http://www.mongodb.org: The MongoDB Java Driver uber-artifact, containing the legacy driver, the mongodb-driver, mongodb-driver-core, and bson
  • Various (MongoDB) 
/*
 * Copyright 2008-present MongoDB, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.mongodb;

import com.mongodb.annotations.NotThreadSafe;
import com.mongodb.client.MongoCursor;
import com.mongodb.client.internal.MongoBatchCursorAdapter;
import com.mongodb.client.internal.OperationExecutor;
import com.mongodb.client.model.Collation;
import com.mongodb.client.model.DBCollectionCountOptions;
import com.mongodb.client.model.DBCollectionFindOptions;
import com.mongodb.lang.Nullable;
import com.mongodb.operation.FindOperation;
import org.bson.codecs.Decoder;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.concurrent.TimeUnit;

import static com.mongodb.DBObjects.toDBObject;
import static com.mongodb.assertions.Assertions.notNull;
import static java.util.concurrent.TimeUnit.MILLISECONDS;


An iterator over database results. Doing a find() query on a collection returns a DBCursor.


 An application should ensure that a cursor is closed in all circumstances, e.g. using a try-with-resources statement:


   try (DBCursor cursor = collection.find(query)) {
       while (cursor.hasNext()) {
           System.out.println(cursor.next();
       }
   }



Warning: Calling toArray or length on a DBCursor will irrevocably turn it into an array. This means that, if the cursor was iterating over ten million results (which it was lazily fetching from the database), suddenly there will be a ten-million element array in memory. Before converting to an array, make sure that there are a reasonable number of results using skip() and limit(). 
For example, to get an array of the 1000-1100th elements of a cursor, use



   List<DBObject> obj = collection.find(query).skip(1000).limit(100).toArray();

 See Mongo.getDB(String) for further information about the effective deprecation of this class. 
@mongodb.driver.manualcore/read-operations Read Operations
/**
 * <p>An iterator over database results. Doing a {@code find()} query on a collection returns a {@code DBCursor}.</p>
 * <p> An application should ensure that a cursor is closed in all circumstances, e.g. using a try-with-resources statement:</p>
 * <blockquote><pre>
 *    try (DBCursor cursor = collection.find(query)) {
 *        while (cursor.hasNext()) {
 *            System.out.println(cursor.next();
 *        }
 *    }
 * </pre></blockquote>
 *
 * <p><b>Warning:</b> Calling {@code toArray} or {@code length} on a DBCursor will irrevocably turn it into an array.  This means that, if
 * the cursor was iterating over ten million results (which it was lazily fetching from the database), suddenly there will be a ten-million
 * element array in memory.  Before converting to an array, make sure that there are a reasonable number of results using {@code skip()} and
 * {@code limit()}.
 *
 * <p>For example, to get an array of the 1000-1100th elements of a cursor, use</p>
 *
 * <pre>{@code
 *    List<DBObject> obj = collection.find(query).skip(1000).limit(100).toArray();
 * }</pre>
 *
 * See {@link Mongo#getDB(String)} for further information about the effective deprecation of this class.
 *
 * @mongodb.driver.manual core/read-operations Read Operations
 */
@NotThreadSafe
@SuppressWarnings("deprecation")
public class DBCursor implements Cursor, Iterable<DBObject> {
    private final DBCollection collection;
    private final DBObject filter;
    private final DBCollectionFindOptions findOptions;
    private final OperationExecutor executor;
    private final boolean retryReads;
    private int options;
    private DBDecoderFactory decoderFactory;
    private Decoder<DBObject> decoder;
    private IteratorOrArray iteratorOrArray;
    private DBObject currentObject;
    private int numSeen;
    private boolean closed;
    private final List<DBObject> all = new ArrayList<DBObject>();
    private MongoCursor<DBObject> cursor;
    // This allows us to easily enable/disable finalizer for cleaning up un-closed cursors
    @SuppressWarnings("UnusedDeclaration")// IDEs will say it can be converted to a local variable, resist the urge
    private OptionalFinalizer optionalFinalizer;

    
Initializes a new database cursor.

Params:
  • collection –     collection to use
  • query –          the query filter to apply
  • fields –         keys to return from the query
  • readPreference – the read preference for this query
/**
     * Initializes a new database cursor.
     *
     * @param collection     collection to use
     * @param query          the query filter to apply
     * @param fields         keys to return from the query
     * @param readPreference the read preference for this query
     */
    public DBCursor(final DBCollection collection, final DBObject query, @Nullable final DBObject fields,
                    @Nullable final ReadPreference readPreference) {
        this(collection, query, fields, readPreference, true);
    }

    
Initializes a new database cursor.

Params:
  • collection –     collection to use
  • query –          the query filter to apply
  • fields –         keys to return from the query
  • readPreference – the read preference for this query
  • retryReads –     true if reads should be retried
/**
     * Initializes a new database cursor.
     *
     * @param collection     collection to use
     * @param query          the query filter to apply
     * @param fields         keys to return from the query
     * @param readPreference the read preference for this query
     * @param retryReads     true if reads should be retried
     */
    public DBCursor(final DBCollection collection, final DBObject query, @Nullable final DBObject fields,
                    @Nullable final ReadPreference readPreference, final boolean retryReads) {
        this(collection, query, new DBCollectionFindOptions().projection(fields).readPreference(readPreference), retryReads);

        addOption(collection.getOptions());
        DBObject indexKeys = lookupSuitableHints(query, collection.getHintFields());
        if (indexKeys != null) {
            hint(indexKeys);
        }
    }

    DBCursor(final DBCollection collection, @Nullable final DBObject filter, final DBCollectionFindOptions findOptions) {
        this(collection, filter, findOptions, true);
    }

    DBCursor(final DBCollection collection, @Nullable final DBObject filter, final DBCollectionFindOptions findOptions,
             final boolean retryReads) {
        this(collection, filter, findOptions, collection.getExecutor(), collection.getDBDecoderFactory(),
                collection.getObjectCodec(), retryReads);
    }

    private DBCursor(final DBCollection collection, @Nullable final DBObject filter, final DBCollectionFindOptions findOptions,
                     final OperationExecutor executor, final DBDecoderFactory decoderFactory, final Decoder<DBObject> decoder,
                     final boolean retryReads) {
        this.collection = notNull("collection", collection);
        this.filter = filter;
        this.executor = notNull("executor", executor);
        this.findOptions = notNull("findOptions", findOptions.copy());
        this.decoderFactory = decoderFactory;
        this.decoder = notNull("decoder", decoder);
        this.retryReads = retryReads;
    }

    
Creates a copy of an existing database cursor. The new cursor is an iterator, even if the original was an array.

