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Java EE has this "mysterious shroud" around it for younger Java developers - one that I've been trying to lift myself for quite a while with little success.
Confusion arises from:
Java EE seems to be both a library and a platform - there are multiple ways to "get" the Java EE library, typically from something like Oracle's Java EE SDK download. However, the Java EE library will not work, nor compile unless if your code is being run on or has access to a Java EE application server (such as JBoss, GlassFish, Tomcat, etc). Why? Can't the libraries function outside of the application server environment? Why do I need something massive as JBoss just to compile simple code to send an email?
Why are Java EE libraries not "standard" and included in the regular JVM download and/or the SDK?
Why are there so many Java EE offerings when there is really only two main flavors of standard Java (Oracle JVM/SDK | OpenJDK JVM/JDK)?
What can one do with Java EE that they cannot do with standard Java?
What can one do with standard Java that they cannot do with Java EE?
When does a developer decide they "need" Java EE?
When does a developer decide they do not need Java EE?
Why is Java EE library version not in sync with standard Java library releases (Java EE 6 vs. Java 7)?
Thanks for helping me clear the flog!
Why can't the libraries function outside of the application server environment?
Actually they can. Most of the libraries can be directly used standalone (in Java SE) or included in a .war (practically that's nearly always Tomcat). Some parts of Java EE, like JPA, have explicit sections in their respective specifications that tells how they should work and be used in Java SE.
If anything, it's not so much an application server environment per se that's at stake here, but the presence of all other libraries and the integration code that unites them.
Because of that, annotations will be scanned only once for all your classes instead of every library (EJB, JPA, etc) doing this scanning over and over itself. Also because of that, CDI annotations can be applied to EJB beans and JPA entity managers can be injected into them.
Why do I need something massive as JBoss just to compile simple code to send an email?
There are a few things wrong with this question:
For compiling you only need the API jar, which is below 1MB for the Web Profile, and a little over 1MB for the full profile.
For running you obviously need an implementation, but "massive" is overstating things. The OpenJDK for example is around 75MB and TomEE (a Web Profile implementation containing mail support) is only 25MB. Even GlassFish (a Full Profile implementation) is only 53MB.
Mail works perfectly fine from Java SE (and thus Tomcat) as well using the standalone mail.jar and activation.jar.
Why are Java EE libraries not "standard" and included in the regular JVM download and/or the SDK?
Java EE in a way was one of the first attempts to split up the already massive JDK into chunks that are easier to manage and download. People are already complaining that the graphical classes (AWT, Swing) and Applets are inside the JRE when all they do is run some commands on a headless server. And then you also want to include all the Java EE libraries in the standard JDK?
With the eventual release of modularity support we'll just have a small base JRE with many things separately installable as packages. Perhaps one day many or even all classes that now make up Java EE will be such package as well. Time will tell.
Why are there so many Java EE offerings when there is really only two main flavors of standard Java (Oracle JVM/SDK | OpenJDK JVM/JDK)?
There are more than just two flavors of Java SE. There is at least the IBM JDK, the previous BEA one (JRocket, which is being merged into the Oracle/Sun one because of the acquisition), various other open source implementations and a slew of implementations for embedded use.
The reason behind Java SE and EE being a specification is that many vendors and organizations can implement it and thus it encourages competition and mitigates the risk of vendor lock-in.
It's really no different with C and C++ compilers, where you have many competing offerings as well all adhering to the C++ standard.
Why is Java EE library version not in sync with standard Java library releases (Java EE 6 vs. Java 7)
Java EE builds on Java SE, so it trails behind. The versions do correspond though. Java EE 5 requires Java SE 5. Java EE 6 requires Java SE 6 and so on. It's just that mostly when Java SE X is current, Java EE X-1 is current.
Here are a few quickly composed answers to your questions...
Why can't JavaEE libraries function without an application server?
The services provided by JavaEE (container managed transactions, container managed dependency injection, timer service, etc..) inherently involve JavaEE compliant Application Servers (for example: GlassFish, JBoss, WebSphere, etc...). Therefore the JavaEE libraries serve no purpose without such a container. "Why do I need something as massive as JBoss just to compile simple code to send an email?" You don't. There are ways to send an email without JavaEE... But if you want to do it the JavaEE way, you need a JavaEE container.
