java - Difference between ResourceConfig and ServletContextListener for Jersey Rest Service -

i want initialize jersey rest service , introduce global application-wide variable should calculated @ application start up-time , should available in each rest resource , each method (here indicated integer globalappvalue=17, complex object later).

in order initialize service , calculate value once @ start found 2 practices: general servletcontextlistener , jersey resourceconfig method. have not understood difference between both of them? both methods fire @ start (both system.out-messages printed).

here implementation of servletcontextlistener works fine:

public class loadconfigurationlistener implements servletcontextlistener {     private int globalappvalue = 17;      @override     public void contextdestroyed (servletcontextevent event)     {     }      @override     public void contextinitialized (servletcontextevent event)     {         system.out.println ("servletcontext init.");          servletcontext context = event.getservletcontext ();         context.setattribute ("globalappvalue", globalappvalue);     } } 

and implementation of jersey rest resourceconfig-method in servletcontext not available. neither application-object later availabe injection resource-methods:

@applicationpath("resources") public class myapplication extends resourceconfig {     @context     servletcontext context;      private int globalappvalue = 17;      public myapplication () throws namingexception     {         system.out.println ("application init.");          // returns nullpointerexception since servletcontext not injected         context.setattribute ("globalappvalue", 17);     }      public int getappvalue ()     {         return globalappvalue;     } } 

this way gain access in resource methods global value:

@path("/") public class testresource {     @context     servletcontext context;     @context     myapplication application;      @path("/test")     @get     public string sayhello () throws sqlexception     {         string result = "hello world: ";          // returns nullpointerexception since application not injected         result += "globalappvalue=" + application.getappvalue ();          // works!         result += "contextvalue=" + context.getattribute ("globalappvalue");          return result;     } } 

so while classic servletcontextlistener works fine got several problems use resourceconfig/application, prefer way because seems integrate more natively jersey. question way best practice use. thanks!

you set property in resourceconfig calling property( key, value ).

public myapplication() {     property("myprop", "myvalue"); } 

in resource class, allowed inject super abstract class javax.ws.rs.core.application, resourceconfig extends from.

then can call 1 of standard application api methods set properties. method of course named getproperties(), returns map of properties.

@path("/") public class testresource {     @context     application application;      @get     public string get() {         string value = (string)application.getproperties().get("myprop");     } } 

also using property method on resourceconfig, property put global javax.ws.rs.core.configuration object, injectable. instead of application, inject configuration

@path("/") public class testresource {     @context     configuration config;      @get     public string get() {         string value = (string)config.getproperty("myprop");     } } 

see also:

• using custom hk2 injectionresolver inject application configuration other interesting ways inject value instead of having retrieve application or configuration