singleton

问题 I have a log4net wrapper class... But i need to instantiate everytime when i call it from other classes to log the error. I need to overcome that.. Recently i came across the singleton class which is not familiar to me.. Hence I need help in converting my current wrapper class to the singleton class.. I am posting my log4net wrapper class which i am currently using below.. using System; using System.Data; using System.Configuration; using Asset.Business; /// <summary> /// Summary description

问题 if I understand EJB correctly, @Singleton is actually the same as Singleton in plain Java and also singleton in spring -> one instance, every call goes through the same instance concurrently. @Stateless declares a bean, that could (but must not) have multiple instance, with the limitation that only one call can be in an instance at the same time. Right sofar? This remains me on the servlet programming model: in theory servlet containers are allowed to make multiple copies of the servlet, in

问题 Why does Foo.val return nil instead of "foo" before calling Foo.set ? Is there any mechanism for initializing @val on class evaluation? In which scope is @val = "foo" stored into? class Foo class << self @val = "foo" attr_reader :val def set(val) @val = val end end end p Foo.val # nil Foo.set("bar") p Foo.val # "bar" 回答1: You can initialize @val in Foo like this: class Foo @val = "foo" class << self attr_reader :val def set(val) @val = val end end end p Foo.val #=> "foo" Foo.set("bar") p Foo

问题 The standard way of doing singletons in Python is class Singleton(object): _instance = None def __new__(cls, *args, **kwargs): if not cls._instance: cls._instance = super(Singleton, cls).__new__(cls, *args, **kwargs) return cls._instance However, this doesn't work on App Engine, since there are may be many servers and we would get one instance per server. So how would we do it for an app engine entity? Something like: class MySingleton(db.models): def __init__(self): all = MySingleton.all()

问题 EDITED: after believing this is a NetBeans 7.0 editor bug. It still compiles and is deployable. I want to convert my webservice which is @WebService;@Stateless implementation into a @Singleton bean but when I replace the @WebService with @Singleton annotation... I get the image below in my IDE Editor of course when I do something silly like having both @WebService and @Stateless and deploy in glassfish I get: severe error: Annotations processing failed for... below is a link (there are more,

问题 I have been getting some strange errors with Mongodb, and in Mongodb, you are supposed to mainatin the Mongo singleton. I just wanted to make sure that this is infact valid. public class DBManager { public static Mongo mongoSingleton = null; public static synchronized void getMongo(){ if(mongoSingleton == null){ mongoSingleton = new Mongo(); } return mongoSingleton; } } Thanks! 回答1: You have to set your public member mongoSingleton as private and to hide the default constructor so private

问题 I'm working on building a PHP framework that behaves according to MVC principles and utilizes dependency injection. I think I have the front-controller part down; there is a working router that instantiates a controller instance and calls the appropriate action based on the requested URI. Next up is dependency injection. I want to implement a Container that resolves dependencies using reflection. In doing so, I think I'm running into a problem with my controllers. There are a number of what I

问题 I have a WCF service that I am calling from multiple clients. I need to store and manage a value globally. On my service I have the following attributes: [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Single)] In my service I have something similar to this: private static int counter; public void PrintCounter() { counter++; StreamWriter sw = new StreamWriter(@"C:\outFile.txt", true); sw.WriteLine("Counter: " + counter); sw.Close(); } With

问题 I'm just starting my first fairly large Qt project which will be mostly a bunch of screens with buttons, tab widgets, and Qwt Plots. The panel stack pattern described in Qt Quarterly 27 seems pretty nice for my application. Each of my screens is a QWidget encapsulated in a Panel which is shown/hidden by a QStackedWidget. However it uses a singleton pattern for each Panel so that they aren't all created immediately as the app starts and so that more than one of each screen isn't ever created.

问题 I have a Typescripted nodejs server and i'm trying to define diffrent swagger paths for seperated controllers, but the swagger-ui-express module seems to only show the last defined doc in the specific route. index.ts for X group of controllers import express from 'express'; import passport from 'passport'; const router = express.Router(); // import all bot routes import { authRoute } from './auth'; import { botCrudRoute } from './bot-crud'; import { aiRoutes } from './ai'; import {