Master Dynamic Configuration Refresh in Spring Cloud Without Nacos – Step‑by‑Step Guide

1. Introduction

In a Spring Cloud micro‑service architecture, configuration management is essential. As services grow, configuration often needs to be adjusted dynamically so that applications can respond in real time. Spring Cloud offers several mechanisms to achieve dynamic updates.

2. Practical Example

2.1 Dependency Management

<code>&lt;spring-cloud.version&gt;2021.0.7&lt;/spring-cloud.version&gt;
&lt;dependencyManagement&gt;
  &lt;dependencies&gt;
    &lt;dependency&gt;
      &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
      &lt;artifactId&gt;spring-cloud-dependencies&lt;/artifactId&gt;
      &lt;version&gt;${spring-cloud.version}&lt;/version&gt;
      &lt;type&gt;pom&lt;/type&gt;
      &lt;scope&gt;import&lt;/scope&gt;
    &lt;/dependency&gt;
  &lt;/dependencies&gt;
&lt;/dependencyManagement&gt;</code>

The project also needs spring-cloud-context ; you can add spring-cloud-starter as shown below.

<code>&lt;dependency&gt;
  &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
  &lt;artifactId&gt;spring-cloud-starter&lt;/artifactId&gt;
&lt;/dependency&gt;</code>

2.2 Enabling Bootstrap Configuration

There are two ways to activate the default bootstrap.yml configuration:

First method – add the starter dependency:

<code>&lt;dependency&gt;
  &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
  &lt;artifactId&gt;spring-cloud-starter-bootstrap&lt;/artifactId&gt;
&lt;/dependency&gt;</code>

Second method – launch the application with the JVM argument:

<code>-Dspring.cloud.bootstrap.enabled=true</code>

The key listener is BootstrapApplicationListener .

2.3 Initial Configuration

Example bootstrap.yml :

<code>pack:
  name: ooxx</code>

Corresponding properties class:

<code>@Component("pp")
@ConfigurationProperties(prefix = "pack")
public class PackProperties {
  private String name;
  public String getName() { return name; }
  public void setName(String name) { this.name = name; }
}</code>

Test controller:

<code>@RestController
@RequestMapping("/pack")
public class PackController {
  @Resource(name = "pp")
  private PackProperties props;
  @GetMapping("")
  public PackProperties p() { return props; }
}</code>

When the configuration file changes, the updated values are displayed as shown in the screenshot below.

2.4 Triggering Refresh

Inject ContextRefresher and expose a refresh endpoint:

<code>@Resource
private ContextRefresher contextRefresher;
@GetMapping("/refresh")
public Object refresh() { return this.contextRefresher.refresh(); }</code>

Calling this endpoint re‑initializes beans in the refresh scope and re‑binds @ConfigurationProperties classes, publishing an EnvironmentChangeEvent .

After modifying bootstrap.yml to:

<code>pack:
  name: ooxx</code>

and invoking /refresh , the new configuration is applied without restarting the service, as demonstrated in the following image.

2.5 Listening to Configuration Changes

Implement an ApplicationListener<EnvironmentChangeEvent> to react to updates:

<code>@Component
public class PackApplicationEventListener implements ApplicationListener<EnvironmentChangeEvent> {
  @Resource
  private Environment env;
  @Override
  public void onApplicationEvent(EnvironmentChangeEvent event) {
    System.out.println(event.getKeys());
    System.out.println(env.getProperty("pack.name"));
  }
}</code>

When the configuration changes, the listener prints the changed keys and the new property value, e.g.:

<code>[pack.name]
xxxooo</code>