How could I add a response header - say X-Time
that would look something like:
X-Time: 112
Where the value given would be the time in milliseconds that the response took to process? Is there a really simple way to add this to an Grails app? Not something I want to leave on permanently but would be nice to have while developing my app.
To simply add a header to the response, you can use an after
Filter.
// grails-app/conf/MyFilters.groovy
class MyFilters {
def filters = {
addHeader(uri: '/*') {
after = {
response.setHeader('X-Time', value)
}
}
}
}
Edit:
To actually compute the time, it'd probably be more proper to use a javax.servlet.Filter
instead of a Grails filter.
src/groovy/com/example/myproject/MyFilter.groovy
package com.example.myproject
import javax.servlet.*
class MyFilter implements Filter {
void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
def start = System.currentTimeMillis()
chain.doFilter(request, response)
def elapsed = System.currentTimeMillis() - start
response.setHeader('X-Time', elapsed as String)
}
void init(FilterConfig config) { }
void destroy() { }
}
src/templates/war/web.xml (run grails install-templates if src/templates isn't already in your source tree)
<filter>
<filter-name>timer</filter-name>
<filter-class>com.example.myproject.MyFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>timer</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
The reason for using the javax.servlet.Filter
is so you don't have to separate out your "before" and "after" actions, and can therefore hold onto the start time throughout the entire filter chain & servlet execution.
Supplementary note:
To me, it seems strange to want to return the server elapsed execution time as a response header. Perhaps you have a decent reason for doing it, but in most cases I'd A) either be more concerned about total round-trip time (as observed by the client), or B) be logging elapsed execution times on the server for my own system administration/metrics purposes.
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