15.4 BookOperation Class

15.4 BookOperation Class

The command pattern can be used to share common implementations of operations. This class provides an abstract implementation for common operations on books that other commands can share. Figure 15-3 shows the class diagram for a number of the use-cases .

Figure 15-3. Inheriting from AbstractUseCase .

This class implements a number of convenience methods that can be used to do the following:

• Query generic fields by passing "field" and "field value,"

• Return found Book instance as a subclass.

• Ensure that only a single instance result is returned; else an error is thrown.

• Copies of a book can be found by "back pointer" or join query; returns all copies that belong to a book.

 Package com.corejdo.casestudy.usecase; import com.corejdo.casestudy.model.*; import javax.jdo.* ; import java.util.* ; /**  * Basic class of all Book operations.  * This class can find a single book.  */ public abstract class BookOperation extends AbstractUseCase {     public BookOperation()     {     }     /**      * Searches for a book that matches a string field      * @param field name of field in the book class.      * @param fieldValue value to match      * @return a book      */     protected Book findBook(String field,                             String fieldValue)     {         PersistenceManager pm = getPM();         // find the book to update.         Query q = pm.newQuery(Book.class, field+" == val");         q.declareParameters("String val");         q.setCandidates(pm.getExtent(Book.class,true));         Collection result =                        (Collection)q.execute(fieldValue);         if (result.size()<1) {             throw new RuntimeException(field+" not found: "+fieldValue);         } else if (result.size()>1) {             throw new RuntimeException(field+" not unique: "+fieldValue);         }         Book book = (Book)result.iterator().next();         return book;     }     protected final Book findBook()     {         Book book = null;         try {             book = findBook("ISBN",this.findISBN);         } catch (Exception e) {             book = findBook("title",this.findTitle);         }         return book;     }     /**      * Find all copies of a publication.      */     protected Copy[] findCopies(Publication publication)     {         PersistenceManager pm = getPM();         // find all copies for a publication         Query q = pm.newQuery(Copy.class, "copyOf == val");         q.declareParameters("com.corejdo.casestudy.model.Publication val");         q.setCandidates(pm.getExtent(Copy.class,true));         Collection result =              (Collection)q.execute(publication);         Copy copies[] = new Copy[result.size()];         result.toArray(copies);         return copies;     }     public void setFindTitle(String findTitle)     {         this.findTitle = findTitle;     }     public void setFindISBN(String findISBN)     {         this.findISBN = findISBN;     }     private String findTitle;     private String findISBN; } 

15.4.1 ListBooks use-case

This use-case shows how to display a list of all books or books that match a specified filter.

 Package com.corejdo.casestudy.usecase; import com.corejdo.casestudy.tools.CmdLine; import com.corejdo.casestudy.model.*; import javax.jdo.* ; import java.util.* ; /**  * This class lists books.  *  */ public class ListBooks     extends BookOperation {     int startNumber = 0;     int count = 10;     List result;     String filterAuthor = "";     Query query;     Extent extent;     /**      * Sets the start offset. Since JDO does not      * support a "seek" operation on      * extents, we implemented our own by simply      * calling iterator.next().      * @param i      */     public void setStartNumber(int i)     {         startNumber = i;     }     /**      * Sets the number of entries      * returned by this operation.      * @param i number of entries      */     public void setCount(int i)     {         count = i;     }     /**      * This data object is used to return the results.      */     public class BookDTO     {         public final String title;         public final String copyright;         public final String ISBN;         public final String author;         BookDTO(Book b)         {             this.title = b.title;             this.copyright = b.copyright;             this.ISBN = b.ISBN;             this.author = b.author;         }         public String toString()         {             return "Title:  "+title+                    "\n   Author: "+author+                    "\n   ISBN:   "+ISBN+                    "\n   : "  "+copyright;         }     }     /**      * Iterates over elements of the book Extent.      * Called by the framework's execute() method.      */     protected void _execute()     {         result = new ArrayList();         extent = getPM().getExtent(Book.class,true);         query = null;         Iterator iter = filter(extent);         int i = this.startNumber;         while (i-- > 0 && iter.hasNext()) iter.next();         i = this.count;         while (i-- > 0 && iter.hasNext()) {             result.add(new BookDTO((Book)iter.next()));         }         if (query != null) {             query.close(iter);         } else {             extent.close(iter);         }     }     protected Iterator filter(Extent extent)     {         if (filterAuthor != null) {             query = getPM().newQuery(Book.clas", "author == "al");             query.declareParameters("java.lang.String  a l");             query.setCandidates(exte nt);             Collection result = (Collection)query.execute(filterAuthor);             return result.iterator();         } else {             return extent.iterator();         }     }     /**      * Command line version.      */     public static void main(String[] args) {         new ListBooks().runCmdLine(args);     }     protected void run(String[] args) {         setStartNumber(CmdLine.getIntV"r("Start"at",0));         setCount(CmdLine.getIntV"r("Co"nt",10));         execute();         System.out.print"n("Resul": ");         Iterator iter = getResult();         int i = 1;         while (iter.hasNext()) {             System.out.print""("""i+": "+iter.next());             i++;         }     }     /**      * The resulting iterator returns BookDTO objects.      */     public Iterator getResult()     {         return result.iterator();     }     public int getCount()     {         return count;     }     public int getStartNumber()     {         return startNumber;     }     public String getFilterAuthor()     {         return filterAuthor;     }     public void setFilterAuthor(String filterAuthor)     {         this.filterAuthor = filterAuthor;     } } 

