Fast Track to EJB 3.0

Transcription

1 Fast Track to EJB 3.0 using JBoss 4/5 and Eclipse LearningPatterns, Inc. Courseware JBoss is a registered trademark of Red Hat, Inc. in the U.S. and other countries. LearningPatterns has no affiliation with Red Hat. LearningPatterns is a trademark of LearningPatterns Inc. Student Guide

2 This material is copyrighted by LearningPatterns Inc. This content and shall not be reproduced, edited, or distributed, in hard copy or soft copy format, without express written consent of LearningPatterns Inc. Copyright LearningPatterns Inc. For more information about Java Enterprise Java, or related courseware, please contact us. Our courses are available globally for license, customization and/or purchase. LearningPatterns. Inc. Global Courseware Services 55 Wanaque Ave. #188 Pompton Lakes, NJ USA voice fax Java, and all Java-based trademarks and logo trademarks are registered trademarks of Sun Microsystems, Inc., in the United States and other countries. LearningPatterns and its logos are trademarks of LearningPatterns Inc. All other products referenced herein are trademarks of their respective holders.

3 Table of Contents - Fast Track to EJB3 ENTERPRISE JAVABEANS V WORKSHOP OVERVIEW... 2 WORKSHOP OBJECTIVES... 3 WORKSHOP AGENDA... 4 COURSE PREREQUISITES... 5 RELEASE LEVEL... 6 SESSION 1: INTRODUCTION... 7 LESSON OBJECTIVES... 8 OVERVIEW... 9 WHAT IS EJB EJB GOALS EJB GOALS (CONTINUED) TYPES OF ENTERPRISE JAVABEANS JAVA PERSISTENCE API EJB AND JAVA EE (ENTERPRISE EDITION) EJB IN JAVA EE ARCHITECTURE SOA AND EJB SOA WITH WEB SERVICES AND EJB EJB EJB 3.0 OVERVIEW EJB 2.X PROBLEMS EJB 3.0 GOALS EJB 3.0 GOALS SESSION BEAN USAGE SESSION BEAN USAGE PERSISTENT ENTITY USAGE MDB USAGE LAB 1.1 SETTING UP THE ENVIRONMENT REVIEW QUESTIONS LESSON SUMMARY SESSION 2: SESSION BEANS LESSON OBJECTIVES SESSION BEAN OVERVIEW WHAT ARE SESSION BEANS STATELESS SESSION BEANS (SLSB) STATEFUL SESSION BEANS (SFSB) SESSION BEANS CAN BE DISTRIBUTED DEFINING A SESSION BEAN STATELESS SESSION BEAN DEFINITION CALCULATOR REMOTE BUSINESS INTERFACE REMOTE AND LOCAL BUSINESS INTERFACES CALCULATOR BEAN LOCAL BUSINESS INTERFACE A BRIEF NOTE ON ANNOTATIONS HOW ANNOTATIONS WORK ANNOTATION DEFINITION USING ANNOTATIONS Copyright , LearningPatterns Inc. All rights reserved i

4 WHAT ELSE IS NEEDED PACKAGING AND DEPLOYMENT J2EE PACKAGING EJB-JAR FILE DEPLOYMENT DESCRIPTOR (DD) DEPLOYMENT DESCRIPTORS IN EJB EJB-JAR FILE STRUCTURE ENTERPRISE ARCHIVE (EAR FILE) APPLICATION.XML FILE SERVER DEPLOYMENT EJB CONTAINER THE EJB CONTAINER...74 SERVER DEPLOYMENT LAB 2.1 WRITE AND DEPLOY AN EJB JNDI OVERVIEW HOW DO REMOTE CLIENTS GET EJB ACCESS JNDI JAVA NAMING AND DIRECTORY INTERFACE EJB CONTAINER BINDS A REFERENCE INTO JNDI CLIENT LOOKS UP REFERENCE IN JNDI JNDI TREE STRUCTURE JNDI TREE STRUCTURE JNDI API OVERVIEW...98 JNDI API THE CONTEXT INTERFACE THE INITIALCONTEXT CLASS SPECIFYING THE INITIALCONTEXT PROPERTIES USING JNDI EJB CLIENT CLIENT VIEW OF A SESSION BEAN CLIENT INVOCATION OF A SESSION EJB PORTABLEREMOTEOBJECT AND CASTING RUNNING A CLIENT LAB 2.2 WRITE AND RUN AN EJB CLIENT REVIEW QUESTIONS LESSON SUMMARY SESSION 3: ADDITIONAL EJB CAPABILITIES LESSON OBJECTIVES DEPENDENCY INJECTION DEPENDENCY INJECTION THE JAVATUNES ONLINE MUSIC STORE AN EJB REFERENCING ANOTHER EJB CATALOGMAINTENANCE INJECTION OF CATALOGMAINTENANCE WHAT IS HAPPENING LAB 3.1 DEPENDENCY INJECTION DEPLOYMENT DESCRIPTORS MORE ABOUT DEPLOYMENT DESCRIPTORS THE XML DEPLOYMENT DESCRIPTOR SAMPLE STANDARD DEPLOYMENT DESCRIPTOR Copyright , LearningPatterns Inc. All rights reserved ii

