How to read from application.properties

Question

I'm trying to read from application.properties and I can't get it working.

this is my code:

package config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;

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

        @Autowired
        private Environment env;

        public String readProperty(String key) {
            return env.getProperty(key);
        }


}

this is where I invoke the readProperty:

public class JwtSettings {

    public String key;

    public long expiration;

    //The JWT signature algorithm we will be using to sign the token
    public SignatureAlgorithm signatureAlgorithm = SignatureAlgorithm.HS256;

    public JwtSettings() {
        PropertiesReader propertiesReader = new PropertiesReader();
        key = propertiesReader.readProperty(ApplicationProperties.JWT_KEY.key);
    }

When I run this code, the env instance is null. My application.properties file is located in the resource folder. I'm out of ideas, please help.

You are overthinking things. Spring Boot already reads the `application.properties` you don't need to do it again. — M. Deinum, Dec 05 '17 at 08:19
so your'e saying I need to remove '@PropertySource("classpath:application.properties")' annotation ? — Gal Sosin, Dec 05 '17 at 08:20
Yes and if you need properties just inject them with `@Value` or bind to a custom properties object (all of this is explained in the Spring Boot reference guide). — M. Deinum, Dec 05 '17 at 08:21
Then you are creating an instance yourself instead of letting Spring create one and inject it. — M. Deinum, Dec 05 '17 at 08:25
As I saw in your comment, your JwtSettings class is used with @Service annotation and I guess it is instantiated by Spring. I cannot see any usage of any instance of your ApplicationService in your JwtSettings. Where do you use your ApplicationService? — L. Hanke, Dec 05 '17 at 10:17

L. Hanke · Answer 1 · 2017-12-05T12:12:12.007

1

Try to use your configuration like this:

@Service 
public class JwtSettings {

   private String key;

   private long expiration;

   //The JWT signature algorithm we will be using to sign the token
   public SignatureAlgorithm signatureAlgorithm = SignatureAlgorithm.HS256;

   @Autowired
   public JwtSettings(PropertiesReader propertiesReader) {
      this.key = propertiesReader.readProperty(ApplicationProperties.JWT_KEY.key);
   }
}

You should never instantiate Spring managed components yourself (by invoking the constructor in your code). Instead you should use Spring Dependency-Injection via @Autowired to make sure that all your dependencies are resolved correctly.

To inject properties with Spring (generally):

If you try to get access to a property value from a property resource, try to inject it with Springs @Value annotation.

Your application.properties may look like:

myproperty.test1=mytestvalue
myproperty.test2=123

Now you have a Spring component, where you want to use the property values and you inject them like:

@Component
private class MyTestComponent {

   @Value("${myproperty.test1:mydefaultvalue}")
   private String test1Value;

   @Value("${myproperty.test2:-1}")
   private int test2Value;

}

Of course you can use other datatypes than String for your property.

edited Dec 05 '17 at 12:12

answered Dec 05 '17 at 08:23

L. Hanke

116
1
5

I want to read the application.properties dynamically by using different 'keys' – Gal Sosin Dec 05 '17 at 08:25
So you have runtime computed keys you want to get resolved? Otherwise you can ofc inject ad many different properties by their keys as you want to. – L. Hanke Dec 05 '17 at 08:30
can you please give me an example? – Gal Sosin Dec 05 '17 at 08:31
I will adapt the above one, to show different keys by injection. For runtime computed keys you may want to have a look [here](https://stackoverflow.com/questions/10822951/how-do-i-get-a-property-value-from-an-applicationcontext-object-not-using-an-a). – L. Hanke Dec 05 '17 at 08:32
You say that your env instance is null. Maybe you try to access the instance (i.e. call readProperty) before Autowiring takes place as described [here](https://stackoverflow.com/questions/19421092/autowired-environment-is-null)? – L. Hanke Dec 05 '17 at 09:31
No that's not the case, because the readProperty is invoked in a endpoint – Gal Sosin Dec 05 '17 at 09:38
I guess your configuration is correctly created by Spring and injected into your Controller/Service? Could you please try to inject the Environment directly into your Controller/Service? – L. Hanke Dec 05 '17 at 09:42
I don't really understand what do you mean by injecting the Environment to My Controller/Service can you please add some more details ? – Gal Sosin Dec 05 '17 at 09:44
Can you please show me how exactly you call your readProperty function? – L. Hanke Dec 05 '17 at 09:50
@Service public class JwtSettings { public String key; public long expiration; //The JWT signature algorithm we will be using to sign the token public SignatureAlgorithm signatureAlgorithm = SignatureAlgorithm.HS256; public JwtSettings() { PropertiesReader propertiesReader = new PropertiesReader(); key = propertiesReader.readProperty(ApplicationProperties.JWT_KEY.key); } } – Gal Sosin Dec 05 '17 at 09:52
Can you please add this with code formatting to your question, so I can open another answer? – L. Hanke Dec 05 '17 at 09:58
have a look now – Gal Sosin Dec 05 '17 at 10:02
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/160494/discussion-between-l-hanke-and-gal-sosin). – L. Hanke Dec 05 '17 at 10:21

How to read from application.properties

1 Answers1