SpringBoot configuration parsing

Configuration parsing SpringBoot is achieved through Environment.

Environment itself implements PropertyResolver interface will eventually entrusted to PropertySourcesPropertyResolver to resolve configuration.

org.springframework.core.env.PropertySourcesPropertyResolver.getProperty

 1 protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) {
 2     if (this.propertySources != null) {
 3         for (PropertySource<?> propertySource : this.propertySources) { // 1. 循环 PropertySources
 4             if (logger.isTraceEnabled()) {
 5                 logger.trace("Searching for key '" + key + "' in PropertySource '" +
 6                         propertySource.getName() + "'");
 7             }
 8             Value = propertySource.getProperty Object (key); // 2. acquired from the key corresponding to the configuration in PropertySource 
. 9              IF (value =! Null ) {
 10                  IF (&& value resolveNestedPlaceholders the instanceof String) {
 . 11                      value = resolveNestedPlaceholders ((String) value ); // 3. analytical placeholder {} $ 
12 is                  }
 13 is                  logKeyFound (Key, propertySource, value);
 14                  return convertValueIfNecessary (value, targetValueType); // 4. converted into the specified type 
15              }
 16          }
 17     }
18     if (logger.isTraceEnabled()) {
19         logger.trace("Could not find key '" + key + "' in any property source");
20     }
21     return null;
22 }