Why are JavaEE libraries not included with JavaSE download?
The same reason that many libraries aren't included: it would be overkill. Since you can't even use the JavaEE libraries without an application server, why bother to include them? JavaEE should be downloaded if and when a developer installs an application server and decides to use JavaEE.
Why are there so many JavaEE offerings?
Are there really "so many" JavaEE offerings? If so, please list some of them. More accurately I believe there are multiple implementations of the same APIs.
What can one do with JavaEE that they can't do without standard Java?
Lots. You can't rely on an application server to manage transactions or persistence contexts without JavaEE. You can't allow an application server to manage EJB dependency injection without JavaEE. You can't use an application managed timer service without JavaEE. The answer to this question should make the answer to the first question quite clear... Most of the services provided by JavaEE require a JavaEE container.
What can you do with JavaSE that you can't do with JavaEE?
Um... I don't know.
When does a developer decide they need JavaEE?
This question is completely subjective... But if you need any of the services provided by JavaEE, you start to think about it. If you don't know what JavaEE is... you probably don't need it.
When does a developer decide they do not need JavaEE?
See previous answer.
Why is JavaEE library version not in sync with JavaSE version?
Good question. I won't pretend to know how to answer it... But I would guess the answer is: "because they're not in sync".
At bird's eye view, Java EE is a platform, i.e. something that we can build on.
Taking a more technical perspective, the Java Enterprise Edition standard defines a set of APIs commonly used for building enterprise applications. These APIs are implemented by application servers - and yes, different application servers are at liberty to use different implementations of the Java EE APIs.
However, the java ee library will not work, nor compile unless if your code is being run on or has access to a Java EE application server (such as JBoss, GlassFish, Tomcat, etc).
You compile against the Java EE APIs, so you only need those APIs at compile time. At runtime, you'll also need an implementation of these APIs, i.e. an application server.
Why do I need something massive as JBoss just to compile simple code to send an email?
You don't. However, if you wish to use the Java EE API for sending mail, you will need an implementation of that API at runtime. This can be provided by an application server, or by provided by a stand alone library you add to your classpath.
Why are Java EE libraries not "standard" and included in the regular JVM download and/or the SDK?
Because only the APIs are standardized, not the implementations.
Why are there so many Java EE offerings
Because people disagree on the right way to implement certain features. Because different vendors compete for market share.
What can one do with Java EE that they cannot do with standard Java?
Since Java EE implementations are built with "standard Java": Nothing. However, leveraging the existing libraries can save a great deal of effort if you are solving typical enterprise problems, and using a standardized API can prevent vendor lock-in.
What can one do with standard Java that they cannot do with Java EE?
Nothing, since Java EE includes Java SE.
When does a developer decide they "need" Java EE? When does a developer decide they do not need Java EE?
Generally speaking, the Java EE APIs solve typical, recurring problems in enterprise computing. If you have such problems, it usually makes sense to use the standard solutions - but if you have different problems, different solutions may be called for. For instance, if you need to talk to a relational database, you should consider using JPA. But if you don't need a relational database, JPA won't help you.
What is Java EE?
Let's start from canonicity definition at wiki:
Java Platform, Enterprise Edition or Java EE is Oracle's enterprise
Java computing platform. The platform provides an API and runtime
environment for developing and running enterprise software, including
network and web services, and other large-scale, multi-tiered,
scalable, reliable, and secure network applications.
The main point here is that Java EE is a platform provides an API, not some concrete library.
What for Java EE needed?
The main scope of Java EE is the network based applications, unlike Java SE oriented to the desktop applications development with simple network support. This is the main diference between them.
Scalability, messaging, transactioning, DB support for every application... the need in all of this has increased with the evolution of the network.
Of course a lot of ready solutions which Java SE provides are useful for network development, so Java EE extends Java SE.
Why do we need application servers to run our code?
Why do we need operation systems? Because there are a lot of painful work with hardware we need to do to make even simpliest application. And without OS you need to do it again and again. Oversimplified OS is just a programmatic container, which provides us a global context to run our applications.