15.4.2 DetailedBook use-case

This use-case gets the detailed information about a particular book; it encapsulates a Book instance and provides an interface to get the detailed information from it without exposing the Book instance itself.

 package com.corejdo.casestudy.usecase; import com.corejdo.casestudy.model.*; import com.corejdo.casestudy.tools.*; /**  * This class gets detailed information about a book.  * It is a good example for information hiding.  * The actual book data  * in the persistent model Book class  * uses a User field for the  * borrower information, but unauthorized users must  * not be able to see detailed information about borrowers.  */ public class DetailedBook extends BookOperation {     public DetailedBook()     {     }     public static void main(String[] args)     {         new DetailedBook().runCmdLine(args);     }     /**      * Command line version of the book editor.      */     protected void run(String[] args)     {         setFindISBN(CmdLine.getStringVar("  "Find I"B"","928394-234-23"44"));         setFindTitle(CmdLine.getStringVar("  "Find Ti"l"",""));         execute();     }     /**      * First, looks up a book, then sets return value      * for detailed book information.      * The implementation of this      * method looks quite simple because JDO does a      * lot of things for us, like fetching other objects      * on demand.      */     protected void _execute()     {         Book book = findBook();         this.ISBN = book.ISBN;         this.author = book.author;         this.title = book.title;         this.published = book.published.toString();         this.firstPublished =                       book.firstPublished.toString();         Copy copies[] = findCopies(book);         availableCopies = 0;         for (int i = 0; i < copies.length; i++) {             if (copies[i].borrower == null)                       availableCopies++;         }         this.isBorrowed = availableCopies > 0;     }     public String getAuthor()     {         return author;     }     public int getAvailableCopies()     {         return availableCopies;     }     public String getFirstPublished()     {         return firstPublished;     }     public String getISBN()     {         return ISBN;     }     public boolean isIsBorrowed()     {         return isBorrowed;     }     public String getPublished()     {         return published;     }     public String getTitle()     {         return title;     }     String ISBN;     String author;     String title;     String published;     String firstPublished;     int availableCopies;     boolean isBorrowed; } 

15.4.3 EditBook use-case

Similar to the previous use-case, this one allows a particular Book instance to be modified. Again, access to the actual Book instance is encapsulated by this class.

