ConfigReflectionPropApplication.java

/**
 * 
 */
package com.rahogata.demowebapp;

import java.lang.reflect.Field;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.core.env.Environment;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;

/**
 * This code snippet is a proposal of managing application configurations
 * at one place and accessing them easily.
 * Feb 7, 2018
 */
@SpringBootApplication
public class ConfigReflectionPropApplication {

  public static void main(String[] args) {
    ApplicationContext ctx = SpringApplication.run(ConfigReflectionPropApplication.class, args);
    SampleService sampleService = ctx.getBean(SampleService.class);
    sampleService.displayAppDetails();
  }
}

/**
 * Using reflections to set static fields during context initialization
 * to eliminate initialization statements inside constructor.
 */
@Component
class Config {
  public static String APPNAME = "app.name";
  public static String APPVERSION = "app.version";
  
  /**
   * @throws IllegalAccessException 
   * 
   */
  @Autowired
  public Config(Environment env) throws IllegalAccessException {
    Field[] fields = this.getClass().getDeclaredFields();
    for (Field field : fields) {
      String key = (String) field.get(null);
      field.set(null, env.getProperty(key));
    }
  }
}

/**
 * Service using a configuration values.
 */
@Service
class SampleService {
  
  public void displayAppDetails() {
    System.out.println("App name:" + Config.APPNAME + ", " + "version:" + Config.APPVERSION);
  }
}