1 /*
2 * $Source$
3 * $Revision$
4 *
5 * Copyright (C) 2000 William Chesters
6 *
7 * Part of Melati (http://melati.org), a framework for the rapid
8 * development of clean, maintainable web applications.
9 *
10 * Melati is free software; Permission is granted to copy, distribute
11 * and/or modify this software under the terms either:
12 *
13 * a) the GNU General Public License as published by the Free Software
14 * Foundation; either version 2 of the License, or (at your option)
15 * any later version,
16 *
17 * or
18 *
19 * b) any version of the Melati Software License, as published
20 * at http://melati.org
21 *
22 * You should have received a copy of the GNU General Public License and
23 * the Melati Software License along with this program;
24 * if not, write to the Free Software Foundation, Inc.,
25 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA to obtain the
26 * GNU General Public License and visit http://melati.org to obtain the
27 * Melati Software License.
28 *
29 * Feel free to contact the Developers of Melati (http://melati.org),
30 * if you would like to work out a different arrangement than the options
31 * outlined here. It is our intention to allow Melati to be used by as
32 * wide an audience as possible.
33 *
34 * This program is distributed in the hope that it will be useful,
35 * but WITHOUT ANY WARRANTY; without even the implied warranty of
36 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
37 * GNU General Public License for more details.
38 *
39 * Contact details for copyright holder:
40 *
41 * William Chesters <williamc At paneris.org>
42 * http://paneris.org/~williamc
43 * Obrechtstraat 114, 2517VX Den Haag, The Netherlands
44 */
45
46 package org.melati.poem;
47
48 import java.util.NoSuchElementException;
49 import java.sql.ResultSet;
50 import java.sql.SQLException;
51 import org.melati.poem.util.SkipEnumeration;
52
53 /**
54 * An <code>Enumeration</code> created by filtering a
55 * <code>ResultSet</code> according to an abstract
56 * function applied to each element of the <code>ResultSet</code>.
57 * <p>
58 * Implementations must provide {@link #mapped(ResultSet)}.
59 */
60 public abstract class ResultSetEnumeration<T> implements SkipEnumeration<T> {
61 private final ResultSet resultSet;
62 private int more = -1;
63
64 /**
65 * Constructor.
66 * @param resultSet the ResultSet property
67 */
68 public ResultSetEnumeration(ResultSet resultSet) {
69 this.resultSet = resultSet;
70 }
71
72 private int resultSetNext() throws SQLException {
73 boolean hasNext;
74 try {
75 hasNext = resultSet.next();
76 } catch (SQLException e) {
77 // Assumed to be closed resultset
78 return 0;
79 }
80 if (hasNext)
81 return 1;
82 else {
83 try {
84 resultSet.close();
85 } catch (SQLException e) {
86 throw new SQLSeriousPoemException(e);
87 }
88 return 0;
89 }
90 }
91
92 /**
93 * {@inheritDoc}
94 * @see java.util.Enumeration#hasMoreElements()
95 */
96 public synchronized boolean hasMoreElements() {
97 try {
98 if (more == -1)
99 more = resultSetNext();
100 return more == 1;
101 } catch (SQLException e) {
102 throw new SQLSeriousPoemException(e);
103 }
104 }
105
106 protected abstract Object mapped(ResultSet resultSetP)
107 throws SQLException, NoSuchRowPoemException;
108
109 /**
110 * Return the next element.
111 * <p>
112 * NOTE A {@link RowDisappearedPoemException} might be thrown
113 * but does not prevent subsequent use of the object.
114 * @see java.util.Enumeration#nextElement()
115 */
116 @SuppressWarnings("unchecked")
117 public synchronized T nextElement() throws NoSuchElementException {
118 try {
119 if (more == -1)
120 more = resultSetNext();
121
122 if (more == 0)
123 throw new NoSuchElementException();
124
125 try {
126 return (T) mapped(resultSet);
127 }
128 finally {
129 more = resultSetNext();
130 }
131 } catch (SQLException e) {
132 throw new SQLSeriousPoemException(e);
133 } catch (NoSuchRowPoemException e) {
134 throw new RowDisappearedPoemException(e);
135 }
136 }
137
138 /**
139 * {@inheritDoc}
140 * @see org.melati.poem.util.SkipEnumeration#skip()
141 */
142 public synchronized void skip() throws NoSuchElementException {
143 try {
144 if (more == -1)
145 more = resultSetNext();
146 if (more == 0)
147 throw new NoSuchElementException();
148 more = resultSetNext();
149 } catch (SQLException e) {
150 throw new SQLSeriousPoemException(e);
151 }
152 }
153 }