public Object getObject() throws Exception {
        if (instance == null) {
            instance = createInstance();
        }
        return instance;
    }
Lazily creates and returns a {@link AbstractShiroFilter} concrete instance via the
{@link #createInstance} method.

@return the application's Shiro Filter instance used to filter incoming web requests.
@throws Exception if there is a problem creating the {@code Filter} instance.
support/spring/src/main/java/org/apache/shiro/spring/web/ShiroFilterFactoryBean.java