Spring SystemPropertyPlaceholderResolver

• 类全路径: org.springframework.util.SystemPropertyUtils.SystemPropertyPlaceholderResolver

    private static class SystemPropertyPlaceholderResolver implements PropertyPlaceholderHelper.PlaceholderResolver {
        private final String text;
        public SystemPropertyPlaceholderResolver(String text) {
            this.text = text;
        }
        @Override
        @Nullable
        public String resolvePlaceholder(String placeholderName) {
            try {
                String propVal = System.getProperty(placeholderName);
                if (propVal == null) {
                    // Fall back to searching the system environment.
                    // 获取系统属性
                    propVal = System.getenv(placeholderName);
                }
                return propVal;
            }
            catch (Throwable ex) {
                System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" +
                        this.text + "] as system property: " + ex);
                return null;
            }
        }
    }