1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Program Listing</title>
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
<link rel="start" href="index.html" title="Getting Started with Replicated Berkeley DB Applications" />
<link rel="up" href="txnapp.html" title="Chapter 2. Transactional Application" />
<link rel="prev" href="txnapp.html" title="Chapter 2. Transactional Application" />
<link rel="next" href="repapp.html" title="Chapter 3. The DB Replication Manager" />
</head>
<body>
<div xmlns="" class="navheader">
<div class="libver">
<p>Library Version 12.1.6.1</p>
</div>
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Program Listing</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="txnapp.html">Prev</a> </td>
<th width="60%" align="center">Chapter 2. Transactional Application</th>
<td width="20%" align="right"> <a accesskey="n" href="repapp.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="simpleprogramlisting"></a>Program Listing</h2>
</div>
</div>
</div>
<div class="toc">
<dl>
<dt>
<span class="sect2">
<a href="simpleprogramlisting.html#repconfiginfo_cxx">
<span>Class: RepConfig</span>
</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="simpleprogramlisting.html#simpletxnusage_java">Class: SimpleTxn</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="simpleprogramlisting.html#simpletxnmain_java">Method: SimpleTxn.main()</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="simpleprogramlisting.html#simpletxn_init_java">Method: SimpleTxn.init()</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="simpleprogramlisting.html#doloop_java">Method: SimpleTxn.doloop()</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="simpleprogramlisting.html#printstocks_c">
<span>Method: SimpleTxn.printStocks()</span>
</a>
</span>
</dt>
</dl>
</div>
<p>
Our example program is a fairly simple transactional
application. At this early stage of its development, the
application contains no hint that it must be network-aware
so the only command line argument that it takes is one that
allows us to specify the environment home directory.
(Eventually, we will specify things like host names and
ports from the command line).
</p>
<p>
Note that the application performs all writes under the
protection of a transaction; however, multiple database
operations are not performed per transaction. Consequently,
we simplify things a bit by using autocommit for our
database writes.
</p>
<p>
Also, this application is single-threaded. It is possible
to write a multi-threaded or multi-process application that
performs replication. That said, the concepts described in
this book are applicable to both single threaded and
multi-threaded applications so nothing
is gained by multi-threading this application other than
distracting complexity. This manual
does, however, identify where care must be taken when
performing replication with a non-single threaded
application.
</p>
<p>
Finally, remember that transaction processing is not described in
this manual. Rather, see the
<em class="citetitle">Berkeley DB Getting Started with Transaction Processing</em> guide for details on
that topic.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="repconfiginfo_cxx"></a>
<span>Class: RepConfig</span>
</h3>
</div>
</div>
</div>
<p>
Before we begin, we present a
class that we will use to maintain useful
information for us. Under normal circumstances,
this class would not be necessary for a simple
transactional example such as this. However, this code will
grow into a replicated example that needs to
track a lot more information for the
application, and so we lay the groundwork for
it here.
</p>
<p>
The class that we create is called
<code class="classname">RepConfig</code>
and its only purpose at this time is to track
the location of our environment home directory.
</p>
<pre class="programlisting">package db.repquote_gsg;
public class RepConfig
{
// Constant values used in the RepQuote application.
public static final String progname = "SimpleTxn";
public static final int CACHESIZE = 10 * 1024 * 1024;
// member variables containing configuration information
public String home; // String specifying the home directory for
// rep files.
public RepConfig()
{
home = "TESTDIR";
}
public java.io.File getHome()
{
return new java.io.File(home);
}
} </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="simpletxnusage_java"></a>Class: SimpleTxn</h3>
</div>
</div>
</div>
<p>
Our transactional example will
consist of a class,
<code class="classname">SimpleTxn</code>, that performs
all our work for us.
</p>
<p>
First, we provide the package declaration and
then a few import statements that the class
needs.
</p>
<pre class="programlisting">package db.repquote_gsg;
import java.io.FileNotFoundException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import com.sleepycat.db.Cursor;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseConfig;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.DatabaseType;
import com.sleepycat.db.Environment;
import com.sleepycat.db.EnvironmentConfig;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;
import db.repquote_gsg.SimpleConfig;
public class SimpleTxn
{
private SimpleConfig simpleConfig;
private Environment dbenv; </pre>
<p>
Next, we provide our class constructor. This simply initializes our
class data members.
