Getting NullPointerException when tried to read @Autowired configuration object [duplicate]

This question already has an answer here:

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

application.properties

@Component

@ConfigurationProperties

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

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;
}

}


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ElasticsearchInterface es=new ElasticsearchInterface();

1 Answer
1

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


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;
}

}


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()
);
}

}


@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";
}
}


@Component
public class ElasticSearchInterface {

@Autowired
private AppConfig configuration;

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

return null;
}

}


@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;
}

}