Using Spring 3 autowire in a standalone Java application

Question

Here is my code   public class Main        public static void main String   args            Main p   new Main            p start args               Autowired     private MyBean myBean      private void start String   args            ApplicationContext context                new ClassPathXmlApplicationContext  META-INF config xml            System out println  my beans method      myBean getStr               Service  public class MyBean       public String getStr             return  string                lt 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-3 0 xsd      http   www springframework org schema context      http   www springframework org schema context spring-context-3 0 xsd  gt        lt context annotation-config   gt        lt context component-scan base-package  mypackage   gt   lt  beans gt    Why doesn t this work  I get NullPointerException  Is it possible to use autowiring in a standalone application

User · Answer

A nice solution would be to do following,

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class SpringContext implements ApplicationContextAware {

private static ApplicationContext context;

/**
 * Returns the Spring managed bean instance of the given class type if it exists.
 * Returns null otherwise.
 * @param beanClass
 * @return
 */
public static <T extends Object> T getBean(Class<T> beanClass) {
    return context.getBean(beanClass);
}

@Override
public void setApplicationContext(ApplicationContext context) throws BeansException {

    // store ApplicationContext reference to access required beans later on
    SpringContext.context = context;
}
}

Then you can use it like:

YourClass yourClass = SpringContext.getBean(YourClass.class);

I found this very nice solution in the following website: https://confluence.jaytaala.com/pages/viewpage.action?pageId=18579463

User · Answer

Spring is moving away from XML files and uses annotations heavily  The following example is a simple standalone Spring application which uses annotation instead of XML files   package com zetcode bean   import org springframework stereotype Component    Component public class Message       private String message    Hello there        public void setMessage String message          this message    message           public String getMessage           return message           This is a simple bean  It is decorated with the  Component annotation for auto-detection by Spring container   package com zetcode main   import com zetcode bean Message  import org springframework beans factory annotation Autowired  import org springframework context ApplicationContext  import org springframework context annotation AnnotationConfigApplicationContext  import org springframework context annotation ComponentScan    ComponentScan basePackages    com zetcode   public class Application        public static void main String   args             ApplicationContext context                   new AnnotationConfigApplicationContext Application class            Application p   context getBean Application class           p start                Autowired     private Message message      private void start             System out println  Message      message getMessage               This is the main Application class  The  ComponentScan annotation searches for components  The  Autowired annotation injects the bean into the message variable  The AnnotationConfigApplicationContext is used to create the Spring application context   My Standalone Spring tutorial shows how to create a standalone Spring application with both XML and annotations

User · Answer

For Spring 4  using Spring Boot we can have the following example without using the anti-pattern of getting the Bean from the ApplicationContext directly   package com yourproject    SpringBootApplication public class TestBed implements CommandLineRunner        private MyService myService        Autowired     public TestBed MyService myService           this myService   myService             public static void main String    args            SpringApplication run TestBed class  args               Override     public void run String    strings  throws Exception           System out println  myService      MyService               Service  public class MyService      public String getSomething             return  something             Make sure that all your injected services are under com yourproject or its subpackages

User · Answer

Spring works in standalone application  You are using the wrong way to create a spring bean  The correct way to do it like this    Component public class Main        public static void main String   args            ApplicationContext context                new ClassPathXmlApplicationContext  META-INF config xml             Main p   context getBean Main class           p start args               Autowired     private MyBean myBean      private void start String   args            System out println  my beans method      myBean getStr               Service  public class MyBean       public String getStr             return  string             In the first case  the one in the question   you are creating the object by yourself  rather than getting it from the Spring context  So Spring does not get a chance to Autowire the dependencies  which causes the NullPointerException     In the second case  the one in this answer   you get the bean from the Spring context and hence it is Spring managed and Spring takes care of autowiring

User · Answer

I case you are running SpringBoot   I just had the same problem  that I could not Autowire one of my services from the static main method   See below an approach in case you are relying on SpringApplication run    SpringBootApplication public class PricingOnlineApplication         Autowired     OrchestratorService orchestratorService       public static void main String   args            ConfigurableApplicationContext context   SpringApplication run PricingOnlineApplication class  args           PricingOnlineApplication application   context getBean PricingOnlineApplication class            application start               private void start             orchestratorService performPricingRequest null              I noticed that SpringApplication run returns a context which can be used similar to the above described approaches  From there  it is exactly the same as above  -

[java] Using Spring 3 autowire in a standalone Java application

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