</p>
<pre class="programlisting"> public SimpleTxn()
throws DatabaseException
{
simpleConfig = null;
dbenv = null;
} </pre>
<p>
And then we provide our <code class="methodname">usage()</code> method. At
this point, this method has very little to report:
</p>
<pre class="programlisting"> public static void usage()
{
System.err.println("usage: " + simpleConfig.progname);
System.err.println("-h home");
System.exit(1);
} </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="simpletxnmain_java"></a>Method: SimpleTxn.main()</h3>
</div>
</div>
</div>
<p>
Having implemented our
<code class="methodname">usage()</code>
method, we can jump directly into our
<code class="methodname">main()</code>
method. This method begins by instantiating a
<code class="classname">RepConfig</code> object, and
then collecting the command line arguments so
that it can populate the object with the
appropriate data (just the environment home
directory, at this time):
</p>
<pre class="programlisting"> public static void main(String[] argv)
throws Exception
{
SimpleConfig config = new SimpleConfig();
// Extract the command line parameters
for (int i = 0; i < argv.length; i++)
{
if (argv[i].compareTo("-h") == 0) {
// home - a string arg.
i++;
config.home = argv[i];
} else {
System.err.println("Unrecognized option: " + argv[i]);
usage();
}
} </pre>
<p>
And then perform a little sanity checking on the command line
input:
</p>
<pre class="programlisting"> // Error check command line.
if (config.home.length() == 0)
usage(); </pre>
<p>
Now we perform the class' work. To begin, we initialize the
object. The <code class="methodname">init()</code> method actually
opens our environment for us (shown in the next section).
</p>
<pre class="programlisting"> SimpleTxn runner = null;
try {
runner = new SimpleTxn();
runner.init(config); </pre>
<p>
And then we call our <code class="methodname">doloop()</code>
method. This method is where we perform all our database
activity. See <a class="xref" href="simpleprogramlisting.html#doloop_java" title="Method: SimpleTxn.doloop()">Method: SimpleTxn.doloop()</a>
for it's details.
</p>
<pre class="programlisting"> runner.doloop(); </pre>
<p>
And then, finally terminate the application (which closes our
environment handle) and end the method.
</p>
<pre class="programlisting"> runner.terminate();
} catch (DatabaseException dbe) {
System.err.println("Caught an exception during " +
"initialization or processing: " + dbe.toString());
if (runner != null)
runner.terminate();
}
System.exit(0);
} // end main </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="simpletxn_init_java"></a>Method: SimpleTxn.init()</h3>
</div>
</div>
</div>
<p>
The <code class="methodname">SimpleTxn.init()</code>
method is used to open our environment handle.
For readers familiar with writing transactional
DB applications, there should be no surprises
here. However, we will be adding to this in later
chapters as we roll replication into this example.
</p>
<p>
The only thing worth noting in this method here is that
we relax our transactional durability guarantee for this application.
We do this because the application will eventually be replicated and
so we don't need a high durability guarantee.
</p>
<pre class="programlisting"> public int init(SimpleConfig config)
throws DatabaseException
{
int ret = 0;
simpleConfig = config;
EnvironmentConfig envConfig = new EnvironmentConfig();
envConfig.setErrorStream(System.err);
envConfig.setErrorPrefix(SimpleConfig.progname);
envConfig.setCacheSize(SimpleConfig.CACHESIZE);
envConfig.setTxnNoSync(true);
envConfig.setAllowCreate(true);
envConfig.setRunRecovery(true);
envConfig.setInitializeLocking(true);
envConfig.setInitializeLogging(true);
envConfig.setInitializeCache(true);
envConfig.setTransactional(true);
try {
dbenv = new Environment(simpleConfig.getHome(), envConfig);
} catch(FileNotFoundException e) {
System.err.println("FileNotFound exception: " + e.toString());
System.err.println(
"Ensure that the environment directory is pre-created.");
ret = 1;
}
return ret;
} </pre>
<p>
Finally, we present the <code class="methodname">SimpleTxn.terminate()</code>
method here. All this does is close the environment handle. Again,
there should be no surprises here, but we provide the
implementation for the sake of completeness anyway.
</p>
<pre class="programlisting"> public void terminate()
throws DatabaseException
{
dbenv.close();
} </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="doloop_java"></a>Method: SimpleTxn.doloop()</h3>
</div>
</div>
</div>
<p>
We now implement our application's
primary data processing method. This
method provides a command prompt at which the
user can enter a stock ticker value and a price for
that value. This information is then entered to the
database.
</p>
<p>
To display the database, simply enter
<code class="literal">return</code> at the prompt.
</p>
<p>
To begin, we declare a database pointer:
</p>
<pre class="programlisting"> public int doloop()
throws DatabaseException, , UnsupportedEncodingException
{
Database db = null; </pre>
<p>
Next, we begin the loop and we immediately open our
database if it has not already been opened.
</p>
<pre class="programlisting"> for (;;)
{
if (db == null) {
DatabaseConfig dbconf = new DatabaseConfig();
dbconf.setType(DatabaseType.BTREE);
dbconf.setAllowCreate(true);
dbconf.setTransactional(true);
try {
db = dbenv.openDatabase(null, // Txn handle
SimpleConfig.progname, // db filename
null, // db name
dbconf);
} catch (FileNotFoundException fnfe) {
System.err.println("File not found exception" +
fnfe.toString());
// Get here only if the environment home directory
// somehow does not exist.