Returns:the new cursor
/**
     * Creates a copy of an existing database cursor. The new cursor is an iterator, even if the original was an array.
     *
     * @return the new cursor
     */
    public DBCursor copy() {
        return new DBCursor(collection, filter, findOptions, executor, decoderFactory, decoder, retryReads);
    }

    
Checks if there is another object available.

Note: Automatically adds the Bytes.QUERYOPTION_AWAITDATA option to any cursors with the Bytes.QUERYOPTION_TAILABLE option set. For non blocking tailable cursors see tryNext.


Returns:true if there is another object available
@mongodb.driver.manual/core/cursors/#cursor-batches Cursor Batches
/**
     * Checks if there is another object available.
     *
     * <p><em>Note</em>: Automatically adds the {@link Bytes#QUERYOPTION_AWAITDATA} option to any cursors with the
     * {@link Bytes#QUERYOPTION_TAILABLE} option set. For non blocking tailable cursors see {@link #tryNext }.</p>
     *
     * @return true if there is another object available
     * @mongodb.driver.manual /core/cursors/#cursor-batches Cursor Batches
     */
    @Override
    public boolean hasNext() {
        if (closed) {
            throw new IllegalStateException("Cursor has been closed");
        }

        if (cursor == null) {
            FindOperation<DBObject> operation = getQueryOperation(decoder);
            if (operation.getCursorType() == CursorType.Tailable) {
                operation.cursorType(CursorType.TailableAwait);
            }
            initializeCursor(operation);
        }

        boolean hasNext = cursor.hasNext();
        setServerCursorOnFinalizer(cursor.getServerCursor());
        return hasNext;
    }

    
Returns the object the cursor is at and moves the cursor ahead by one.

Note: Automatically adds the Bytes.QUERYOPTION_AWAITDATA option to any cursors with the Bytes.QUERYOPTION_TAILABLE option set. For non blocking tailable cursors see tryNext.


Returns:the next element
@mongodb.driver.manual/core/cursors/#cursor-batches Cursor Batches
/**
     * Returns the object the cursor is at and moves the cursor ahead by one.
     *
     * <p><em>Note</em>: Automatically adds the {@link Bytes#QUERYOPTION_AWAITDATA} option to any cursors with the
     * {@link Bytes#QUERYOPTION_TAILABLE} option set. For non blocking tailable cursors see {@link #tryNext }.</p>
     *
     * @return the next element
     * @mongodb.driver.manual /core/cursors/#cursor-batches Cursor Batches
     */
    @Override
    public DBObject next() {
        checkIteratorOrArray(IteratorOrArray.ITERATOR);
        if (!hasNext()) {
            throw new NoSuchElementException();
        }

        return nextInternal();
    }

    
Non blocking check for tailable cursors to see if another object is available.

Returns the object the cursor is at and moves the cursor ahead by one or
return null if no documents is available.


Throws:
Returns:the next element or null
@mongodb.driver.manual/core/cursors/#cursor-batches Cursor Batches
/**
     * Non blocking check for tailable cursors to see if another object is available.
     *
     * <p>Returns the object the cursor is at and moves the cursor ahead by one or
     * return null if no documents is available.</p>
     *
     * @return the next element or null
     * @throws MongoException if failed
     * @throws IllegalArgumentException if the cursor is not tailable
     * @mongodb.driver.manual /core/cursors/#cursor-batches Cursor Batches
     */
    @Nullable
    public DBObject tryNext() {
        if (cursor == null) {
            FindOperation<DBObject> operation = getQueryOperation(decoder);
            if (!operation.getCursorType().isTailable()) {
                throw new IllegalArgumentException("Can only be used with a tailable cursor");
            }
            initializeCursor(operation);
        }
        DBObject next = cursor.tryNext();
        setServerCursorOnFinalizer(cursor.getServerCursor());
        return currentObject(next);
    }


    
Returns the element the cursor is at.

Returns:the current element
/**
     * Returns the element the cursor is at.
     *
     * @return the current element
     */
    public DBObject curr() {
        return currentObject;
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }

    
Adds a query option. See Bytes.QUERYOPTION_* for list.

Params:
  • option – the option to be added
See Also:
Returns:this so calls can be chained
@mongodb.driver.manual../meta-driver/latest/legacy/mongodb-wire-protocol/#op-query Query Flags
Deprecated:Prefer per-option methods, e.g. cursorType(CursorType), noCursorTimeout(boolean), etc.
/**
     * Adds a query option. See Bytes.QUERYOPTION_* for list.
     *
     * @param option the option to be added
     * @return {@code this} so calls can be chained
     * @see Bytes
     * @mongodb.driver.manual ../meta-driver/latest/legacy/mongodb-wire-protocol/#op-query Query Flags
     * @deprecated Prefer per-option methods, e.g. {@link #cursorType(CursorType)}, {@link #noCursorTimeout(boolean)}, etc.
     */
    @Deprecated
    public DBCursor addOption(final int option) {
        setOptions(this.options |= option);
        return this;
    }

    
Sets the query option - see Bytes.QUERYOPTION_* for list.

