001    package log;
002    
003    import java.io.*;
004    
005    /**
006     * A stream that can be used to read and process log files.
007     *
008     * <p>The LogInputStream will take an {@link InputStream} and try to interpret the data from that stream as
009     * a log file. You can then obtain the {@link LogEntry LogEntries} in the order they were put into the log
010     * by calling {@link #readEntry}.</p>
011     *
012     * <p><code>LogInputStreams</code> can be filtered in which case you will only see the LogEntries that are
013     * {@link LogEntryFilter#accept accepted} by the {@link LogEntryFilter filter}.</p>
014     *
015     * @author Steffen Zschaler
016     * @version 2.0 14/07/1999
017     * @since v2.0
018     */
019    public class LogInputStream extends Object implements Serializable {
020    
021        /**
022         * The input stream that backs this stream.
023         */
024        protected InputStream m_isSource;
025    
026        /**
027         * The object input stream that is build on top of the input stream. This objects in this stream are
028         * expected to be {@link LogEntry LogEntries}.
029         */
030        protected ObjectInputStream m_oisSource;
031    
032        /**
033         * The filter to be applied on the stream, if any.
034         */
035        protected LogEntryFilter m_lefFilter;
036    
037        /**
038         * Create a new LogInputStream. There will be no filter.
039         *
040         * @param isSource the InputStream that is the base for this stream.
041         *
042         * @exception IOException if an error occured or the stream is not a valid log file.
043         */
044        public LogInputStream(InputStream isSource) throws IOException {
045            this(isSource, null);
046        }
047    
048        /**
049         * Create a new LogInputStream.
050         *
051         * @param isSource the InputStream that is the base for this stream.
052         * @param lef the filter to be applied on the stream.
053         *
054         * @exception IOException if an error occured or the stream is not a valid log file.
055         */
056        public LogInputStream(InputStream isSource, LogEntryFilter lef) throws IOException {
057    
058            super();
059    
060            m_isSource = isSource;
061    
062            // skip the leading zero
063            m_isSource.skip(1);
064    
065            m_oisSource = new ObjectInputStream(m_isSource);
066    
067            m_lefFilter = lef;
068        }
069    
070        /**
071         * Close the stream and all streams that it relies on.
072         *
073         * @exception IOException if there was an error on closing.
074         *
075         * @override Never
076         */
077        public void close() throws IOException {
078            m_oisSource.close();
079            m_isSource.close();
080    
081            m_oisSource = null;
082            m_isSource = null;
083        }
084    
085        /**
086         * Read the next log entry that is {@link LogEntryFilter#accept accepted} by the filter from the stream.
087         *
088         * @exception IOException if an <code>IOException</code> occurred while reading from the underlying stream.
089         * Especially, this may be an <code>EOFException</code> if the end of the stream has been reached. This is
090         * the only way to find out whether there are more entries in the stream.
091         * @exception ClassNotFoundException if the exception was thrown by the underlying stream.
092         *
093         * @override Never
094         */
095        public LogEntry readEntry() throws IOException, ClassNotFoundException {
096    
097            while (true) {
098                try {
099                    LogEntry le = (LogEntry)m_oisSource.readObject();
100    
101                    if ((m_lefFilter == null) || (m_lefFilter.accept(le))) {
102                        return le;
103                    }
104                }
105                catch (StreamCorruptedException sce) {
106                    m_oisSource = new ObjectInputStream(m_isSource);
107                }
108            }
109        }
110    }