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    5    * This code is free software; you can redistribute it and/or modify it
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    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
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   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.util.logging;
   27   
   28   /**
   29    * <tt>Handler</tt> that buffers requests in a circular buffer in memory.
   30    * <p>
   31    * Normally this <tt>Handler</tt> simply stores incoming <tt>LogRecords</tt>
   32    * into its memory buffer and discards earlier records.  This buffering
   33    * is very cheap and avoids formatting costs.  On certain trigger
   34    * conditions, the <tt>MemoryHandler</tt> will push out its current buffer
   35    * contents to a target <tt>Handler</tt>, which will typically publish
   36    * them to the outside world.
   37    * <p>
   38    * There are three main models for triggering a push of the buffer:
   39    * <ul>
   40    * <li>
   41    * An incoming <tt>LogRecord</tt> has a type that is greater than
   42    * a pre-defined level, the <tt>pushLevel</tt>.
   43    * <li>
   44    * An external class calls the <tt>push</tt> method explicitly.
   45    * <li>
   46    * A subclass overrides the <tt>log</tt> method and scans each incoming
   47    * <tt>LogRecord</tt> and calls <tt>push</tt> if a record matches some
   48    * desired criteria.
   49    * </ul>
   50    * <p>
   51    * <b>Configuration:</b>
   52    * By default each <tt>MemoryHandler</tt> is initialized using the following
   53    * LogManager configuration properties.  If properties are not defined
   54    * (or have invalid values) then the specified default values are used.
   55    * If no default value is defined then a RuntimeException is thrown.
   56    * <ul>
   57    * <li>   java.util.logging.MemoryHandler.level
   58    *        specifies the level for the <tt>Handler</tt>
   59    *        (defaults to <tt>Level.ALL</tt>).
   60    * <li>   java.util.logging.MemoryHandler.filter
   61    *        specifies the name of a <tt>Filter</tt> class to use
   62    *        (defaults to no <tt>Filter</tt>).
   63    * <li>   java.util.logging.MemoryHandler.size
   64    *        defines the buffer size (defaults to 1000).
   65    * <li>   java.util.logging.MemoryHandler.push
   66    *        defines the <tt>pushLevel</tt> (defaults to <tt>level.SEVERE</tt>).
   67    * <li>   java.util.logging.MemoryHandler.target
   68    *        specifies the name of the target <tt>Handler </tt> class.
   69    *        (no default).
   70    * </ul>
   71    *
   72    * @since 1.4
   73    */
   74   
   75   public class MemoryHandler extends Handler {
   76       private final static int DEFAULT_SIZE = 1000;
   77       private Level pushLevel;
   78       private int size;
   79       private Handler target;
   80       private LogRecord buffer[];
   81       int start, count;
   82   
   83       // Private method to configure a ConsoleHandler from LogManager
   84       // properties and/or default values as specified in the class
   85       // javadoc.
   86       private void configure() {
   87           LogManager manager = LogManager.getLogManager();
   88           String cname = getClass().getName();
   89   
   90           pushLevel = manager.getLevelProperty(cname +".push", Level.SEVERE);
   91           size = manager.getIntProperty(cname + ".size", DEFAULT_SIZE);
   92           if (size <= 0) {
   93               size = DEFAULT_SIZE;
   94           }
   95           setLevel(manager.getLevelProperty(cname +".level", Level.ALL));
   96           setFilter(manager.getFilterProperty(cname +".filter", null));
   97           setFormatter(manager.getFormatterProperty(cname +".formatter", new SimpleFormatter()));
   98       }
   99   
  100       /**
  101        * Create a <tt>MemoryHandler</tt> and configure it based on
  102        * <tt>LogManager</tt> configuration properties.
  103        */
  104       public MemoryHandler() {
  105           sealed = false;
  106           configure();
  107           sealed = true;
  108   
  109           String name = "???";
  110           try {
  111               LogManager manager = LogManager.getLogManager();
  112               name = manager.getProperty("java.util.logging.MemoryHandler.target");
  113               Class clz = ClassLoader.getSystemClassLoader().loadClass(name);
  114               target = (Handler) clz.newInstance();
  115           } catch (Exception ex) {
  116               throw new RuntimeException("MemoryHandler can't load handler \"" + name + "\"" , ex);
  117           }
  118           init();
  119       }
  120   
  121       // Initialize.  Size is a count of LogRecords.
  122       private void init() {
  123           buffer = new LogRecord[size];
  124           start = 0;
  125           count = 0;
  126       }
  127   
  128       /**
  129        * Create a <tt>MemoryHandler</tt>.
  130        * <p>
  131        * The <tt>MemoryHandler</tt> is configured based on <tt>LogManager</tt>
  132        * properties (or their default values) except that the given <tt>pushLevel</tt>
  133        * argument and buffer size argument are used.
  134        *
  135        * @param target  the Handler to which to publish output.
