Refactor Scanner related code (#2592)

Author: brfrn169

core/src/main/java/com/scalar/db/common/AbstractScanner.java

@@ -0,0 +1,60 @@
+package com.scalar.db.common;
+
+import com.google.errorprone.annotations.concurrent.LazyInit;
+import com.scalar.db.api.Result;
+import com.scalar.db.api.Scanner;
+import com.scalar.db.exception.storage.ExecutionException;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+import javax.annotation.Nonnull;
+import javax.annotation.concurrent.NotThreadSafe;
+
+public abstract class AbstractScanner implements Scanner {
+
+  @LazyInit private ScannerIterator scannerIterator;
+
+  @Override
+  @Nonnull
+  public Iterator<Result> iterator() {
+    if (scannerIterator == null) {
+      scannerIterator = new ScannerIterator(this);
+    }
+    return scannerIterator;
+  }
+
+  @NotThreadSafe
+  public static class ScannerIterator implements Iterator<Result> {
+
+    private final Scanner scanner;
+    private Result next;
+
+    public ScannerIterator(Scanner scanner) {
+      this.scanner = Objects.requireNonNull(scanner);
+    }
+
+    @Override
+    public boolean hasNext() {
+      if (next != null) {
+        return true;
+      }
+
+      try {
+        return (next = scanner.one().orElse(null)) != null;
+      } catch (ExecutionException e) {
+        throw new RuntimeException(e.getMessage(), e);
+      }
+    }
+
+    @Override
+    public Result next() {
+      if (!hasNext()) {
+        throw new NoSuchElementException();
+      }
+
+      Result ret = next;
+      next = null;
+      return ret;
+    }
+  }
+}

core/src/main/java/com/scalar/db/common/EmptyScanner.java

@@ -6,7 +6,10 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.Optional;
+import javax.annotation.Nonnull;
+import javax.annotation.concurrent.NotThreadSafe;
 
+@NotThreadSafe
 public class EmptyScanner implements Scanner {
 
   @Override
@@ -23,6 +26,7 @@ public List<Result> all() {
   public void close() {}
 
   @Override
+  @Nonnull
   public Iterator<Result> iterator() {
     return Collections.emptyIterator();
   }

core/src/main/java/com/scalar/db/common/FilterableScanner.java

@@ -1,6 +1,5 @@
 package com.scalar.db.common;
 
-import com.google.errorprone.annotations.concurrent.LazyInit;
 import com.scalar.db.api.Result;
 import com.scalar.db.api.Scan;
 import com.scalar.db.api.Scanner;
@@ -11,22 +10,19 @@
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Optional;
 import java.util.Set;
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
 
 @NotThreadSafe
-public class FilterableScanner implements Scanner {
+public class FilterableScanner extends AbstractScanner {
 
   private final Scanner scanner;
   private final List<String> projections;
   private final Set<Conjunction> conjunctions;
   @Nullable private Integer left = null;
-  @LazyInit private ScannerIterator scannerIterator;
 
   public FilterableScanner(Selection selection, Scanner scanner) {
     this.scanner = scanner;
@@ -72,15 +68,6 @@ public List<Result> all() throws ExecutionException {
     return ret;
   }
 
-  @Override
-  @Nonnull
-  public Iterator<Result> iterator() {
-    if (scannerIterator == null) {
-      scannerIterator = new ScannerIterator(this);
-    }
-    return scannerIterator;
-  }
-
   @Override
   public void close() throws IOException {
     scanner.close();

core/src/main/java/com/scalar/db/common/ScannerIterator.java

@@ -5,22 +5,18 @@
 import com.datastax.driver.core.ResultSet;
 import com.datastax.driver.core.Row;
 import com.scalar.db.api.Result;
-import com.scalar.db.api.Scanner;
-import com.scalar.db.common.ScannerIterator;
+import com.scalar.db.common.AbstractScanner;
 import java.util.ArrayList;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Optional;
 import javax.annotation.Nonnull;
 import javax.annotation.concurrent.NotThreadSafe;
 
 @NotThreadSafe
-public final class ScannerImpl implements Scanner {
+public final class ScannerImpl extends AbstractScanner {
   private final ResultSet resultSet;
   private final ResultInterpreter resultInterpreter;
 
-  private ScannerIterator scannerIterator;
-
   public ScannerImpl(ResultSet resultSet, ResultInterpreter resultInterpreter) {
     this.resultSet = checkNotNull(resultSet);
     this.resultInterpreter = checkNotNull(resultInterpreter);
@@ -44,15 +40,6 @@ public List<Result> all() {
     return results;
   }
 
-  @Override
-  @Nonnull
-  public Iterator<Result> iterator() {
-    if (scannerIterator == null) {
-      scannerIterator = new ScannerIterator(this);
-    }
-    return scannerIterator;
-  }
-
   @Override
   public void close() {}
 }

core/src/main/java/com/scalar/db/storage/cassandra/ScannerImpl.java

@@ -4,8 +4,7 @@
 
 import com.azure.cosmos.models.FeedResponse;
 import com.scalar.db.api.Result;
-import com.scalar.db.api.Scanner;
-import com.scalar.db.common.ScannerIterator;
+import com.scalar.db.common.AbstractScanner;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -16,12 +15,11 @@
 import javax.annotation.concurrent.NotThreadSafe;
 