And this is what the application servers are. They are allows us to run our applications in their context and provides us a lot of highlevel functionality which is needed for enterprise highloaded network applications. And we are don't want to write our own bicycles to solve this problems, we are want to write code which will satisfy our business needs.
Another example here could be JVM for Java.
Why Java EE doesn't contains onboard app server?
Hard to say for me. I think, it was done for more flexibility. Java EE says what they should do, they decide how to do it.
Why JVM doesn't include Java EE?
Because they directed to different market sectors. Java EE has a bunch of functionality which is doesn't need for usual desktops.
Why are there so many Java EE offerings?
Because Java EE only describes the behaviour. Everybody can implement it.
What can one do with Java EE that they cannot do with Java SE?
To conquer the internet. It's really hard to do with Java SE applets and sockets :)
What can one do with Java SE that they cannot do with Java EE?
As mentioned above Java EE extends Java SE, so with Java EE you should be able to do everything what is available for Java SE.
When does a developer decide they "need" Java EE?
When they need the power of Java EE. All what is mentioned above.
When does a developer decide they do not need Java EE?
When they write a usual console or desktop application.
Why versions of Java SE and Java EE are unsynced?
Java always had troubles with it's technologies naming and versioning. So this situation is not an exception.
Java EE is all about container concept. Container is an execution context within which will run your application and which provide this last a set of services. Each kind of service is defined by a specification named JSR. For example JSR 907, JTA (java transaction Api) which provide a standard way to manage distributed transaction against different resources. There are generally many different implementations for a given JSR, the implementation you will use depends on the container provider, but you don't really mind about that as you are sure the behavior respect the predefined contract : the JSR API. So to take advantage of Java EE, you need to run your application inside a container. The two main ones are EJB and servlet container which are both present on any Java EE certified application server.
The aim of all of this is to defined a standard execution environment to allow to package your application with only the essentials, id.est. your business. It avoids to depend on a unknown and various set of third-party libraries that you would have to package and provide with your app otherwise, and which may be sources of conflict with other apps on the server. In Java EE you know that all standard non functional requirements like security, transaction, scalability, remote invocation, and many more will be provided by the container (factorized for all apps running inside it) and you just have to base your work on its.
I have been doing Java SE for some years now and moving on to Java EE. However, I have some trouble understanding some aspects of Java EE.
Is Java EE just a specification? What I mean is: Is EJB Java EE?
Are EJB/Spring different implementations of Java EE?
I am sorry to ask but I have some difficulties to understand what Java EE is.
Could someone explain what Java EE is? And EJB?
(Updated Feb 2022)
First of all, "Java EE" has since Sep 2019 been renamed to "Jakarta EE", starting with version 8. Historically, there was also the term "J2EE" which covered versions 1.2 until 1.4. The term "Java EE" covered versions 5 until 8. See also Jakarta EE, History on Wikipedia.
Is Jakarta EE just a specification? What I mean is: Is EJB Jakarta EE?
Jakarta EE is indeed an abstract specification. Anybody is open to develop and provide a working implementation of the specification. The concrete implementations are the so-called application servers, like WildFly, TomEE, GlassFish, Liberty, WebLogic, etc. There are also servlet containers which implement only the JSP/Servlet part of the huge Jakarta EE API, such as Tomcat, Jetty, etc.
We, Jakarta EE developers, should write code utilizing the specification (i.e. import only jakarta.* classes in our code instead of implementation specific classes such as org.jboss.wildfly.*, com.sun.glassfish.*, etc) and then we'll be able to run our code on any implementation (thus, on any application server). If you're familiar with JDBC, it's basically the same concept as how JDBC drivers work. See also a.o. In simplest terms, what is a factory?
EJB is part of the Jakarta EE specification. Look, it's in the Jakarta EE API. Full-fledged Jakarta EE application servers support it out the box, but simple JSP/Servlet containers don't.
See also:
Where can I find a list of all the reference implementations for Java EE 6?
Java / Jakarta EE web development, where do I start and what skills do I need?
What to learn for making Java web applications in Java EE 6?
Are EJB/Spring different implementations of Jakarta EE?