Params:
  • options – the bitmask of options
See Also:
Returns:this so calls can be chained
@mongodb.driver.manual../meta-driver/latest/legacy/mongodb-wire-protocol/#op-query Query Flags
/**
     * Sets the query option - see Bytes.QUERYOPTION_* for list.
     *
     * @param options the bitmask of options
     * @return {@code this} so calls can be chained
     * @see Bytes
     * @mongodb.driver.manual ../meta-driver/latest/legacy/mongodb-wire-protocol/#op-query Query Flags
     */
    @Deprecated
    public DBCursor setOptions(final int options) {
        if ((options & Bytes.QUERYOPTION_EXHAUST) != 0) {
            throw new UnsupportedOperationException("exhaust query option is not supported");
        }
        this.options = options;
        return this;
    }

    
Resets the query options.

Returns:this so calls can be chained
@mongodb.driver.manual../meta-driver/latest/legacy/mongodb-wire-protocol/#op-query Query Flags
/**
     * Resets the query options.
     *
     * @return {@code this} so calls can be chained
     * @mongodb.driver.manual ../meta-driver/latest/legacy/mongodb-wire-protocol/#op-query Query Flags
     */
    @Deprecated
    public DBCursor resetOptions() {
        this.options = 0;
        return this;
    }

    
Gets the query options.

Returns:the bitmask of options
@mongodb.driver.manual../meta-driver/latest/legacy/mongodb-wire-protocol/#op-query Query Flags
/**
     * Gets the query options.
     *
     * @return the bitmask of options
     * @mongodb.driver.manual ../meta-driver/latest/legacy/mongodb-wire-protocol/#op-query Query Flags
     */
    @Deprecated
    public int getOptions() {
        return options;
    }

    
Gets the query limit.

Returns:the limit, or 0 if no limit is set
/**
     * Gets the query limit.
     *
     * @return the limit, or 0 if no limit is set
     */
    public int getLimit() {
        return findOptions.getLimit();
    }

    
Gets the batch size.

Returns:the batch size
/**
     * Gets the batch size.
     *
     * @return the batch size
     */
    public int getBatchSize() {
        return findOptions.getBatchSize();
    }

    
Adds a special operator like $comment or $returnKey. For example:

   addSpecial("$returnKey", 1)
   addSpecial("$comment", "this is a special query)



Params:
  • name –  the name of the special query operator
  • value – the value of the special query operator
Returns:this so calls can be chained
@mongodb.driver.manualreference/operator Special Operators
Deprecated:Prefer per-operator methods, e.g. comment(String), explain(), etc.
/**
     * Adds a special operator like $comment or $returnKey. For example:
     * <pre>
     *    addSpecial("$returnKey", 1)
     *    addSpecial("$comment", "this is a special query)
     * </pre>
     *
     * @param name  the name of the special query operator
     * @param value the value of the special query operator
     * @return {@code this} so calls can be chained
     * @mongodb.driver.manual reference/operator Special Operators
     * @deprecated Prefer per-operator methods, e.g. {@link #comment(String)}, {@link #explain()}, etc.
     */
    @SuppressWarnings("deprecation")
    @Deprecated
    public DBCursor addSpecial(@Nullable final String name, @Nullable final Object value) {
        if (name == null || value == null) {
            return this;
        }

        if ("$comment".equals(name)) {
            comment(value.toString());
        } else if ("$explain".equals(name)) {
            findOptions.getModifiers().put("$explain", true);
        } else if ("$hint".equals(name)) {
            if (value instanceof String) {
                hint((String) value);
            } else {
                hint((DBObject) value);
            }
        } else if ("$maxScan".equals(name)) {
            maxScan(((Number) value).intValue());
        } else if ("$maxTimeMS".equals(name)) {
            maxTime(((Number) value).longValue(), MILLISECONDS);
        } else if ("$max".equals(name)) {
            max((DBObject) value);
        } else if ("$min".equals(name)) {
            min((DBObject) value);
        } else if ("$orderby".equals(name)) {
            sort((DBObject) value);
        } else if ("$returnKey".equals(name)) {
            returnKey();
        } else if ("$showDiskLoc".equals(name)) {
            showDiskLoc();
        } else if ("$snapshot".equals(name)) {
            snapshot();
        } else if ("$natural".equals(name)) {
            sort(new BasicDBObject("$natural", ((Number) value).intValue()));
        } else {
            throw new IllegalArgumentException(name + "is not a supported modifier");
        }
        return this;
    }

    
Adds a comment to the query to identify queries in the database profiler output.

Params:
  • comment – the comment that is to appear in the profiler output
Returns:this so calls can be chained
@mongodb.driver.manualreference/operator/meta/comment/ $comment
Since:2.12
/**
     * Adds a comment to the query to identify queries in the database profiler output.
     *
     * @param comment the comment that is to appear in the profiler output
     * @return {@code this} so calls can be chained
     * @mongodb.driver.manual reference/operator/meta/comment/ $comment
     * @since 2.12
     */
    public DBCursor comment(final String comment) {
        findOptions.comment(comment);
        return this;
    }

    
Limits the number of documents a cursor will return for a query.

Params:
  • max – the maximum number of documents to return
See Also:
Returns:this so calls can be chained
@mongodb.driver.manualreference/operator/meta/maxScan/ $maxScan
Since:2.12
Deprecated:Deprecated as of MongoDB 4.0 release
/**
     * Limits the number of documents a cursor will return for a query.
     *
     * @param max the maximum number of documents to return
     * @return {@code this} so calls can be chained
     * @mongodb.driver.manual reference/operator/meta/maxScan/ $maxScan
     * @see #limit(int)
     * @since 2.12
     * @deprecated Deprecated as of MongoDB 4.0 release
     */
    @Deprecated
    public DBCursor maxScan(final int max) {
        findOptions.getModifiers().put("$maxScan", max);
        return this;
    }

    
Specifies an exclusive upper limit for the index to use in a query.

