1    /
2     * BerkeleyDBStorageDemo is a Storage implementation that stores 
3     * serialized objects into the Berekeley DB. One object is stored in each
4     * node of Btree with object id. 
5     * 

6     * We assume for now that something higher-level (e.g., a Cache object)
7     * will only tell us to write the object when it needs to (i.e., rather
8     * than after every change). Hence this implementation writes 
9     * immediately on a put. Similarly, we do no caching of objects for get() 
10    * operations.
11    * 

12    * $Id: BerkeleyDBStorageDemo.java,v 1.5 2002/08/19 11:20 kikim Exp $
13    
14    *  See the file LICENSE for redistribution information.
15    
16    *  Copyright (c) 1997-2001
17    *	 Sleepycat Software.  All rights reserved.
18    
19    * Implementation of the Storage interface that uses the GPL'd JSX classes:
20    * 
21    *     http://www.csse.monash.edu.au/~bren/JSX/
22    * 
23    * to save and restore objects as XML files.
24    */

25   package edu.vt.cs.collab.cork.storage;

26   import com.sleepycat.db.*;
27   import java.io.File;
28   import java.io.FileNotFoundException;
29   import java.io.InputStreamReader;
30   import java.io.IOException;
31   import java.io.PrintStream;
32   import java.io.*;
33   import java.util.Enumeration;
34   import java.util.Vector;
35   import JSX.*;

36   import edu.vt.cs.collab.cork.*;

37   public class BerkeleyDBStorageDemo implements Serializable, Storage
38   {
39     /
40	  * Nonvolatile persistent object storage file name.
41      * table is database handle 
42	  */ 

43      private static final String FileName = "BDBCorkTest.db";	
44      private Db table;

45     /
46      * Constructs a new BerkeleyDBStorage object. 
47      * Create database handler and set flags for retrieving values by key.
48      * Also set error stream and prefix for error messages.
49      * Open database with the specified mode
50      * 
51      */
	
52       public BerkeleyDBStorageDemo()
53       {
54		try
55		{
56			table = new Db(null, 0);
		
57			table.set_flags(Db.DB_RECNUM);
		
58			table.set_error_stream(System.err);
59			table.set_errpfx("BDBCorkTest");
60			table.open(FileName, null, Db.DB_BTREE, Db.DB_CREATE, 0644);
61		}
62		catch (DbException dbe)
63           {
64                      System.out.println(dbe.toString());
65           }
66		catch(IOException ioe)
67		{
68			System.out.println(ioe.toString());
69		}
		
70       }


71	/
72	 * Here's an example of how we can extend a Dbt(Berkeley DB data structure)
73	 * in a straightforward way to allow easy storage/retrieval of objects, or 
74	 * whatever kind of data you wish.  We've declared it as a static inner
75     * class, but it need not be.
76	 */

77       static class ObjectDbt extends Dbt
78       {
79         ObjectDbt()
80         {
81            set_flags(Db.DB_DBT_MALLOC); // Berekeley DB allocates a properly sized byte array 
82	               	                   // to contain the data.   
83         }
84		/
85		 * Using Object Byte Streams, serialize the object
86		 * then create XML output using JSX API
87		 * then transform XML output into Dbt(Berkeley DB data structure).
88		 */
89		ObjectDbt(Object obj)
90		{
91			 try
92                   {
93      		    ByteArrayOutputStream baos = new ByteArrayOutputStream();
                 
94                     ObjOut out = new ObjOut(baos); //using JSX API
				 
95			    out.writeObject(obj);
96                     out.flush();
				 
97                     byte[] outbytes = baos.toByteArray();
98			    out.close();
99			    set_data(outbytes);
100			    set_size(outbytes.length);
101			 }
102			 catch(IOException ioe)
103			 {
104			   System.out.println(ioe.toString());
105			 }	
106		}//ObjectDbt(Object obj);
		
107    }// Class ObjectDbt

108	/
109      * Puts the specified element into the Storage object, using the specified
110      * key.  The element may be retrieved by doing a get() with the same 
111      * key.  The key and the element cannot be null.
112      * @param key the specified object id
113      * @param value the specified element 
114      * @return the old value of the key, or null if it did not have one.
115      * @exception NullPointerException If the value of the specified element is null.
116      * @see Storage#get
117      */

118	public Object put(ObjectID key, Object value)
119	{
		
120	       /* 
121		* Doing this here so that at least we won't blow away a file
122     	* if we get a null value.
123     	*/
 
124	        if (key == null)
125	           throw new NullPointerException("Null key in put(). value=" + value);
126 	        if (value == null)
127	           throw new NullPointerException("Null value in put(). key=" + key);

128		    try
129                 {
130		       /
131			*  Wrapping object to Dbt type
132			*/
			      
133			ObjectDbt dbtKey = new ObjectDbt(key);
134			ObjectDbt dbtData = new ObjectDbt(value);
				 
135		       /
136			*  Add to database, if key already exists, print out error message
137			*/
138                     int err;
		 
139                     if ((err = table.put(null, dbtKey, dbtData, 0)) == Db.DB_KEYEXIST) 
140  	         	      {
141		        	     System.out.println("BDBTest:" + dbtKey + " already exists.");
142                     }
		 
143                     table.sync(0); // flushing all modified records from database cache to disk
144            }
145            catch (DbException dbe)
146            {
147                System.out.println(dbe.toString());
148            }
  
149	         return value;

150	}//put();
	
151	/
152      * Gets the object associated with the specified key in the Storage object.
153      * @param key the specified object id
154      * @returns the element for the key, or null if the key
155      * 		is not defined in the Storage.
156      * @see Storage#put
157      */
	
