How can the configuration file be dynamically modified in Spring?

In Spring, the ability to dynamically modify configurations can be achieved by loading external configuration files. The specific steps are as follows:

1. Use the property-placeholder element.

<context:property-placeholder location="classpath:config.properties" />

This way, Spring will load the property values from the config.properties file into the Spring environment.

1. What is the value of this?

@Value("${property.key}")
private String propertyValue;

The ${property.key} corresponds to the property name in the config.properties file.

1. Configurer for property sources placeholders

@Autowired
private ConfigurableApplicationContext context;

public void reloadConfig() {
    ConfigurableEnvironment env = context.getEnvironment();
    MutablePropertySources sources = env.getPropertySources();
    PropertySourcesPlaceholderConfigurer configurer = new PropertySourcesPlaceholderConfigurer();
    configurer.setLocation(new ClassPathResource("config.properties"));
    configurer.setIgnoreResourceNotFound(true);
    configurer.setIgnoreUnresolvablePlaceholders(true);
    configurer.postProcessBeanFactory(context.getBeanFactory());
    sources.replace("class path resource [config.properties]", configurer.getAppliedPropertySources().get("class path resource [config.properties]"));
}

In the above code, configurer.setLocation(new ClassPathResource(“config.properties”)) specifies the location of the configuration file, while sources.replace(“class path resource [config.properties]”, configurer.getAppliedPropertySources().get(“class path resource [config.properties]”)) replaces the original configuration file.

By following the above steps, the functionality of dynamically modifying Spring configuration files can be achieved.