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The rest of the XML elements are nested one within the other and are delimited by a beginning tag and ending tag. The structure is really not very complicated. If you have done any HTML coding you should already understand the format. An element always starts with tag and ends with tag. Everything in between even other elements is part of the enclosing element. The first major element is the element, which is the root of the document. All the other elements must lie within this element. Next is the element. Every bean declared in an XML file must be included in this section. This file only describes the Cabin EJB, but we could define several beans in one deployment descriptor. The element shows that the beans defined within this tag are entity beans. Similarly, a element describes session beans; since the Cabin EJB is an entity bean, we don t need a element. In addition to a description, the element provides the fully qualified class names of the remote interface, home interface, bean class, and primary key. The elements list all the container-managed fields in the entity bean class. These are the fields that will be persisted in the database and are managed by the container at runtime. The element also includes a element that can be set as True or False depending on whether the bean allows reentrant loopbacks or not. EJB 2.0 specifies a name which is used in EJB QL to identify the entity bean in queries. This isn t important right now. The 2.0 deployment descriptor also specifies as , which simply means the bean will propagate the calling clients security identity when access resources or other beans. This was covered in detail in Chapter 3. The next section of the XML file, after the element, is enclosed by the element, which describes the security roles and transactional attributes of the bean. This section is the same for both EJB 2.0 and EJB 1.1 in this example. … This role represents everyone who is allowed full access to the Cabin EJB. everyone Copyright (c) 2001 O’Reilly & Associates 12
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name deckLevel shipId bedCount
id … EJB 1.1: The Cabin EJB s Deployment Descriptor CabinEJB com.titan.cabin.CabinHomeRemote com.titan.cabin.CabinRemote com.titan.cabin.CabinBean
Container java.lang.Integer False id name deckLevel shipId bedCount
id … EJB 2.0 and 1.1: Defining the XML elements The element describes the purpose of the XML file, its root element, and the location of its DTD. The DTD is used to verify that the document is structured correctly. This element is discussed in detail in Chapter 16. One important distinction between EJB 2.0 and EJB 1.1 is that they use different DTD for deployment descriptors. EJB 2.0 specifies the ejbjar_ 2_0.dtd while EJB 1.1 specifies the ejb-jar_1_1.dtd. Copyright (c) 2001 O’Reilly & Associates 11
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which classes make up a enterprise bean and how the enterprise bean should be managed at runtime. During deployment, the deployment descriptor is read and its properties are displayed for editing. The deployer can then modify and add settings as appropriate for the application s operational environment. Once the deployer is satisfied with the deployment information, he or she uses it to generate the entire supporting infrastructure needed to deploy the enterprise bean in the EJB server. This may include adding the enterprise bean to the naming system and generating the enterprise bean s EJB object and EJB home, persistence infrastructure, transactional support, resolving enterprise bean references, and so forth. Although most EJB server products provide a wizard for creating and editing deployment descriptors, we will create ours directly so that the enterprise bean is defined in a vendor-independent manner.4 This requires some manual labor, but it gives you a much better understanding of how deployment descriptors are created. Once the deployment descriptor is finished, the enterprise bean can be placed in a JAR file and deployed on any EJB-compliant server of the appropriate version. An XML deployment descriptor for every example in this book has already been created and is available from the download site. Here s a quick peek at the deployment descriptor for the Cabin EJB, so you can get a feel for how an XML deployment descriptor is structured and the type of information it contains: EJB 2.0: The Cabin EJB s Deployment Descriptor CabinEJB com.titan.cabin.CabinHomeRemote com.titan.cabin.CabinRemote com.titan.cabin.CabinBean
Container java.lang.Integer False Cabin id 4 The workbooks show you how to use the vendor s tools for creating deployment descriptors. Copyright (c) 2001 O’Reilly & Associates 10
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method. When a client invokes the create() method on the remote home interface, it is delegated to a matching ejbCreate() method on the entity bean instance. The ejbCreate() method initializes the fields; in the case of the CabinBean, it sets the namevirtual field. The ejbCreate() method always returns the primary key type; with container- managed persistence, this method returns the null value. It s the container s responsibility to create the primary key. Why does it return null? Simply put, it makes it easier for a bean-managed enterprise bean to extend a container-managed enterprise bean. This is valuable for EJB vendors who support container-managed persistence beans by extending them with bean- managed persistence beans implementations it s a technique that was more common in EJB 1.1. Bean-managed persistence beans, which are covered in Chapter 10, always return the primary key type. Once the ejbCreate() method has executed, the ejbPostCreate() method is called to perform any follow-up operations. The ejbCreate() and ejbPostCreate() methods must have signatures that match the parameters and (optionally) the exceptions of the home interface s create() method. The ejbPostCreate() method is used to perform any post processing on the bean after its created, but before it can be used by the client. Both methods will execute, one right after the other, when the client invokes the create() method on the remote home interface. The findByPrimaryKey() method