Best Practices to improve performance in Servlets

Use init() method to cache static data
Use StringBuffer / StringBuilder rather than using + operator when you concatenate multiple strings
Use print() method rather than println() method
Use ServletOutputStream rather than PrintWriter to send binary data
Initialize the PrintWriter with proper size
Flush the data partly
Minimize code in the synchronized block
Set the content length
Release resources in destroy() method.
Implement getLastModified() method to use browser cache and server cache
Use application server caching facility
Use Mixed session mechanisms such as HttpSession with hidden fields
Remove HttpSession objects explicitly in your program whenever you finish the task
Reduce session time out value as much as possible
Use 'transient' variables to reduce serialization overhead if your HttpSession tracking mechanism uses serialization process
Disable servlet auto reloading feature.
Use thread pool for your servlet engine and define the size as per application requirement.

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