Servlets are a fundamental part of Java web development. They are Java classes that are used to process requests and produce responses. When a servlet is created, it goes through a series of phases that are collectively known as the servlet life cycle. Understanding the servlet life cycle is essential for developing effective and efficient Java web applications.
In this blog post, we will discuss the servlet life cycle in detail, including the life cycle methods of a servlet, and how they are used in Java web development.
Life Cycle Methods of a Servlet
The servlet life cycle has three stages and we call them in different methods. These are: init(), service(), and destroy(). Let’s discuss each of these methods in detail.
init() method
Called by the servlet container to indicate to a servlet that the servlet is being placed into service.
The servlet container calls the init method exactly once after instantiating the servlet. The init method must complete successfully before the servlet can receive any requests.
The servlet container cannot place the servlet into service if the init method
- Throws a
ServletException - Does not return within a time period defined by the Web server
service() method
Called by the servlet container to allow the servlet to respond to a request.
This method is only called after the servlet’s init() method has completed successfully.
The status code of the response always should be set for a servlet that throws or sends an error.
Servlets typically run inside multithreaded servlet containers that can handle multiple requests concurrently. Developers must be aware to synchronize access to any shared resources such as files, network connections, and as well as the servlet’s class and instance variables.
destroy() method
Called by the servlet container to indicate to a servlet that the servlet is being taken out of service. This method is only called once all threads within the servlet’s service method have exited or after a timeout period has passed. After the servlet container calls this method, it will not call the service method again on this servlet.
This method gives the servlet an opportunity to clean up any resources that are being held (for example, memory, file handles, threads) and make sure that any persistent state is synchronized with the servlet’s current state in memory.
Conclusion
In conclusion, the servlet life cycle is an essential part of Java web development. Understanding the life cycle methods of a servlet is critical to developing effective and efficient Java web applications. By understanding the servlet life cycle, you can ensure that your servlets are properly initialized, handle requests efficiently, and clean up resources when they are no longer needed.
Reference: https://docs.oracle.com/javaee/6/api/javax/servlet/Servlet.html