**
  *
  */
@@ -46,7 +48,7 @@ public class DfsPhase implements SearchPhase {
 
     @Override
     public Map<String, ? extends SearchParseElement> parseElements() {
-        return ImmutableMap.of();
+        return emptyMap();
     }
 
     @Override

core/src/test/java/org/elasticsearch/common/path/PathTrieTests.java

@@ -20,7 +20,6 @@
 package org.elasticsearch.common.path;
 
 import org.elasticsearch.test.ESTestCase;
-import org.junit.Test;
 
 import java.util.HashMap;
 import java.util.Map;

core/src/test/java/org/elasticsearch/gateway/ReplicaShardAllocatorTests.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.gateway;
 
 import com.carrotsearch.randomizedtesting.generators.RandomPicks;
+
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.ClusterInfo;
 import org.elasticsearch.cluster.ClusterState;
@@ -27,7 +28,15 @@ import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
-import org.elasticsearch.cluster.routing.*;
+import org.elasticsearch.cluster.routing.IndexRoutingTable;
+import org.elasticsearch.cluster.routing.IndexShardRoutingTable;
+import org.elasticsearch.cluster.routing.RoutingNode;
+import org.elasticsearch.cluster.routing.RoutingNodes;
+import org.elasticsearch.cluster.routing.RoutingTable;
+import org.elasticsearch.cluster.routing.ShardRouting;
+import org.elasticsearch.cluster.routing.ShardRoutingState;
+import org.elasticsearch.cluster.routing.TestShardRouting;
+import org.elasticsearch.cluster.routing.UnassignedInfo;
 import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
 import org.elasticsearch.cluster.routing.allocation.decider.AllocationDecider;
 import org.elasticsearch.cluster.routing.allocation.decider.AllocationDeciders;
@@ -49,6 +58,7 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import static java.util.Collections.unmodifiableMap;
 import static org.hamcrest.Matchers.equalTo;
 
 /**
@@ -358,7 +368,8 @@ public class ReplicaShardAllocatorTests extends ESAllocationTestCase {
             if (syncId != null) {
                 commitData.put(Engine.SYNC_COMMIT_ID, syncId);
             }
-            data.put(node, new TransportNodesListShardStoreMetaData.StoreFilesMetaData(allocated, shardId, new Store.MetadataSnapshot(filesAsMap, commitData, randomInt())));
+            data.put(node, new TransportNodesListShardStoreMetaData.StoreFilesMetaData(allocated, shardId,
+                    new Store.MetadataSnapshot(unmodifiableMap(filesAsMap), unmodifiableMap(commitData), randomInt())));
             return this;
         }
 

core/src/test/java/org/elasticsearch/index/store/StoreTests.java

@@ -24,9 +24,35 @@ import org.apache.lucene.codecs.FilterCodec;
 import org.apache.lucene.codecs.SegmentInfoFormat;
 import org.apache.lucene.codecs.lucene50.Lucene50SegmentInfoFormat;
 import org.apache.lucene.codecs.lucene53.Lucene53Codec;
-import org.apache.lucene.document.*;
+import org.apache.lucene.document.Document;
-import org.apache.lucene.index.*;
+import org.apache.lucene.document.Field;
-import org.apache.lucene.store.*;
+import org.apache.lucene.document.SortedDocValuesField;
+import org.apache.lucene.document.StringField;
+import org.apache.lucene.document.TextField;
+import org.apache.lucene.index.CorruptIndexException;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexFileNames;
+import org.apache.lucene.index.IndexFormatTooNewException;
+import org.apache.lucene.index.IndexFormatTooOldException;
+import org.apache.lucene.index.IndexNotFoundException;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.index.KeepOnlyLastCommitDeletionPolicy;
+import org.apache.lucene.index.NoDeletionPolicy;
+import org.apache.lucene.index.NoMergePolicy;
+import org.apache.lucene.index.SegmentInfo;
+import org.apache.lucene.index.SegmentInfos;
+import org.apache.lucene.index.SnapshotDeletionPolicy;
+import org.apache.lucene.index.Term;
+import org.apache.lucene.store.AlreadyClosedException;
+import org.apache.lucene.store.BaseDirectoryWrapper;
+import org.apache.lucene.store.ChecksumIndexInput;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IOContext;
+import org.apache.lucene.store.IndexInput;
+import org.apache.lucene.store.IndexOutput;
+import org.apache.lucene.store.MockDirectoryWrapper;
+import org.apache.lucene.store.RAMDirectory;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.TestUtil;
@@ -55,14 +81,30 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Date;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Random;
+import java.util.Set;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.zip.Adler32;
 