5 THE EJB ENVIRONMENT ISSUES WITH OBTAINING RESOURCES REFERENCING RESOURCES EXTERNAL TO EAR REFERENCES & DEPLOYMENT DESCRIPTOR USAGE RESOLVING A JNDI NAME RESOLVING A JNDI NAME SIMPLE ENVIRONMENT ENTRIES SIMPLE ENVIRONMENT ENTRY EXAMPLE DECLARING SIMPLE ENVIRONMENT ENTRIES SETTER INJECTION RESOURCE MANAGER CONNECTION FACTORIES RESOURCE MANAGER CONNECTION FACTORIES DATASOURCE REFERENCE EXAMPLE - BEAN DATASOURCE REFERENCE EXAMPLE - DD MORE ON THE ENTERPRISE BEAN ENVIRONMENT THE ENVIRONMENT IS A LEVEL OF INDIRECTION LOOKING UP RESOURCES IN THE ENVIRONMENT LOOKING UP VIA EJBCONTEXT LOOKING UP VIA JNDI API MORE ON ANNOTATION... EXAMPLE MORE ON ANNOTATION MORE ON ANNOTATION DEPLOYMENT DESCRIPTOR VS ANNOTATION LAB 3.2 SIMPLE ENVIRONMENT ENTRY STATELESS SESSION BEAN LIFECYCLE & INTERCEPTORS OVERVIEW STATELESS SESSION BEAN STATE DIAGRAM LIFE CYCLE OF SSB CLIENT CALL OF A STATELESS SB METHOD INTERCEPTORS BUSINESS METHOD INTERCEPTORS BUSINESS METHOD INTERCEPTORS EXAMPLE INVOCATIONCONTEXT INTERFACE DETAILS INTERCEPTOR METHOD DETAILS INTERCEPTOR CLASS USING INTERCEPTOR CLASSES METHOD LEVEL INTERCEPTORS LIFECYCLE CALLBACK INTERCEPTORS LIFECYCLE INTERCEPTOR IN THE BEAN CLASS LIFECYCLE INTERCEPTOR IN A SEPARATE CLASS LAB 3.3 INTERCEPTORS STATEFUL SESSION BEANS STATEFUL SESSION BEAN (SFSB) OVERVIEW CODING A STATEFUL SESSION BEAN STATEFUL SESSION BEAN CLIENTS STATEFUL SESSION BEAN REMOVAL STATEFUL SESSION PASSIVATION/ACTIVATION WHEN TO USE STATEFUL SESSION BEANS... CALLBACKS STATEFUL SESSION BEAN STATE DIAGRAM LAB 3.4 STATEFUL SESSION BEANS THE TIMER SERVICE Copyright , LearningPatterns Inc. All rights reserved iii

6 OVERVIEW BEAN REQUIREMENTS THE JAVAX.EJB.TIMER INTERFACE THE JAVAX.EJB.TIMERSERVICE INTERFACE TIMER EXAMPLE HOW THE TIMER WORKS ISSUES WITH USING THE TIMER SERVICE REVIEW QUESTIONS LESSON SUMMARY LESSON SUMMARY SESSION 4: MESSAGE-DRIVEN BEANS LESSON OBJECTIVES OVERVIEW OF MESSAGING SYSTEMS WHAT IS MESSAGING? LOOSE COUPLING WHEN IS MESSAGING USED? TWO MESSAGING MODELS PUBLISH/SUBSCRIBE - ILLUSTRATED MORE ON PUBLISH/SUBSCRIBE POINT-TO-POINT - ILLUSTRATED MORE ON POINT-TO-POINT (P2P) MESSAGE DELIVERY - PUSH VERSUS PULL OVERVIEW OF JMS API WHAT IS JAVA MESSAGE SERVICE? API STRUCTURE JMS INTERFACES ADMINISTERED OBJECTS ADMINISTERED OBJECTS AND JNDI - ILLUSTRATED CLIENT WORKFLOW QUEUE PRODUCER CLIENT EXAMPLE QUEUE PRODUCER CLIENT EXAMPLE SYNCHRONOUS QUEUE CONSUMER CLIENT ASYNCHRONOUS QUEUE CONSUMER CLIENT MESSAGE LISTENER EXAMPLE JMS MESSAGE TYPES MESSAGE HEADER FIELDS MESSAGE-DRIVEN BEANS J2EE MESSAGE PRODUCERS AND CONSUMERS MESSAGE-DRIVEN BEAN (MDB) OVERVIEW GOALS OF MESSAGE-DRIVEN BEANS SIMPLE MDB EXAMPLE MDB CONSUMPTION OF A MESSAGE... DETAILS ACTIVATION CONFIGURATION PROPERTIES SPECIFYING A DESTINATION FOR AN MDB SPECIFYING A DESTINATION USING A DD MESSAGE-DRIVEN BEAN LIFECYCLE LIFECYCLE OVERVIEW MDB STATE DIAGRAM INTERCEPTOR METHODS LAB 4.1 MESSAGE DRIVEN BEAN Copyright , LearningPatterns Inc. All rights reserved iv

7 REVIEW QUESTIONS LESSON SUMMARY SESSION 5: TRANSACTIONS AND SECURITY LESSON OBJECTIVES TRANSACTION DEFINITION TRANSACTION OVERVIEW TRANSACTION LIFECYCLE TRANSACTIONS CLARIFY SYSTEMS TRANSACTIONAL SYSTEM OVERVIEW OVERVIEW OF A TRANSACTIONAL SYSTEM TRANSACTIONAL SYSTEM COMPONENTS TRANSACTIONAL SYSTEM COMPONENTS TRANSACTIONAL OBJECT EJB TRANSACTION SUPPORT TRANSACTIONS IN EJB EJB DECLARATIVE TRANSACTION MANAGEMENT TRANSACTIONAL SCOPE EJB TRANSACTION ATTRIBUTES SPECIFYING TRANSACTION ATTRIBUTES SPECIFYING TRANSACTION ATTRIBUTES NOTSUPPORTED SUPPORTS REQUIRED REQUIRESNEW MANDATORY NEVER BEANS HAVE A SAY IN TRANSACTIONS BEANS CAN BE NOTIFIED OF TRANSACTION STATUS TRANSACTION EXAMPLE TRANSACTION ATTRIBUTES SOME CHOICES TRANSACTION ATTRIBUTES - SOME CHOICES EXPLICIT / BEAN-MANAGED TRANSACTIONS USERTRANSACTION & BEAN-MANAGED EXAMPLE TRANSACTION ISOLATION LEVELS TRANSACTION ISOLATION LEVELS USAGE MULTI-PROCESS TX AND TWO PHASE COMMIT LAB 5.1 TRANSACTIONS SECURITY IN EJB SECURITY REQUIREMENTS J2EE SECURITY ROLES J2EE SECURITY OVERVIEW EJB SECURITY OVERVIEW ANNOTATION EXAMPLE EXAMPLE: ROLES AND METHOD PERMISSIONS ANNOTATION EXAMPLE SAME EXAMPLE WITH ANNOTATIONS AUTHENTICATION PROGRAMMATIC SECURITY EXAMPLE OF PROGRAMMATIC SECURITY TRANSPORT LEVEL SECURITY WITH SSL Copyright , LearningPatterns Inc. All rights reserved v