No, as said, EJB is part of Jakarta EE. Spring is a standalone framework which substitutes and improves many parts of Jakarta EE. Spring doesn't necessarily require Jakarta EE to run. A bare-bones servlet container like Tomcat is already sufficient. Simply put, Spring is a competitor of Jakarta EE. E.g. "Spring" (standalone) competes EJB/JTA, Spring MVC competes JSF/JAX-RS/MVC, Spring DI/IoC/AOP competes CDI, Spring Security competes JAAS/JASPIC, etc.
Back during the old J2EE/EJB2 times, the EJB2 API was terrible to implement and maintain. Spring was then a much better alternative to EJB2. But since EJB3 (Java EE 5), the EJB API was much improved based on lessons learnt from Spring. Since CDI (Java EE 6), there's not really a reason to look at again another framework like Spring to make the developers more easy as to developing among others the service layer.
Only when you're using a bare-bones servlet container such as Tomcat and can't move on to a Jakarta EE server, then Spring is more attractive as it's easier to install Spring on Tomcat. It isn't possible to install e.g. an EJB container on Tomcat without modifying the server itself, you would basically be reinventing TomEE.
See also:
When is it necessary or convenient to use Spring or EJB3 or all of them together?
Java EE 6 vs. Spring 3 stack
Using JSF as view technology of Spring MVC
Java Enterprise Edition (Java EE) is an umbrella specification that references a number of other more detailed specifications, of which Enterprise JavaBeans (EJB) is one of the more important ones.
Read this - it explains the difference between Java EE and Spring
Thanks...
Source -- Java 2 Platform, Enterprise Edition (J2EE) defines the standard for developing component-based multitier enterprise applications. J2EE simplifies building enterprise applications that are portable, scalable, and that integrate easily with legacy applications and data .
Source -- Enterprise JavaBeans (EJB) technology is the server-side component architecture for Java Platform, Enterprise Edition (Java EE). EJB technology enables rapid and simplified development of distributed, transactional, secure and portable applications based on Java technology.
Is Java EE just a specification? What I mean is: Is EJB Java EE?
Java EE is a specification.
EJB is server side component architecture for Java EE
Are EJB/Spring different implementations of Java EE?
Both EJB and Spring are different frameworks following Java EE.
J2EE/JEE/Jakarta EE
Java Enterprise Edition (JEE) is used to develop distributed application &
web services.
It’s a component based approach to develop web app.
JEE web apps are considered as 3 tiered apps, since it is divided on 3
different machines/tiers
Client (Presentation)
J2EE sever (Application/Business)
Database (Data Access)
Everything you need to know about Java EE may be found by starting # Oracle official website, among other. You may also find interesting to read the specification APIs for release 8. It is worth taking the time to go through the Java EE 8 tutorial. You may want to start with it actually, because it provides a very good overview of the whole platform.
To put simply - JavaEE is a platform.
It is made up of many specifications which are just APIs. The specific concrete implementations of these APIs are the so called 'Reference Implementation'
EJB is just one specification within the JavaEE platform
No, Spring is a application framework that can allow you/has support for you to develop JavaEE applications
EJB is Enterprise Java Beans
My organization is considering switching from an in-house proprietary
application server (and adhoc protocols) to a Java EE 5 / Java EE 6 framework +
web services for new development, and we're trying to get our heads
around how we'd do that.
We're experiencing something of a culture shock; we're comfortable
with emacs/vi, command-line tools, shell scripts and calling libraries;
all the documentation we encounter seems to assume we're using Eclipse,
IDE plugins, ant and/or maven and some huge framework which makes it
hard to even understand what code is executing. I think an example
would help enormously, so my question is:
Is there a modern, non-trivial example Java EE application (or real-world open source application) out there that provides a WS-I style web service interface and ideally also demonstrates using a relational database?
I've found various "hello world" applications and tutorials that
create some sort of web service using a Java EE framework, but never
anything more complicated than a temperature conversion service!
I was in a similar situation a few years ago. I was a C programmer using vi and pico on Linux, and I got hired onto a J2EE project. They may be slightly dated references and there are some differences in the newer versions, but I used the books Developing Web Services with Apache Axis and J2EE 1.4: The Big Picture as great jumping off points for me and the team I was working with. I highly recommend each book. Also check out Sun/Oracle's J2EE tutorial online. Your first iteration won't be production quality code, and should be considered a throwaway from the start, but it will get you off the ground with an IDE and the J2EE framework.
