Spring @Autowired bean not initialising; Null Pointer Exception

Question

Target.java:

package me;

@Component
public class Target implements Runnable {   
    @Autowired
    private Properties properties;

    public Target(){
        properties.getProperty('my.property');
    }

    public void run() {
        //do stuff
    }
}

Config.java:

@Configuration
@ComponentScan(basePackages = {"me"})
public class Config {
    @Bean(name="properties")
    public PropertiesFactoryBean properties() {
        PropertiesFactoryBean bean = new PropertiesFactoryBean();
        bean.setLocation(new FileSystemResource("src/my.properties"));
        return bean;
    }

    public static void main(String[] argv) throws Exception {
        ApplicationContext context = new AnnotationConfigApplicationContext(Application.class);
        Target t = context.getBean(Target.class);
        t.run();
    }
}

With the above code. Bottom of stack:

Caused by: java.lang.NullPointerException
 at me.Target.<init>(Target.java:9)
 ....

src/ can not be resolved, use classpath:my.properties instead. — Grim
– Grim, Commented Apr 5, 2016 at 6:30
when i walk through with the debugger the bean is successfully returned and I can query the property file when inside Config. The properties file is seen fine. — user1561108
– user1561108, Commented Apr 5, 2016 at 6:39

TheKojuEffect · Accepted Answer · 2016-04-05 06:44:33Z

3

You are doing field injection. You're referencing "to-be-autowired" instance variable inside constructor. In constructor, properties field is null because it has not been autowired yet. You can use constructor injection.

package me;

@Component
public class Target implements Runnable {   
    private final Properties properties;

    @Autowired
    public Target(Properties properties){
        this.properties = properties;
        properties.getProperty('my.property');
    }

    public void run() {
        //do stuff
    }
}

answered Apr 5, 2016 at 6:44

TheKojuEffect

21.2k20 gold badges94 silver badges127 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Liviu Stirb · Accepted Answer · 2016-04-05 06:58:28Z

2

The constructor is called before properties is set. You are calling a method on properties in constructor before spring gets to set it. Use something like PostConstruct:

package me;

@Component
public class Target implements Runnable {   
    @Autowired
    private Properties properties;

    public Target(){}

    @PostConstruct
    public void init() {
        properties.getProperty('my.property');
    }

    public void run() {
      //do stuff
   }

}

edited Apr 5, 2016 at 6:58

answered Apr 5, 2016 at 6:39

Liviu Stirb

6,0953 gold badges39 silver badges44 bronze badges

Collectives™ on Stack Overflow

Spring @Autowired bean not initialising; Null Pointer Exception

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related