Develop Reference

Design considerations for J2EE webapp on Tomcat in Amazon WebServices

My project is looking to deploy a new j2ee application to Amazon's cloud. ElasticBeanstalk supports Tomcat apps, which seems perfect. Are there any particular design considerations to keep in mind when writing said app that might differ from just a standalone tomcat on a server?
For example, I understand that the server is meant to scale automatically. Is this like a cluster? Our application framework tends to like to stick state in the HttpSession, is that a problem? Or when it says it scales automatically, does that just mean memory and CPU?

Automatic scaling on AWS is done via adding more servers, not adding more CPU/RAM. You can add more CPU/RAM manually, but it requires shutting down the server for a minute to make the change, and then configuring any software running on the server to take advantage of the added RAM, so that's not the way automatic scaling is done.
Elastic Beanstalk is basically a management interface for Amazon EC2 servers, Elastic Load Balancers and Auto Scaling Groups. It sets all that up for you and provides a convenient way of deploying new versions of your application easily. Elastic Beanstalk will create EC2 servers behind an Elastic Load Balancer and use an Auto Scaling configuration to add more servers as your application load increases. It handles adding the servers to the load balancer when they are ready to receive traffic, and removing them from the load balancer and deleting the extra servers when they are no longer needed.
For your Java application running on Tomcat you have a few options to handle horizontal scaling well. You can enable sticky sessions on the Load Balancer so that all requests from a specific user will go to the same server, thus keeping the HttpSession tied to the user. The main problem with this is that if a server is removed from the pool you may lose some HttpSessions and cause any users that were "stuck" to that server to be logged out of your application. The solution to this is to configure your Tomcat instances to store sessions in a shared location. There are Tomcat session store implementations out there that work with AWS services like ElastiCache (Redis) and DynamoDB. I would recommend using one of those, probably the Redis implementation if you aren't already familiar with DynamoDB.
Another consideration for moving a Java application to AWS is that you cannot use any tools or libraries that rely on multi-cast. You may not be using multi-cast for anything, but in my experience every Java app I've had to migrate to AWS relied on multi-cast for clustering and I had to modify it to use a different clustering method.
Also, for a successful migration to AWS I suggest you read up a bit on VPCs, private IP versus public IP, and Security Groups. A solid understanding of those topics is key to setting up your network so that your web servers can communicate with your DB and cache servers in a secure and performant manner.

JConsole Web Application

I need to have the information and operations of my MBeans in my applications and I need this to be as a web application.
My app server is Weblogic 10.3.2
Actually I need an application which can do the things(only about MBeans) like JConsole does(both functionally and visually).
ANy applications u know? or any code examples to do it easilly?
Thanks
Ali

Take a look at:
Jolokia: Deploys as a WAR or a JavaAgent and exposes JMX ops and attributes through a REST API. There's no actual console as yet, but check here and here for possible implementations.
OpenDMK: This is the open-sourced Java Dynamic Management Kit. It contains, among other things, a HTML Protocol Adaptor which provides a very basic browser accessible view of your MBeanServer.
MX4J: Also provides an HTTP Protocol Adaptor.
The last 2 are not particularly active any more, but I can attest to their stability.

What are the specific uses of Java Application Server that cannot be done with web servers?

I am a little confused about the roles of a java application server and its differences from a web server.
I found many sites explaining the same difference between the two but not to my satisfaction.
So please explain me about the two following cases:-
1)App. Server and its difference with web server:
From these two links:
Difference between an application server and a servlet container?
What is the difference between application server and web server?
web server: It handles everything through http protocol by accepting requests from clients and sending
responses to them with the help of its servlet container(e.g Apache Tomcat)
App. Server: An application server supports the whole of JavaEE like JMS,JPA,RPC etc.
Now what I am confused with is that how can I use a lot of JavaEE APIs like JMS,JPA etc. with my Tomcat
by adding their jar files in my web application ?
Does that mean that if I use an appliation server I don't have to add those jar files?(I don't think so)
2)The roles of an appl. server (This is very important to me)
From Wikipedia
http://en.wikipedia.org/wiki/Application_Server
An application server provides services such as security,transaction support etc.
"The term is often used for web servers which support the JavaEE" -- It sounds like if we add the required jar files of JavaEE APIs a web server becomes an appl. server.What about it.
Now my question is how an application server performs the tasks of security control or transaction management by itself ?
E.g. in my web application using Spring framework I am providing security by using spring-security and transaction management by using #Transactional annotation and all those things you know.
So does the appl. server have anything to do with my security or transaction management or it has its own ways ?
Forgive my ignorance.

Using Spring, you're in fact embedding some kind of Java EE container inside your application. But even when using Spring, if you need JTA support (because you need distributed XA transactions), you'll need to use an additional transaction manager. If you need JMS, you'll need to install an additional JMS broker. If you need connection pooling, you'll need to use an additional connection pool. Sometimes it's as simple as adding additional jars to the classpath and properties or XML files. Sometimes it's harder.
A Java EE app server comes with everything bundled. You have less flexibility, but you don't need to install, configure and make everything work by yourself.