8 LAB 5.2 SECURITY REVIEW QUESTIONS LESSON SUMMARY SESSION 6: EXCEPTION HANDLING AND BEST PRACTICES LESSON OBJECTIVES EXCEPTION HANDLING OVERVIEW OF EXCEPTIONS EXCEPTION HIERARCHY APPLICATION EXCEPTIONS IN EJB DEFINING APPLICATION EXCEPTIONS APPLICATION EXCEPTION EXAMPLE CONTAINER HANDLING OF APPLICATION EXCEPTION BEAN THROWING OF APPLICATION EXCEPTION CLIENT HANDLING OF APPLICATION EXCEPTIONS SYSTEM EXCEPTIONS INDICATE FAILURE CONTAINER HANDLING OF SYSTEM EXCEPTION CLIENT HANDLING OF SYSTEM EXCEPTIONS EJB 3 BEST PRACTICES WHEN TO USE EJB KEEP BUSINESS INTERFACES COARSE GRAINED SESSION FAÇADE STRUCTURE USE CONTAINER-MANAGED TRANSACTIONS TRANSACTION DURATION LOCAL AND REMOTE BUSINESS INTERFACE TUNING SESSION BEAN TUNING CLUSTERING CLUSTERING SESSION BEANS REVIEW QUESTIONS LESSON SUMMARY LESSON SUMMARY SESSION 7: INTRODUCTION TO THE JAVA PERSISTENCE API (JPA) LESSON OBJECTIVES JPA OVERVIEW THE ISSUES WITH PERSISTENCE LAYERS OBJECT-RELATIONAL MAPPING (ORM) ISSUES ISSUES WITH JDBC ALONE JAVA PERSISTENCE API OVERVIEW JPA BENEFITS JAVA PERSISTENCE ENVIRONMENTS MAPPING A SIMPLE CLASS ENTITY CLASSES ENTITY CLASS REQUIREMENTS AN EXAMPLE ENTITY CLASS THE ENTITY DECLARATION THE EVENT CLASS THE ID PROPERTY FIELD ACCESS OR PROPERTY ACCESS THE EVENTS TABLE GENERATED ID PROPERTY Copyright , LearningPatterns Inc. All rights reserved vi

9 MAPPING PROPERTIES BASIC MAPPING TYPES PERSISTING TO THE DATABASE LAB 7.1 MAPPING AN ENTITY CLASS ENTITY MANAGER AND PERSISTENCE CONTEXT THE ENTITY MANAGER & PERSISTENCE CONTEXT THE ENTITYMANAGER THE ENTITYMANAGER INTERFACE PERSISTENCE UNIT INJECTING AN ENTITYMANAGER RETRIEVING PERSISTENT OBJECTS CONTAINER-MANAGED ENTITY MANGER THE PERSISTENCE UNIT PERSISTENCE.XML LAB 7.2 USING AN ENTITY CLASS REVIEW QUESTIONS LESSON SUMMARY SESSION 8: UPDATES AND QUERIES LESSON OBJECTIVES INSERTING AND UPDATING TRANSIENT, PERSISTENT, DETACHED INSTANCES REMOVED INSTANCES PERSISTING A NEW ENTITY PERSISTING A NEW ENTITY EXAMPLE SYNCHRONIZATION TO THE DATABASE UPDATING A PERSISTENT INSTANCE LAB 8.1 INSERTING AND UPDATING QUERYING AND JAVA PERSISTENCE QUERY LANGUAGE (JPQL) JAVA PERSISTENCE QUERY LANGUAGE EXECUTING A QUERY EXECUTING A QUERY WHERE CLAUSE QUERY PARAMETERS USING QUERY PARAMETERS NAMED QUERIES NAMED QUERIES LAB 8.2 BASIC QUERYING REVIEW QUESTIONS LESSON SUMMARY [OPTIONAL] SESSION 9: ENTITY RELATIONSHIPS LESSON OBJECTIVES MAPPING RELATIONSHIPS OBJECT RELATIONSHIPS MAPPINGS OVERVIEW UNIDIRECTIONAL MANY-TO-ONE RELATIONSHIP THE TABLE STRUCTURE MANY-TO-ONE THE OWNING SIDE BIDIRECTIONAL ONE-TO-MANY RELATIONSHIP MAPPING THE ONE-TO-MANY RELATIONSHIP Copyright , LearningPatterns Inc. All rights reserved vii

10 USING THE RELATIONSHIP MORE ON THE INVERSE SIDE OTHER TYPES OF RELATIONSHIPS LAZY AND EAGER LOADING CASCADING OPERATIONS QUERIES ACROSS RELATIONSHIPS MAPPING INHERITANCE ENTITY INHERITANCE DETAILS OF ENTITY INHERITANCE JOINED (TABLE PER SUBCLASS) ENTITY DEFINITIONS FOR JOINED JOINED: PROS AND CONS SINGLE TABLE MAPPING STRATEGY TABLE PER CONCRETE CLASS REVIEW QUESTIONS REVIEW QUESTIONS LESSON SUMMARY [OPTIONAL] SESSION 10: ADDITIONAL JAVA PERSISTENCE CAPABILITIES LESSON OBJECTIVES VERSIONING OPTIMISTIC LOCKING / DETACHED INSTANCES VERSIONING MORE ON QUERYING PROJECTION QUERIES AGGREGATE QUERIES BULK UPDATE AND DELETE NATIVE SQL QUERIES EMBEDDED OBJECTS USING EMBEDDED OBJECTS EMBEDDABLE CLASS JAVA PERSISTENCE WITH JAVA SE USING JPA WITH JAVA SE JAVA SE APIS EXAMPLE OF JPA IN JAVA SE RESOURCES (EJB3 AND JPA) RESOURCES END OF SESSION Copyright , LearningPatterns Inc. All rights reserved viii

11 Enterprise JavaBeans V3.0 The Java Developer Education Series LearningPatterns Inc. Java, EJB, Enterprise JavaBeans and all Java-based trademarks are registered trademarks of Sun Microsystems, Inc Copyright LearningPatterns Inc. All rights reserved. 1

12 Preface Workshop Overview This is a three hands-on course providing a thorough introduction to Enterprise JavaBeans V3.0, including The needs EJB is designed to address The basic concepts and architecture Thorough coverage of the EJB API and details on its use An introduction to the Java Persistence API (JPA) Design principles for correct usage The workshop consists of 50% discussion, 50% hands-on lab exercises, including a series of labs designed to exercise all important concepts Most of the labs follow a common fictional case study - JavaTunes, an online music store CDs (Item table), Inventory (Inventory table) and others Copyright LearningPatterns Inc. All rights reserved. 2

13 Preface Workshop Objectives At completion you should be able to Understand how EJB relates to the rest of Java/J2EE Understand EJB concepts and architecture Be familiar with the EJB API, including the Java Persistence API (JPA) Be able to write and use EJBs, both Session Beans and Message Driven Beans Be familiar with the JPA API, and be able to write and use persistent entities Understand the tradeoffs involving EJB Understand important design principles for EJB Copyright LearningPatterns Inc. All rights reserved. 3