is not defined in container-managed bean classes. Instead, find methods are generated at deployment and implemented by the container. With bean-managed entity beans (entity beans that explicitly manage their own persistence), find methods must be defined in the bean class. In Chapter 10, when you develop bean-managed entity beans, you will define the find methods in the bean classes you develop. The CabinBeanclass implements javax.ejb.EntityBean, which defines five callback methods: setEntityContext(), unsetEntityContext(), ejbActivate(), ejbPassivate(), ejbLoad(), ejbStore(), and ejbRemove(). The container uses these callback methods to notify the CabinBean of certain events in its life cycle. Although the callback methods are implemented, the implementations are empty. The CabinBean is simple enough that it doesn t need to do any special processing during its life cycle. When we study entity beans in more detail in Chapters 6 through 11, we will take advantage of these callback methods. The Deployment Descriptor You are now ready to create a deployment descriptor for the Cabin EJB. The deployment descriptor performs a function similar to a properties file. It describes Copyright (c) 2001 O’Reilly & Associates 9
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} public int getDeckLevel() { return deckLevel; } public void setDeckLevel(int level ) { deckLevel = level; } public void setEntityContext(EntityContext ctx) { // Not implemented. } public void unsetEntityContext() { // Not implemented. } public void ejbActivate() { // Not implemented. } public void ejbPassivate() { // Not implemented. } public void ejbLoad() { // Not implemented. } public void ejbStore() { // Not implemented. } public void ejbRemove() { // Not implemented. } } Declared fields in a bean class can be persistent fields and property fields. These categories are not mutually exclusive. The persistent field declarations describe the fields that will be mapped to the database. A persistent field is often a property (in the JavaBeans sense): any attribute that is available using public set and get methods. Of course, a bean can have any fields that it needs; they need not all be persistent, or properties. Fields that aren t persistent won t be saved in the database. In CabinBean, all the fields are persis tent. The id field is persistent, but it is not a property. In other words, id is mapped to the database but cannot be accessed through the remote interface. The name, deckLevel, ship, and bedCount fields are persistent fields. They will be mapped to the database at deployment time. These fields are also properties because they are publicly available through the remote interface. EJB 2.0 and 1.1: The callback methods In the case of the Cabin EJB, there was only one create() method, so there is only one corresponding ejbCreate() method and one ejbPostCreate() Copyright (c) 2001 O’Reilly & Associates 8
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throw the RemoteException like the matching methods in the remote interface. There is no requirement that CMP fields must be exposed. The id field is another container-managed field, but its abstract accessor methods are not exposed to the client through the CabinRemote interface. This field is the primary key of the Cabin EJB; it s the entity bean s index to its data in the database. It s bad practice to expose the primary key of an entity bean so that it can be modified by a client. You don t want client applications changing that index. EJB 1.1: The Bean Class Here is the complete definition of the CabinBean class in EJB 1.1: package com.titan.cabin; import javax.ejb.EntityContext; public class CabinBean implements javax.ejb.EntityBean { public Integer id; public String name; public int deckLevel; public int shipId; public int bedCount; public Integer ejbCreate(Integer id) { this.id = id; return null; } public void ejbPostCreate(Integer id) { // Do nothing. Required. } public String getName() { return name; } public void setName(String str) { name = str; } public int getShipId() { return shipId; } public void setShipId(int sp) { shipId = sp; } public int getBedCount() { return bedCount; } public void setBedCount(int bc) { bedCount = bc; Copyright (c) 2001 O’Reilly & Associates 7
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public void ejbActivate() { // Not implemented. } public void ejbPassivate() { // Not implemented. } public void ejbLoad() { // Not implemented. } public void ejbStore() { // Not implemented. } public void ejbRemove() { // Not implemented. } } The CabinBean class can be divided into four sections for discussion: declarations for the container-managed fields, the ejbCreate() methods, the callback methods, and the remote interface implementations. The CabinBean defines several abstract accessor methods that appear in pairs. For example, the abstract methods setName() and getName() are a pair of abstract accessor methods. These methods will be responsible for setting and getting the entity bean s name field. When the bean is deployed, the EJB container automatically implements all the abstract accessor methods so that the bean state can be synchronized with the database. These implementations map the abstract accessor methods to fields in the database. Although all the abstract accessor methods have corresponding methods in the remote interface, CabinRemote, it s not necessary that they do so. Some accessor methods are for the entity bean s use only and are never exposed to the client through the remote or local interfaces. It s customary in EJB 2.0 to consider the abstract accessor methods as providing access to virtual fields and to refer to those fields by their method name, less the get or set prefix. For example, the getName()/setName() abstract accessor methods define a virtual container-managed persistence field called name the first letter is always changed to lower case. The getDeckLevel()/setDeckLevel() abstract accessor methods define a virtual container-managed persistence field called deckLevel, and so on. The name, deckLevel, ship, and bedCount virtual container-managed persistence fields represent the Cabin EJB s persistent state. They will be mapped to the database at deployment time. These fields are also publicly available through the entity bean s remote interface. Invoking the getBedCount() method on a CabinRemote EJB object at runtime causes the container to delegate that call to the corresponding getBedCount() method on the CabinBean instance. The abstract accessor methods do not Copyright (c) 2001 O’Reilly & Associates 6
