Java Enterprise Best Practices

Use Lazy Loading

Most BMP entity beans are implemented so that ejbLoad( ) populates all data fields in the bean. In nearly every case this is fine because all this data will be used at some point. However, there are instances when you should delay loading parts of the data until it’s actually needed. This process, called lazy-loading, will save memory and decrease database access times.

The most common example of this is an entity bean that contains large binary or text data in Blob or Clob form. If this data is accessed less often than other data fields in the entity bean, it makes sense to delay reading this data until the client requests it. To implement this lazy-loading technique, you simply have to use a flag to indicate whether the data has been loaded. Example 2-7 shows a basic instance of this.

Example 2-7. Using a lazy-loading technique

public class ForumMessageBean implements EntityBean { // Persisted fields private Integer id; private String title; private String author; private String messageText; // This is your large data field. private boolean isMessageTextLoaded; // Skipping irrelevant EJB methods . . . public Integer ejbCreate (String title, String author, StringBuffer message) throws CreateException { // Create new record in the database: // INSERT INTO message VALUES (.....) // and get ID back. this.id = id; this.title = title; this.author = author; this.messageText = messageText; // Indicate that the text is in the bean. isMessageTextLoaded = true; } public ...