14 Preface Workshop Agenda Session 1: Introduction to EJB Session 2: Session Bean Architecture and API Session 3: Additional EJB Capabilities Session 4: Message-Driven Bean Architecture and API Session 5:Transactions and Security Session 6: Exceptions and Best Practices Session 7: Java Persistence API (Entity Beans) Intro Session 8: Java Persistence API Inserts and Queries Session 9: Java Persistence API Associations Session 10: Java Persistence API Additional Capabilities Copyright LearningPatterns Inc. All rights reserved. 4

15 Preface Course Prerequisites Proficiency in Java and Object-Oriented programming General knowledge of Java EE (Enterprise Edition) Knowledge of relational databases Copyright LearningPatterns Inc. All rights reserved. 5

16 Preface Release Level Lab This course contains instructions for running the EJB 3 labs using the following platforms: Java 5 (Java Development Kit 1.5.0_xx) Java 5 is required since EJB 3 depends on Java 5 annotations JBoss 4.2.x.GA or JBoss 5.0.x.GA Eclipse 3.4 Java EE Edition (Ganymede) All labs have been tested on Microsoft Windows XP, Java 5, JBoss GA and JBoss GA JBoss is a registered trademarks of Red Hat, Inc in the U.S. and other countries. LearningPatterns is not in any way associated with Red Hat or its JBoss Division. It is likely that using Java-6 will work without problems However, we have not tested it using Java 6 Note that JBoss 5 has separate downloads for running under Java 5 and Java 6 Copyright LearningPatterns Inc. All rights reserved. 6

17 Session 1: Introduction Session 1: Introduction Overview EJB 3.0 Copyright LearningPatterns Inc. All rights reserved. 7

18 Session 1: Introduction Lesson Objectives Gain a high level understanding of EJB and EJB architecture Understand how EJB fits into the Java EE architecture Understand how EJB relates to other technologies Become acquainted with EJB 3.0, its goals, and the problems with earlier versions Copyright LearningPatterns Inc. All rights reserved. 8

19 Session 1: Introduction Overview Overview EJB 3.0 Copyright LearningPatterns Inc. All rights reserved. 9

20 Session 1: Introduction What is EJB EJB is a framework for creating server-side components that are: Transactional, Distributed, Portable, Reliable, Secure, Scalable It simplifies the building of multi-tier distributed object applications EJB is a technology to create business-tier components for these kinds of applications EJB provides a server-side framework for providing a core set of system services to Java components Services such as low-level transaction and state management, multi-threading, and connection pooling Copyright LearningPatterns Inc. All rights reserved. 10

21 Session 1: Introduction EJB Goals Provide a standard distributed component architecture for Java applications Allowing easy creation of distributed business applications Portable across many vendors (write once, run anywhere) Fitting into the Java EE (Enterprise Edition) architecture Enabling the use of third-party development tools Generally meant for creating business tier components Relieve developers from managing transactions, threads, security, resource management, while still providing access to low-level APIs These kinds of issues are generally taken care of by the EJB framework Copyright LearningPatterns Inc. All rights reserved. 11

22 Session 1: Introduction EJB Goals (continued) Provide a persistence framework to simplify Object-Relational Mapping (ORM) The issue of mapping a set of (Java) objects to information in a relational database is complex The data is in different forms Going from one form to the other is difficult, and writing the code is tedious Persistent entities provide a framework to automate the mapping of Java objects to relational data A mapping is defined via metadata, and the framework generates the JDBC code to work with the data Copyright LearningPatterns Inc. All rights reserved. 12

23 Session 1: Introduction Types of Enterprise JavaBeans Session Beans provide a business service Distributed, transactional Bean instances live in a software environment called the EJB container The container manages the lifecycle of instances, as well as distributed access, transactions, etc. Message Driven Beans (MDB) integrate EJB with messaging (JMS) systems An MDB is an asynchronous message consumer It consumes messages from a queue or topic Makes asynchronous processing of incoming messages on the server simpler Allows for concurrent processing of a stream of messages by means of container managed pooling Copyright LearningPatterns Inc. All rights reserved. 13

24 Session 1: Introduction Java Persistence API The brand new Java Persistence API defines a Java persistence framework Persistent Entities provide Object-Relational Mapping (ORM) capabilities Persistent entities are lightweight persistent domain objects Primary concern is mapping objects to relational data Persistent entities are not distributed objects, though they may be accessed in a distributed way using a session bean façade Persistent entities are not really "Entity Beans" They are a separate part of the specification now Can be used separately from other parts of EJB In a new package, javax.persistence, not in javax.ejb The Java Persistence API is a separate part of the same specification defining EJB (JSR-220) It is required for all EJB containers However, it can also be used separately if only Java Persistence is needed Copyright LearningPatterns Inc. All rights reserved. 14

25 Session 1: Introduction EJB and Java EE (Enterprise Edition) Java EE is an architecture for building multi-tier enterprise applications Umbrella for many other Java technologies including: EJB, Servlets/JSP, JMS, RMI EJB serves as the distributed component technology and persistence framework for Java EE Generally, EJB is used on the server side It is often invoked from the Web tier, but may be invoked by thick clients (e.g. Swing clients) It can also be used in Service Oriented Architectures (SOA) Java EE was previously known as J2EE With the release of Java 5, the 2 was dropped from the name Copyright LearningPatterns Inc. All rights reserved. 15

26 Session 1: Introduction EJB in Java EE Architecture Web clients communicate via HTTP Rich clients can communicate via HTTP or RMI presentation business persistence client application server DB server browser HTTP client HTTP servlets JSPs Session EJB Persistent Entity database Swing GUI RMI This architecture may be attractive because you can support both Web browser clients and Swing clients, and do so in several different ways. Web browser clients interact with the EJB business tier indirectly, via the servlet/jsp presentation tier. Swing clients can generate HTTP requests to the servlet/jsp presentation tier or can interact directly with the EJB business tier. You might want to do this to reuse an existing servlet/jsp interface or to use HTTP to get through a firewall. We will talk about MDB later Copyright LearningPatterns Inc. All rights reserved. 16

