Source Code Cross Referenced for ResultSetIterator.java in  » RSS-RDF » Jena-2.5.5 » com » hp » hpl » jena » db » impl » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » RSS RDF » Jena 2.5.5 » com.hp.hpl.jena.db.impl 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         *  (c) Copyright 2003, 2004, 2005 2006, 2007, 2008 Hewlett-Packard Development Company, LP
003:         *  All rights reserved.
004:         *
005:         *
006:         */
007:
008:        //=======================================================================
009:        // Package
010:        package com.hp.hpl.jena.db.impl;
011:
012:        //=======================================================================
013:        // Imports
014:        import java.sql.*;
015:        import java.util.*;
016:        import com.hp.hpl.jena.util.iterator.*;
017:        import com.hp.hpl.jena.shared.*;
018:
019:        import org.apache.commons.logging.Log;
020:        import org.apache.commons.logging.LogFactory;
021:
022:        //=======================================================================
023:        /**
024:         * Iterates over an SQL result set returning each row as an ArrayList of
025:         * objects. The returned array is shared at each iteration so calling next() or even hasNext()
026:         * changes the array contents. When the iterator terminates the resources
027:         * are cleaned up and the underlying SQL PreparedStatement is returned to
028:         * the SQLCache pool from whence it came.
029:         * 
030:         * <p>Override the extractRow, getRow, and remove methods in subclasses 
031:         * to return an object collection derived from the row contents instead 
032:         * of the raw row contents.
033:         *
034:         * @author <a href="mailto:der@hplb.hpl.hp.com">Dave Reynolds</a>
035:         * @version $Revision: 1.14 $ on $Date: 2008/01/02 12:08:24 $
036:         */
037:
038:        public class ResultSetIterator implements  ExtendedIterator {
039:
040:            /** The ResultSet being iterated over */
041:            protected ResultSet m_resultSet;
042:
043:            /** The originating SQLcache to return the statement to, can be null */
044:            protected SQLCache m_sqlCache;
045:
046:            /** The source Statement to be cleaned up when the iterator finishes - return it to cache or close it if no cache */
047:            protected PreparedStatement m_statement;
048:
049:            /** If true, clean/close the prepared statement when iterator is closed */
050:            protected boolean m_statementClean = true;
051:
052:            /** The name of the original operation that lead to this statement, can be null if SQLCache is null */
053:            protected String m_opname;
054:
055:            /** The contents of the current row */
056:            protected ArrayList m_row;
057:
058:            /** The number of columns in this result set */
059:            protected int m_nCols;
060:
061:            /** Flag that the iteration has finished */
062:            protected boolean m_finished = false;
063:
064:            /** Flag if we have prefeteched the next row but not yet returned it */
065:            protected boolean m_prefetched = false;
066:
067:            protected static Log logger = LogFactory
068:                    .getLog(ResultSetIterator.class);
069:
070:            /**
071:             * Create an empty iterator.
072:             * Needs to be initialized by reset
073:             * before it can be accessed. Useful to allow generic functions like
074:             * {@link SQLCache#runSQLQuery runSQLQuery}
075:             * to return different iterator types to the client.
076:             */
077:            public ResultSetIterator() {
078:                m_finished = true; // Prevent reading until reset
079:            }
080:
081:            /**
082:             * Iterate over the results of a PreparedStatement generated by an SQLCache
083:             * @param resultSet the result set being iterated over
084:             * @param sourceStatement The source Statement to be cleaned up when the iterator finishes - return it to cache or close it if no cache
085:             * @param cache The originating SQLcache to return the statement to, can be null
086:             * @param opname The name of the original operation that lead to this statement, can be null if SQLCache is null
087:             */
088:            public ResultSetIterator(ResultSet resultSet,
089:                    PreparedStatement sourceStatement, SQLCache cache,
090:                    String opname) {
091:                m_resultSet = resultSet;
092:                m_sqlCache = cache;
093:                m_statement = sourceStatement;
094:                m_opname = opname;
095:            }
096:
097:            /**
098:             * Iterate over the results of a PreparedStatement, close the statement when finished.