158	public Object get(ObjectID key)
159	{
		
160		Dbc iterator;
161		Object obj1=null;
		
162		/
163		 * Acquire an iterator for the table.
164		 * Travel Storage to get elements for the specific key
165		 * Decode a byte stream to XML 
166		 * and deserialize XML into the object to return.
167		 */

168		try
169		{
170		     iterator = table.cursor(null, 0);

171       	     ObjectDbt dbtKey = new ObjectDbt(key);
172		     ObjectDbt dbtData = new ObjectDbt();
                        
173               int err;
174     	     if ((err = iterator.get(dbtKey, dbtData, Db.DB_SET)) == Db.DB_NOTFOUND)
175		         System.out.println("BDBTest" + dbtKey + " is not found.");
			
176		     byte[] inbytesData = dbtData.get_data();
177		     ByteArrayInputStream baisData = new ByteArrayInputStream(inbytesData);
			
178		     ObjIn inData = new ObjIn(baisData); //using JSX API
179		     iterator.close();
		    
180		     obj1 = inData.readObject();
181		}
182		catch (DbException dbe)
183          {
184                 System.out.println(dbe.toString());
185          }
186		catch(IOException ioe)
187		{
188		    System.out.println(ioe.toString());
189		}
190		catch(ClassNotFoundException cnfe)
191		{
192		    System.out.println(cnfe.toString());
193		}
		
194		return obj1;
195    }//get();
	
	
196    /
197     * Returns the number of elements contained within the Storage object. 
198     * Is an int big enough here?
199     */
200	public int size()
201	{
202		int numberOfKeys=0;
203		try
204		{
205		   DbBtreeStat dbts = (DbBtreeStat)table.stat(Db.DB_FAST_STAT);
206		   numberOfKeys = dbts.bt_nkeys;
207		}
208		catch (DbException dbe)
209          {
210                System.out.println(dbe.toString());
211          }
		
212		return numberOfKeys;
213	}//size();

	
214	/
215      * Returns true if the Storage object contains no elements.
216      */
217      public boolean isEmpty()
218      {
219		boolean bool=false;
220		if(size()== 0) bool= true;
221		return bool;
222      }//isEmpty();
	
	
223	/
224      * Removes the element corresponding to the key. Does nothing if the
225      * key is not present.
226      * @param key the key that needs to be removed
227      * @return the value of key, or null if the key was not found.
228      */
	
229      public Object remove(ObjectID key)
230 	 {
231		try
232		{
233		    ObjectDbt dbtKey = new ObjectDbt(key);
234		    table.del(null, dbtKey, 0);
235		}
236		catch (DbException dbe)
237          {
238                 System.out.println(dbe.toString());
239          }

240		return null;
241	  }//remove();
	
	
242 	 /
243       * Returns an enumeration of the Storage object's keys.
244       * Using similar approach for get() method.
245       * @see Storage#elements
246       * @see Storage#get
247       */

248       public Enumeration keys()
249       {
		
250	      Dbc iterator;
251		Object obj1=null;
252		Vector ids=new Vector();
		
253	        try
254		 {	
255		    iterator = table.cursor(null, 0);

256       	    ObjectDbt dbtKey = new ObjectDbt();
257               ObjectDbt dbtData = new ObjectDbt();
            
258		    while (iterator.get(dbtKey, dbtData, Db.DB_NEXT) == 0)
259              {
260			byte[] inbytes = dbtKey.get_data();
261			ByteArrayInputStream bais = new ByteArrayInputStream(inbytes);
			
262			ObjIn in = new ObjIn(bais);
263			Object key = in.readObject();
			
264			synchronized(ids) {
265			    if (! ids.contains(key))
266				ids.addElement(key);
267			}
268               }//while
			
269		     iterator.close();		
270		}
271		catch (DbException dbe)
272          {
273                  System.out.println(dbe.toString());
274          }
275		catch(IOException ioe)
276		{
277		      System.out.println(ioe.toString());
278		}
279		catch(ClassNotFoundException cnfe)
280		{
281		      System.out.println(cnfe.toString());
282		}
		
283		return ids.elements();
284    }//keys();
	
	
285    /
286     * Returns an enumeration of the elements. 
287     * Using similar approach for get() method.
288     * @see Storage#keys
289     * @see Storage#get 
290     */
	
291	public Enumeration elements()		
292	{
293		Dbc iterator;
294		Object obj1=null;
295		Vector ids=new Vector();
		
296	        try
297		{
			
298     	   iterator = table.cursor(null, 0);

299       	   ObjectDbt dbtKey = new ObjectDbt();
300                ObjectDbt dbtData = new ObjectDbt();
            
301		   while (iterator.get(dbtKey, dbtData, Db.DB_NEXT) == 0)
302             {
303			byte[] inbytes = dbtData.get_data();
304			ByteArrayInputStream bais = new ByteArrayInputStream(inbytes);
			
305			ObjIn in = new ObjIn(bais);
306			Object data = in.readObject();
			
307			synchronized(ids) {
308			   if (! ids.contains(data))
309				ids.addElement(data);
310			}
311              }//while
			
312		    iterator.close();		
313		}
314		catch (DbException dbe)
315          {
316                  System.out.println(dbe.toString());
317          }
318		catch(IOException ioe)
319		{
320		     System.out.println(ioe.toString());
321		}
322		catch(ClassNotFoundException cnfe)
323		{
324		     System.out.println(cnfe.toString());
325		}
		
326		return ids.elements();
327	}//elements();
	
	
328	/
329	 * Close database
330	 */

331	public void dbclose()
332		throws DbException
333	{
334		   try
335             {
336			table.close(0);
337		   }
338		   catch (DbException dbe)
339             {
340                  System.out.println(dbe.toString());
341             }
342	}//dbclose()
	
343 }//BerkeleyDBStorageDemo