27 Session 1: Introduction SOA and EJB SOA (Service Oriented Architecture) is an important basis for enterprise architectures Based on providing resources on a network As independent services independent of their implementation Results in loosely coupled architecture EJB can support SOA in multiple ways The services can be exposed directly as a session EJB SOA is usually thought of in terms of Web Services (e.g. SOAP), but EJB may be a useful alternative in some cases This usually requires Java clients A Web Service can be implemented using EJB Web Services are just a façade for exposing a service The service has to be implemented in some way either as an EJB or as a regular Java object Choosing to use EJB in a service oriented architecture is entirely valid Web Services add a layer of complexity and inefficiency If you don't need the advantages of Web Services, then don't use them In fact, you can even invoke EJB from non-java clients This uses CORBA It's not really a practical architecture unless you're already using a CORBA architecture Copyright LearningPatterns Inc. All rights reserved. 17

28 Session 1: Introduction SOA with Web Services and EJB Another popular Java EE architecture Provides loosely coupled access via standard protocols Web services business Java Client application server Web Services.NET Client SOAP/ HTTP SOAP/ HTTP Web Services Servlet EJB Web Services In this type of architecture, SOAP/HTTP is used as the communication protocol, and the service is implemented using EJB Servlets are used purely to support SOAP over HTTP, and are not really involved in presentation layer aspects Copyright LearningPatterns Inc. All rights reserved. 18

29 Session 1: Introduction EJB 3.0 Overview EJB 3.0 Copyright LearningPatterns Inc. All rights reserved. 19

30 Session 1: Introduction EJB 3.0 Overview Complete reworking of EJB specification Major differences from EJB 2.x Some areas have changed completely Uses Java 5 annotations heavily Reduces the use of XML configuration files (Deployment Descriptor), and can eliminate them Persistence is completely different Total overhaul of EJB persistence Persistent entities much lighter weight Based on mature ORM technologies such as Hibernate & Toplink Persistent entities can't be invoked remotely Persistence can be used separately from other parts of EJB Copyright LearningPatterns Inc. All rights reserved. 20

31 Session 1: Introduction EJB 2.x Problems Cumbersome and difficult to program Each EJB required (at a minimum) an implementation class, a home interface, a remote interface, and a deployment descriptor The API was invasive all the interfaces and classes were directly tied to EJB specific types (via inheritance, implementing an interface, etc.) Client programs were also exposed to some of this complexity Entity beans were not very useable Some would say they were broken The specification was also incomplete in terms of what was required in terms of ORM, and how it was to be done They were not used very much Copyright LearningPatterns Inc. All rights reserved. 21

32 Session 1: Introduction EJB 3.0 Goals Simplify development Annotations make programming simpler Fewer classes required API is simpler Use POJOs and POJIs Bean implementations can be POJO (Plain Old Java Objects) Remote interfaces can be POJI (Plain Old Java Interfaces) These are much easier to program Reduces coupling to EJB specific types Interceptor capability for session and message-driven beans Remove need for home interfaces Copyright LearningPatterns Inc. All rights reserved. 22

33 Session 1: Introduction EJB 3.0 Goals Make the most common usage easy Defaults for most things, to reduce need for developer to specify common, expected behaviors e.g. no empty ejbactivate() methods as in EJB 2.x Resource and environmental dependencies easier Dependency injection, annotations simplify programming Support entity persistence well Simpler API Much more powerful capabilities, including support for inheritance, polymorphism, relationships, embedded components No required interfaces used - entities are POJOs Copyright LearningPatterns Inc. All rights reserved. 23

34 Session 1: Introduction Session Bean Usage Session beans provide a number of useful capabilities Transaction Management Session beans provide easy access to the transaction service available in EJB Transactional behavior can be easily specified with annotations in the bean class Resource Management / Concurrent Access EJB container manages bean instances, threads, memory issues Very important for scalability in enterprise applications Distributed Services / SOA Session beans can be accessed remotely (directly via RMI) Can also be used to implement Web Services Copyright LearningPatterns Inc. All rights reserved. 24

35 Session 1: Introduction Session Bean Usage Fault Tolerance / Scalability Most EJB containers support failover/high availability and some form of load balancing / clustering Security Beans and individual methods in beans can be tied into the J2EE security system to secure access to them Can be done by setting security attributes (in bean class via annotations, or in XML DD) Copyright LearningPatterns Inc. All rights reserved. 25

36 Session 1: Introduction Persistent Entity Usage ORM Persistent entities are exclusively devoted to ORM They model business data, and handle the interaction with the database You define a mapping from the bean class to the database, and the framework generates all the JDBC code Eliminates the need for complex, tedious, hand coded JDBC Persistence available in Java SE - The persistence framework (javax.persistence) can be used independently Does not need Java EE server Can be used directly from Java SE (Standard Edition) program Copyright LearningPatterns Inc. All rights reserved. 26

37 Session 1: Introduction MDB Usage Integrate EJB/server with messaging Allows you to easily receive messages asynchronously on the server side Previous to MDB, there was no standard way to do this Transaction Management Allows you to easily start/control transactions when receiving JMS messages Can't be done directly for asynchronous message receipt with the JMS API Copyright LearningPatterns Inc. All rights reserved. 27

38 Lab 1.1: Setting up the Environment Lab 1.1 Setting Up the Environment Copyright LearningPatterns Inc. All rights reserved. 28

39 Lab 1.1: Setting up the Environment Lab 1.1 Set up the Server Lab Overview: In this lab you will become familiar with and set up your application server and development environment The server you'll be using is the JBoss Application Server The development environment is the Eclipse IDE You'll also set up the lab directory Objectives: Set up the JBoss application server Set up the development environment Become familiar with starting and stopping JBoss Review some of the JBoss monitoring tools Builds on previous labs: None Approximate Time: minutes Copyright LearningPatterns Inc. All rights reserved. 29

40 Lab 1.1: Setting up the Environment Information Content and Task Content Lab Within a lab, information only content is presented in the normal way the same as in the student manual pages Like these bullets at the top of the page Tasks that the student needs to perform are in a box with a slightly different look to help you identify them An example appears below Tasks to Perform Look at these instructions, and notice the different look of the box as compared to that above Make a note of how it looks, as future labs will use this format OK Now get out your setup CD; we're ready to start working Copyright LearningPatterns Inc. All rights reserved. 30

41 Lab 1.1: Setting up the Environment Extract the Lab Setup Zip File Lab To set up the labs, you'll need the setup zip file for the course This will either be on a CD for the course, or given by the instructor The file name should be EJB3_LabSetup_.zip Our base working directory for this course will be C:\StudentWork\EJB3 This directory will be created when we extract the Setup zip It includes a directory structure and files (e.g., Java files, XML files, other files) that will be needed in the labs All instructions assume that this zip file is extracted to C:\. If you choose a different directory, please adjust accordingly Tasks to Perform Unzip the lab setup file to C:\ This will create the directory structure, described in the next slide, containing files that you will need for doing the labs The CD will also contain the following folders Resources: Documentation, specifications, etc. Copyright LearningPatterns Inc. All rights reserved. 31