Params:
  • max – a document specifying the fields, and the upper bound values for those fields
Returns:this so calls can be chained
@mongodb.driver.manualreference/operator/meta/max/ $max
Since:2.12
/**
     * Specifies an <em>exclusive</em> upper limit for the index to use in a query.
     *
     * @param max a document specifying the fields, and the upper bound values for those fields
     * @return {@code this} so calls can be chained
     * @mongodb.driver.manual reference/operator/meta/max/ $max
     * @since 2.12
     */
    public DBCursor max(final DBObject max) {
        findOptions.max(max);
        return this;
    }

    
Specifies an inclusive lower limit for the index to use in a query.

Params:
  • min – a document specifying the fields, and the lower bound values for those fields
Returns:this so calls can be chained
@mongodb.driver.manualreference/operator/meta/min/ $min
Since:2.12
/**
     * Specifies an <em>inclusive</em> lower limit for the index to use in a query.
     *
     * @param min a document specifying the fields, and the lower bound values for those fields
     * @return {@code this} so calls can be chained
     * @mongodb.driver.manual reference/operator/meta/min/ $min
     * @since 2.12
     */
    public DBCursor min(final DBObject min) {
        findOptions.min(min);
        return this;
    }

    
Forces the cursor to only return fields included in the index.

Returns:this so calls can be chained
@mongodb.driver.manualreference/operator/meta/returnKey/ $returnKey
Since:2.12
/**
     * Forces the cursor to only return fields included in the index.
     *
     * @return {@code this} so calls can be chained
     * @mongodb.driver.manual reference/operator/meta/returnKey/ $returnKey
     * @since 2.12
     */
    public DBCursor returnKey() {
        findOptions.returnKey(true);
        return this;
    }

    
Modifies the documents returned to include references to the on-disk location of each document. The location will be returned in a property named $diskLoc 
Returns:this so calls can be chained
@mongodb.driver.manualreference/operator/meta/showDiskLoc/ $showDiskLoc
Since:2.12
Deprecated:showDiskLoc has been deprecated in the MongoDB server.  There is no replacement for it.
/**
     * Modifies the documents returned to include references to the on-disk location of each document.  The location will be returned in a
     * property named {@code $diskLoc}
     *
     * @return {@code this} so calls can be chained
     * @mongodb.driver.manual reference/operator/meta/showDiskLoc/ $showDiskLoc
     * @since 2.12
     * @deprecated showDiskLoc has been deprecated in the MongoDB server.  There is no replacement for it.
     */
    @Deprecated
    public DBCursor showDiskLoc() {
        findOptions.getModifiers().put("$showDiskLoc", true);
        return this;
    }

    
Informs the database of indexed fields of the collection in order to improve performance.

Params:
  • indexKeys – a DBObject with fields and direction
Returns:same DBCursor for chaining operations
@mongodb.driver.manualreference/operator/meta/hint/ $hint
/**
     * Informs the database of indexed fields of the collection in order to improve performance.
     *
     * @param indexKeys a {@code DBObject} with fields and direction
     * @return same DBCursor for chaining operations
     * @mongodb.driver.manual reference/operator/meta/hint/ $hint
     */
    public DBCursor hint(final DBObject indexKeys) {
        findOptions.hint(indexKeys);
        return this;
    }

    
Informs the database of an indexed field of the collection in order to improve performance.

Params:
  • indexName – the name of an index
Returns:same DBCursor for chaining operations
@mongodb.driver.manualreference/operator/meta/hint/ $hint
Deprecated:Prefer hint(DBObject)
/**
     * Informs the database of an indexed field of the collection in order to improve performance.
     *
     * @param indexName the name of an index
     * @return same DBCursor for chaining operations
     * @mongodb.driver.manual reference/operator/meta/hint/ $hint
     * @deprecated Prefer {@link #hint(DBObject)}
     */
    @Deprecated
    public DBCursor hint(final String indexName) {
        findOptions.getModifiers().put("$hint", indexName);
        return this;
    }

    
Set the maximum execution time for operations on this cursor.

Params:
  • maxTime –  the maximum time that the server will allow the query to run, before killing the operation. A non-zero value requires
                a server version >= 2.6
  • timeUnit – the time unit
Returns:same DBCursor for chaining operations
@mongodb.server.release2.6
@mongodb.driver.manualreference/operator/meta/maxTimeMS/ $maxTimeMS
Since:2.12.0
/**
     * Set the maximum execution time for operations on this cursor.
     *
     * @param maxTime  the maximum time that the server will allow the query to run, before killing the operation. A non-zero value requires
     *                 a server version &gt;= 2.6
     * @param timeUnit the time unit
     * @return same DBCursor for chaining operations
     * @mongodb.server.release 2.6
     * @mongodb.driver.manual reference/operator/meta/maxTimeMS/ $maxTimeMS
     * @since 2.12.0
     */
    public DBCursor maxTime(final long maxTime, final TimeUnit timeUnit) {
        findOptions.maxTime(maxTime, timeUnit);
        return this;
    }

    
Use snapshot mode for the query. Snapshot mode prevents the cursor from returning a document more than once because an intervening
write operation results in a move of the document. Even in snapshot mode, documents inserted or deleted during the lifetime of the
cursor may or may not be returned.  Currently, snapshot mode may not be used with sorting or explicit hints.

See Also:
Returns:this so calls can be chained
@mongodb.driver.manualreference/operator/meta/snapshot/ $snapshot
Deprecated:Deprecated in MongoDB 3.6 release and removed in MongoDB 4.0 release
/**
     * Use snapshot mode for the query. Snapshot mode prevents the cursor from returning a document more than once because an intervening
     * write operation results in a move of the document. Even in snapshot mode, documents inserted or deleted during the lifetime of the
     * cursor may or may not be returned.  Currently, snapshot mode may not be used with sorting or explicit hints.
     *
     * @return {@code this} so calls can be chained
     *
     * @see com.mongodb.DBCursor#sort(DBObject)
     * @see com.mongodb.DBCursor#hint(DBObject)
     * @mongodb.driver.manual reference/operator/meta/snapshot/ $snapshot
     * @deprecated Deprecated in MongoDB 3.6 release and removed in MongoDB 4.0 release
     */
    @Deprecated
    public DBCursor snapshot() {
        findOptions.getModifiers().put("$snapshot", true);
        return this;
    }

