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at-m42:lecture15 [2009/04/25 10:01] – eechrisat-m42:lecture15 [2011/01/14 12:45] (current) – external edit 127.0.0.1
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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> 
 + 
 +===== 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> </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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 ===== Home interface for the TimeHere (EJB 2) ===== ===== Home interface for the TimeHere (EJB 2) =====
-<code java 1|Example 2: Remote interface for the DateHereBean (at-m42/Examples/lecture14/TimeHereHome.java)> +<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/lecture14/TimeHereHome.java+extern> http://cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHereHome.java
 </code> </code>
  
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   - 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) EJB 2 Version ===== +===== TimeHereBean (Session Bean) EJB 2 Version ===== 
-<code java 1: Example 3: SessionBean implemented using EJB 2 conventions>+ 
 +<code java 1| Example 4: SessionBean implemented using EJB 2 conventions>
 // Simple Stateless Session Bean // Simple Stateless Session Bean
- // that returns current system time.+// that returns current system time.
  
- import java.rmi.*; +package uk.ac.swan.atm42.ejb; 
 + 
 +import java.rmi.*;
 import javax.ejb.*; import javax.ejb.*;
- +
 public class TimeHereBean implements SessionBean { public class TimeHereBean implements SessionBean {
-   private SessionContext sessionContext; +  private SessionContext sessionContext; 
-   //return time here   +  //return time here   
-  public String getTimeHere() { +  public String getTimeHere() {
     return new Date().toString();     return new Date().toString();
-   }    +  }   
-  // EJB methods    +  // EJB methods  
-  public void ejbCreate() throws CreateException {}    +  public void ejbCreate() throws CreateException {}   
-  public void ejbRemove() {}    +  public void ejbRemove() {} 
-  public void ejbActivate() {}    +  public void ejbActivate() {} 
-  public void ejbPassivate() {}    +  public void ejbPassivate() {} 
-  public void setSessionContext(SessionContext ctx) {  +  public void setSessionContext(SessionContext ctx) { 
-    sessionContext = ctx; +    sessionContext = ctx;
   }   }
 } }
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   * EJB is now a "Plain Old Java Object" (POJO)) annotated with ''javax.ejb.Stateless''   * EJB is now a "Plain Old Java Object" (POJO)) annotated with ''javax.ejb.Stateless''
  
-===== PerfectTimeBean (Session Bean) EJB 2 Version ===== +===== TimeHereBean (Session Bean) EJB 3 Version ===== 
-<code java 1: Example 4: SessionBean implemented using EJB 3 conventions (at-m42/Examples/lecture14/TimeHereBean.java)> +<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/lecture14/TimeHereBean.java+extern> http://www.cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHereBean.java
 </code> </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 =====
  
 +  * 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. 
  
-Deployment Descriptor +===== The Client ===== 
-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 +  * Here a simple Java program but could just as easily be a servlet, a JSP or even a CORBA or RMI distributed object. 
-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. +<code java 1|Example 7: Client program for TimeHereBean (at-m42/Examples/lecture15/TimeHereClient.java)> 
-The deployment process is quite “GUI intensive” and specific to the individual EJB Container. +extern> http://www.cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHereClient.java 
-The deployment process creates some client stubs for calling the EJB component. These classes should be placed on the classpath of the client application. +</code> 
-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.  +<code java 1| Example 7: Client program for TimeHereBean (at-m42/Examples/lecture15/TimeHereClient.java)>  
-The Client +extern> http://www.cpjobling.org.uk/~eechris/at-m42/Examples/lecture15/TimeHereClient.java 
-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); +</code>
-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 ===== =====  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? =====
  
 +  * 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.
  
-===== Is the Java Solution a Good Solution? ===== +=====  Lecture Summary =====
-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 =====+
  
   * [[#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]] 
  
-=====  Lecture Content ===== 
- 
-  * [[#An example]] 
-  * [[#The key business tier services]] 
-  * [[#The Java solution: Enterprise Java Beans]] 
-  * [[#Reimplementing PerfectTime as a session bean]] 
-  * **[[#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 ===== 
- 
-  * [[#An example]] 
-  * [[#The key business tier services]] 
-  * [[#The Java solution: Enterprise Java Beans]] 
-  * [[#Reimplementing PerfectTime as a session bean]] 
-  * [[#Is the Java solution a good solution?]] 
- 
- 
- 
----- 
  
-[[Home]] | [[lecture14|Previous Lecture]] | [[Lectures]] | [[lecture16|Next Lecture]]  
at-m42/lecture15.1240653716.txt.gz · Last modified: 2011/01/14 12:24 (external edit)