099:             * @param resultSet the result set being iterated over
100:             * @param sourceStatement The source Statement to be closed when the iterator finishes
101:             */
102:            public ResultSetIterator(ResultSet resultSet,
103:                    PreparedStatement sourceStatement) {
104:                m_resultSet = resultSet;
105:                m_statement = sourceStatement;
106:            }
107:
108:            /**
109:             * Reset an existing iterator to scan a new result set.
110:             * @param resultSet the result set being iterated over
111:             * @param sourceStatement The source Statement to be cleaned up when the iterator finishes - return it to cache or close it if no cache
112:             * @param cache The originating SQLcache to return the statement to, can be null
113:             * @param opname The name of the original operation that lead to this statement, can be null if SQLCache is null
114:             */
115:            public void reset(ResultSet resultSet,
116:                    PreparedStatement sourceStatement, SQLCache cache,
117:                    String opname) {
118:                m_resultSet = resultSet;
119:                m_sqlCache = cache;
120:                m_statement = sourceStatement;
121:                m_opname = opname;
122:                m_finished = false;
123:                m_prefetched = false;
124:                m_row = null;
125:                m_statementClean = true;
126:            }
127:
128:            /**
129:             * Reset an existing iterator to scan a new result set.
130:             * @param resultSet the result set being iterated over
131:             * @param sourceStatement The source Statement to be cleaned up when the iterator finishes - return it to cache or close it if no cache
132:             * note: the sourceStatement is not closed or returned when the iterator is closed.
133:             */
134:            public void reset(ResultSet resultSet,
135:                    PreparedStatement sourceStatement) {
136:                m_resultSet = resultSet;
137:                m_sqlCache = null;
138:                m_statement = sourceStatement;
139:                m_opname = null;
140:                m_finished = false;
141:                m_prefetched = false;
142:                m_row = null;
143:                m_statementClean = false;
144:            }
145:
146:            /**
147:             * Test if there is a next result to return
148:             */
149:            public boolean hasNext() {
150:                if (!m_finished && !m_prefetched)
151:                    moveForward();
152:                return !m_finished;
153:            }
154:
155:            public Object removeNext() {
156:                cantRemove();
157:                return null;
158:            }
159:
160:            /**
161:             * Return the current row
162:             */
163:            public Object next() {
164:                if (!m_finished && !m_prefetched)
165:                    moveForward();
166:                m_prefetched = false;
167:                if (m_finished) {
168:                    throw new NoSuchElementException();
169:                }
170:                return getRow();
171:            }
172:
173:            /**
174:             * Delete the current row entry
175:             */
176:            public void remove() {
177:                cantRemove();
178:            }
179:
180:            protected void cantRemove() {
181:                throw new UnsupportedOperationException(
182:                        "ResultSetIterator can't remove database rows");
183:            }
184:
185:            /**
186:             * More forward one row. Sets the m_finished flag if there is no more to fetch
187:             */
188:            protected void moveForward() {
189:                try {
190:                    if (!m_finished && m_resultSet.next()) {
191:                        extractRow();
192:                        m_prefetched = true;
193:                    } else {
194:                        close();
195:                    }
196:                } catch (Exception e) {
197:                    //  TODO do we need this catch at all?
198:                    logger.warn("Problem in iterator over db result set, op = "
199:                            + m_opname, e);
200:                    // Added by kers for debugging
201:                    throw new JenaException(e);
202:                }
203:            }
204:
205:            /**
206:             * Extract the current row
207:             * Override in subclasses.
208:             */
209:            protected void extractRow() throws Exception {
210:                if (m_row == null) {
211:                    m_nCols = m_resultSet.getMetaData().getColumnCount();
212:                    m_row = new ArrayList(m_nCols);
213:                    for (int i = 0; i < m_nCols; i++)
214:                        m_row.add(null);
215:                }
216:                for (int i = 0; i < m_nCols; i++) {
217:                    m_row.set(i, m_resultSet.getObject(i + 1));
218:                }
219:            }
220:
221:            /**
222:             * Return the current row,should have already been extracted.
223:             * Override in subclasses.
224:             */
225:            protected Object getRow() {
226:                return m_row;
227:            }
228:
229:            /**
230:             * Clean up the allocated resources - result set and statement.