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CabinBean: The Bean Class You have now defined the complete client-side API for creating, locating, removing, and using the Cabin EJB. Now we need to define CabinBean, the class that provides the implementation on the server for the Cabin EJB. The CabinBean class is an entity bean that uses container-managed persistence, so its definition will be fairly simple. In addition to the callback methods discussed in Chapters 2 and 3, we must also define abstract accessor methods for the methods defined in the CabinRemote interface and an implementation of the create method defined in the CabinHomeRemote interface. EJB 2.0: The Cabin Bean Here is the complete definition of the CabinBean class: package com.titan.cabin; public abstract class CabinBean implements javax.ejb.EntityBean { public Integer ejbCreate(Integer id){ this.setId(id); } public void ejbPostCreate(String name){ } public abstract void setId(Integer id); public abstract Integer getId(); public abstract void setShipId(int ship); public abstract int getShipId( ); public abstract void setName(String name); public abstract String getName( ); public abstract void setBedCount(int count); public abstract int getBedCount( ); public abstract void setDeckLevel(int level); public abstract int getDeckLevel( ); public void setEntityContext(EntityContext ctx) { // Not implemented. } public void unsetEntityContext() { // Not implemented. } Copyright (c) 2001 O’Reilly & Associates 5
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for the use of the Titan cruise line, we place these packages in the com.titan package hierarchy. We also create directory structures that match package structures. If you are using an IDE that works directly with Java files, create a new directory somewhere called dev (for development) and create the directory structure shown in Figure 4-1. Copy the CabinRemote interface into your IDE and save its definition to the cabin directory. Compile the CabinRemote interface to ensure that its definition is correct. The CabinRemote.class file, generated by the IDE s compiler, should be written to the cabin directory, the same directory as the CabinRemote. java file. The rest of the Cabin bean s classes will be placed in this same directory. [FIGURE] Figure 4-1: Directory structure for the Cabin bean CabinHome: The Home Interface Once we have defined the remote interface of the Cabin EJB, we have defined the remote view of this simple entity bean. Next, we need to define the Cabin EJB s remote home interface, which specifies how the enterprise bean can be created, located, and destroyed by remote clients; in other words, the Cabin EJB s life- cycle behavior. Here is a complete definition of the CabinHomeRemote home interface: package com.titan.cabin; import java.rmi.RemoteException; import javax.ejb.CreateException; import javax.ejb.FinderException; public interface CabinHomeRemote extends javax.ejb.EJBHome { public CabinRemote create(Integer id) throws CreateException, RemoteException; public CabinRemote findByPrimaryKey(Integer pk) throws FinderException, RemoteException; } The CabinHomeRemote interface extends the javax.ejb.EJBHome and defines two life- cycle methods: create() and findByPrimaryKey(). These methods create and locate remote references to Cabin EJBs. Remove methods (for deleting enterprise beans) are defined in the javax.ejb.EJBHome interface, so the CabinHomeRemote interface inherits them. for most products. The workbooks provide additional help for organizing your development projects, and will point out any vendor-specific requirements. Copyright (c) 2001 O’Reilly & Associates 4
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Developing an Entity Bean There seems to be no better place to start than the Cabin EJB, which we have been examining throughout the previous chapters. The Cabin EJB is an entity bean that encapsulates the data and behavior associated with a cruise ship cabin in Titan s business domain. Cabin: The Remote Interface When developing an entity bean, we first want to define the enterprise bean s remote interface. The remote interface defines the enterprise bean s business purpose; the methods of this interface must capture the concept of the entity. We defined the remote interface for the Cabin EJB in Chapter 2; here, we add two new methods for setting and getting the ship ID and the bed count. The ship ID identifies the ship that the cabin belongs to, and the bed count tells how many people the cabin can accommodate. package com.titan.cabin; import java.rmi.RemoteException; public interface CabinRemote extends javax.ejb.EJBObject { public String getName() throws RemoteException; public void setName(String str) throws RemoteException; public int getDeckLevel() throws RemoteException; public void setDeckLevel(int level) throws RemoteException; public int getShipId() throws RemoteException; public void setShipId(int sp) throws RemoteException; public int getBedCount() throws RemoteException; public void setBedCount(int bc) throws RemoteException; } The CabinRemote interface defines four properties: the name, deckLevel, ship, and bedCount. Properties are attributes of an enterprise bean that can be accessed by public set and get methods. The methods that access these properties are not explicitly defined in the CabinRemote interface, but the interface clearly specifies that these attributes are readable and changeable by a client. Notice that we have made the CabinRemote interface a part of a new package named com.titan.cabin. Place all the classes and interfaces associated with each type of bean in a package specific to the bean.3 Because our beans are 3 The examples, which can be downloaded from www.oreilly.com, provide a good guide for how to organize your code; the code is organized in a directory structure that s typical Copyright (c) 2001 O’Reilly & Associates 3
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