Spring ServletContextPlaceholderResolver

• 类全路径: org.springframework.web.util.ServletContextPropertyUtils.ServletContextPlaceholderResolver

    private static class ServletContextPlaceholderResolver
            implements PropertyPlaceholderHelper.PlaceholderResolver {
        private final String text;
        private final ServletContext servletContext;
        public ServletContextPlaceholderResolver(String text, ServletContext servletContext) {
            this.text = text;
            this.servletContext = servletContext;
        }
        @Override
        @Nullable
        public String resolvePlaceholder(String placeholderName) {
            try {
                // servlet 上下文获取
                String propVal = this.servletContext.getInitParameter(placeholderName);
                if (propVal == null) {
                    // Fall back to system properties.
                    propVal = System.getProperty(placeholderName);
                    if (propVal == null) {
                        // Fall back to searching the system environment.
                        propVal = System.getenv(placeholderName);
                    }
                }
                return propVal;
            }
            catch (Throwable ex) {
                System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" +
                        this.text + "] as ServletContext init-parameter or system property: " + ex);
                return null;
            }
        }
    }