E.3 The com.mediamania.hotcache package
This package contains the classes that can be used to support a hot
cache, as presented in Chapter 14.
E.3.1 com.mediamania.hotcache.AbstractCache
1 package com.mediamania.hotcache;
2
3 import java.util.Map;
4 import java.util.HashMap;
5
6 import com.mediamania.prototype.PrototypeQueries;
7 import com.mediamania.MediaManiaApp;
8 import com.mediamania.prototype.Movie;
9
10 public abstract class AbstractCache extends MediaManiaApp
11 implements com.mediamania.hotcache.CacheAccess {
12
13 protected Map cache = new HashMap( );
14
15 /** Creates a new instance of AbstractCache. The AbstractCache is the
16 * base class for MasterCache and SlaveCache.
17 */
18 protected AbstractCache( ) {
19 }
20
21 /** Get the Movie by title. If the movie is not in the cache, put it in.
22 * @param title the title of the movie
23 * @return the movie instance
24 */
25 public Movie getMovieByTitle(String title) {
26 Movie movie = (Movie) cache.get(title);
27 if (movie == null) {
28 movie = PrototypeQueries.getMovie (pm, title);
29 if (movie != null) {
30 cache.put (title, movie);
31 }
32 }
33 return movie;
34 }
35 }
E.3.2 com.mediamania.hotcache.AbstractDriver
1 package com.mediamania.hotcache;
2
3 import java.io.InputStream;
4 import java.io.InputStreamReader;
5 import java.io.IOException;
6 import java.io.Reader;
7 import java.io.BufferedReader;
8
9 import java.util.StringTokenizer;
10
11 import java.net.URL;
12 import java.net.MalformedURLException;
13
14 import com.mediamania.Utilities;
15
16 import com.mediamania.prototype.Movie;
17
18 public class AbstractDriver {
19 protected BufferedReader requestReader;
20 protected BufferedReader updateReader;
21 protected CacheAccess cache;
22 protected int timeoutMillis;
23 protected AbstractDriver(String updateURL, String requestURL,
24 String timeout) {
25 updateReader = openReader(updateURL);
26 requestReader = openReader(requestURL);
27 timeoutMillis = Integer.parseInt(timeout);
28 }
29
30 protected BufferedReader openReader (String urlName) {
31 try {
32 URL url = new URL(urlName);
33 InputStream is = url.openStream( );
34 Reader r = new InputStreamReader(is);
35 return new BufferedReader(r);
36 } catch (Exception ex) {
37 return null;
38 }
39 }
40
41 protected void serviceReaders( ) {
42 boolean done = false;
43 boolean lastTime = false;
44 try {
45 while (!done) {
46 if (updateReader.ready( )) {
47 handleUpdate( );
48 done = false;
49 lastTime = false;
50 } else if (requestReader.ready( )) {
51 handleRequest( );
52 done = false;
53 lastTime = false;
54 } else {
55 try {
56 Thread.sleep (timeoutMillis);
57 if (lastTime) done = true;
58 lastTime = true;
59 } catch (InterruptedException ex) {
60 done = true;
61 }
62 }
63 }
64 } catch (Exception ex) {
65 return;
66 }
67 }
68
69 protected void handleRequest( ) throws IOException {
70 String request = requestReader.readLine( );
71 Movie movie = cache.getMovieByTitle(request);
72 System.out.println("Movie: " + movie.getTitle( ));
73 }
74
75 protected void handleUpdate( ) throws IOException {
76 String update = updateReader.readLine( );
77 StringTokenizer tokenizer = new StringTokenizer(update, ";");
78 String movieName = tokenizer.nextToken( );
79 String webSite = tokenizer.nextToken( );
80 cache.updateWebSite (movieName, webSite);
81 }
82 }
E.3.3 com.mediamania.hotcache.CacheAccess
1 package com.mediamania.hotcache;
2
3 import com.mediamania.prototype.Movie;
4
5 /** Manage a cache of persistent Movie instances.