 @NotThreadSafe
-public final class ScannerImpl implements Scanner {
+public final class ScannerImpl extends AbstractScanner {
 
   private final ResultInterpreter resultInterpreter;
   private Iterator<FeedResponse<Record>> recordsPages;
   private Iterator<Record> currentPageRecords;
-  private ScannerIterator scannerIterator;
 
   /**
    * Create a Scanner for Cosmos DB query operations
@@ -73,15 +71,6 @@ public List<Result> all() {
     return ret;
   }
 
-  @Override
-  @Nonnull
-  public Iterator<Result> iterator() {
-    if (scannerIterator == null) {
-      scannerIterator = new ScannerIterator(this);
-    }
-    return scannerIterator;
-  }
-
   @Override
   public void close() {}
 }

core/src/main/java/com/scalar/db/storage/cosmos/ScannerImpl.java

@@ -2,18 +2,17 @@
 
 import com.google.common.collect.ImmutableList;
 import com.scalar.db.api.Result;
-import com.scalar.db.api.Scanner;
+import com.scalar.db.common.AbstractScanner;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.util.Collections;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Optional;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.NotThreadSafe;
 
 @NotThreadSafe
-public final class SingleRecordScanner implements Scanner {
+public final class SingleRecordScanner extends AbstractScanner {
 
   @Nullable private Record record;
   private final ResultInterpreter resultInterpreter;
@@ -48,12 +47,6 @@ record = null;
     }
   }
 
-  @Override
-  @Nonnull
-  public Iterator<Result> iterator() {
-    return all().iterator();
-  }
-
   @Override
   public void close() {}
 }

core/src/main/java/com/scalar/db/storage/cosmos/SingleRecordScanner.java

@@ -1,11 +1,9 @@
 package com.scalar.db.storage.dynamo;
 
 import com.scalar.db.api.Result;
-import com.scalar.db.api.Scanner;
-import com.scalar.db.common.ScannerIterator;
+import com.scalar.db.common.AbstractScanner;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.util.Collections;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
@@ -17,12 +15,11 @@
 import software.amazon.awssdk.services.dynamodb.model.GetItemResponse;
 
 @NotThreadSafe
-public final class GetItemScanner implements Scanner {
+public final class GetItemScanner extends AbstractScanner {
   private final Map<String, AttributeValue> item;
   private final ResultInterpreter resultInterpreter;
 
   private boolean hasNext;
-  private ScannerIterator scannerIterator;
 
   @SuppressFBWarnings("EI_EXPOSE_REP2")
   public GetItemScanner(
@@ -61,15 +58,6 @@ public List<Result> all() {
     return Collections.singletonList(result);
   }
 
-  @Override
-  @Nonnull
-  public Iterator<Result> iterator() {
-    if (scannerIterator == null) {
-      scannerIterator = new ScannerIterator(this);
-    }
-    return scannerIterator;
-  }
-
   @Override
   public void close() {}
 }

core/src/main/java/com/scalar/db/storage/dynamo/GetItemScanner.java

@@ -1,8 +1,7 @@
 package com.scalar.db.storage.dynamo;
 
 import com.scalar.db.api.Result;
-import com.scalar.db.api.Scanner;
-import com.scalar.db.common.ScannerIterator;
+import com.scalar.db.common.AbstractScanner;
 import com.scalar.db.storage.dynamo.request.PaginatedRequest;
 import com.scalar.db.storage.dynamo.request.PaginatedRequestResponse;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
@@ -17,7 +16,7 @@
 import software.amazon.awssdk.services.dynamodb.model.AttributeValue;
 
 @NotThreadSafe
-public class QueryScanner implements Scanner {
+public class QueryScanner extends AbstractScanner {
 
   private final PaginatedRequest request;
   private final ResultInterpreter resultInterpreter;
@@ -26,8 +25,6 @@ public class QueryScanner implements Scanner {
   @Nullable private Integer remainingLimit;
   @Nullable private Map<String, AttributeValue> lastEvaluatedKey;
 
-  private ScannerIterator scannerIterator;
-
   @SuppressFBWarnings("EI_EXPOSE_REP2")
   public QueryScanner(PaginatedRequest request, int limit, ResultInterpreter resultInterpreter) {
     this.request = request;
@@ -95,15 +92,6 @@ public List<Result> all() {
     return ret;
   }
 
-  @Override
-  @Nonnull
-  public Iterator<Result> iterator() {
-    if (scannerIterator == null) {
-      scannerIterator = new ScannerIterator(this);
-    }
-    return scannerIterator;
-  }
-
   @Override
   public void close() {}
 }