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

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";
    }
}

<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"> 
    <context:annotation-config /> 
    <context:component-scan base-package="mypackage"/>
</beans>

Why doesn't this work? I get NullPointerException. Is it possible to use autowiring in a standalone application?

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.

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 ;-)

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

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.