42 Lab 1.1: Setting up the Environment Lab Directory Structure Lab StudentWork\EJB3 contains Derby: Database files Resources : Extra files (e.g. docs) Setup: Files needed for lab work workspace: Lab working directories StudentWork\EJB3\workspace contains the following folders: LabNN : Lab directories LabNN\build\classes : compiled code * LabNN\bin : compiled code * LabNN\src\ : Java source files LabNN\src\META-INF\: ejb-jar.xml (if used), etc There are two folders used by Eclipse for compiled Java code For an EJB Project, the folder build\classes is used For a regular Java project, the folder is bin These folders are created by Eclipse when you create the project We'll learn more about the projects in later labs Some of the labs are Web applications These labs will include additional Web related directories The LabNN\WebContent and LabNN\WebContent\WEB-INF directories Copyright LearningPatterns Inc. All rights reserved. 32

43 Lab 1.1: Setting up the Environment The JBoss Application Server Lab We will be using JBoss as our application server It is an open source, J2EE Application server It is full featured, and used very widely by developers Fast growing market share for production We will use it for our labs Very easy to use Highly scalable Advanced features Open Source! Supported by JBoss Group Inc. (a division or Red Hat) For profit corporation created to support users of JBoss with Production and Development support Copyright LearningPatterns Inc. All rights reserved. 33

44 Lab 1.1: Setting up the Environment Setup Environment Lab Tasks to Perform Make sure that you have Java 5 installed Likely installed in a directory like C:\Program Files\Java\jdk1.5.x It's best to set the following environment variables for Java 5: JAVA_HOME=C:\Program Files\Java\jdk1.5.x (e.g., 1.5.0_11) Add entries to the PATH environment variable PATH should include %JAVA_HOME%\bin (for the JDK) Make sure JBoss is installed in a directory like C:\jboss GA (JBoss 4) or C:\jboss GA (JBoss 5) If it isn't installed, download it from and install Make sure that Eclipse is installed - usually in C:\eclipse If it isn't installed, download it from and install * If any software was installed in a different directory, you'll need to modify the instructions in the lab to refer to your install directory Set the environment variable permanently via the Control Panel by going to: System Advanced tab Environment Variables The value for JAVA_HOME shown above is based on your installing Java 5 in the normal location If you've installed it in a different location, then adjust the value accordingly Setting this will ensure that Eclipse uses the Java version you want it to The Eclipse version you should use is the Ganymede - IDE for Java EE Developers The JBoss and Eclipse installs are zip files - just unzip them A common location is to C:\ but you can unzip the anywhere, as long as you know where, and you modify the lab instructions to refer to your correct locations Copyright LearningPatterns Inc. All rights reserved. 34

45 Lab 1.1: Setting up the Environment The Eclipse Development Environment Lab Eclipse is an open source platform for building integrated development environments (IDEs) Used mainly for Java development Can be extended via plugins to create applications useful in many areas (e.g. C# programming) is the main website The remainder of this lab gives detailed instructions on using Eclipse to work with the JBoss server Starting Eclipse, creating and configuring servers Many labs in the course do not include specific details regarding Eclipse they just say build/deploy as before For these labs, you should use the same procedures to build/deploy as in the first lab where a task is done Refer back to previous lab instructions as needed The Eclipse source base was originally developed by IBM It was released by IBM into open source IBM's RAD environment is built on top of Eclipse Copyright LearningPatterns Inc. All rights reserved. 35

46 Lab 1.1: Setting up the Environment Launch Eclipse Lab Tasks to Perform To launch eclipse, go to c:\eclipse and run eclipse.exe Dialog box should appear prompting for workbench location Set the workbench location to C:\StudentWork\EJB\workspace If a different default Workbench location is set, change it Click OK In the window that opens, click the Workbench icon If Eclipse was installed elsewhere, adjust the paths to the Eclipse executable accordingly You can put a shortcut to this executable on your desktop Copyright LearningPatterns Inc. All rights reserved. 36

47 Lab 1.1: Setting up the Environment The J2EE Perspectice Lab Eclipse starts up in the J2EE Perspective - shown below Note the Servers view at bottom, which we'll use soon For basic information on Eclipse, go to the end of this lab Copyright LearningPatterns Inc. All rights reserved. 37

48 Lab 1.1: Setting up the Environment Create a Server Instance Lab Tasks to Perform We'll configure a JBoss server in Eclipse to run our services 1. Go to the Servers view, right click in it, and select New Server 2. In the next dialog, select JBoss 4.2 or JBoss 5.0 * and click Next 3. In the next dialog, configure the server install directory, & click Next 4. The defaults should be fine in the next dialog (ports and server config) 5. Click Finish (See next slide for any problems with JBoss 5 server) Screen shots are based on JBoss Select the server that you are using (JBoss 4 or JBoss 5) The images above show us configuring a JBoss GA server The standard JBoss location is C:\jboss GA The standard JBoss location is C:\jboss GA If you have a different version, or have installed JBoss in a different directory, then configure the server accordingly Eclipse assumes the default ports for JBoss - which are shown in the next to last dialog If your server is using different ports, configure these accordingly Likewise, if you are not using the default server configuration, then change this accordingly. Note that you want to create the server before we do any other labs Creating a server sets up a server runtime, which needs to be associated with lab projects that we'll create later (this will be done automatically by Eclipse if you have only one server runtime in the workspace) Copyright LearningPatterns Inc. All rights reserved. 38

49 Lab 1.1: Setting up the Environment Eclipse/JBoss 5 Server Creation Problem Lab If you are using JBoss 5 with Eclipse you may see the following error when setting the Application server directory "Missing classpath entry C:\jboss GA\server\default\lib\mail.jar" Caused by a bug in the JBoss 5 server def of Eclipse 3.4 If you don't see the error, ignore this slide Otherwise, follow the instructions below to fix this problem Exit Eclipse Tasks to Perform Go to StudentWork\EJB3\Setup\Lab01.1, and copy the file jboss5.serverdef to C:\eclipse\plugins\org.eclipse.jst.server.generic.jboss_nnn\servers * Restart Eclipse, and try to create the server again - it should work If you have installed Eclipse in a location other than the default (C:\Eclipse), then adjust the directory locations given above accordingly The name of the directory under C:\eclipse\plugins will be something like: org.eclipse.jst.server.generic.jboss_ v The numbers in this name will vary depending on which version of Eclipse you have installed Copyright LearningPatterns Inc. All rights reserved. 39

