001    /*
002     * Copyright 2009-2016 UnboundID Corp.
003     * All Rights Reserved.
004     */
005    /*
006     * Copyright (C) 2009-2016 UnboundID Corp.
007     *
008     * This program is free software; you can redistribute it and/or modify
009     * it under the terms of the GNU General Public License (GPLv2 only)
010     * or the terms of the GNU Lesser General Public License (LGPLv2.1 only)
011     * as published by the Free Software Foundation.
012     *
013     * This program is distributed in the hope that it will be useful,
014     * but WITHOUT ANY WARRANTY; without even the implied warranty of
015     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
016     * GNU General Public License for more details.
017     *
018     * You should have received a copy of the GNU General Public License
019     * along with this program; if not, see <http://www.gnu.org/licenses>.
020     */
021    package com.unboundid.ldap.sdk;
022    
023    
024    
025    import java.io.Closeable;
026    
027    import com.unboundid.util.NotExtensible;
028    import com.unboundid.util.ThreadSafety;
029    import com.unboundid.util.ThreadSafetyLevel;
030    
031    
032    
033    /**
034     * This class defines an API that may be implemented by a class that provides
035     * access to a sequence of entries, one entry at a time (e.g., entries read from
036     * an LDIF file, or returned as part of an LDAP search).  It provides a
037     * convenient way to operate on a set of entries without regard for the source
038     * of those entries.  Implementations currently available include the
039     * {@link LDAPEntrySource} class, which can be used to iterate across entries
040     * returned from a directory server in response to a search request, and the
041     * {@link com.unboundid.ldif.LDIFEntrySource} class, which can be used to
042     * iterate across entries in an LDIF file.
043     * <BR><BR>
044     * Note that the {@link #close} method MUST be called if the entry source is to
045     * be discarded before guaranteeing that all entries have been read.  The
046     * {@code close} method may be called after all entries have been read, but it
047     * is not required.  All entry source implementations MUST ensure that all
048     * resources are properly released if the caller has read through all entries,
049     * or if an error occurs that prevents the caller from continuing to read
050     * through the entries (i.e., if {@link #nextEntry} throws an
051     * {@link EntrySourceException} and the
052     * {@link EntrySourceException#mayContinueReading()} method returns
053     * {@code false}).
054     * <BR><BR>
055     * <H2>Example</H2>
056     * The following example demonstrates the process that may be used for iterating
057     * across the entries provided by an entry source:
058     * <PRE>
059     * LDIFReader ldifReader = new LDIFReader(ldifFilePath);
060     * EntrySource entrySource = new LDIFEntrySource(ldifReader);
061     *
062     * int entriesRead = 0;
063     * int exceptionsCaught = 0;
064     * try
065     * {
066     *   while (true)
067     *   {
068     *     try
069     *     {
070     *       Entry entry = entrySource.nextEntry();
071     *       if (entry == null)
072     *       {
073     *         // There are no more entries to be read.
074     *         break;
075     *       }
076     *       else
077     *       {
078     *         // Do something with the entry here.
079     *         entriesRead++;
080     *       }
081     *     }
082     *     catch (EntrySourceException e)
083     *     {
084     *       // Some kind of problem was encountered (e.g., a malformed entry
085     *       // found in an LDIF file, or a referral returned from a directory).
086     *       // See if we can continue reading entries.
087     *       exceptionsCaught++;
088     *       if (! e.mayContinueReading())
089     *       {
090     *         break;
091     *       }
092     *     }
093     *   }
094     * }
095     * finally
096     * {
097     *   entrySource.close();
098     * }
099     * </PRE>
100     */
101    @NotExtensible()
102    @ThreadSafety(level=ThreadSafetyLevel.INTERFACE_NOT_THREADSAFE)
103    public abstract class EntrySource
104           implements Closeable
105    {
106      /**
107       * Retrieves the next entry from the entry source, if there is at least one
108       * remaining entry.  This method may block if no entries are immediately
109       * available.
110       *
111       * @return  The next entry from the entry source, or {@code null} if there are
112       *          no more entries to retrieve..
113       *
114       * @throws  EntrySourceException  If a problem occurs while attempting to read
115       *                                the next entry from the entry source.
116       */
117      public abstract Entry nextEntry()
118             throws EntrySourceException;
119    
120    
121    
122      /**
123       * Indicates that this entry source will no longer be needed and any resources
124       * associated with it may be closed.  This method MUST be called if the entry
125       * source is no longer needed before all entries have been read.  It MAY be
126       * called after all entries have been read with no ill effects, but this is
127       * not necessary as the entry source will have already been closed after all
128       * entries have been read.
129       */
130      public abstract void close();
131    }