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at-m42:lecture15 [2009/04/25 09:35] – eechrisat-m42:lecture15 [2009/04/25 11:37] – eechris
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 ~~SLIDESHOW~~ ~~SLIDESHOW~~
-====== Business-tier Services ======+====== Enterprise Integration Tier Services ======
    
 In principle, the business logic of an enterprise application could be performed by //domain objects// which implement a model of the business concept as Plain-Old Java Objects (POJOs). In principle, the business logic of an enterprise application could be performed by //domain objects// which implement a model of the business concept as Plain-Old Java Objects (POJOs).
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   * [[#The key business tier services]]   * [[#The key business tier services]]
   * [[#The Java solution: Enterprise Java Beans]]   * [[#The Java solution: Enterprise Java Beans]]
-  * [[#Reimplementing PerfectTime as a session bean]]+  * [[#Reimplementing TimeHere as a session bean]]
   * [[#Is the Java solution a good solution?]]   * [[#Is the Java solution a good solution?]]
  
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   * **[[#The key business tier services]]**   * **[[#The key business tier services]]**
   * [[#The Java solution: Enterprise Java Beans]]   * [[#The Java solution: Enterprise Java Beans]]
-  * [[#Reimplementing PerfectTime as a session bean]]+  * [[#Reimplementing TimeHere as a session bean]]
   * [[#Is the Java solution a good solution?]]   * [[#Is the Java solution a good solution?]]
  
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     * Or simply to be stored in non-volatile memory.     * Or simply to be stored in non-volatile memory.
   * Your business objects want this to //just happen//!   * Your business objects want this to //just happen//!
-    * **Transparent persistence**, as discussed in the [[lecture14|last lecture]], is obviously important,+    * **Transparent persistence**, as discussed in the [[lecture15|last lecture]], is obviously important,
     * but persistence should also be a key part of transaction management and is a cornerstone of data integrity.     * but persistence should also be a key part of transaction management and is a cornerstone of data integrity.
  
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   * [[#The key business tier services]]   * [[#The key business tier services]]
   * **[[#The Java solution: Enterprise Java Beans]]**   * **[[#The Java solution: Enterprise Java Beans]]**
-  * [[#Reimplementing PerfectTime as a session bean]]+  * [[#Reimplementing TimeHere as a session bean]]
   * [[#Is the Java solution a good solution?]]   * [[#Is the Java solution a good solution?]]
  
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   * [[#The key business tier services]]   * [[#The key business tier services]]
   * [[#The Java solution: Enterprise Java Beans]]   * [[#The Java solution: Enterprise Java Beans]]
-  * **[[#Reimplementing PerfectTime as a session bean]]**+  * **[[#Reimplementing TimeHere as a session bean]]**
   * [[#Is the Java solution a good solution?]]   * [[#Is the Java solution a good solution?]]
  
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   * Each method in the remote interface must declare java.rmi.RemoteException in its throws clause in addition to any application-specific exceptions.    * Each method in the remote interface must declare java.rmi.RemoteException in its throws clause in addition to any application-specific exceptions. 
   * Any object passed as an argument or return value (either directly or embedded within a local object) must be a valid RMI-IIOP data type (this includes other EJB objects).   * Any object passed as an argument or return value (either directly or embedded within a local object) must be a valid RMI-IIOP data type (this includes other EJB objects).
-  * In EJB 3, the details can be left to the container: interface is a plain-old-Java interface //annotated//  with ''javax.ejb.Remote''. 
-   
-===== Remote interface for the DateHere EJB ===== 
  
-<code java 1|Example 1: Remote interface for the DateHereBean (at-m42/Examples/lecture14/TimeHere.java)> +===== Remote interface for the DateHere EJB (EJB 2 version) ===== 
-extern> http://cpjobling.org.uk/~eechris/at-m42/Examples/lecture14/TimeHere.java+ 
 +<code java 1| Example 1: Remote interface for the DateHereBean (EJB 2)> 
 +import java.rmi.*; 
 +import javax.ejb.*; 
 + 
 +package uk.ac.swan.atm42.ejb; 
 + 
 +public interface TimeHere extends EJBObject { 
 +  public String getTimeHere() throws RemoteException; 
 +}
 </code> </code>
 +
 +===== Remote interface for the DateHere EJB (EJB 3 version) =====
 +
 +In EJB 3, the details can be left to the container: interface is a plain-old-Java interface //annotated//  with ''javax.ejb.Remote''.
 +  
 +<code java 1|Example 2: Remote interface for the DateHereBean (at-m42/Examples/lecture15/TimeHere.java)>
 +extern> http://cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHere.java
 +</code>
 +
  