6 */
7 public interface CacheAccess {
8
9 /** Get the Movie by title.
10 * @param title the title of the movie
11 * @return the movie instance
12 */
13 Movie getMovieByTitle (String title);
14
15 /** Update the Movie website.
16 * @param title the title of the movie
17 * @param website the new website for the movie
18 */
19 void updateWebSite (String title, String website);
20 }
E.3.4 com.mediamania.hotcache.MasterCache
1 package com.mediamania.hotcache;
2
3 import java.util.Map;
4 import java.util.HashMap;
5
6 import com.mediamania.prototype.PrototypeQueries;
7 import com.mediamania.prototype.Movie;
8
9 public class MasterCache extends AbstractCache
10 implements com.mediamania.hotcache.CacheAccess {
11
12 /** Creates a new instance of MasterCache. The MasterCache performs
13 * updates of the database and manages a cache of Movie.
14 */
15 public MasterCache( ) {
16 }
17
18 /** Update the Movie website.
19 * @param title the title of the movie
20 * @param website the new website for the movie
21 */
22 public void updateWebSite(String title, String website) {
23 Movie movie = getMovieByTitle (title);
24 if (movie != null) {
25 tx.begin( );
26 movie.setWebSite (website);
27 tx.commit( );
28 }
29 }
30
31 public void execute( ) {
32 }
33
34 protected static Map getPropertyOverrides( )
35 {
36 Map overrides = new HashMap( );
37 overrides.put ("javax.jdo.options.NontransactionalRead", "true");
38 overrides.put ("javax.jdo.options.RetainValues", "true");
39 return overrides;
40 }
41 }
E.3.5 com.mediamania.hotcache.MasterDriver
1 package com.mediamania.hotcache;
2
3 public class MasterDriver extends AbstractDriver {
4 protected MasterDriver(String updateURL, String requestURL,
5 String timeout) {
6 super(updateURL, requestURL, timeout);
7 cache = new MasterCache( );
8 }
9
10 public static void main(String[] args) {
11 MasterDriver master = new MasterDriver(
12 args[0], args[1], args[2]);
13 master.serviceReaders( );
14 }
15 }
E.3.6 com.mediamania.hotcache.SlaveCache
1 package com.mediamania.hotcache;
2
3 import java.util.Map;
4 import java.util.HashMap;
5
6 import com.mediamania.prototype.Movie;
7
8 public class SlaveCache extends AbstractCache
9 implements com.mediamania.hotcache.CacheAccess {
10
11 /** Creates a new instance of SlaveCache. The SlaveCache performs
12 * lookups of the database and manages a cache of Movie.
13 */
14 public SlaveCache( ) {
15 }
16
17 /** Update the Movie website in the cache, only if it is already there.
18 * The datastore will be updated by the MasterCache.
19 * @param title the title of the movie
20 * @param website the new website for the movie
21 */
22 public void updateWebSite(String title, String website) {
23 Movie movie = (Movie)cache.get (title);
24 if (movie == null)
25 return;
26 movie.setWebSite (website);
27 }
28
29 public void execute( ) {
30 }
31
32 protected static Map getPropertyOverrides( )
33 {
34 Map overrides = new HashMap( );
35 overrides.put ("javax.jdo.options.NontransactionalRead", "true");
36 overrides.put ("javax.jdo.options.NontransactionalWrite", "true");
37 return overrides;
38 }
39 }
E.3.7 com.mediamania.hotcache.SlaveDriver
1 package com.mediamania.hotcache;
2
3 public class SlaveDriver extends AbstractDriver {
4 protected SlaveDriver(String updateURL, String requestURL,
5 String timeout) {
6 super(updateURL, requestURL, timeout);
7 cache = new SlaveCache( );
8 }
9
10 public static void main(String[] args) {
11 SlaveDriver slave = new SlaveDriver(
12 args[0], args[1], args[2]);
13 slave.serviceReaders( );
14 }
15 }
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