    
Returns an object containing basic information about the execution of the query that created this cursor. This creates a 
DBObject with a number of fields, including but not limited to: 
    
    
  • cursor: cursor type
    • 
    
  • nScanned: number of records examined by the database for this query 
    • 
    
  • n: the number of records that the database returned
    • 
    
  • millis: how long it took the database to execute the query
    • 



Throws:
Returns:a DBObject containing the explain output for this DBCursor's query
@mongodb.driver.manualreference/explain Explain Output
/**
     * Returns an object containing basic information about the execution of the query that created this cursor. This creates a {@code
     * DBObject} with a number of fields, including but not limited to:
     * <ul>
     *     <li><i>cursor:</i> cursor type</li>
     *     <li><i>nScanned:</i> number of records examined by the database for this query </li>
     *     <li><i>n:</i> the number of records that the database returned</li>
     *     <li><i>millis:</i> how long it took the database to execute the query</li>
     * </ul>
     *
     * @return a {@code DBObject} containing the explain output for this DBCursor's query
     * @throws MongoException if the operation failed
     * @mongodb.driver.manual reference/explain Explain Output
     */
    public DBObject explain() {
        return toDBObject(executor.execute(getQueryOperation(collection.getObjectCodec())
                                           .asExplainableOperation(ExplainVerbosity.QUERY_PLANNER),
                                           getReadPreference(), getReadConcern()));
    }

    
Sets the cursor type.

Params:
  • cursorType – the cursor type, which may not be null
Returns:this
Since:3.9
/**
     * Sets the cursor type.
     *
     * @param cursorType the cursor type, which may not be null
     * @return this
     * @since 3.9
     */
    public DBCursor cursorType(final CursorType cursorType) {
        findOptions.cursorType(cursorType);
        return this;
    }

    
Users should not set this under normal circumstances.

Params:
  • oplogReplay – if oplog replay is enabled
Returns:this
Since:3.9
/**
     * Users should not set this under normal circumstances.
     *
     * @param oplogReplay if oplog replay is enabled
     * @return this
     * @since 3.9
     */
    public DBCursor oplogReplay(final boolean oplogReplay) {
        findOptions.oplogReplay(oplogReplay);
        return this;
    }

    
The server normally times out idle cursors after an inactivity period (10 minutes)
to prevent excess memory use. Set this option to prevent that.

Params:
  • noCursorTimeout – true if cursor timeout is disabled
Returns:this
Since:3.9
/**
     * The server normally times out idle cursors after an inactivity period (10 minutes)
     * to prevent excess memory use. Set this option to prevent that.
     *
     * @param noCursorTimeout true if cursor timeout is disabled
     * @return this
     * @since 3.9
     */
    public DBCursor noCursorTimeout(final boolean noCursorTimeout) {
        findOptions.noCursorTimeout(noCursorTimeout);
        return this;
    }

    
Get partial results from a sharded cluster if one or more shards are unreachable (instead of throwing an error).

Params:
  • partial – if partial results for sharded clusters is enabled
Returns:this
Since:3.9
/**
     * Get partial results from a sharded cluster if one or more shards are unreachable (instead of throwing an error).
     *
     * @param partial if partial results for sharded clusters is enabled
     * @return this
     * @since 3.9
     */
    public DBCursor partial(final boolean partial) {
        findOptions.partial(partial);
        return this;
    }

    @SuppressWarnings("deprecation")
    private FindOperation<DBObject> getQueryOperation(final Decoder<DBObject> decoder) {
        FindOperation<DBObject> operation = new FindOperation<DBObject>(collection.getNamespace(), decoder)
                                                .filter(collection.wrapAllowNull(filter))
                                                .batchSize(findOptions.getBatchSize())
                                                .skip(findOptions.getSkip())
                                                .limit(findOptions.getLimit())
                                                .maxAwaitTime(findOptions.getMaxAwaitTime(MILLISECONDS), MILLISECONDS)
                                                .maxTime(findOptions.getMaxTime(MILLISECONDS), MILLISECONDS)
                                                .modifiers(collection.wrapAllowNull(findOptions.getModifiers()))
                                                .projection(collection.wrapAllowNull(findOptions.getProjection()))
                                                .sort(collection.wrapAllowNull(findOptions.getSort()))
                                                .collation(findOptions.getCollation())
                                                .comment(findOptions.getComment())
                                                .hint(collection.wrapAllowNull(findOptions.getHint()))
                                                .min(collection.wrapAllowNull(findOptions.getMin()))
                                                .max(collection.wrapAllowNull(findOptions.getMax()))
                                                .returnKey(findOptions.isReturnKey())
                                                .showRecordId(findOptions.isShowRecordId())
                                                .retryReads(retryReads);

        if ((this.options & Bytes.QUERYOPTION_TAILABLE) != 0) {
            if ((this.options & Bytes.QUERYOPTION_AWAITDATA) != 0) {
                operation.cursorType(CursorType.TailableAwait);
            } else {
                operation.cursorType(CursorType.Tailable);
            }
        } else {
            operation.cursorType(findOptions.getCursorType());
        }
        if ((this.options & Bytes.QUERYOPTION_OPLOGREPLAY) != 0) {
            operation.oplogReplay(true);
        } else {
            operation.oplogReplay(findOptions.isOplogReplay());
        }
        if ((this.options & Bytes.QUERYOPTION_NOTIMEOUT) != 0) {
            operation.noCursorTimeout(true);
        } else {
            operation.noCursorTimeout(findOptions.isNoCursorTimeout());
        }
        if ((this.options & Bytes.QUERYOPTION_PARTIAL) != 0) {
            operation.partial(true);
        } else {
            operation.partial(findOptions.isPartial());
        }
        return operation;
    }

    
Sorts this cursor's elements. This method must be called before getting any object from the cursor.

