INF5040 (Open Distributed Systems) · Remote Method Invocation Java RMI Load Balancing Transparent...

INF5040 (Open Distributed Systems)

Lucas Provensi ([email protected])

Department of InformaticsUniversity of Oslo

September 13, 2010

mailto:[email protected]�

Features of Distributed Systems Java EE Architecture Enterprise Java Beans (EJB) J2EE Application Servers◦ Jboss

Example

2INF5040 - Group Meetings

Remote Method Invocation◦ Java RMI

Load Balancing Transparent failover Integration to legacy systems Transactions Clustering◦ State replication across servers

Resource pooling◦ Grouping together resources

Security …..


Middleware services provides those features Goal: To separate these concerns from the

application logic.◦ Business logic is more important for developers

Too costly to build from scratch Distributed apps should be portable across

middleware service providers


"The Java Platform Enterprise Edition reduces the cost and complexity of developing ... multi‐tier services, resulting in services that can be rapidly deployed and easily enhanced“

Introduced in June, 1999


Distributed multitiered application model for enterprise applications.


A web client consists of two parts: ◦ Dynamic web pages containing various types of

markup language (HTML, XML, and so on), which are generated by web components running in the web tier, and ◦ A web browser, which renders the pages received

from the server. Sometimes called a thin client◦ Usually do not query databases, execute complex

business rules, or connect to legacy applications


The client communicates with the business tier running on the server either directly or by going through JSP pages or servlets running in the web tier.


Business code is logic that solves the needs of a particular business domain◦ Receives data from clients, processes it (if necessary),

and sends it to the enterprise information system tier for storage


A server‐side software component model for distributed enterprise applications

Core of the Java EE technology Goal: To provide a standard way to manage

distribution issues in enterprise applications through reusable code◦ By implementing the back‐end 'business' code

typically to enterprise applications◦ Addressing the same types of problems through the

same code



EJB

Entity Bean(persistent)

Session Bean(non-persistent)

Stateful StatelessContainer Managed

Persistence

Bean Managed

Persistence


EJB

Message Driven Bean

(non-persistent)Session Bean

(non-persistent)

Stateful Stateless

JPA

Persistent Entities

Entity Beans (deprecated)◦ Now JPA Entity◦ Represent persistent business Entity◦ Persist in storage system ( usually Database)

JPA Entity represents a table in a relational database, and each entity instance corresponds to a row in that table ◦ The class must be annotated with the

javax.persistence.Entity annotation;◦ Entities are managed by one entity manager.


Session Beans◦ Perform work for individual clients on the server◦ Encapsulate complex business logic◦ Can coordinate transactional work on multiple

entity beans Session beans can be◦ Stateless‐The SBs belong to the client for duration

of the method call only◦ Stateful‐The SBs belong to the client for duration of

client lifetime


Message driven beans◦ Business objects whose execution is triggered by

messages instead of by method calls;◦ Receive messages asynchronously.

The Message Driven Bean is used among others to provide a high level ease-of-use abstraction for the lower level JMS (Java Message Service) specification.

It may subscribe to JMS message queues or message topics, which are typically injected into the bean.


http://en.wikipedia.org/wiki/Java_Message_Service�

http://en.wikipedia.org/wiki/Java_Message_Service�

Industry standard◦ Vendors design containers to EJB specs

Portability possible across containers◦ The application assembler can build new

applications from existing beans. RAD ability because of the services provided

by container◦ The EJB container, rather than the bean developer,

is responsible for system-level services such as transaction management and security authorization.


Rarely necessary for web‐based applications Spring, a lightweight container, can achieve most

of the EJB services◦ makes it easy to use many different services and

frameworks◦ accepts any Java bean instead of specific components

Complexity◦ Specifications were getting more complex◦ EJB 3.0 tries to address this issue

Difficulty in Unit testing◦ If anything goes wrong, is it container related or app

related?


Definition◦ Is a software framework dedicated to the efficient

execution of n‐tiered web applications.

Java EE Application Server. ◦ A software package that implements all of the Java

EE APIs and frameworks that allow you to deliver Java EE applications.


Connectivity to various applications and DBs on various operating environments and hardware

Provides an integrated IDE for all aspects Support for reusable distributed components

(CORBA, COM, EJB) Performance management (load balancing,

caching, monitoring) Robust and reliable software –redundancy,

backup/recovery User‐friendly administrative, diagnostic tools Strong security framework


A Java EE Application Server provides (at a minimum):◦ Servlet engine/container◦ EJB engine/container◦ Web Server (or ability to integrate with a web server)◦ Concrete implementations of all the J2EE APIs Java Mail Messaging RMI etc.

A vendor‐bought App Server will have additional functionalities


Full Java EE App Servers:◦ Apache Geronimo (Apache Software Foundation) ◦ Glassfish Application Server (Oracle Corporation)◦ Caucho Resin Application Server ◦ WebSphere Application Server ◦ JBoss (Red Hat) ◦ Jetty (Eclipse Foundation) ◦ JRun (Adobe Systems)◦ WebLogic Server (Oracle)

Others◦ Tomcat (servlet only)


Introduced in 1999 The product of an Open Source developer

community dedicated to developing the best J2EE‐compliant application server in the market

With 1000 developers worldwide and a steadily growing number of downloads per month, reaching 72,000 for October ’01 (per independent www.sourceforge.net), Jboss is arguably the most downloaded application server in the world today

Distributed under an LGPL license, Jboss is absolutely FREE for use.


JBoss 4.0 is compliant to the Java EE specification. So Java EE components such as EJBs can be reused even if they were developed for other application servers

It also supports Java EE Web Services and Service Oriented Architecture

Since JBoss is java based, it can be used on any operating system that supports java

JBoss requires smaller memory than some other application servers and is considerablly faster

It has a very powerful documentation on its web page


Some Features◦ Clustering◦ Failover (including sessions)◦ Load balancing◦ Distributed caching (using JBoss Cache, a standalone product)◦ Distributed deployment (farming)◦ Aspect-Oriented Programming (AOP) support◦ JSP/Servlet 2.1/2.5 (Tomcat)◦ JavaServer Faces 1.2 (Mojarra)◦ Enterprise Java Beans versions 3 and 2.1◦ JNDI (Java Naming and Directory Interface)◦ Hibernate-integration (for persistence programming: JPA)◦ JDBC◦ JTA (Java Transaction API)◦ Etc.


Using Eclipse IDE for Java EE Downloading JBoss and integrating with

eclipse Sample EJB Application◦ Creating a Session Bean◦ Execution using JBoss


1. Create a EJB project1. Create a Session Bean and define its business

methods2. Create a Servlet that uses the Session Bean

1. Use the @EJB annotation to create a container managed bean

2. Use the doGet() method to interact with the bean3. Package the application in a EAR(Enterprise

Archive) file4. Deploy the application in the JBoss server


INF5040 (Open Distributed Systems) · Remote Method Invocation Java RMI Load Balancing Transparent...

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