-import static org.elasticsearch.common.settings.Settings.Builder.EMPTY_SETTINGS;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.unmodifiableMap;
 import static org.elasticsearch.test.VersionUtils.randomVersion;
-import static org.hamcrest.Matchers.*;
+import static org.hamcrest.Matchers.empty;
+import static org.hamcrest.Matchers.endsWith;
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.greaterThan;
+import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.not;
+import static org.hamcrest.Matchers.notNullValue;
+import static org.hamcrest.Matchers.nullValue;
 
 public class StoreTests extends ESTestCase {
 
@@ -800,9 +842,9 @@ public class StoreTests extends ESTestCase {
         Map<String, StoreFileMetaData> metaDataMap = new HashMap<>();
         metaDataMap.put("segments_1", new StoreFileMetaData("segments_1", 50, null, null, new BytesRef(new byte[]{1})));
         metaDataMap.put("_0_1.del", new StoreFileMetaData("_0_1.del", 42, "foobarbaz", null, new BytesRef()));
-        Store.MetadataSnapshot first = new Store.MetadataSnapshot(metaDataMap, Collections.EMPTY_MAP, 0);
+        Store.MetadataSnapshot first = new Store.MetadataSnapshot(unmodifiableMap(new HashMap<>(metaDataMap)), emptyMap(), 0);
 
-        Store.MetadataSnapshot second = new Store.MetadataSnapshot(metaDataMap, Collections.EMPTY_MAP, 0);
+        Store.MetadataSnapshot second = new Store.MetadataSnapshot(unmodifiableMap(new HashMap<>(metaDataMap)), emptyMap(), 0);
         Store.RecoveryDiff recoveryDiff = first.recoveryDiff(second);
         assertEquals(recoveryDiff.toString(), recoveryDiff.different.size(), 2);
     }
@@ -1068,7 +1110,7 @@ public class StoreTests extends ESTestCase {
         Map<String, StoreFileMetaData> metaDataMap = new HashMap<>();
         metaDataMap.put("segments_1", new StoreFileMetaData("segments_1", 50, null, null, new BytesRef(new byte[]{1})));
         metaDataMap.put("_0_1.del", new StoreFileMetaData("_0_1.del", 42, "foobarbaz", null, new BytesRef()));
-        Store.MetadataSnapshot snapshot = new Store.MetadataSnapshot(metaDataMap, Collections.EMPTY_MAP, 0);
+        Store.MetadataSnapshot snapshot = new Store.MetadataSnapshot(unmodifiableMap(metaDataMap), emptyMap(), 0);
 
         final ShardId shardId = new ShardId(new Index("index"), 1);
         DirectoryService directoryService = new LuceneManagedDirectoryService(random());
@@ -1202,7 +1244,7 @@ public class StoreTests extends ESTestCase {
         Map<String, String> commitUserData = new HashMap<>();
         commitUserData.put("userdata_1", "test");
         commitUserData.put("userdata_2", "test");
-        return new Store.MetadataSnapshot(storeFileMetaDataMap, commitUserData, 0);
+        return new Store.MetadataSnapshot(unmodifiableMap(storeFileMetaDataMap), unmodifiableMap(commitUserData), 0);
     }
 
     @Test