barcode font vb.net These steps are summarized in figure 14.5. in Java

Generator Data Matrix 2d barcode in Java These steps are summarized in figure 14.5.

These steps are summarized in figure 14.5.
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Figure 14.5 The changes necessary to migrate JDBC DAOs to the EJB 3 JPA
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The next three sections break down each of these steps, and we provide examples to illustrate exactly what you need to do.
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14.5.1 Identifying entities
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This is the most challenging task in the migration process and requires a good understanding of your application. The good news is that applications using DAOs don t have any impact on the business logic tier of the application, and the migration effort is limited only in the persistence tier. If you followed the DAO design pattern religiously, you most likely created value or transfer objects (similar to DTOs) that are used by the business tier to retrieve or update data from the database. A careful look reveals that these transfer objects resemble entities. A little
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Migrating to EJB 3
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analysis is all that is required to understand the relationship between these transfer objects, allowing them to safely be converted to entities. Suppose that ActionBazaar initially used JDBC DAOs for persistence and the transfer object BidTO looked similar to listing 14.6.
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Listing 14.6 Bid transfer object used with a DAO
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public class BidTO implements Serializable { private Timestamp bidDate; Instance fields private Long bidId; private Double bidPrice; private String bidStatus; private ItemTO item; private UserTO bidder; public BidTO() { }
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Pointer to other transfer objects Constructor
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public Timestamp getBidDate() { return bidDate; } public void setBidDate(Timestamp bidDate) { this.bidDate = bidDate; } }
Get/set methods
If you look at the code for BidTO carefully, it looks surprisingly similar to the Bid entity that we discussed in chapter 2. It even has references to the associated transfer objects. The only difference is that it does not have JPA annotations. You can use JPA annotations to convert your transfer objects to entities. The steps are similar to those we listed in section 14.4.2 when we discussed considering DTOs to be entities. Next you ll see how to make the switch to the EntityManager.
14.5.2 Reworking a DAO implementation class to use the EntityManager API
The database-specific implementation class has JDBC code to persist the value or transfer object to the database. Assume that the BidDAOImpl class uses JDBC to persist and retrieve data. The next step in the process is for you to migrate the JDBC code to use the EntityManager API.
Migrating JDBC DAOs to use the EJB 3 JPA
Replace the code that opens and closes JDBC connections to obtain an instance of an EntityManager. For example, your BidDAOImpl class has a method that returns a database connection. You can change that method to return an EntityManager instance. Replace your SQL INSERT/UPDATE/DELETE statements to use the EntityManager API. For instance, one of BidDAOImpl s methods has an INSERT statement that creates an instance of Bid in the database, as seen here:
private final static String INSERT_BID_QUERY_STR = "INSERT INTO BIDS " + "(BID_ID,BIDDER_ID,ITEM_ID,BID_STATUS,BID_PRICE) " + "VALUES ( , , , , )"; private void insertBid(BidTO bid) { ... stmt = dbConnection.prepareStatement(INSERT_BID_QUERY_STR); stmt.setLong(1, bid.getBidId()); stmt.setString(2, bid.getBidder().getUserId().trim()); stmt.setLong(3, bid.getItem().getId()); stmt.setString(4, bid.getStatus().trim()); stmt.setDouble(5, bid.getBidPrice()); }
After migrating the JDBC code to use the EntityManager API, the migrated code will look like this:
private void insertBid(Bid bid) { ... em.persist(bid); }
Wow! Can you believe that Similarly, you can use the em.remove and em.merge methods to migrate the JDBC code for remove or update operations. Next we ll explain how you can migrate your SQL SELECT statements to use JPQL.
14.5.3 Swapping SQL queries for JPQL
Although it may be a little difficult to let go, you have to remember that there are no equivalents for ResultSet and Rowset in the EJB 3 JPA. Most typical applications use SQL statements to retrieve data and construct transfer objects, which are returned to the client instead of returning a ResultSet. Not following the DAO and Transfer Object design patterns will mean additional work for you. Listing 14.7 shows a method in the BidDAOImpl class that returns a list of BidTOs by retrieving a ResultSet from the database.
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