I'm the only one among my people who navigate in .NET water, the rest is in the Java world. So, I'd like to have some common points to talk with them. What are the equivalent concepts in Java for: (by concept, I mean the purpose of such technology)
Visual Studio
IIS
Linq
Development server that ships with VS (I don't know the name)
NHibernate, Subsonic, ...
ASP.NET WebForm (Is there any equivalent in Java with drag and drop)
ASP.NET MVC
etc.(Please, add some other concepts if they are important to know)
Thanks for helping
Javaland is a pretty big ecosystem. There is plethora of tools and framework to choose from and combine.
There are also popular combo like Tomcat/Spring/Hibernate, but there are of course other.
Many IDE available: Eclipse, NetBeans, JDevelopper, ...
Web container, or application server: Tomcat, Glassfish, Jetty, WebLogic, ...
Some third-party libraries mimic Linq, but it's not widely popular
?
Several ORM available: JPA (specification), Hibernate, EclipseLink, TopLink, ...
Several component-based web framework: JSF, Wicket, ...
Several action-based web framework: Spring MVC, Struts (old school), ...
And I would add:
Build tools: Ant, Mavan
Version control: SVN, Git
Documentation: Javadoc
Issue trackers: JIRA, ...
Collaboration: Eclipse Mylin
Visual Studio
Visual studio is an IDE (Integrated development environment), and it doesn't just support .net. There are lots of others Eclipse or NetBeans are popular Java focused ones.
IIS
IIS is a web server. Again, this is not .net specific. IIS can serve all kinds of content. Apache is a popular alternative web server.
Linq
Language integrated query. Linq is made up of various extension methods to support searching and querying of data and some extra language syntax to support calling those methods in a declarative style. This is rather specific to VB & C#.
Development server that ships with VS (I don't know the name)
I assume you are talking about the development Web Server. This is based on the Cassini code, and there is an extended version - UltiDev Cassini 2.0 (Free but not open source). Like IIS, it is just a web server. It can host asp.net and static html content.
NHibernate, Subsonic, ...
NHibernate is actually a port of Hibernate which is a Java ORM. There are plenty of other Java ORMs available too (see this question). Most are based around the Java Persistence API (JPA).
ASP.NET WebForm (Is there any equivalent in Java with drag and drop)
ASP.NET MVC
Java Server Pages (JSP) and Java Servlets are some technologies for dynamically generating html content in server side Java. There are lots of visual editors for JSP. See this question for some visual JSP plugins for eclipse.
Java Server Faces (JSF) is a web app framework for Java. It follows an MVC based pattern. Again, there are various visual IDEs available for it. I think Eclipse has several visual JSF editor available as plugins.
Etc...
C# is a language. Java is a language.
C# is compiled to the Common Intermediate Language, Java compiles to Java Bytecode
CIL runs on the CLR. Java Bytecode runs on the JVM.
The CLR and the JVM perform JIT compilation to generate machine code for the specific platform the app is being run on.
Both are described as managed languages.
For most of these there isn't a 1:1 equivalent. There are several IDEs (Eclipse, NetBeans, IDEA etc.), plenty of application servers (JBoss, BEA WebLogic etc.), web frameworks etc.
One exception is NHibernate, which is actually coming from the Java Hibernate project.
Eclipse
WebSphere
Uh, nothing there
RSA (Rational Software Architect from IBM) comes with Websphere (I think) and is based on Eclipse
Hibernate
JSF, Struts ... loads of them
JSF, Struts ... same
etc
This question already has answers here:
Difference between Java SE/EE/ME?
(14 answers)
Closed 7 years ago.
What's the main difference between Java SE and Java EE?
Java SE (formerly J2SE) is the basic Java environment. In Java SE, you make all the "standards" programs with Java, using the API described here. You only need a JVM to use Java SE.
Java EE (formerly J2EE) is the enterprise edition of Java. With it, you make websites, Java Beans, and more powerful server applications. Besides the JVM, you need an application server Java EE-compatible, like Glassfish, JBoss, and others.
