Menu
Java Servlet life cycle is managed by the servlet container. When first web request comes in, the container will load the Servlet class, calls its init method, then calls its service method to process the web request. It says there can be only one instance of servlet class. The container creates multiple threads and manages these threads to process multiple web requests (this is what I know from my knowledge). But I want to understand, how multiple threads are running and processing multiple simultaneous web requests given that there is only one instance of the servlet class. Can some one shed light on this?
355
A Java servlet container / web server is typically multithreaded. That means, that multiple requests to the same servlet may be executed at the same time.
Multithreading in Java is a process of executing two or more threads simultaneously to maximum utilization of CPU. Multithreaded applications execute two or more threads run concurrently. Hence, it is also known as Concurrency in Java. Each thread runs parallel to each other.
Multiple threads can also read data from the same FITS file simultaneously, as long as the file was opened independently by each thread. This relies on the operating system to correctly deal with reading the same file by multiple processes.
Java supports multithreading through Thread class. Java Thread allows us to create a lightweight process that executes some tasks. We can create multiple threads in our program and start them. Java runtime will take care of creating machine-level instructions and work with OS to execute them in parallel.
An object instance('s methods) can be called simultaneously by more than one thread. This isn't specific for servlets though and is true in general.
What happens when this occurs? Each thread will still have their own stack, which means, each thread will have a different copy of local variables to work on. As a result there will be no interference between threads and you won't have to worry about concurrent calls. Only when a shared resource, e.g. instance/class variable is accessed, there can be a problem. Same thing if instance/class variable is directly accessed concurrently.
EJBs in contrast do exactly what you seem to suggest. The EJB container makes sure that only one thread enters an EJB instance at a time, and hence an EJB programmer doesn't have to worry about concurrency so long as he/she doesn't break the EJB programming contract. There is no reason why the servlet spec didn't do this. Most likely no body came up with it during the meetings? It does have the advantage though that you can use a more efficient concurrency management than EJB's "one thread per instance".
109
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