 package com.corejdo.casestudy.usecase; import com.corejdo.casestudy.model.Book; import com.corejdo.casestudy.tools.CmdLine; import javax.jd o.*; import java.uti l.*; import java.text.DateFor mat; import java.text.ParseExcept ion; /**  * This class is used to change properties of books.  */ public class EditBook extends BookOperation {     public static void main(String[] args)     {         new EditBook().runCmdLine(args);     }     /**      * Command line version of the book editor.      *      */     protected void run(String[] args)     {         setFindISBN(CmdLine.getStringVar("  "Find I"B"","928394-234-23"44"));         setFindTitle(CmdLine.getStringVar("  "Find Ti"l"",""));         setISBN(CmdLine.getStringVar("  "I"B"","928394-234-23"44"));         setTitle(CmdLine.getStringVar("  "Ti"l"","new Ti"le"));         setAuthor(CmdLine.getStringVar("  "Aut"o"","H. Bob"in"));         setCopyright(CmdLine.getStringVar("  "Copyri"h"","(C) 2003 Prentice H"ll"));         execute();     }     /**      * First, looks up a book, then updates the fields with      * the values of this bean.      */     protected void _execute()     {         Book book = findBook();         book.title = this.title;         book.author = this.author;         book.copyright = this.copyright;         book.ISBN = this.ISBN;     }     public void setISBN(String ISBN)     {         this.ISBN = ISBN;     }     public void setAuthor(String author)     {         this.author = author;     }     public void setTitle(String title)     {         this.title = title;     }     public void setCopyright(String copyright)     {         this.copyright = copyright;     }     private String ISBN;     private String author;     private String title;     private String copyright; } 

15.4.4 DeleteBook use-case

This use-case simply deletes the specified Book instance. Interestingly, it doesn't try to find all the Copy instances that reference this Book and delete them, although this would be a fairly straightforward addition. Instead, the Copy instances are left as-is, now referencing a delete persistent object.

 package com.corejdo.casestudy.usecase; import com.corejdo.casestudy.tools.*; import com.corejdo.casestudy.model.*; import javax.jd o.*; import java.uti l.*; public class DeleteBook extends BookOperation {     public static void main(String[] args)     {         new DeleteBook().runCmdLine(args);     }     /**      * Command line version.      */     protected void run(String[] args)     {         setFindISBN(CmdLine.getStringVar("  "Find I"B"","928394-234-23"44"));         setFindTitle(CmdLine.getStringVar("  "Find Ti"l"",""));         execute();     }     public boolean isAllowed()     {         return getContext().userRights.canManage();     }     /**      * First, looks up a book, then delete it.      */     protected void _execute()     {         Book book = findBook();         PersistenceManager pm = getPM();         pm.deletePersistent(book);     } } 

15.4.5 BorrowReturn class

This abstract class implements behavior common to borrowing or returning a book.

 package com.corejdo.casestudy.usecase; import com.corejdo.casestudy.model.*; import com.corejdo.casestudy.tools.CmdLine; import javax.jd o.*; import java.uti l.*; import java.text.DateFor mat; import java.text.ParseExcept ion; /**  * The common operations "f "bor"ow"  * a"d "ret"rn" are implemented in this class.  */ public abstract class BorrowReturn extends BookOperation {     public boolean isAllowed()     {         if (!getContext().isLoggedIn()) return false;         return getContext().userRights.canBorrow();     }     /**      * First, looks up a book, then checks for a copy.      * If copy exists, the book is borrowed or returned.      */     protected void _execute()     {         Book book = findBook();         process(book);     }     protected abstract void process(Book book);     public String getLocation()     {         return location;     }     public String getReturnDate()     {         return returnDate;     }     protected String returnDate;     protected String location; } 

15.4.6 Borrow use-case

This use-case tries to find available copies of a book and allocates one to the borrower.

 package com.corejdo.casestudy.usecase; ...     public final long borrowTime                = 1000L*60L*10L; // ten minutes     protected void process(Book book)     {         Copy copy[] = findCopies(book);         for (int i = 0; i < copy.length; i++) {             Copy c = copy[i];             if (c.borrower == null) {                 c.borrower = getContext().user;                 c.borrowDate = new Date(); // now.                 c.returnDate = new Date(c.borrowDate.getTime()+borrowTime);                 this.returnDate = c.returnDate.toString();                 this.location = c.location;                 return;             }         }         throw new UseCaseException("  "No copy available. Please ask cle"k.");     } } 

15.4.7 Return use-case

This use-case tries to find the copy of a book that was previously borrowed and returns it.

 package com.corejdo.casestudy.usecase; ...     protected void process(Book book)     {         Copy copy[] = findCopies(book);         for (int i = 0; i < copy.length; i++) {             Copy c = copy[i];             if (c.borrower == getContext().user) {                 c.borrower = null;                 this.location = c.location;                 return ;             }         }         throw new UseCaseException("  "This book is not borrowed "y "+              getContext().us"r+". Please ask cle"k.");     }