231:             * If we know of an SQLCache return the statement there, otherwise close it.
232:             */
233:            public void close() {
234:                if (!m_finished) {
235:                    if (m_resultSet != null) {
236:                        try {
237:                            m_resultSet.close();
238:                            m_resultSet = null;
239:                        } catch (SQLException e) {
240:                            logger
241:                                    .warn(
242:                                            "Error while finalizing result set iterator",
243:                                            e);
244:                        }
245:                    }
246:                    if (m_statementClean) {
247:                        if (m_sqlCache != null && m_opname != null) {
248:                            m_sqlCache.returnPreparedSQLStatement(m_statement);
249:                        } else {
250:                            try {
251:                                m_statement.close();
252:                            } catch (SQLException e) {
253:                                logger
254:                                        .warn(
255:                                                "Error while finalizing result set iterator",
256:                                                e);
257:                            }
258:                        }
259:                    }
260:                }
261:                m_finished = true;
262:            }
263:
264:            /**
265:             * Get a singleton result (single column from single row) and close the iterator.
266:             * This may be too specialized but seems to come up a lot - rethink.
267:             */
268:            public Object getSingleton() throws SQLException {
269:                List row = (List) next();
270:                close();
271:                return row.get(0);
272:            }
273:
274:            /**
275:             * Clean up the database cursor. Noramlly the client should read to the end
276:             * or explicity close but....
277:             */
278:            protected void finalize() throws SQLException {
279:                if (!m_finished && m_resultSet != null)
280:                    close();
281:            }
282:
283:            /**
284:                 return a new iterator which delivers all the elements of this iterator and
285:                 then all the elements of the other iterator. Does not copy either iterator;
286:                 they are consumed as the result iterator is consumed.
287:             */
288:            public ExtendedIterator andThen(ClosableIterator other) {
289:                return NiceIterator.andThen(this , other);
290:            }
291:
292:            public Set toSet() {
293:                return NiceIterator.asSet(this );
294:            }
295:
296:            public List toList() {
297:                return NiceIterator.asList(this );
298:            }
299:
300:            /* (non-Javadoc)
301:             * @see com.hp.hpl.jena.util.iterator.ExtendedIterator#filterKeep(com.hp.hpl.jena.util.iterator.Filter)
302:             */
303:            public ExtendedIterator filterKeep(Filter f) {
304:                return new FilterIterator(f, this );
305:            }
306:
307:            /* (non-Javadoc)
308:             * @see com.hp.hpl.jena.util.iterator.ExtendedIterator#filterDrop(com.hp.hpl.jena.util.iterator.Filter)
309:             */
310:            public ExtendedIterator filterDrop(final Filter f) {
311:                Filter notF = new Filter() {
312:                    public boolean accept(Object x) {
313:                        return !f.accept(x);
314:                    }
315:                };
316:                return new FilterIterator(notF, this );
317:            }
318:
319:            /* (non-Javadoc)
320:             * @see com.hp.hpl.jena.util.iterator.ExtendedIterator#mapWith(com.hp.hpl.jena.util.iterator.Map1)
321:             */
322:            public ExtendedIterator mapWith(Map1 map1) {
323:                return new Map1Iterator(map1, this );
324:            }
325:
326:        } // End class
327:
328:        /*
329:         *  (c) Copyright 2003, 2004, 2005, 2006, 2007, 2008 Hewlett-Packard Development Company, LP
330:         *  All rights reserved.
331:         *
332:         * Redistribution and use in source and binary forms, with or without
333:         * modification, are permitted provided that the following conditions
334:         * are met:
335:         * 1. Redistributions of source code must retain the above copyright
336:         *    notice, this list of conditions and the following disclaimer.
337:         * 2. Redistributions in binary form must reproduce the above copyright
338:         *    notice, this list of conditions and the following disclaimer in the
339:         *    documentation and/or other materials provided with the distribution.
340:         * 3. The name of the author may not be used to endorse or promote products
341:         *    derived from this software without specific prior written permission.
342:
343:         * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
344:         * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
345:         * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
346:         * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
347:         * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
348:         * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
349:         * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
350:         * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
351:         * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
352:         * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
353:         */
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