Performance Improvement - Java

DURING DESIGN APPLICATION:
1) Excessive logging
              Use log into buffer and write at the end.
              Use async logging for better performance.
              Use framework like log4j, SLF4J. 
              Don't use System.err, System.out - There is no way to turn it off. 

2) Incorrect application server configuration.
               Use appropiate heap size based on JVM.
               Use proper thread pool, connection pool, connection time, child connection settings, logger levels, etc.

3) Incorrect usage of Java EE
             
4) Improper usage of caching.
               What is the cache hit ratio?
               How much memory the cache take?
               How performance testing with respect to cache? Is it disabled?
               Can cache monitored / managed at run time? (No of objects in cache, hit ratio, amount of memory used, enable/disable cache, flushing the content, etc).
               Use cache if and only if caching is needed.
               Verify the functional and performance behaviour of your cache with performance tests.
               Make sure your cache can be managed and monitored at runtime.

5) Excessive memory usage

6) Badly performing libraries               

• without checking whether that library is really needed (and does not overlap with functionality already offered by other libraries used),
• without checking whether that library can offer good performance or whether a better performing alternative is available,
• without defining how the library is going to be used within the application.

DEPLOYMENT:
Environment tunning, Like tomcat tunning on Memory, thread, Time to live, etc.
    Few other options you should be aware of during Environment tunning:

1. Add the -server option to the JVM options for Tomcat, which should result in better performance for server applications. Note that this option, in some cases, causes the JVM to crash for no apparent reason. If you face this problem, remove the option.
2. Minimize logging in Tomcat by setting debug="0" everywhere in <Tomcat>/conf/server.xml.
3. Remove any unnecessary resources from the Tomcat configuration file. Some examples include the Tomcat examples Web application and extra <Connector>, <Listener> elements.
4. Set the autodeploy attribute of the <Host> tag to false (unless you need any of the default Tomcat applications like Tomcat Manager).
5. Make sure you have set reloadable="false" for all your Web application contexts in <Tomcat>/conf/server.xml.

Database tunning. Size, ram, no of connection, etc.

Application tunning, Like code optimization, SQL query optimization, Sql profiler, etc

1. Avoid using synchronized block in the code.
2. Classes, Methods, Variables - where every possible use final variable.
3. provide proper logging to help dubugging.