Couple tweaks to generate less garbage

driver/src/main/java/org/neo4j/driver/internal/BoltServerAddress.java

@@ -25,6 +25,7 @@
 import java.net.UnknownHostException;
 
 import static java.lang.String.format;
+import static java.util.Objects.requireNonNull;
 
 /**
  * Holds a host and port pair that denotes a Bolt server address.
@@ -49,23 +50,23 @@ public BoltServerAddress( URI uri )
 
     public BoltServerAddress( String host, int port )
     {
-        this.host = host;
+        this.host = requireNonNull( host );
         this.port = port;
     }
 
     @Override
-    public boolean equals( Object obj )
+    public boolean equals( Object o )
     {
-        if ( this == obj )
+        if ( this == o )
         {
             return true;
         }
-        if ( !(obj instanceof BoltServerAddress) )
+        if ( o == null || getClass() != o.getClass() )
         {
             return false;
         }
-        BoltServerAddress address = (BoltServerAddress) obj;
-        return host.equals( address.host ) && port == address.port;
+        BoltServerAddress that = (BoltServerAddress) o;
+        return port == that.port && host.equals( that.host );
     }
 
     @Override

driver/src/main/java/org/neo4j/driver/internal/Bookmark.java

@@ -19,7 +19,6 @@
 package org.neo4j.driver.internal;
 
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Objects;
@@ -28,6 +27,7 @@
 
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.singleton;
+import static org.neo4j.driver.internal.util.Iterables.newHashMapWithSize;
 import static org.neo4j.driver.v1.Values.value;
 
 public final class Bookmark
@@ -93,7 +93,7 @@ public Map<String,Value> asBeginTransactionParameters()
         // {bookmarks: ["one", "two", "max"]} for backwards compatibility reasons. Old servers can only accept single
         // bookmark that is why driver has to parse and compare given list of bookmarks. This functionality will
         // eventually be removed.
-        Map<String,Value> parameters = new HashMap<>( 4 );
+        Map<String,Value> parameters = newHashMapWithSize( 2 );
         parameters.put( BOOKMARK_KEY, value( maxValue ) );
         parameters.put( BOOKMARKS_KEY, value( values ) );
         return parameters;

driver/src/main/java/org/neo4j/driver/internal/ExplicitTransaction.java

@@ -47,6 +47,7 @@
 
 import static java.util.Collections.emptyMap;
 import static java.util.concurrent.CompletableFuture.completedFuture;
+import static org.neo4j.driver.internal.util.Futures.completedWithNull;
 import static org.neo4j.driver.internal.util.Futures.failedFuture;
 import static org.neo4j.driver.v1.Values.value;
 
@@ -163,7 +164,7 @@ else if ( state == State.ACTIVE || state == State.MARKED_FAILED || state == Stat
         }
         else
         {
-            return completedFuture( null );
+            return completedWithNull();
         }
     }
 
@@ -172,7 +173,7 @@ public CompletionStage<Void> commitAsync()
     {
         if ( state == State.COMMITTED )
         {
-            return completedFuture( null );
+            return completedWithNull();
         }
         else if ( state == State.ROLLED_BACK )
         {
@@ -200,13 +201,13 @@ public CompletionStage<Void> rollbackAsync()
         }
         else if ( state == State.ROLLED_BACK )
         {
-            return completedFuture( null );
+            return completedWithNull();
         }
         else if ( state == State.TERMINATED )
         {
             // transaction has been terminated by RESET and should be rolled back by the database
             state = State.ROLLED_BACK;
-            return completedFuture( null );
+            return completedWithNull();
         }
         else
         {

driver/src/main/java/org/neo4j/driver/internal/InternalDriver.java

@@ -29,7 +29,7 @@
 import org.neo4j.driver.v1.Logging;
 import org.neo4j.driver.v1.Session;
 
