CODEWITHSUNDEEP
javaspringpropertiesautowired
kosmičák
kosmičák

Reputation: 1043

autowired component is null

I'm developing a web application with spring. I've had no problem autowiring and using database @Service classes. Now I'm trying to read a global property file and provide the values to all classes that need them. The solution I've come up with so far seem to be overly complicated (too many classes - AppConfig, ServerConfig iface, ElasticServerConfig) for such a trivial task but I could live with it if it worked.

my applicationContext.xml contains

<context:component-scan base-package="my.package" />

AppConfig.java:

package my.package.configuration;

@Configuration
@PropertySource("classpath:application.properties")
public class AppConfig {

}

ServerConfig.java:

public interface ServerConfig {
    String getUrl();
    String getUser();
    String getPassword();
}

ElasticSearchConfig.java:

package my.package.configuration;

@Component(value = "elasticServerConfig")
public class ElasticServerConfig implements ServerConfig {

    private static final Logger LOGGER = LogManager.getLogger(ElasticServerConfig.class);

    private String url;
    private String user;
    private String password;

    @Autowired
    public ElasticServerConfig(final Environment env) {
        this.url = env.getProperty("elastic_server.url");
        this.user = env.getProperty("elastic_server.user");
        this.password = env.getProperty("elastic_server.password");
        LOGGER.debug("url=" + url + "; user=" + user + "; password=" + password); // this works!
    }

    @Override
    public final String getUrl() {
        return url;
    }

    @Override
    public final String getUser() {
        return user;
    }

    @Override
    public final String getPassword() {
        return password;
    }
}

When the web application boots, the ElasticServerConfig constructor prints out the correct url/user/pwd as read from application.properties. However an instance of ElasticServerConfig is not injected into a Search object:

package my.package.util;

public class Search {

    @Autowired
    @Qualifier("elasticServerConfig") 
    private ServerConfig elasticServerConfig;

    public final List<Foobar> findByPatternAndLocation() {
      if (elasticServerConfig == null) {
         LOGGER.error("elasticServerConfig is null!");
      }
      // and i get a NullPointerException further on
      // snip
    }
}

Upvotes: 1

Views: 3225

Answers (1)

Evgeni Dimitrov
Evgeni Dimitrov

Reputation: 22506

You have to register the Search class as a Spring Bean and take it from the Spring context when you want to use it. It's important to get the bean from the spring context. If you create an object of that class with new, Spring has no way to know about that class and mange it's dependencies.

You can get get a bean from the Spring context by @Autowire it somewhere or by accessing an instance of the context and use the getBean method:

@Configuration
@PropertySource("classpath:application.properties")
public class AppConfig {
     public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(AppConfig.class, args);
        ctx.getBean...
    }
}

Either use @Component annotation on the class and make sure that the class is in package thats under my.package

or register it in the configuration class 

@Configuration
@PropertySource("classpath:application.properties")
public class AppConfig {
    @Bean
    public Search search(){
        return new Search();
    }
}

Upvotes: 2

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