  136        * @param size    the number of log records to buffer (must be greater than zero)
  137        * @param pushLevel  message level to push on
  138        *
  139        * @throws IllegalArgumentException if size is <= 0
  140        */
  141       public MemoryHandler(Handler target, int size, Level pushLevel) {
  142           if (target == null || pushLevel == null) {
  143               throw new NullPointerException();
  144           }
  145           if (size <= 0) {
  146               throw new IllegalArgumentException();
  147           }
  148           sealed = false;
  149           configure();
  150           sealed = true;
  151           this.target = target;
  152           this.pushLevel = pushLevel;
  153           this.size = size;
  154           init();
  155       }
  156   
  157       /**
  158        * Store a <tt>LogRecord</tt> in an internal buffer.
  159        * <p>
  160        * If there is a <tt>Filter</tt>, its <tt>isLoggable</tt>
  161        * method is called to check if the given log record is loggable.
  162        * If not we return.  Otherwise the given record is copied into
  163        * an internal circular buffer.  Then the record's level property is
  164        * compared with the <tt>pushLevel</tt>. If the given level is
  165        * greater than or equal to the <tt>pushLevel</tt> then <tt>push</tt>
  166        * is called to write all buffered records to the target output
  167        * <tt>Handler</tt>.
  168        *
  169        * @param  record  description of the log event. A null record is
  170        *                 silently ignored and is not published
  171        */
  172       public synchronized void publish(LogRecord record) {
  173           if (!isLoggable(record)) {
  174               return;
  175           }
  176           int ix = (start+count)%buffer.length;
  177           buffer[ix] = record;
  178           if (count < buffer.length) {
  179               count++;
  180           } else {
  181               start++;
  182               start %= buffer.length;
  183           }
  184           if (record.getLevel().intValue() >= pushLevel.intValue()) {
  185               push();
  186           }
  187       }
  188   
  189       /**
  190        * Push any buffered output to the target <tt>Handler</tt>.
  191        * <p>
  192        * The buffer is then cleared.
  193        */
  194       public synchronized void push() {
  195           for (int i = 0; i < count; i++) {
  196               int ix = (start+i)%buffer.length;
  197               LogRecord record = buffer[ix];
  198               target.publish(record);
  199           }
  200           // Empty the buffer.
  201           start = 0;
  202           count = 0;
  203       }
  204   
  205       /**
  206        * Causes a flush on the target <tt>Handler</tt>.
  207        * <p>
  208        * Note that the current contents of the <tt>MemoryHandler</tt>
  209        * buffer are <b>not</b> written out.  That requires a "push".
  210        */
  211       public void flush() {
  212           target.flush();
  213       }
  214   
  215       /**
  216        * Close the <tt>Handler</tt> and free all associated resources.
  217        * This will also close the target <tt>Handler</tt>.
  218        *
  219        * @exception  SecurityException  if a security manager exists and if
  220        *             the caller does not have <tt>LoggingPermission("control")</tt>.
  221        */
  222       public void close() throws SecurityException {
  223           target.close();
  224           setLevel(Level.OFF);
  225       }
  226   
  227       /**
  228        * Set the <tt>pushLevel</tt>.  After a <tt>LogRecord</tt> is copied
  229        * into our internal buffer, if its level is greater than or equal to
  230        * the <tt>pushLevel</tt>, then <tt>push</tt> will be called.
  231        *
  232        * @param newLevel the new value of the <tt>pushLevel</tt>
  233        * @exception  SecurityException  if a security manager exists and if
  234        *             the caller does not have <tt>LoggingPermission("control")</tt>.
  235        */
  236       public void setPushLevel(Level newLevel) throws SecurityException {
  237           if (newLevel == null) {
  238               throw new NullPointerException();
  239           }
  240           LogManager manager = LogManager.getLogManager();
  241           checkAccess();
  242           pushLevel = newLevel;
  243       }
  244   
  245       /**
  246        * Get the <tt>pushLevel</tt>.
  247        *
  248        * @return the value of the <tt>pushLevel</tt>
  249        */
  250       public synchronized Level getPushLevel() {
  251           return pushLevel;
  252       }
  253   
  254       /**
  255        * Check if this <tt>Handler</tt> would actually log a given
  256        * <tt>LogRecord</tt> into its internal buffer.
  257        * <p>
  258        * This method checks if the <tt>LogRecord</tt> has an appropriate level and
  259        * whether it satisfies any <tt>Filter</tt>.  However it does <b>not</b>
  260        * check whether the <tt>LogRecord</tt> would result in a "push" of the
  261        * buffer contents. It will return false if the <tt>LogRecord</tt> is null.
  262        * <p>
  263        * @param record  a <tt>LogRecord</tt>
  264        * @return true if the <tt>LogRecord</tt> would be logged.
  265        *
  266        */
  267       public boolean isLoggable(LogRecord record) {
  268           return super.isLoggable(record);
  269       }
  270   }

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