}
} </pre>
<p>
Now we implement our command prompt. This is a simple and not
very robust implementation of a command prompt.
If the user enters the keywords <code class="literal">exit</code>
or <code class="literal">quit</code>, the loop is exited and the
application ends. If the user enters nothing and instead simply
presses <code class="literal">return</code>, the entire contents of the
database is displayed. We use our
<code class="methodname">printStocks()</code> method to display the
database. (That implementation is shown next in this chapter.)
</p>
<p>
Notice that very little error checking is performed on the data
entered at this prompt. If the user fails to enter at least one
space in the value string, a simple help message is printed and
the prompt is returned to the user. That is the only error
checking performed here. In a real-world application,
at a minimum the application would probably check to ensure
that the price was in fact an integer or float value.
However, in order to keep this example code as simple as
possible, we refrain from implementing a thorough user interface.
</p>
<pre class="programlisting"> BufferedReader stdin =
new BufferedReader(new InputStreamReader(System.in));
// listen for input, and add it to the database.
System.out.print("QUOTESERVER> ");
System.out.flush();
String nextline = null;
try {
nextline = stdin.readLine();
} catch (IOException ioe) {
System.err.println("Unable to get data from stdin");
break;
}
String[] words = nextline.split("\\s");
// A blank line causes the DB to be dumped to stdout.
if (words.length == 0 ||
(words.length == 1 && words[0].length() == 0)) {
try {
printStocks(db);
} catch (DatabaseException e) {
System.err.println("Got db exception reading " +
"DB: " + e.toString());
break;
}
continue;
}
if (words.length == 1 &&
(words[0].compareToIgnoreCase("quit") == 0 ||
words[0].compareToIgnoreCase("exit") == 0)) {
break;
} else if (words.length != 2) {
System.err.println("Format: TICKER VALUE");
continue;
} </pre>
<p>
Now we assign data to the <code class="classname">DatabaseEntry</code>
classes that we will use to write the new information to the database.
</p>
<pre class="programlisting"> DatabaseEntry key =
new DatabaseEntry(words[0].getBytes("UTF-8"));
DatabaseEntry data =
new DatabaseEntry(words[1].getBytes("UTF-8")); </pre>
<p>
Having done that, we can write the new information to the
database. Remember that because a transaction handle is not
explicitly used, but we did open the database such that it
supports transactions, then autocommit is automatically
used for this database write.
</p>
<p>
Autocommit is described in the
<em class="citetitle">Berkeley DB Getting Started with Transaction Processing</em> guide.
</p>
<p>
Also, the database is not configured for duplicate records, so
the data portion of a record is overwritten if the provided
key already exists in the database. However, in this case
DB returns <code class="methodname">OperationStatus.KEYEXIST</code> — which
we ignore.
</p>
<pre class="programlisting"> db.put(null, key, data); </pre>
<p>
Finally, we close our database before returning from the
method.
</p>
<pre class="programlisting"> }
if (db != null)
db.close(true);
return 0;
} </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="printstocks_c"></a>
<span>Method: SimpleTxn.printStocks()</span>
</h3>
</div>
</div>
</div>
<p>
The
<code class="methodname">printStocks()</code>
<span>method</span>
simply takes a database handle, opens a cursor, and uses
it to display all the information it finds in a database.
This is trivial cursor operation that should hold
no surprises for you. We simply provide it here for
the sake of completeness.
</p>
<p>
If you are unfamiliar with basic cursor operations,
please see the <em class="citetitle">Getting Started with Berkeley DB</em>
guide.
</p>
<pre class="programlisting"> public void terminate()
throws DatabaseException
{
dbenv.close();
}
/*
* void return type since error conditions are propagated
* via exceptions.
*/
private void printStocks(Database db)
throws DatabaseException
{
Cursor dbc = db.openCursor(null, null);
System.out.println("\tSymbol\tPrice");
System.out.println("\t======\t=====");
DatabaseEntry key = new DatabaseEntry();
DatabaseEntry data = new DatabaseEntry();
OperationStatus ret;
for (ret = dbc.getFirst(key, data, LockMode.DEFAULT);
ret == OperationStatus.SUCCESS;
ret = dbc.getNext(key, data, LockMode.DEFAULT)) {
String keystr = new String
(key.getData(), key.getOffset(), key.getSize());
String datastr = new String
(data.getData(), data.getOffset(), data.getSize());
System.out.println("\t"+keystr+"\t"+datastr);
}
dbc.close();
}
} // end class </pre>
</div>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="txnapp.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="txnapp.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="repapp.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Chapter 2. Transactional Application </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Chapter 3. The DB Replication Manager</td>
</tr>
</table>
</div>
</body>
</html>
|
