1. Application Properties  & YAML configuration

2. YAML Configuration file.

3.

4. DemoApplication Class
package com.example.externalconfig;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class DemoApplication {

public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}

5. PageController Class

package com.example.externalconfig;

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

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

@RestController

public class PageController {

@Value("${pageController.msg}")

private String pageControllerMsg;

@RequestMapping("/")

public String home(){

return pageControllerMsg;

}

}

6. application.properties

server.port=9009

#pageController.msg=Hello from application.properties

Run the programmer.

7. Application.yml

pageController:
 msg: "Hello From YML config"

Run the programmer.

8. Changing from Command line arguments

Run the programmer.

10.  Using properties value in application.properties

my.secret=${random.value}

my.number=${random.int}

my.bignumber=${random.long}

my.number.less.than.ten=${random.int(10)}

my.number.in.range=${random.int[1024,65536]}

11. Modify PageController  

package com.example.externalconfig;

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

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RestController;

@RestController

public class PageController {

@Value("${pageController.msg}")

private String pageControllerMsg;

@Value("${my.secret}")

private String mysecret;

@RequestMapping("/")

public String home(){

return mysecret;

}

}

Run the program.