 ===== The Home interface ===== ===== The Home interface =====
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   * It can define create methods, to create instances of EJBs   * It can define create methods, to create instances of EJBs
   * //finder// methods, which locate existing EJBs and are used for Entity Beans only.   * //finder// methods, which locate existing EJBs and are used for Entity Beans only.
 +  
 ===== The Home Interface Specification ===== ===== The Home Interface Specification =====
  
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   - The return value of a //finder method// (Entity Beans only) must be a Remote Interface or //java.util.Enumeration// or //java.util.Collection//.    - The return value of a //finder method// (Entity Beans only) must be a Remote Interface or //java.util.Enumeration// or //java.util.Collection//. 
   - Any object passed as an argument (either directly or embedded within a local object) must be a valid RMI-IIOP data type (this includes other EJB objects)   - Any object passed as an argument (either directly or embedded within a local object) must be a valid RMI-IIOP data type (this includes other EJB objects)
-  - In EJB 3 the home interface is provided automatically by the container.+  - In EJB 3 the Home interface is provided automatically by the container and you don't need to provide code. 
 + 
 +===== Home interface for the TimeHere (EJB 2) ===== 
 +<code java 1|Example 3: Remote interface for the DateHereBean (at-m42/Examples/lecture15/TimeHereHome.java)> 
 +extern> http://cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHereHome.java 
 +</code> 
 + 
 +===== Business Logic =====
  
-Home interface for the TimeHere (EJB 2) 
- // Home Interface of PerfectTimeBean. import java.rmi.*; import javax.ejb.*; public interface PerfectTimeHome extends EJBHome {   public PerfectTime create() throws     CreateException, RemoteException; } 
-Business Logic 
 You can now implement the business logic. When you create your EJB implementation class, you must follow these guidelines: You can now implement the business logic. When you create your EJB implementation class, you must follow these guidelines:
-The class must be public.  +  - The class must be ''public''.  
-The class must implement an EJB interface (either javax.ejb.SessionBean or javax.ejb.EntityBean).  +  - The class must implement an EJB interface (either ''javax.ejb.SessionBean'' or ''javax.ejb.EntityBean'').  
-The class should define methods that map directly to the methods in the Remote interface. Note that the class does not implement the Remote interface; it mirrors the methods in the Remote interface but does not throw java.rmi.RemoteException.  +  - The class should define methods that map directly to the methods in the Remote interface. Note that the class does not implement the Remote interface; it mirrors the methods in the Remote interface but does not throw ''java.rmi.RemoteException''.   - Define one or more ''ejbCreate()'' methods to initialize your EJB.  
-Define one or more ejbCreate( ) methods to initialize your EJB.  +  - The return value and arguments of all methods must be valid RMI-IIOP data types.
-The return value and arguments of all methods must be valid RMI-IIOP data types. +
-PerfectTimeBean (Session Bean) +
- // Simple Stateless Session Bean // that returns current system time. import java.rmi.*; import javax.ejb.*; public class PerfectTimeBean implements SessionBean {   private SessionContext sessionContext;   //return current time   public long getPerfectTime() {     return System.currentTimeMillis();   }   // EJB methods   public void ejbCreate() throws CreateException {}   public void ejbRemove() {}   public void ejbActivate() {}   public void ejbPassivate() {}   public void setSessionContext(SessionContext ctx) {     sessionContext = ctx;   } +
-  } +
-Deployment Descriptor +
-An XML file that describes the EJB component. Should be stored in a file called ejb-jar.xml. <?xml version="1.0" encoding="Cp1252"?> <!DOCTYPE ejb-jar PUBLIC '-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 1.1//EN' 'http://java.sun.com/j2ee/dtds/ejb-jar_1_1.dtd'> <ejb-jar>   <description>Example for Chapter 15</description>   <display-name></display-name>   <small-icon></small-icon>   <large-icon></large-icon>   <enterprise-beans>     <session>       <ejb-name>PerfectTime</ejb-name>       <home>PerfectTimeHome</home>       <remote>PerfectTime</remote>       <ejb-class>PerfectTimeBean</ejb-class>       <session-type>Stateless</session-type>       <transaction-type>Container</transaction-type>     </session>   </enterprise-beans>   <ejb-client-jar></ejb-client-jar> </ejb-jar> +
-Deploying the EJB +
-The files must be archived inside a standard Java Archive (JAR) file. The deployment descriptors should be placed inside the /META-INF sub-directory of the Jar file. +
-Once the EJB component is defined in the deployment descriptor, the deployer should then deploy the EJB component into the EJB Container. +
-The deployment process is quite “GUI intensive” and specific to the individual EJB Container. +
-The deployment process creates some client stubs for calling the EJB component. These classes should be placed on the classpath of the client application. +
-When a client program wishes to invoke an EJB, it must look up the EJB component inside JNDI and obtain a reference to the home interface of the EJB component. The Home interface is used to create an instance of the EJB.  +
-The Client +
-Here a simple Java program but could just as easily be a servlet, a JSP or even a CORBA or RMI distributed object. // Client program for PerfectTimeBean public class PerfectTimeClient {   public static void main(String[] args) throws Exception {     // Get a JNDI context using     // the JNDI Naming service:     javax.naming.Context context = new       javax.naming.InitialContext();     // Look up the home interface in the     // JNDI Naming service:     Object ref = context.lookup("perfectTime");     // Cast the remote object to the home interface:     PerfectTimeHome home = (PerfectTimeHome)       javax.rmi.PortableRemoteObject.narrow(         ref, PerfectTimeHome.class); +
-The Client … cont +
-    // Create a remote object from the home interface:     PerfectTime pt = home.create();     // Invoke getPerfectTime()     System.out.println(       "Perfect Time EJB invoked, time is: " +         pt.getPerfectTime());   } } +
  
