newshelper.java

Oracle的J2EE Sample

/*
 * @author : Elangovan
 * @version 1.0
 *
 * Development Environment : Oracle9i JDeveloper
 * Name of the File        : NewsHelper.java
 * 
 * Creation / Modification History
 *    Elangovan           20-Aug-2003        Created
 *
 */
package oracle.otnsamples.ibfbs.usermanagement.helper;

import java.util.Collection;
import java.util.ArrayList;

import oracle.toplink.tools.sessionmanagement.SessionManager;
import oracle.toplink.sessions.UnitOfWork;
import oracle.toplink.tools.sessionconfiguration.XMLLoader;
import oracle.toplink.threetier.ServerSession;
import oracle.toplink.threetier.ClientSession;
import oracle.toplink.expressions.ExpressionBuilder;
import oracle.toplink.queryframework.ReadAllQuery;
import oracle.toplink.queryframework.ReportQuery;
import oracle.toplink.exceptions.DatabaseException;

import oracle.otnsamples.ibfbs.toplink.News;

import oracle.otnsamples.ibfbs.usermanagement.exception.UserManagementEventException;

/**
 * This class encapsulates and manages all access to News information. It 
 * loads/fetches latest news using Toplink persistence framewok.
 * 
 * @see oracle.otnsamples.ibfbs.toplink.News.java
 */
public class NewsHelper {

  // Toplink server session
  private ServerSession server = null;

  /**
   * Creates a new instance of NewsHelper
   * 
   * @exception UserManagementEventException if initializing server session fails
   */
  public NewsHelper() 
    throws UserManagementEventException{
    try {
      // Initialize ServerSession from session.xml 
      server = (ServerSession) SessionManager.getManager().getSession(new XMLLoader(),
                                "FBSServerSession",
                                Thread.currentThread().getContextClassLoader());
    }catch(DatabaseException dbEx) {
      throw new UserManagementEventException(" Error initializing Server Session :"+dbEx);
    }
    
  }

  /**
   * Method to get the Stock News for the particular symbol.
   * 
   * @param symbol Stock Symbol of the Company in which user is interested.
   * @return Collection containing the News objects corresponding to the given symbol.
   * @exception UserManagementEventException if retrieving latest news fails
   * 
   */
  public Collection getLatestNews(String symbol)
      throws UserManagementEventException {

    ClientSession client = null;
    ArrayList newsList = new ArrayList(3);
    try {
      // Initialize client session 
      client = server.acquireClientSession();
      
      // Initilize read query to read multiple news items
      ReadAllQuery readNews = new ReadAllQuery(News.class);
      
      ExpressionBuilder newsBuilder = new ExpressionBuilder();
      ExpressionBuilder symbolBuilder = new ExpressionBuilder();
      
      ReportQuery subQuery = new ReportQuery(News.class, symbolBuilder);
      
      // SELECT MAX(NewsDate) FROM News WHERE Symbol = ? 
      subQuery.addMaximum("newsdate");      
      subQuery.setSelectionCriteria(symbolBuilder.get("symbol").equalsIgnoreCase(symbol));
      
      // Specify the return collection class [ default: Vector ]      
      readNews.useCollectionClass(ArrayList.class);

      // SELECT News WHERE Symbol = ? AND NewsDate = ?
      readNews.setSelectionCriteria(newsBuilder.get("newsdate").equal(subQuery).and(
                                  newsBuilder.get("symbol").equalsIgnoreCase(symbol)));
      
      newsList.addAll((ArrayList)client.executeQuery(readNews));

    } catch (DatabaseException ex) {     
      throw new UserManagementEventException(" Error while getting "
                                     + " News:\n" + ex.toString());
    } 
    return newsList;    
  }

  /**
   * Method to populate News into the database tables.
   * 
   * @param newsCollection Collection of News objects
   * @exception DatabaseException if retrieving news fails
   */
  public void loadNews(Collection newsCollection) 
    throws DatabaseException {

    // Initialize  client session
    ClientSession client = server.acquireClientSession();
    
    // Enable batch-writing [ Write Optimization ]
    client.getLogin().useBatchWriting();
        
    // Get a transaction
    UnitOfWork uow = client.acquireUnitOfWork();
    
    // Register the objects with transaction
    uow.registerAllObjects(newsCollection);
    
    // Commit
    uow.commit();  
          
  }

  /**
   * Method to get the Stock News for a list of symbols.
   * 
   * @param symbols list of symbols for which stock news is required
   * @return Collection containing the News objects corresponding to the given symbols.
   * @exception UserManagementEventException if retrieving latest news fails
   * @since 1.0
   */
  public Collection getLatestNews(String[] symbols)
      throws UserManagementEventException {

    ClientSession client = null;
    ArrayList newsList = new ArrayList(symbols.length);
    
    try {
      
      client = server.acquireClientSession();
      
      // Initialize read query to read multiple news items
      ReadAllQuery readNews = new ReadAllQuery(News.class);
      
      ExpressionBuilder newsBuilder = new ExpressionBuilder();
      ExpressionBuilder symbolBuilder = new ExpressionBuilder();
      
      ReportQuery subQuery = new ReportQuery(News.class, symbolBuilder);
            
      subQuery.addMaximum("newsdate");
      
      for(int i=0;i<symbols.length;i++) {
        // SELECT MAX(NewsDate) FROM News WHERE Symbol = ? 
        subQuery.setSelectionCriteria(symbolBuilder.get("symbol").equalsIgnoreCase(symbols[i]));
        
        // Specify to use return collection as ArrayList [ default: Vector ]
        readNews.useCollectionClass(ArrayList.class);

        // SELECT News WHERE Symbol = ? AND NewsDate = ?
        readNews.setSelectionCriteria(newsBuilder.get("newsdate").equal(subQuery)
                                 .and(newsBuilder.get("symbol").equalsIgnoreCase(symbols[i])));
        
        newsList.addAll((ArrayList)client.executeQuery(readNews));
            
      }
    } catch (DatabaseException ex) {     
      throw new UserManagementEventException(" Error while getting "
                                     + " Stock News:\n" + ex.toString());
    } 
    return newsList;    
        
  }
    
}