Hi, >?am interested to know which topic prompts your question ? As you can see from the log file (below) the spring framework creates and destroys a singleton of a bean. So the singleton pattern is used by the container. I was also informed that the singleton is used to create a login screen. That also appears to be the case from the page http://www.blackwasp.co.uk/Singleton.aspx.
The login screen I will be using is the login.java and login.jsp in the struts2 "blank app" in "struts-examples-master". The struts framework also helps me with duplicate form submission. So do I need to use the singleton pattern ? 2019-12-13 21:01:06,882 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@6f1d30d: defining beans [numberGenerator]; root of factory hierarchy 2019-12-13 21:01:06,882 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Creating shared instance of singleton bean 'numberGenerator' 2019-12-13 21:01:06,882 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Creating instance of bean 'numberGenerator' 2019-12-13 21:01:06,895 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Eagerly caching bean 'numberGenerator' to allow for resolving potential circular references 2019-12-13 21:01:06,896 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Finished creating instance of bean 'numberGenerator' 2019-12-13 21:01:06,897 [main] [DEBUG] o.s.c.s.ClassPathXmlApplicationContext - Unable to locate LifecycleProcessor with name 'lifecycleProcessor': using default [org.springframework.context.support.DefaultLifecycleProcessor@d967f908] 2019-12-13 21:01:06,897 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor' 2019-12-13 21:01:06,900 [main] [DEBUG] o.s.c.e.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source 2019-12-13 21:01:06,910 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'numberGenerator' 2019-12-13 21:01:06,910 [main] [INFO ] academy.learnprogramming.Main - number = 0 2019-12-13 21:01:06,912 [main] [INFO ] o.s.c.s.ClassPathXmlApplicationContext - Closing org.springframework.context.support.ClassPathXmlApplicationContext@3e92e10: startup date [Fri Dec 13 21:01:06 GMT 2019]; root of context hierarchy 2019-12-13 21:01:06,912 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor' 2019-12-13 21:01:06,912 [main] [DEBUG] o.s.b.f.s.DefaultListableBeanFactory - Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@6f1d30d: defining beans [numberGenerator]; root of factory hierarchy On Fri, 13 Dec 2019 at 01:33, Martin Gainty <mgai...@hotmail.com> wrote: > Singleton: > i prefer thread-safe implementations and generally eschew singletons > (unless extreme political pressure dictates otherwise) > https://www.geeksforgeeks.org/singleton-design-pattern/ > [https://www.geeksforgeeks.org/wp-content/uploads/gfg_200X200.png]< > https://www.geeksforgeeks.org/singleton-design-pattern/> > Singleton Design Pattern | Implementation - GeeksforGeeks< > https://www.geeksforgeeks.org/singleton-design-pattern/> > The singleton pattern is one of the simplest design patterns. Sometimes we > need to have only one instance of our class for example a single DB > connection shared by multiple objects as creating a separate DB connection > for every object may be costly. Similarly, there can be a single > configuration ... > www.geeksforgeeks.org > > Design Patterns: > have a look at this discussion from stackoverflow on Visitor Pattern vs > Command Pattern for lambda expresssions > https://stackoverflow.com/questions/2186931/java-pass-method-as-parameter > [ > https://cdn.sstatic.net/Sites/stackoverflow/img/apple-touch-i...@2.png?v=73d79a89bded > ]< > https://stackoverflow.com/questions/2186931/java-pass-method-as-parameter> > interface - Java Pass Method as Parameter - Stack Overflow< > https://stackoverflow.com/questions/2186931/java-pass-method-as-parameter> > In Java 8, you can now pass a method more easily using Lambda Expressions > and Method References. First, some background: a functional interface is an > interface that has one and only one abstract method, although it can > contain any number of default methods (new in Java 8) and static methods. A > lambda expression can quickly implement the abstract method, without all > the unnecessary syntax ... > stackoverflow.com > although this discussion is more specific on when to implement Visitor > Pattern vs when to use Command Pattern > > https://stackoverflow.com/questions/2857880/command-pattern-vs-visitor-pattern > [ > https://cdn.sstatic.net/Sites/stackoverflow/img/apple-touch-i...@2.png?v=73d79a89bded > ]< > https://stackoverflow.com/questions/2857880/command-pattern-vs-visitor-pattern > > > Command Pattern vs. Visitor Pattern - Stack Overflow< > https://stackoverflow.com/questions/2857880/command-pattern-vs-visitor-pattern > > > Each pattern has it's own pros, cons and use cases. You can use Command > pattern to . Decouple the invoker & receiver of command . Implement > callback mechanism. Implement undo and redo functionality. Maintain a > history of commands. Use Visitor pattern in below scenarios:. Similar > operations have to be performed on objects of different types grouped in a > structure ; You need to execute many ... > stackoverflow.com > > ?am interested to know which topic prompts your question? > > /br/ > Martin > ________________________________ > From: Lukasz Lenart <lukaszlen...@apache.org> > Sent: Thursday, December 12, 2019 1:56 AM > To: Struts Users Mailing List <user@struts.apache.org> > Subject: Re: Java Singleton , Framework Design Patterns > > czw., 12 gru 2019 o 06:13 Zahid Rahman <zahidr1...@gmail.com> napisał(a): > > So my point is I have not been able to find accurate information , if > some > > one could furnish me a Java language specification or recommend a book > > which accurately describes these I would be grateful. > > Start with Gang of Four > http://www.blackwasp.co.uk/gofpatterns.aspx > > > Regards > -- > Łukasz > + 48 606 323 122 http://www.lenart.org.pl/ > > --------------------------------------------------------------------- > To unsubscribe, e-mail: user-unsubscr...@struts.apache.org > For additional commands, e-mail: user-h...@struts.apache.org > >