50 Lab 1.1: Setting up the Environment Start the JBoss Server Lab Tasks to Perform Right click on the server in the Servers view, and select Start This will start up the server and produce copious debugging information in the console view, as shown below To restart (stop/start) a server, right click and select Restart To stop a server - right click and select Stop See notes for other useful information on controlling the server Screen shots are based on JBoss The screen shots are from JBoss other releases will be similar Note - if you have problems timing out when starting, you can change the server configuration Double click on the server in the Servers view A window will open in the editor, that allows you to edit various configuration settings You can change the Timeout settings here -e.g., if you have a slow machine, you may need to increase the default timeout for starting the server from the default of 50 seconds You can also change the Publishing settings, which determine how and when Eclipse pushes any changes you make to the server - for example, you may not want to publish automatically, as this can be annoying if a partially changed project gets published Note - Check the JBoss console for exceptions - sometimes there are port conflicts starting JBoss If this happens, you can open a command prompt, and execute netstat -o to see the ports in use, and the PID of the process using it You can then go to Task Manager to see what process is associated with the given PID, and hopefully shut the process down so you can boot JBoss Note that the Eclipse/JBoss coordination appears to depend on several services deployed in JBoss For example - JNDI and the Remote Invoker Adapter If you have a custom JBoss configuration, it would need to support all the needed service Copyright LearningPatterns Inc. All rights reserved. 40

51 Lab 1.1: Setting up the Environment JBoss Web Console Lab You can monitor some basic server statistics with the JBoss Web Console The Web Console is a web application located (by default) at: Tasks to Perform Launch a browser, point to the URL above You will need to have the Java Plug-in installed for your browser to run the console If you don't have the java plug-in installed, you can look at the jmx console instead: If you have configured your server or ports differently from the standard installation, the URL for the consoles will need to conform to your hostname and HTTP port Copyright LearningPatterns Inc. All rights reserved. 41

52 Lab 1.1: Setting up the Environment JBoss Web Console Lab Tasks to Perform Click the JBoss Management Console node at the upper left This will show some basic server statistics on the right Copyright LearningPatterns Inc. All rights reserved. 42

53 Lab 1.1: Setting up the Environment Look at Documentation Lab Tasks to Perform Look at the EJB3 & JPA javadocs located in the Resources folder Unzip the zip file in this directory onto your computer Open the docs\api\index.html file and look at it This is the main javadoc page for the Java 5 EE documentation * There is also a helper sheet for EJB3 annotations called ejb3.0-anno-cheat-1.2.pdf It's a good idea to download and look at the EJB3 specs * ejb-3_0-fr-spec-simplified.pdf: Overview document for EJB3 ejb-3_0-fr-spec-ejbcore.pdf: Specification for EJB3, not including persistence API ejb-3_0-fr-spec-persistence.pdf: Specification for JPA (Java Persistence API) STOP The EJB-3 specs can be downloaded from Sun's web site The specification shouldn't be the first thing you read, but it is valuable after you have some understanding of EJB3 The javadocs are NOT the complete Java 5 EE javadoc To save space, we've only supplied the EJB-3 relevant docs The documentation is important Come back to it later when you have questions about the API or the specification ejb3.0-anno-cheat-1.2.pdf is not part of the official documentation It has been included just to help you keep track of the annotations Copyright LearningPatterns Inc. All rights reserved. 43

54 Session 1: Introduction Review Questions What is EJB? What are the different kinds of beans defined in EJB, and what are they used for? How is EJB 3.0 better than previous versions of EJB? Copyright LearningPatterns Inc. All rights reserved. 44

55 Session 1: Introduction Lesson Summary EJB is a framework for creating server-side components Transactional, Distributed, Portable, Reliable, Secure, Scalable It also defines a persistence API EJB defines session beans, message-driven beans and persistent entities Session beans provide distributed business services, and access to container services such as transactions, concurrency control, etc. Message-driven beans receive JMS messages asynchronously, and integrate JMS with the EJB tier Persistent Entities provide an ORM framework to map between Java objects and relational data Copyright LearningPatterns Inc. All rights reserved. 45

56 Session 1: Introduction Lesson Summary EJB 3.0 simplifies and improves EJB in a number of ways Uses Java annotations to eliminate/reduce the need for XML deployment descriptors Developers work with POJOs and POJIs rather than having to derive from EJB specific interfaces and classes The persistence technology has been completely rewritten based on proven ORM technology The persistence technology has been separated from the rest of the specification and can be used independently Copyright LearningPatterns Inc. All rights reserved. 46

57 Session 6: Exception Handling and Best Practices Session 6: Exception Handling and Best Practices Exception Handling EJB 3 Best Practices Copyright LearningPatterns Inc. All rights reserved. 345

58 Session 6: Exception Handling and Best Practices Lesson Objectives Become familiar with exceptions, and how Java classifies them Understand how EJB functions with respect to exceptions Understand core design principles for using EJB Copyright LearningPatterns Inc. All rights reserved. 346

59 Session 6: Exception Handling and Best Practices Exception Handling Exception Handling EJB 3 Best Practices Copyright LearningPatterns Inc. All rights reserved. 347

60 Session 6: Exception Handling and Best Practices Overview of Exceptions Exceptions in Java are used to notify calling code of some unusual condition In general, they are used to signal errors, either in your code, or in the input obtained from the user, a database, etc. Exceptions are objects in Java They are not errors; they are used to handle errors The type (or class) of the exception object indicates the kind of exception The exception object may have data that can be used to convey information about the exception Exceptions cause a jump in program flow The program must stop what it is doing and respond to the exception Copyright LearningPatterns Inc. All rights reserved. 348

61 Session 6: Exception Handling and Best Practices Exception Hierarchy Throwable Exception Error Other Exception Classes RuntimeException Checked exceptions Unchecked exceptions Java divides exceptions into broad categories To help organize how you deal with them in your code Exceptions that must be handled, or declared in a throws clause, are checked exceptions "Checked" means checked by the compiler Such exceptions must be handled in some way, and the compiler enforces this Code that does not handle checked exceptions will not compile All others are called unchecked exceptions You are not forced to handle unchecked exceptions (by the compiler) You might wish to handle some of them It's unlikely that you'll want to explicitly handle things like NullPointerException In general, you won't use Throwable directly it is subclassed into two main branches Exception a subclass of Throwable that programs must handle in some way Error a subclass of Throwable for abnormal events that should not normally occur, such as an out-of-memory condition do not try to handle Errors unless you really know what you are doing Exceptions are further categorized by subclassing into RuntimeException a subclass of Exception which can't be foreseen before runtime, thus the compiler cannot enforce the handling of them Copyright LearningPatterns Inc. All rights reserved. 349

