001/*
002 * Copyright 2009-2017 UnboundID Corp.
003 * All Rights Reserved.
004 */
005/*
006 * Copyright (C) 2009-2017 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 */
021package com.unboundid.ldap.sdk;
022
023
024
025import java.io.Closeable;
026
027import com.unboundid.util.NotExtensible;
028import com.unboundid.util.ThreadSafety;
029import 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)
103public 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}