Getting NullPointerException when tried to read @Autowired configuration object

Question

I am trying to read some properties from application.properties. I have created a configuration class with @Component and @ConfigurationProperties annotations.

When I am trying to access the configuration from a controller class, its working fine. But when I am trying to access the configuration from one component class, its throwing a null pointer exception.

Following are the application.properties and classes.

application.properties

elasticsearch.ip=localhost

InputManagementController.java

@RestController
public class InputManagementController {


    @Autowired
    private Configuration configuration;

    @GetMapping("/crawler/start")
    public String start(){
        try{

            System.out.println(configuration.getIp()); ----> getting value localhost
            ElasticsearchInterface es=new ElasticsearchInterface();
            es.getInputs();
        }catch (Exception e){
            e.printStackTrace();
        }
        return "started";
    }
}

ElasticsearchInterface.java

@Component
public class ElasticsearchInterface {


    @Autowired
    private Configuration configuration;

    public List<Map<String, Object>> getInputs() {
            System.out.println(configuration.getIp()); ---> getting java.lang.NullPointerException here
        return null;

    }

}

Configuration.java

@Component
@ConfigurationProperties("elasticsearch")
public class Configuration {

    private String ip;
    private int port;
    private String cluster;

    public String getIp() {
        return ip;
    }
    public void setIp(String ip) {
        this.ip = ip;
    }

}

Answer 1

A - How To Read Custom Property From application.properties In Spring Boot

A-1) Application Properties file

On of the default location of application.properties file is src/main/resources. Create this folder and also this file. Assuming your scenario, put the following properties inside application.properties file;

myconfig.ip=192.168.166.42
myconfig.port=8090

A-2) Configuration Class : AppConfig

In order to read the properties file, you need a class with @Configuration annotation. You need appropriate fields with @Value annotation for all the properties that you need to read. In addition, also you need the getter methods for these fields marked with @Value annotation. Please note that naming this class as "Configuration" is a very bad choice because there is also an annotation with the same name, thus I name it as "AppConfig"

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {

    @Value("${myconfig.ip}")
    private String ip;

    @Value("${myconfig.port}")
    private int port;

    public String getIp() {
        return ip;
    }

    public int getPort() {
        return port;
    }

}

A-3) Demo

Then you create a fields of this AppConfig class which is written above, and mark it with @Autowired annotation. Then you can read the properties files easily;

@RestController
@RequestMapping("/")
public class InputManagementController {

    @Autowired
    private AppConfig config;

    @RequestMapping("/test")
    public String test() {
        return String.format(
                "Configuration Parameters: Port: %s, Ip: %s", 
                config.getPort(),
                config.getIp()
        );
    }

}

A-4) Output

B - Solution To Problem

B-1) InputManagementController.java

@RestController
public class InputManagementController {

    @Autowired
    private AppConfig configuration;

    @Autowired
    private ElasticSearchInterface elasticSearchInterface;

    @GetMapping("/crawler/start")
    public String start() {
        try {

            System.out.println(configuration.getIp());
            es.getInputs();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "started";
    }
}

B-2) ElasticSearchInterface.java

@Component
public class ElasticSearchInterface {

    @Autowired
    private AppConfig configuration;

    public List<Map<String, Object>> getInputs() {
        System.out.println(configuration.getIp());

        return null;
    }

}

B-3) AppConfig.java

@Configuration
public class AppConfig {

    @Value("${myconfig.ip}")
    private String ip;

    @Value("${myconfig.port}")
    private int port;

    public String getIp() {
        return ip;
    }

    public int getPort() {
        return port;
    }

}