Params:
  • orderBy – the fields by which to sort
Returns:a cursor pointing to the first element of the sorted results
/**
     * Sorts this cursor's elements. This method must be called before getting any object from the cursor.
     *
     * @param orderBy the fields by which to sort
     * @return a cursor pointing to the first element of the sorted results
     */
    public DBCursor sort(final DBObject orderBy) {
        findOptions.sort(orderBy);
        return this;
    }

    
Limits the number of elements returned. Note: parameter limit should be positive, although a negative value is supported for legacy reason. Passing a negative value will call batchSize(int) which is the preferred method. 
Params:
  • limit – the number of elements to return
Returns:a cursor to iterate the results
@mongodb.driver.manualreference/method/cursor.limit Limit
/**
     * Limits the number of elements returned. Note: parameter {@code limit} should be positive, although a negative value is
     * supported for legacy reason. Passing a negative value will call {@link DBCursor#batchSize(int)} which is the preferred method.
     *
     * @param limit the number of elements to return
     * @return a cursor to iterate the results
     * @mongodb.driver.manual reference/method/cursor.limit Limit
     */
    public DBCursor limit(final int limit) {
        findOptions.limit(limit);
        return this;
    }

    
Limits the number of elements returned in one batch. A cursor typically fetches a batch of result objects and store them
locally.


If batchSize is positive, it represents the size of each batch of objects retrieved. It can be adjusted to optimize performance and limit data transfer.


If batchSize is negative, it will limit of number objects returned, that fit within the max batch size limit (usually 4MB), and cursor will be closed. For example if batchSize is -10, then the server will return a maximum of 10 documents and as many as can fit in 4MB, then close the cursor. Note that this feature is different from limit() in that documents must fit within a maximum size, and it removes the need to send a request to close the cursor server-side.


Params:
  • numberOfElements – the number of elements to return in a batch
Returns:this so calls can be chained
/**
     * <p>Limits the number of elements returned in one batch. A cursor typically fetches a batch of result objects and store them
     * locally.</p>
     *
     * <p>If {@code batchSize} is positive, it represents the size of each batch of objects retrieved. It can be adjusted to optimize
     * performance and limit data transfer.</p>
     *
     * <p>If {@code batchSize} is negative, it will limit of number objects returned, that fit within the max batch size limit (usually
     * 4MB), and cursor will be closed. For example if {@code batchSize} is -10, then the server will return a maximum of 10 documents and
     * as many as can fit in 4MB, then close the cursor. Note that this feature is different from limit() in that documents must fit within
     * a maximum size, and it removes the need to send a request to close the cursor server-side.</p>
     *
     * @param numberOfElements the number of elements to return in a batch
     * @return {@code this} so calls can be chained
     */
    public DBCursor batchSize(final int numberOfElements) {
        findOptions.batchSize(numberOfElements);
        return this;
    }

    
Discards a given number of elements at the beginning of the cursor.

Params:
  • numberOfElements – the number of elements to skip
Throws:
Returns:a cursor pointing to the new first element of the results
/**
     * Discards a given number of elements at the beginning of the cursor.
     *
     * @param numberOfElements the number of elements to skip
     * @return a cursor pointing to the new first element of the results
     * @throws IllegalStateException if the cursor has started to be iterated through
     */
    public DBCursor skip(final int numberOfElements) {
        findOptions.skip(numberOfElements);
        return this;
    }

    @Override
    public long getCursorId() {
        if (cursor != null) {
            ServerCursor serverCursor = cursor.getServerCursor();
            if (serverCursor == null) {
                return 0;
            }
            return serverCursor.getId();
        } else {
            return 0;
        }
    }

    
Returns the number of objects through which the cursor has iterated.

Returns:the number of objects seen
/**
     * Returns the number of objects through which the cursor has iterated.
     *
     * @return the number of objects seen
     */
    public int numSeen() {
        return numSeen;
    }

    @Override
    public void close() {
        closed = true;
        if (cursor != null) {
            cursor.close();
            cursor = null;
            setServerCursorOnFinalizer(null);
        }

        currentObject = null;
    }

    
Declare that this query can run on a secondary server.

See Also:
Returns:a copy of the same cursor (for chaining)
Deprecated:Replaced with ReadPreference.secondaryPreferred()
/**
     * Declare that this query can run on a secondary server.
     *
     * @return a copy of the same cursor (for chaining)
     * @see ReadPreference#secondaryPreferred()
     * @deprecated Replaced with {@link com.mongodb.ReadPreference#secondaryPreferred()}
     */
    @Deprecated
    public DBCursor slaveOk() {
        return addOption(Bytes.QUERYOPTION_SLAVEOK);
    }

    
Creates a copy of this cursor object that can be iterated. Note: - you can iterate the DBCursor itself without calling this method
- no actual data is getting copied.


Note that use of this method does not let you call close the underlying cursor in the case of either an exception or an early
break.  The preferred method of iteration is to use DBCursor as an Iterator, so that you can call close() on it in a finally
block.


Returns:an iterator
/**
     * <p>Creates a copy of this cursor object that can be iterated. Note: - you can iterate the DBCursor itself without calling this method
     * - no actual data is getting copied.</p>
     *
     * <p>Note that use of this method does not let you call close the underlying cursor in the case of either an exception or an early
     * break.  The preferred method of iteration is to use DBCursor as an Iterator, so that you can call close() on it in a finally
     * block.</p>
     *
     * @return an iterator
     */
    @Override
    public Iterator<DBObject> iterator() {
        return this.copy();
    }

    
Converts this cursor to an array.

Throws:
Returns:an array of elements
/**
     * Converts this cursor to an array.
     *
     * @return an array of elements
     * @throws MongoException if failed
     */
    public List<DBObject> toArray() {
        return toArray(Integer.MAX_VALUE);
    }

    
Converts this cursor to an array.