-import static java.util.concurrent.CompletableFuture.completedFuture;
+import static org.neo4j.driver.internal.util.Futures.completedWithNull;
 
 public class InternalDriver implements Driver
 {
@@ -116,7 +116,7 @@ public CompletionStage<Void> closeAsync()
             log.info( "Closing driver instance %s", this );
             return sessionFactory.close();
         }
-        return completedFuture( null );
+        return completedWithNull();
     }
 
     public CompletionStage<Void> verifyConnectivity()

driver/src/main/java/org/neo4j/driver/internal/InternalStatementResultCursor.java

@@ -18,7 +18,6 @@
  */
 package org.neo4j.driver.internal;
 
-import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionStage;
@@ -118,9 +117,7 @@ public CompletionStage<List<Record>> listAsync()
     @Override
     public <T> CompletionStage<List<T>> listAsync( Function<Record,T> mapFunction )
     {
-        CompletableFuture<List<T>> resultFuture = new CompletableFuture<>();
-        internalListAsync( new ArrayList<>(), resultFuture, mapFunction );
-        return resultFuture;
+        return pullAllHandler.listAsync( mapFunction );
     }
 
     public CompletionStage<Throwable> failureAsync()
@@ -160,40 +157,4 @@ else if ( record != null )
             }
         } );
     }
-
-    private <T> void internalListAsync( List<T> result, CompletableFuture<List<T>> resultFuture,
-            Function<Record,T> mapFunction )
-    {
-        CompletionStage<Record> recordFuture = nextAsync();
-
-        // use async completion listener because of recursion, otherwise it is possible for
-        // the caller thread to get StackOverflowError when result is large and buffered
-        recordFuture.whenCompleteAsync( ( record, completionError ) ->
-        {
-            Throwable error = Futures.completionExceptionCause( completionError );
-            if ( error != null )
-            {
-                resultFuture.completeExceptionally( error );
-            }
-            else if ( record != null )
-            {
-                T value;
-                try
-                {
-                    value = mapFunction.apply( record );
-                }
-                catch ( Throwable mapError )
-                {
-                    resultFuture.completeExceptionally( mapError );
-                    return;
-                }
-                result.add( value );
-                internalListAsync( result, resultFuture, mapFunction );
-            }
-            else
-            {
-                resultFuture.complete( result );
-            }
-        } );
-    }
 }

driver/src/main/java/org/neo4j/driver/internal/NetworkSession.java

@@ -46,7 +46,7 @@
 import org.neo4j.driver.v1.exceptions.ClientException;
 import org.neo4j.driver.v1.types.TypeSystem;
 
-import static java.util.concurrent.CompletableFuture.completedFuture;
+import static org.neo4j.driver.internal.util.Futures.completedWithNull;
 import static org.neo4j.driver.internal.util.Futures.failedFuture;
 import static org.neo4j.driver.v1.Values.value;
 
@@ -60,9 +60,9 @@ public class NetworkSession implements Session
     protected final Logger logger;
 
     private volatile Bookmark bookmark = Bookmark.empty();
-    private volatile CompletionStage<ExplicitTransaction> transactionStage = completedFuture( null );
-    private volatile CompletionStage<Connection> connectionStage = completedFuture( null );
-    private volatile CompletionStage<InternalStatementResultCursor> resultCursorStage = completedFuture( null );
+    private volatile CompletionStage<ExplicitTransaction> transactionStage = completedWithNull();
+    private volatile CompletionStage<Connection> connectionStage = completedWithNull();
+    private volatile CompletionStage<InternalStatementResultCursor> resultCursorStage = completedWithNull();
 
     private final AtomicBoolean open = new AtomicBoolean( true );
 
@@ -168,7 +168,7 @@ public CompletionStage<Void> closeAsync()
             {
                 if ( cursor == null )
                 {
-                    return completedFuture( null );
+                    return completedWithNull();
                 }
                 return cursor.failureAsync();
             } ).thenCompose( error -> releaseResources().thenApply( ignore ->
@@ -186,7 +186,7 @@ public CompletionStage<Void> closeAsync()
                 }
             } ) );
         }
-        return completedFuture( null );
+        return completedWithNull();
     }
 
