为什么Java应用程序需要应用程序服务器而.Net只需要IIS Web服务器？

Question

Why is there so much confusion in the java world with various servers like apache, tomcat, jboss, jetty, etc and in .Net world it is just IIS that does that job. I would like to understand the need and use of it and am not starting a java vs. .net.

Answer 1

There are several reasons.

A Java EE app server is a transaction monitor for distributed components. It provides a number of abstractions (eg, naming, pooling, component lifecycle, persistence, messaging, etc.) to help accomplish this.

Lots of these services are part of the Windows operating system. Java EE needs the abstraction because it's independent of operating system.

It should also be said that the full Java EE specification isn't necessary for developing web applications. JDBC, the part of Java that deals with relational databases, is part of Java SE proper. Java EE adds on servlets, which are HTTP listeners, and Java Server Pages, which is a markup language for generating servlets. You can develop fully functional web applications using just these technologies and Java SE. Tomcat and Jetty are two servlet/JSP engines that can stand in for full Java EE app servers.

If you take note of the fact that .NET has HTTP listeners built into the System.Net module, you realize that it's as if .NET took a page from Java and folded the javax.servlet functionality into the framework.

If you add Spring and a messaging functionality like ActiveMQ or RabbitMQ, you can write complete applications without having to resort to WebLogic, WebSphere, JBoss, or Glassfish. You don't need EJBs or the full Java EE spec.

UPDATE:

Spring Boot offers the possibility of developing and running full-featured Java applications as an executable JAR file. There's no need for any Java EE app server, just JDK 8 or higher.

Answer 2

This is because Sun and Microsoft had very different goals with their software, and ways to reach that goal.

The Sun mantra for Java has been right from the beginning "Write once, run everywhere", and that has resulted in that much effort has been put into creating _API_s that specify how the environment should look like to allow a minimalistic piece of code do its job.

The API for "process a web request and return a web response" was named Servlets, and has been extremely successful due to it filling a void and being well specified. All mainstream Java based web servers I know of allow to run servlets. An early implementation of a complete servlet capable web server is only 1500 lines Later this was expanded to include JSP's to provide for HTML with server side code (like PHP).

For any solution to be truly scalable, including web solutions, it means that eventually the load is so high that one computer is not powerful enough to run it on its own anymore. A scalable solution MUST be able to spread over multiple computers aware of each other, and that single requirement brings a LOT of other things to the table:

• Code must be able to invoke code running on a different computer (EJB's).
• Data must be available to all computers in a consistent way (database).
• Access to said database must be efficient (database connection pooling). ... and much much more

Sun then created API's for all of the functions they found were necessary for this to run, and named it "Java Enterprise Edition" (those days the word "Enterprise" was used for a lot of things), and created a system implementing all these API's which people could buy and use.

The difference between Microsoft and Sun now comes in play. Here Microsoft would just make IIS public, and say "use these API's" in clients but not actually want anybody to create another server providing these APIs. Because they want to sell Windows to run it!

Sun wanted people to use the language instead, so they made it possible for ANYONE to implement the Java EE specification, but they had to pass a rigorious test suite from Sun (and pay) to be allowed to use the Java EE brand. This has caused a large number of Java EE servers to be available where you usually can reuse the core business logic, but have to configure the Java EE server to provide the resources the application needs.

See http://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition#Certified_application_servers for the state of servers today. Both commercial and open source are available based on your needs - pick the one that suits you best.

So, the reason is that Java EE is a set of well defined API's that anyone can implement, and they have.

Answer 3

First off, you can run .NET code off Apache using mod_mono, so it is not limited to IIS. There are also several other web servers (Cassini and XPS come to mind) that will run ASP.NET as well.

In order to run a dynamic web application you need both a web server and an application server. Sometimes these integrate so well they appear to be one and the same, sometimes not.

In regards to Java - it has always supported more platforms than .NET and has been more open, therefore got integrated to more web servers (on the Linux stack).

As both .NET and IIS are technologies that came from Microsoft, ASP.NET and the application server aspects of it (aspnet_isapi.dll) were bundled with IIS and the different .NET installers integrate with IIS. Of course, Microsoft only implemented it on their OS and for their web server.

Answer 4

Apache is very analogous to IIS, and doesn't have much to do with Java.

Application Servers in Java provide additional services that .NET provides in various ways, with different products or from the Windows operating system.

Apache is typically used in Java deployments as a proxy to an application server behind it, and potentially serves static content, or handles SSL, and similar concerns. It is entirely optional, although there are good reasons to use it.

Tomcat and Jetty are basically java web servers, which provide a defined framework (Servlets among other things) for creating dynamic web sites with Java code. They are often components of a larger application server, or can be deployed alone.

JBoss is an example of an application server (Glassfish and Weblogic are two very common others), which provides the full J2EE specification. The idea behind the J2EE specification is to allow a defined way to build an application server so that an application can be switched between different application servers from different vendors that comply with the spec. The specification is about how to interact with defined services that are useful for server-side program.

Answer 5

Because Java EE is a specification, not a product itself. Remember that Java is a lot more open than .NET (In the specification sense).

Each application server has different features, different performance, different target users/enterprises, different price tags, runs in different platforms, require different hardware. Differentiation is why those all application servers exists, one size does not fit all.

Answer 6

One reason is that writing a servlet is as easy as implementing the javax.servlet.Servlet interface in a concrete class. Servlet containers, then, only need to support a fairly simple API in order to call themselves web servers. This makes setting out to develop a servlet container extremely simple because of this limited contract of functionality.

Answer 7

The choices off tools are one of the advantages and disadvantages of Java, look at the available Java Web Developement Frameworks,you could evaluate them endlessly just to decide. in .Net it's pretty much MVC. With servers it's relatively simple. Most go to Tomcat if they need a web server and JBoss if they need a free application server though. The reasons for this have already been said, J2EE is a specification.