Params:
  • max – the maximum number of objects to return
Throws:
Returns:an array of objects
/**
     * Converts this cursor to an array.
     *
     * @param max the maximum number of objects to return
     * @return an array of objects
     * @throws MongoException if failed
     */
    public List<DBObject> toArray(final int max) {
        checkIteratorOrArray(IteratorOrArray.ARRAY);
        fillArray(max - 1);
        return all;
    }

    
Counts the number of objects matching the query. This does not take limit/skip into consideration, and does initiate a call to the
server.

Throws:
See Also:
Returns:the number of objects
/**
     * Counts the number of objects matching the query. This does not take limit/skip into consideration, and does initiate a call to the
     * server.
     *
     * @return the number of objects
     * @throws MongoException if the operation failed
     * @see DBCursor#size
     */
    public int count() {
        DBCollectionCountOptions countOptions = getDbCollectionCountOptions();
        return (int) collection.getCount(getQuery(), countOptions);
    }

    
Returns the first document that matches the query.

Returns:the first matching document
Since:2.12
/**
     * Returns the first document that matches the query.
     *
     * @return the first matching document
     * @since 2.12
     */
    @Nullable
    public DBObject one() {
        DBCursor findOneCursor = copy().limit(-1);
        try {
            return findOneCursor.hasNext() ? findOneCursor.next() : null;
        } finally {
            findOneCursor.close();
        }
    }

    
Pulls back all items into an array and returns the number of objects. Note: this can be resource intensive.

Throws:
See Also:
Returns:the number of elements in the array
/**
     * Pulls back all items into an array and returns the number of objects. Note: this can be resource intensive.
     *
     * @return the number of elements in the array
     * @throws MongoException if failed
     * @see #count()
     * @see #size()
     */
    public int length() {
        checkIteratorOrArray(IteratorOrArray.ARRAY);
        fillArray(Integer.MAX_VALUE);
        return all.size();
    }

    
For testing only! Iterates cursor and counts objects

Throws:
See Also:
Returns:num objects
/**
     * For testing only! Iterates cursor and counts objects
     *
     * @return num objects
     * @throws MongoException if failed
     * @see #count()
     */
    public int itcount() {
        int n = 0;
        while (this.hasNext()) {
            this.next();
            n++;
        }
        return n;
    }

    
Counts the number of objects matching the query this does take limit/skip into consideration

Throws:
See Also:
Returns:the number of objects
/**
     * Counts the number of objects matching the query this does take limit/skip into consideration
     *
     * @return the number of objects
     * @throws MongoException if the operation failed
     * @see #count()
     */
    public int size() {
        DBCollectionCountOptions countOptions = getDbCollectionCountOptions().skip(findOptions.getSkip()).limit(findOptions.getLimit());
        return (int) collection.getCount(getQuery(), countOptions);
    }

    
Gets the fields to be returned.

Returns:the field selector that cursor used
/**
     * Gets the fields to be returned.
     *
     * @return the field selector that cursor used
     */
    @Nullable
    public DBObject getKeysWanted() {
        return findOptions.getProjection();
    }

    
Gets the query.

Returns:the query that cursor used
/**
     * Gets the query.
     *
     * @return the query that cursor used
     */
    public DBObject getQuery() {
        return filter;
    }

    
Gets the collection.

Returns:the collection that data is pulled from
/**
     * Gets the collection.
     *
     * @return the collection that data is pulled from
     */
    public DBCollection getCollection() {
        return collection;
    }

    @Override
    @Nullable
    public ServerAddress getServerAddress() {
        if (cursor != null) {
            return cursor.getServerAddress();
        } else {
            return null;
        }
    }

    
Sets the read preference for this cursor. See the documentation for ReadPreference for more information. 
Params:
  • readPreference – read preference to use
Returns:this so calls can be chained
/**
     * Sets the read preference for this cursor. See the documentation for {@link ReadPreference} for more information.
     *
     * @param readPreference read preference to use
     * @return {@code this} so calls can be chained
     */
    public DBCursor setReadPreference(final ReadPreference readPreference) {
        findOptions.readPreference(readPreference);
        return this;
    }

    
Gets the default read preference.

Returns:the readPreference used by this cursor
/**
     * Gets the default read preference.
     *
     * @return the readPreference used by this cursor
     */
    public ReadPreference getReadPreference() {
        ReadPreference readPreference = findOptions.getReadPreference();
        if (readPreference != null) {
            return readPreference;
        }
        return collection.getReadPreference();
    }


    
Sets the read concern for this collection.

Params:
  • readConcern – the read concern to use for this collection
Since:3.2
@mongodb.server.release3.2
@mongodb.driver.manualreference/readConcern/ Read Concern
/**
     * Sets the read concern for this collection.
     *
     * @param readConcern the read concern to use for this collection
     * @since 3.2
     * @mongodb.server.release 3.2
     * @mongodb.driver.manual reference/readConcern/ Read Concern
     */
    DBCursor setReadConcern(@Nullable final ReadConcern readConcern) {
        findOptions.readConcern(readConcern);
        return this;
    }

    
Get the read concern for this collection.

Returns:the ReadConcern
Since:3.2
@mongodb.server.release3.2
@mongodb.driver.manualreference/readConcern/ Read Concern
/**
     * Get the read concern for this collection.
     *
     * @return the {@link com.mongodb.ReadConcern}
     * @since 3.2
     * @mongodb.server.release 3.2
     * @mongodb.driver.manual reference/readConcern/ Read Concern
     */
    ReadConcern getReadConcern() {
        ReadConcern readConcern = findOptions.getReadConcern();
        if (readConcern != null) {
            return readConcern;
        }
        return collection.getReadConcern();
    }

    
Returns the collation options

Returns:the collation options
Since:3.4
@mongodb.server.release3.4
/**
     * Returns the collation options
     *
     * @return the collation options
     * @since 3.4
     * @mongodb.server.release 3.4
     */
    @Nullable
    public Collation getCollation() {
        return findOptions.getCollation();
    }

    
Sets the collation options

A null value represents the server default.


