java - Spring 4: NullPointerException during instantiation of ClassPathXmlApplicationContext -

i developing standalone spring 4 application, uses javafx. however, when try create new classpathxmlapplicationcontext, autowired fields null, leading npes, though let spring instantiate classes.

this main class:

public class main extends application {  public static void main(string[] args) {     launch(); }  public void start(stage stage) {     configurableapplicationcontext context = new classpathxmlapplicationcontext("spring-config.xml");     gui gui = context.getbean(gui.class);     stage.setscene(new scene(gui, 400, 400));     stage.show(); } } 

this spring-config.xml:

<beans xmlns="http://www.springframework.org/schema/beans"   xmlns:xsi="http://www.w3.org/2001/xmlschema-instance"   xmlns:context="http://www.springframework.org/schema/context"   xsi:schemalocation="http://www.springframework.org/schema/beans   http://www.springframework.org/schema/beans/spring-beans-4.2.xsd   http://www.springframework.org/schema/context   http://www.springframework.org/schema/context/spring-context-4.2.xsd">    <context:annotation-config />   <context:component-scan base-package="org.my.package" />  </beans> 

gui class:

@controller @scope("singleton") public class gui extends gridpane {      @autowired     private netmanager netmanager;     @autowired     private messengercomponent messenger;      public gui() {         netmanager.init("username");             ...     } } 

netmanager.class:

@service @scope("singleton") public class netmanager {     ... } 

the npe occurs before retrieve first bean, during creation of application context. idea why?

the order of injection following:

1. constructor args
2. fields
3. setters/methods

under hood, spring (or di framework) create class calling constructor, , inject dependencies. can't use injected fields in constructor: injected after.

you should inject needed dependencies in constructor:

@autowired public gui(netmanager netmanager) {   this.netmanager = netmanager;   netmanager.init("username");             ... }