-=====  Lecture Content =====+===== TimeHereBean (Session Bean) EJB 2 Version =====
  
-  * [[#An example]] +<code java 1| Example 4: SessionBean implemented using EJB 2 conventions> 
-  * [[#The key business tier services]] +// Simple Stateless Session Bean 
-  * [[#The Java solution: Enterprise Java Beans]] +// that returns current system time.
-  * [[#Reimplementing PerfectTime as a session bean]] +
-  * **[[#Is the Java solution a good solution?]]**+
  
 +package uk.ac.swan.atm42.ejb;
  
 +import java.rmi.*;
 +import javax.ejb.*;
  
-===== Is the Java Solution a Good Solution? ===== +public class TimeHereBean implements SessionBean { 
-During 2004, the developer community decided that the answer is probably no. +  private SessionContext sessionContext; 
-We will discuss this issue, and some of the alternatives in the final lecture. +  //return time here   
-Eckel’s PerfectTime session EJB example gives a flavour of the complexity! To run the example, you’ll need an implementation of a J2EE container to which you can deploy the bean. +  public String getTimeHere() { 
-It’s a good example of a bad design if nothing else!+    return new Date().toString(); 
 +  }   
 +  // EJB methods  
 +  public void ejbCreate() throws CreateException {}   
 +  public void ejbRemove() {} 
 +  public void ejbActivate() {} 
 +  public void ejbPassivate() {} 
 +  public void setSessionContext(SessionContext ctx) { 
 +    sessionContext = ctx; 
 +  } 
 +} 
 +</code>
  
-=====  Lecture Content =====+===== Version 3 EJBs =====
  
-  * [[#An example]] +  * Most of the code in previous example is "//boiler plate//" providiing "hooks" for the container.  
-  * [[#The key business tier services]] +  * EJB uses Java 5 annotations to enable the container to provide its own hooks. 
-  * [[#The Java solution: Enterprise Java Beans]] +  * EJB is now a "Plain Old Java Object" (POJO)) annotated with ''javax.ejb.Stateless''
-  * [[#Reimplementing PerfectTime as a session bean]] +
-  * [[#Is the Java solution a good solution?]]+
  
 +===== TimeHereBean (Session Bean) EJB 3 Version =====
 +<code java 1| Example 5: SessionBean implemented using EJB 3 conventions (at-m42/Examples/lecture15/TimeHereBean.java)>
 +extern> http://www.cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHereBean.java
 +</code>
  
