"Design Patterns for Optimizing the Performance of J2EE Applications"
Vol. 6, Issue 9, p. 48

	


Listing 1: Servlet that uses a CatalogEJB to read a list of objects

// All required imports


public class DisplayServices extends HttpServlet {


    // variable declarations


    public void init() {
        // all inits required
    }


    public void doPost(HttpServletRequest request, HttpServletResponse
      response)
         throws IOException, ServletException {


        // other processing, if any


        InitialContext ctxt = new InitialContext();
        Object obj = ctxt.lookup("java:comp/env/ejb/Catalog/Services");
        CatalogHome catHome = (CatalogHome)
                    PortableRemoteObject.narrow(obj, CatalogHome.class);
        Catalog catList = catHome.create();
        Collection list = catList.getServiceNames();
        while(int i=0; i < list.size(); i++) {


            // get the service name


            // display the service name received


        }
        // do other processing required
    }
    // other methods definitions
}


// The following is the sample code of the CatalogEJB
// For simplicity sake, the definitions of the home and remote
// interfaces are not shown


// All required imports


public class CatalogEJB implements EntityBean {


    // Methods like ejbCreate etc go here


    // Business methods start here
    public Collection getServiceNames() {
        // Access the database and get the list of service names
        // Form a collection of the service names
        // Return this collection
    }


    public int updateServices(arg1, arg2) {
        // this method will allow the CatalogEJB to update the list of
             Services;
        // for example, this method might build the SQL query for updating
             the
        // list services in the catalog and use JDBC to execute the query
    }


    public int addServices(arg1, arg2) {
        // this method will allow the CatalogEJB to add to the list of
             Services
    }


    // Other business methods
}



Listing 2: Data Access Object that encapsulates all types of access to the Catalog

// all required imports


public class CatalogDataAccessObject {


    private Connection dbConnection;
    private DataSource datasource;


    public CatalogDataAccessObject() {


        // appropriate exceptions to be caught
        InitialContext ic = new InitialContext();
        datasource = (DataSource)
                ic.lookup("java:comp/env/jdbc/CatalogDataSource");
        dbConnection = datasource.getConnection();
    }


    public int updateServices(arg1, arg2) {
        // this method will allow the CatalogEJB to update the list of
             Services;
        // for example, this method might build the SQL query for updating
             the
        // list services in the catalog and use JDBC to execute the query
    }


    public int addServices(arg1, arg2) {
        // this method will allow the CatalogEJB to add to the list of
             Services
    }


    public Collection getServiceNames() {
        // this method will allow the catalogEJB or any client
             using Fast Lane
        // Reader pattern to get the list of services
    }


    // other method definitions as required
}



Listing 3: Servlet that uses Fast Lane Reader pattern

// All required imports


public class DisplayServices extends HttpServlet {


    private CatalogDataAccessObject dao;
    // other declarations


    public void init() {
        CatalogDataAccessObject dao = new
          CatalogDataAccessObject();


        // all other inits required
    }


    public void doPost(HttpServletRequest reqest,
      HttpServletResponse response)
         throws IOException, ServletException {


        // other processing, if any


        Collection list = dao.getServiceNames();
        for(int i=0; i<list.size(); list++) {


            // get the service name received
            // display the list name
        }


        // do other processing as required
    }


    // other method definitions, if any
}



Listing 4: Page-by-Page Iterator pattern returned to the client

// all required imports


public class PageByPageIteratorImpl {


/*
"start" represents the starting index of the first element of this
   sublist.
*/
    private int start;


/*
"size" represents the number of elements that are in this sublist.
*/
    private int size;


/*
"totalCount" represents the total number of objects that would
   have been
returned in the absence of the Page-By-Page Iterator; very useful
   information
for the clients in deciding to iterate more or not
*/
    private int totalCount;


/*
"objs" has the actual collection of objects
*/
    private Collection objs;


    public PageByPageIteratorImpl(int start, int size, int total,
      Collection
coll) {
        this.start = start;
        this.size = size;
        this.totalCount = total;
        this.objs = coll;
    }


    public int getStartIndex() {
        return start;
    }


    // Other similar accessor methods for size, totalCount, objs
}



 Listing 5: Data Access Object
 
   public PageByPageIteratorImpl getServiceNames(int startIndex,
      int size) {
        // get the total count of the number of service into
      variable "total";
        // access the database and get the collection of service
             names in
        // "retObjs";
        // the collection obtained will be of requested size only
             starting from
        // the index specified;
        // return the collection of service names as part of the
             Page-by-Page Iterator
        return(new PageByPageInteratorImpl(startIndex, size,
             total, retObjs));
    }
    // other method definitions as required
}



Listing 6: Servlet using Fast Lane Reader and Page-by-Page Iterator

// All required imports


public class DisplayServices extends HttpServlet {


    private CatalogDataAccessObject dao;
    // other declarations


    public void init() {
        CatalogDataAccessObject dao = new
          CatalogDataAccessObject();
        // all other inits required
    }


    public void doPost(HttpServletRequest request,
      HttpServletResponse response)
            throws IOException, ServletException {
        // other processing, if any
        Integer startIndex = new
          Integer(request.getParameter("StartIndex"));
        Integer listSize = new
          Integer(request.getParameter("ListSize"));
        PageByPageIteratorImpl list =
          dao.getServiceNames(startIndex.intValue(),
                                            listSize.
                                              intValue());
        Collection objs = list.getCollection();
        // Now the list received is of requested size only
        // iterate thro the list and display the service names
             received
        // do other processing as required
    }
    // other method definitions
}



Listing 7: Value Object class for a service


// all imports required


public class ServiceInformation implements java.io.Serializable {


    private String serviceName;
    private double serviceCost;
    private String[] serviceTerms;
    // other attributes of a service


    public ServiceInformation(String name, double cost, String[]
      terms) {
        serviceName = name;
        serviceCost = cost;
        serviceTerms = terms;
    }


    public String getName() {
        return(serviceName);
    }


    public double getCost() {
         return(serviceCost);
    }


    public String[] getTerms() {
         return(serviceTerms);
    }
    // similar accessor methods for other attributes
}



Listing 8: Using all these patterns discussed

// All required imports


public class DisplayServices extends HttpServlet {


    private CatalogDataAccessObject dao;
    // other declarations


    public void init() {
        CatalogDataAccessObject dao = new
          CatalogDataAccessObject();
        // all other inits required
    }


    public void doPost(HttpServletRequest request,
      HttpServletResponse response)
            throws IOException, ServletException {
        // other processing, if any
        Integer startIndex = new
          Integer(request.getParameter("StartIndex"));
        Integer listSize = new
          Integer(request.getParameter("ListSize"));
        PageByPageIteratorImpl list =
          dao.getServiceNames(startIndex.intValue(),
                                        listSize.intValue());
        Collection objs = list.getCollection();
        // The collection is a collection of the value objects
        // Now the list received is of requested size only
        // extract the service names and the attributes from the
             value objects
        // display everything and do other processing as required
    }
    // other method definitions
}