In the actual project, every time you modify the ftl file, you have to restart tomcat to see the modified content.
Generally speaking, template files do not change very frequently. In a website with a lot of traffic, frequent reading of template files will cause a great burden on the system. Therefore, FreeMarker caches the content of template files to reduce templates. The frequency of file reading to reduce the system load.
When processing a template, FreeMarker directly returns the corresponding Template object from the cache, and has a default mechanism to ensure that the template object is synchronized with the template file.
In freemarker.properties, template_update_delay is used to specify the interval for updating the template file, which is equivalent to how long to check whether it is necessary to reload the template file, 0 means reload every time, otherwise, how many milliseconds to check whether the template has changed.