 +===== Deployment Descriptor (EJB 2) =====
  
-----+An XML file that describes the EJB component. Should be stored in a file called ''ejb-jar.xml''. 
 +<code xml 1|Example 6: Deployment Descriptor for the TimeHereBean (not required in EJB 3 containers) (at-m42/Examples/lecture15/ejb-jar.xml)> 
 +extern> http://www.cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/ejb-jar.xml 
 +</code> 
 +===== Deploying the EJB =====
  
-[[Home]] | [[lecture14|Previous Lecture]] | [[Lectures]] | [[lecture16|Next Lecture]] +  * The files must be archived inside a standard Java Archive (JAR) file. The deployment descriptors (if used) should be placed inside the ''/META-INF'' sub-directory of the Jar file. 
 +  * Once the EJB component is defined in the deployment descriptor, the deployer should then deploy the EJB component into the EJB Container. 
 +  * The deployment process is quite "GUI intensive2 and specific to the individual EJB Container. 
 +  * The deployment process creates some client stubs for calling the EJB component. These classes should be placed on the CLASSPATH of the client application. 
 +  * When a client program wishes to invoke an EJB it must look up the EJB component inside JNDI and obtain a reference to the home interface of the EJB component. The Home interface is used to create an instance of the EJB.  
 + 
 +===== The Client ===== 
 + 
 +  * Here a simple Java program but could just as easily be a servlet, a JSP or even a CORBA or RMI distributed object. 
 + 
 +<code java 1|Example 7: Client program for TimeHereBean (at-m42/Examples/lecture15/TimeHereClient.java)> 
 +extern> http://www.cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHereClient.java 
 +</code> 
 +<code java 1| Example 7: Client program for TimeHereBean (at-m42/Examples/lecture15/TimeHereClient.java)>  
 +extern> http://www.cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHereClient.java 
 +</code>
  
 =====  Lecture Content ===== =====  Lecture Content =====
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   * [[#The key business tier services]]   * [[#The key business tier services]]
   * [[#The Java solution: Enterprise Java Beans]]   * [[#The Java solution: Enterprise Java Beans]]
-  * [[#Reimplementing PerfectTime as a session bean]]+  * [[#Reimplementing TimeHere as a session bean]]
   * **[[#Is the Java solution a good solution?]]**   * **[[#Is the Java solution a good solution?]]**
- 
- 
  
 ===== Is the Java Solution a Good Solution? ===== ===== Is the Java Solution a Good Solution? =====
-During 2004, the developer community decided that the answer is probably no. 
-We will discuss this issue, and some of the alternatives in the final lecture. 
-Eckel’s PerfectTime session EJB example gives a flavour of the complexity! To run the example, you’ll need an implementation of a J2EE container to which you can deploy the bean. 
-It’s a good example of a bad design if nothing else! 
  
-=====  Lecture Content =====+  * During 2004, the developer community decided that the answer is probably no. 
 +  * EJB 3 was a response to this, and uses annotations to simplify it. 
 +  * We will discuss this issue, and some of the alternatives in the final lecture. 
 +  * The TimeHere session EJB example gives a flavour of the complexity! To run the example, you’ll need an implementation of a Java EE container (e.g. Glassfish) to which you can deploy the bean. 
 + 
 +=====  Lecture Summary =====
  
   * [[#An example]]   * [[#An example]]
   * [[#The key business tier services]]   * [[#The key business tier services]]
   * [[#The Java solution: Enterprise Java Beans]]   * [[#The Java solution: Enterprise Java Beans]]
-  * [[#Reimplementing PerfectTime as a session bean]]+  * [[#Reimplementing TimeHere as a session bean]]
   * [[#Is the Java solution a good solution?]]   * [[#Is the Java solution a good solution?]]
  
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 ---- ----
  
-[[Home]] | [[lecture14|Previous Lecture]] | [[Lectures]] | [[lecture16|Next Lecture]] +[[Home]] | [[lecture15|Previous Lecture]] | [[Lectures]] | [[lecture16|Next Lecture]]  
 + 
at-m42/lecture15.txt · Last modified: 2011/01/14 12:45 by 127.0.0.1