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    }