Modify the rendered string of a response in Grails 3 before sending to the client - html

Question

I need to create a benchmark report regarding whether in the grand scheme of things: minifying + GZIP dynamic HTML responses (generated through GSPs) on every request, which will lead to an additional overhead due to parsing of the generated dynamic HTML string then compressing using a Java library (which results to a smaller response size) is actually better than GZIP without minifying (which results to faster response time but a little larger response size). I got the feeling that this "improvement" maybe is insignificant, but I need the benchmark report to back it up to the team.
To do that, I modify controller actions like so:
// import ...MinifyPlugin
class HomeController {
def get() {
Map model = [:]
String htmlBody = groovyPageRenderer.render(view: "/get", model: model)
// This adds a few milliseconds and reduce few characters.
htmlBody = MinifyPlugin.minifyHtmlString(htmlBody)
render htmlBody
}
}
But the Grails project has almost a hundred actions and doing this on every existing action is impractical and not maintainable, especially that after the benchmarking, we may decide to not minify the HTML response. So I was thinking of doing this inside an Interceptor instead:
void afterView() {
if(response.getContentType().contains("text/html")) {
// This throws IllegalStateException: getWriter() has already been called for this response
OutputStream servletOutputStream = response.getOutputStream()
String htmlBody = new String(servletOutputStream.toByteArray())
htmlBody = MinifyingPlugin.minifyHtmlString(htmlBody)
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream()
byteArrayOutputStream.write(htmlBody.getBytes())
response.setCharacterEncoding("UTF-8")
response.setContentType("text/html")
response.outputStream << byteArrayOutputStream
}
}
But it seems that modification of the response body is impossible once it enters the afterView interceptor...? So is any other way to do this using Grails 3 Interceptors, or should I update every controller action we have manually and perform the modification there instead?

Answer 1

This is what I like to use Interceptors for.
The after() part of the interceptor can act on the model after it is returned from the controller (wherein 'before()' acts on the request before it is sent to the controller)
This allows you to manipulate all data for a set of endpoints (or one specific endpoint) prior to return to client
If you are wanting to render to a view, you do that in the interceptor rather than in the controller; you merely return data from the controller