Params:
  • collation – the collation options to use
Returns:this
Since:3.4
@mongodb.server.release3.4
/**
     * Sets the collation options
     *
     * <p>A null value represents the server default.</p>
     * @param collation the collation options to use
     * @return this
     * @since 3.4
     * @mongodb.server.release 3.4
     */
    public DBCursor setCollation(@Nullable final Collation collation) {
        findOptions.collation(collation);
        return this;
    }

    
Sets the factory that will be used create a DBDecoder that will be used to decode BSON documents into DBObject instances. 
Params:
  • factory – the DBDecoderFactory
Returns:this so calls can be chained
/**
     * Sets the factory that will be used create a {@code DBDecoder} that will be used to decode BSON documents into DBObject instances.
     *
     * @param factory the DBDecoderFactory
     * @return {@code this} so calls can be chained
     */
    public DBCursor setDecoderFactory(final DBDecoderFactory factory) {
        this.decoderFactory = factory;

        //Not creating new CompoundDBObjectCodec because we don't care about encoder.
        this.decoder = new DBDecoderAdapter(factory.create(), collection, getCollection().getBufferPool());
        return this;
    }

    
Gets the decoder factory that creates the decoder this cursor will use to decode objects from MongoDB.

Returns:the decoder factory.
/**
     * Gets the decoder factory that creates the decoder this cursor will use to decode objects from MongoDB.
     *
     * @return the decoder factory.
     */
    public DBDecoderFactory getDecoderFactory() {
        return decoderFactory;
    }

    @Override
    public String toString() {
        return "DBCursor{"
               + "collection=" + collection
               + ", find=" + findOptions
               + (cursor != null ? (", cursor=" + cursor.getServerCursor()) : "")
               + '}';
    }

    private void initializeCursor(final FindOperation<DBObject> operation) {
        cursor = new MongoBatchCursorAdapter<DBObject>(executor.execute(operation, getReadPreferenceForCursor(), getReadConcern()));
        if (isCursorFinalizerEnabled() && cursor.getServerCursor() != null) {
            optionalFinalizer = new OptionalFinalizer(collection.getDB().getMongo(), collection.getNamespace());
        }
    }

    private boolean isCursorFinalizerEnabled() {
        return collection.getDB().getMongo().getMongoClientOptions().isCursorFinalizerEnabled();
    }

    private void setServerCursorOnFinalizer(@Nullable final ServerCursor serverCursor) {
        if (optionalFinalizer != null) {
            optionalFinalizer.setServerCursor(serverCursor);
        }
    }

    private void checkIteratorOrArray(final IteratorOrArray expected) {
        if (iteratorOrArray == null) {
            iteratorOrArray = expected;
            return;
        }

        if (expected == iteratorOrArray) {
            return;
        }

        throw new IllegalArgumentException("Can't switch cursor access methods");
    }

    private ReadPreference getReadPreferenceForCursor() {
        ReadPreference readPreference = getReadPreference();
        if ((options & Bytes.QUERYOPTION_SLAVEOK) != 0 && !readPreference.isSlaveOk()) {
            readPreference = ReadPreference.secondaryPreferred();
        }
        return readPreference;
    }

    private void fillArray(final int n) {
        checkIteratorOrArray(IteratorOrArray.ARRAY);
        while (n >= all.size() && hasNext()) {
            all.add(nextInternal());
        }
    }

    private DBObject nextInternal() {
        if (iteratorOrArray == null) {
            checkIteratorOrArray(IteratorOrArray.ITERATOR);
        }

        DBObject next = cursor.next();
        setServerCursorOnFinalizer(cursor.getServerCursor());
        return currentObjectNonNull(next);
    }

    @Nullable
    private DBObject currentObject(@Nullable final DBObject newCurrentObject){
        if (newCurrentObject != null) {
            currentObject = newCurrentObject;
            numSeen++;

            DBObject projection = findOptions.getProjection();
            if (projection != null && !(projection.keySet().isEmpty())) {
                currentObject.markAsPartialObject();
            }
        }
        return newCurrentObject;
    }

    private DBObject currentObjectNonNull(final DBObject newCurrentObject){
        currentObject = newCurrentObject;
        numSeen++;

        DBObject projection = findOptions.getProjection();
        if (projection != null && !(projection.keySet().isEmpty())) {
            currentObject.markAsPartialObject();
        }
        return newCurrentObject;
    }

    @Nullable
    private static DBObject lookupSuitableHints(final DBObject query, @Nullable final List<DBObject> hints) {
        if (hints == null) {
            return null;
        }

        Set<String> keys = query.keySet();

        for (final DBObject hint : hints) {
            if (keys.containsAll(hint.keySet())) {
                return hint;
            }
        }
        return null;
    }

    private enum IteratorOrArray {
        ITERATOR,
        ARRAY
    }

    private static class OptionalFinalizer {
        private final Mongo mongo;
        private final MongoNamespace namespace;
        private volatile ServerCursor serverCursor;

        private OptionalFinalizer(final Mongo mongo, final MongoNamespace namespace) {
            this.namespace = notNull("namespace", namespace);
            this.mongo = notNull("mongo", mongo);
        }

        private void setServerCursor(@Nullable final ServerCursor serverCursor) {
            this.serverCursor = serverCursor;
        }

        @Override
        @SuppressWarnings("deprecation")
        protected void finalize() {
            if (serverCursor != null) {
                mongo.addOrphanedCursor(serverCursor, namespace);
            }
        }
    }

    private DBCollectionCountOptions getDbCollectionCountOptions() {
        DBCollectionCountOptions countOptions = new DBCollectionCountOptions()
                .readPreference(getReadPreferenceForCursor())
                .readConcern(getReadConcern())
                .collation(getCollation())
                .maxTime(findOptions.getMaxTime(MILLISECONDS), MILLISECONDS);

        Object hint = findOptions.getHint() != null ? findOptions.getHint() : findOptions.getModifiers().get("$hint");
        if (hint != null) {
            if (hint instanceof String) {
                countOptions.hintString((String) hint);
            } else {
                countOptions.hint((DBObject) hint);
            }
        }
        return countOptions;
    }
}