如何从application.properties中读取

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.

Answer 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.