     @Override
@@ -274,10 +274,6 @@ public TypeSystem typeSystem()
 
     CompletionStage<Boolean> currentConnectionIsOpen()
     {
-        if ( connectionStage == null )
-        {
-            return completedFuture( false );
-        }
         return connectionStage.handle( ( connection, error ) ->
                 error == null && // no acquisition error
                 connection != null && // some connection has actually been acquired
@@ -363,7 +359,7 @@ private <T> CompletionStage<T> safeExecuteWork( ExplicitTransaction tx, Transact
             CompletionStage<T> result = work.execute( tx );
 
             // protect from given transaction function returning null
-            return result == null ? completedFuture( null ) : result;
+            return result == null ? completedWithNull() : result;
         }
         catch ( Throwable workError )
         {
@@ -459,7 +455,7 @@ private CompletionStage<Connection> acquireConnection( AccessMode mode )
         {
             if ( cursor == null )
             {
-                return completedFuture( null );
+                return completedWithNull();
             }
             // make sure previous result is fully consumed and connection is released back to the pool
             return cursor.failureAsync();
@@ -508,7 +504,7 @@ private CompletionStage<Void> rollbackTransaction()
             {
                 return tx.rollbackAsync();
             }
-            return completedFuture( null );
+            return completedWithNull();
         } ).exceptionally( error ->
         {
             Throwable cause = Futures.completionExceptionCause( error );
@@ -519,13 +515,13 @@ private CompletionStage<Void> rollbackTransaction()
 
     private CompletionStage<Void> releaseConnection()
     {
-        return existingConnectionOrNull().thenCompose( connection ->
+        return connectionStage.thenCompose( connection ->
         {
             if ( connection != null )
             {
                 return connection.release();
             }
-            return completedFuture( null );
+            return completedWithNull();
         } );
     }
 
@@ -574,15 +570,10 @@ private CompletionStage<Void> ensureNoOpenTx( String errorMessage )
     private CompletionStage<ExplicitTransaction> existingTransactionOrNull()
     {
         return transactionStage
-                .exceptionally( error -> null ) // handle previous acquisition failures
+                .exceptionally( error -> null ) // handle previous connection acquisition and tx begin failures
                 .thenApply( tx -> tx != null && tx.isOpen() ? tx : null );
     }
 
-    private CompletionStage<Connection> existingConnectionOrNull()
-    {
-        return connectionStage.exceptionally( error -> null ); // handle previous acquisition failures
-    }
-
     private void ensureSessionIsOpen()
     {
         if ( !open.get() )

driver/src/main/java/org/neo4j/driver/internal/async/ResultCursorsHolder.java

@@ -26,6 +26,7 @@
 import org.neo4j.driver.internal.InternalStatementResultCursor;
 
 import static java.util.concurrent.CompletableFuture.completedFuture;
+import static org.neo4j.driver.internal.util.Futures.completedWithNull;
 
 public class ResultCursorsHolder
 {
@@ -41,14 +42,14 @@ public CompletionStage<Throwable> retrieveNotConsumedError()
     {
         return cursorStages.stream()
                 .map( this::retrieveFailure )
-                .reduce( completedFuture( null ), this::nonNullFailureFromEither );
+                .reduce( completedWithNull(), this::nonNullFailureFromEither );
     }
 
     private CompletionStage<Throwable> retrieveFailure( CompletionStage<InternalStatementResultCursor> cursorStage )
     {
         return cursorStage
                 .exceptionally( cursor -> null )
-                .thenCompose( cursor -> cursor == null ? completedFuture( null ) : cursor.failureAsync() );
+                .thenCompose( cursor -> cursor == null ? completedWithNull() : cursor.failureAsync() );
     }
 
     private CompletionStage<Throwable> nonNullFailureFromEither( CompletionStage<Throwable> stage1,