Java SE stands for Java standard edition and is normally for developing desktop applications, forms the core/base API.
Java EE stands for Java enterprise edition for applications which run on servers, for example web sites.
Java ME stands for Java micro edition for applications which run on resource constrained devices (small scale devices) like cell phones, for example games.
http://www.dreamincode.net/forums/topic/99678-j2se-vs-j2ee-what-are-main-differences/
As far as the language goes it is not as though java changes. Java EE has access to all of the SE libraries. However EE adds a set of libraries for dealing with enterprise applications.
Java EE is more like a "platform" or an general area of development.
In Java SE you write applications that run as standalone java programs or as Applets. In JavaEE you can still do this, but you can also write applications that run inside of a Java EE container. The container can do a great amount of management for you such as scaling an application across threads, providing resource pools, and management features.
Java EE has a web framework based upon Servlets. It has JSP (Java Server Pages) which is a templating language that compiles from JSP to a Java servlet where it can be run by the container.
So Java EE is more or less Java SE + Enterprise platform technologies.
Java EE is far more than just a couple of extra libraries (that is what I thought when I first looked at it) since there are a ton of frameworks and technologies built upon the Java EE specifications.
But it all boils down to just plain old java.
Java SE refers to the standard version of Java and its libraries. Java EE refers to the Enterprise edition of Java which is used to deploy web applications.
Java EE is enterprise edition.
Includes jsp, servlets, beans, and some other stuff for server programming.
Java SE is standard edition. This is plain old Java. Includes GUI stuff.
First, J2SE and J2EE have been renamed. They're now Java SE and Java EE.
Essentially, Java SE is your standard Java designed for end-users. That's what you'd develop to for desktop applications. Java EE is the enterprise edition, designed for server programming, such as SOA and web applications.
Best description i've encounter so far is available on Oracle website.
Java SE's API provides the core functionality of the Java programming language. It defines everything from the basic types and objects of the Java programming language to high-level classes that are used for networking, security, database access, graphical user interface (GUI) development, and XML parsing.
The Java EE platform is built on top of the Java SE platform. The Java EE platform provides an API and runtime environment for developing and running large-scale, multi-tiered, scalable, reliable, and secure network applications.
If you consider developing application using for example Spring Framework you will use both API's and would have to learn key concept of JavaServer Pages and related technologies like for ex.: JSP, JPA, JDBC, Dependency Injection etc.
Java SE contains all the base packages. Some of the base packages are written in Java and some are written in C/C++. The base packages are the fastest because there are no additional layers on top of their core functionality.
Java EE is a set of specifications and the respective implementations are all built using Java SE base packages which happen to already contain everything required for any application. For example, for a web application, here is a Java SE Web Server and a Java SE Database.
Java SE 9/10 is expected to contain better support for native in order to improve the inherent performance issues it has from being an interpreted language. Using the enormous Java EE implementations implies a willingness to sacrifice performance, scalability and a lot of time and money for education and updates, in exchange for project standardization.
JavaSE and JavaEE both are computing platform which allows the developed software to run.
There are three main computing platform released by Sun Microsystems, which was eventually taken over by the Oracle Corporation. The computing platforms are all based on the Java programming language. These computing platforms are:
Java SE, i.e. Java Standard Edition. It is normally used for
developing desktop applications. It forms the core/base API.
Java EE, i.e. Java Enterprise Edition. This was originally known as
Java 2 Platform, Enterprise Edition or J2EE. The name was eventually
changed to Java Platform, Enterprise Edition or Java EE in version 5.
Java EE is mainly used for applications which run on servers, such as
web sites.
Java ME, i.e. Java Micro Edition. It is mainly used for applications
which run on resource constrained devices (small scale devices) like
cell phones, most commonly games.
In Java SE you need software to run the program like if you have developed a desktop application and if you want to share the application with other machines all the machines have to install the software for running the application. But in Java EE there is no software needed to install in all the machines. Java EE has the forward capabilities. This is only one simple example. There are lots of differences.
The biggest difference are the enterprise services (hence the ee) such as an application server supporting EJBs etc.