When you use the Java EE framework, that is a specification. So the application server, if it is Java EE compliant, needs to implement this. So once it is implemented the specification, then it will address Security,transaction etc because it is mentioned in the spec. So it is a contract. Whereas, in a web server, it will just pull out your static resource. There is no need for handling other stuff.
In case of the Spring framework, the framework knows how to handle transaction, security etc. So particularly the developer need not look into these aspects which are implemented by the Application Server in the other scenario.
how an application server performs the tasks of security control or transaction management by itself
It is rather the specification that address these issues, not the application server. So, the duty of the app server is to implement these.
So, if your application is Java EE compliant, then these areas will be addressed and the implementation would have been done by the app server.

May be this is oversimplification,
A web server is basically a HTTP server serving contents over http protocol. So a web server is simply about serving the contents over http protocol. A typical example would be Apache web server. This is simply a file server.
Now the question is where does the web server gets the contents from ? Possible sources are
Static contents (the contents like images/css etc) which are not generated on request but statically served.
Dynamic contents: Simply put, the contents to be served are generated upon the user request.
For the static contents, the web server does not need anything as it simply reads the file and serves it.
For dynamic contents, the web server might need help of additional components which will generate the contents to be served.
Here the Application Server comes into picture.
Now these additional components referred earlier, might interact with database or some other system etc.
In a web environment where your website is exposed to huge number of users (intended/unintended), you need typical services like transaction/security/concurrency etc. so that the user get expected responses and do not see inconsistencies in the behavior of the application.
An application server has inbuilt abilities to manage transaction/security/concurrency/resource management. generally these are referred as Managed services and environment offered by them is called Managed Environment where these basic services are managed by the application server and programmer does not have be bother for them.
Application Server needs web servers or we can say Web servers use Application server's services to generate dynamic contents.
For example, JBoss uses Tomcat as inbuilt web server. Whereas web logic has its own web server. Tomcat again can be called as application server (in principle) as it also offers managed environment for servlets (it manages concurrency and instance pool of servlets/JSPs ).
Coming your your example of Spring:
An Application server will come inbuilt with transaction/security etc whether you need it or not. The Spring offers a very nice way handling this. Spring has all these things BUT you use what you need. Not just these, but just a Java Web Sever like Tomcat is sufficient to build a full fledged services that needs an application server.

Why do we need Application Server in Java

Why do we need Application Server in Java like JBoss or WebSphere. Is it possible that we develop large scale website only with Java (Apache Tomcat). Where thousand of user connect on site at a moment. An example is a website like b2b.
What is the cost of a Application Server? I will be thankful if you compare price among different application server and if there is any free version kindly highlight it.

Application Servers are mostly used if you want to use advanced features like transaction management, hot code swapping and advanced persistence.
There are application servers that are open source. E.g. GlassFish and JBoss.
I don't think you need an application server for building a popular web site, you'll also be fine with a servlet container like Tomcat or Jetty.

In short Application Servers provide you with few services like
Transaction Management
Load Balancing
Security
Threading
etc.
You have to take care of these things yourself in a Web Server.
There are few Open Source Application servers which are free of cost.
I have used Glassfish.

Apart from answers given above, App Servers are required for EJBs.

You need Application Server as follow:
It provides you useful services like automatic transaction,Authentication,Authorization,Lifecycle management.
To remember large user data across pages using ejb's pertaining to a client.
Load balance the user request and buisness logic.
To interact with different Client UI like Java Swing,Browsers.

It is possible to handle the httpheaders yourself. We have done socket servers in java for 20 years. You do not need a container for java swing.
Persistence can be done through databases or server side files unless you need real high speed stuff. I have yet to find a real requirement for an ejb
except that some systems simply require them

This may be because jboss can provide better after-sales service, and jboss, etc. can provide operation and maintenance support, etc. This may be the reason why many large companies choose commercial versions of servers.
But you must know that tomcat and netty are not bad. For example, many large B2B or C2C or B2C companies still use tomcat, such as Internet companies such as Alibaba.
Choose a server
Operation and maintenance costs
Scalable costs
Server cost

Java Tomcat enable caching

What is the best way to set up caching on tomcat?
Also how caching works?Is it url based,dir based or what?
I need url specific caching so the database don't make the same calculations for the same url's

The simplest way, is to use a dedicated web cache provider. Tomcat does not have one OOTB, but you could employ Apache with mod_cache (and obviously mod_jk). In this configuration, Apache tends to act as a proxy-cache that caches the dynamic content served by Tomcat; you will have to ensure that Tomcat serves the right headers to ensure that Apache will cache the responses.
There are other commerical web-cache solutions, but they're typically used for high-end uses.
You could also employ Squid instead of Apache, to act as a reverse proxy that is also capable of serving cached content; in this case, Squid performs caching of the dynamic content.
If you do not wish to invest in an additional server, like the above solutions suggest, you might consider using EHCache to perform web page caching on Tomcat itself.
Related
Java Web Application: How to implement caching techniques?

Tomcat doesn't support what you want out of the box, so you'll need some extra stuff. I'm not fully aware of all mod_cache capabilities but if you're not using Apache, OSCache can do what you're requesting.

Can you use the Expires Filter?
http://tomcat.apache.org/tomcat-7.0-doc/config/filter.html#Expires_Filter
See also this question:
Enable caching in Tomcat 6?