CODEWITHSUNDEEP
javaspring
vyeluri5
vyeluri5

Reputation: 487

Java Spring application @autowired returns null pointer exception

Im fairly new to Java Spring IoC and here's my problem

I have a FactoryConfig class with all beans and annotation @Configuration and @ComponentScan written as below.

import org.springframwork.*

@Configuration
@ComponentScan(basePackages="package.name")
public class FactoryConfig {

    public FactoryConfig() {

    }

    @Bean
    public Test test(){
         return new Test();
    }

    //And few more @Bean's
}

My Test class has a simple Print method 

public class Test {

    public void Print() {
        System.out.println("Hello Test");

    }
}

Now in my Main Class Ive created an ApplicationContentext of FactoryConfig. (I'm expecting all of my @Beans in Factory config will be initialised. However, it returns null when I access the Test class using @Autowired

My Main Class

public class Main {

     @Autowired
     protected static Test _autoTest;

     public static void main(String[] args) throws InterruptedException {
          // TODO Auto-generated method stub
     ApplicationContext context = 
               new AnnotationConfigApplicationContext(FactoryConfig.class);

     FactoryConfig config = context.getBean(FactoryConfig.class);

     config.test().Print();  

    // _autoTest.Print();   <--- Im getting NULL Pointer Ex here 
   }

}

What is the correct way to @Autowire and use objects/beans? any clearer explanation would be much appreciated.

Upvotes: 0

Views: 11048

Answers (5)

Francisco MEza
Francisco MEza

Reputation: 81

remove the static argument protected Test _autoTest;

Upvotes: 0

Bhushan
Bhushan

Reputation: 148

Spring does not manage your Main class, that's why you are getting Nullpointer Exception. Using ApplicationContext to load beans, you can get your beans and access Methods as you are already doing - 

ApplicationContext context = 
           new AnnotationConfigApplicationContext(FactoryConfig.class);

 FactoryConfig config = context.getBean(FactoryConfig.class);

 config.test().Print();

Upvotes: 0

Francesco Pitzalis
Francesco Pitzalis

Reputation: 2102

The reason is that your Main is not managed by Spring. Add it as bean in your configuration:

import org.springframwork.*

@Configuration
@ComponentScan(basePackages="package.name")
public class FactoryConfig {

    public FactoryConfig() {

    }

    @Bean
    public Test test(){
         return new Test();
    }

    @Bean
    public Main main(){
         return new Main();
    }

    //And few more @Bean's
}

And then you can edit your main() as follows:

public class Main {

     @Autowired
     protected Test _autoTest;

     public static void main(String[] args) throws InterruptedException {
         ApplicationContext context = 
               new AnnotationConfigApplicationContext(FactoryConfig.class);

         Test test = context.getBean(Test.class);
         Main main = context.getBean(Main.class);

         test.Print();  
         main._autoTest.Print();
     }

}

Upvotes: -1

Oli
Oli

Reputation: 840

Your class

public class Test {
    public void Print() {
        System.out.println("Hello Test");
    }
}

is not visible to Spring. Try adding an appropriate annotation to it, like @Component.

Upvotes: -1

J&#233;r&#233;mie B
J&#233;r&#233;mie B

Reputation: 11022

Only beans managed by Spring can have @Autowire annotations. Your main class is not managed by Spring: it's created by you and not declared in a Spring context: Spring doesn't known anything about your class, and doesn't inject this property.

You can just access in your main method the Test bean with :

context.getBean(Test.class).Print();

Usually, you get a "bootstrap" from the context, and call this bootstrap to start your application.

Moreover:

  • On Java, a method shouldn't start with an uppercase. Your Test class should have a print method, not Print.
  • If you start with Spring, you should maybe try Spring Boot

Upvotes: 8

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