62 Session 6: Exception Handling and Best Practices Application Exceptions in EJB An application exception is an exception defined by the Bean Provider as part of the business logic of an application Used by business methods to inform the client of abnormal application-level conditions, such as unacceptable values of the input arguments to a business method The client is expected to deal with the exception A client can typically recover from an application exception Not intended for reporting system-level problems For example, an Account bean may use an application exception to report that a withdraw operation can't be performed because of insufficient funds An application exception may be defined in the throws clause of a method of an enterprise bean s business interface Copyright LearningPatterns Inc. All rights reserved. 350

63 Session 6: Exception Handling and Best Practices Defining Application Exceptions The Bean Provider defines application exceptions An application exception may be a checked exception Checked exceptions listed in the methods of the beans business interface are automatically considered application exceptions An application exception may be an unchecked (runtime) exception that is defined as an application exception by annotating it Application exceptions should only be used for reporting business logic exceptions Should not be used to report system exceptions They are designed to be handled by the client An application exception may not be a subclass of the java.rmi.remoteexception The java.rmi.remoteexception and its subclasses are reserved for system exceptions Copyright LearningPatterns Inc. All rights reserved. 351

64 Session 6: Exception Handling and Best Practices Application Exception Example // Checked exceptions are automatically application exceptions public class ItemNotFoundException extends Exception { //... } // Declare a Runtime exception to be an application public class MyRuntimeException extends RuntimeException { //... } If your application exception is a checked exception, you would need to declare it in the business interface for any business method that might throw it public interface Catalog { public void removeitem(musicitem item) throws ItemNotFoundException; public void additem(musicitem item); } Copyright LearningPatterns Inc. All rights reserved. 352

65 Session 6: Exception Handling and Best Practices Container Handling of Application Exception If a bean throws an application exception: The container will re-throw the exception exactly as it was received The client will receive the exception exactly as it was thrown by the bean The container will not automatically roll back the current transaction Unless the application exception was defined to cause transaction rollback as shown public class ItemNotFoundException extends Exception { //... } Copyright LearningPatterns Inc. All rights reserved. 353

66 Session 6: Exception Handling and Best Practices Bean Throwing of Application Exception Before throwing an application exception the bean developer must ensure that the bean does one of the following Ensure that the instance is in a state such that a client s attempt to continue and/or commit the transaction does not result in loss of data integrity For example, throw an application exception indicating an invalid input parameter before performing any database updates If the application exception is not specified to cause transaction rollback, mark the transaction for rollback using the EJBContext.setRollbackOnly method before throwing the application exception This ensures that the transaction can never commit Since the container does not roll back a transaction automatically if an application exception is thrown, it is up to the bean developer to make sure that there is no loss of data integrity Taking either of the above actions will ensure this is the case Copyright LearningPatterns Inc. All rights reserved. 354

67 Session 6: Exception Handling and Best Practices Client Handling of Application Exceptions Client programs receive application exceptions exactly as thrown The bean instance is also still available to the client, since the container does not remove it The client is responsible for deciding what action to take when it receives an application exception Note that although the container won't automatically roll back an ongoing transaction, the bean instance might have rolled it back The caller should check the transaction state before proceeding This can be done statically by checking documentation to see if the exception was marked for rollback EJB callers can use EJBContext.getRollbackOnly() Non-EJB callers can get a UserTransaction instance to check the status of the transaction A javax.transaction.usertransaction object is available via JNDI lookup in any Java EE compliant application server UserTransaction.getStatus() returns the status of the transaction associated with the current thread Copyright LearningPatterns Inc. All rights reserved. 355

68 Session 6: Exception Handling and Best Practices System Exceptions Indicate Failure A system exception is an exception that is a java.rmi.remoteexception (or one of its subclasses) or a RuntimeException that is not an application exception If your bean encounters a system exception or some other error, it needs to be handled differently than an application error For example, if a bean can't get a database connection, or if it gets a RemoteException when invoking another EJB These kinds of errors are either unexpected, or non-recoverable If a bean encounters a system exception or error, it should throw a suitable non-application exception It should propagate any system exceptions or errors encountered If it encounters a checked exception it can't recover from, it should throw an EJBException that wraps the original exception It should throw an EJBException for any other errors The guidelines that the specification gives are not mandatory You should follow them unless you have a good reason not to Copyright LearningPatterns Inc. All rights reserved. 356

69 Session 6: Exception Handling and Best Practices Container Handling of System Exception If a bean throws a system (non-application) exception: The container catches it, logs & throws an exception to the caller The transaction in which the bean method participated will be rolled back Resources acquired through resource factories declared in the enterprise bean environment will be released No other method will be invoked on an instance that threw a nonapplication exception Generally, the container destroys the instance The caller will generally receive an EJBException that wraps the original exception Unless the caller started the transaction, in which case it will receive an EJBTransactionRolledbackException Note that if a bean acquires "unmanaged" resources without involving the container, then the container will not know to release them That's one of the reasons we declare them in the environment so the container can manage them We give the details here for the most common situation of Java clients coding to the EJB 3 API In other situations, the details might differ For example, a Web Service client where the service is implemented by an EJB Or a client invoking an EJB 3 bean through the EJB 2.1 API See the specification for more details on these kinds of situations Copyright LearningPatterns Inc. All rights reserved. 357

70 Session 6: Exception Handling and Best Practices Client Handling of System Exceptions If an EJB client receives a system exception, it doesn't really know if the invocation completed or not The exception may have occurred in the communication subsystem If the client is executing in the context of a transaction, the client s transaction may, or may not, have been marked for rollback by the communication subsystem or target bean s container If a client is executing in a transaction context it can: Roll back the transaction Check the transaction status, and if it hasn't been rolled back, it can proceed The bean instance that threw the exception will not be valid, so the client has to reacquire an instance, or do something else Copyright LearningPatterns Inc. All rights reserved. 358

71 Session 6: Exception Handling and Best Practices EJB 3 Best Practices Exception Handling EJB 3 Best Practices Copyright LearningPatterns Inc. All rights reserved. 359