Grails 3.3 with Servlet Filter

I had a scenario (I don’t really want to get into it) where I needed to implement a proper servlet filter which would run before the Grails dispatcher got involved in the request. The Grails documentation says it can be done, but the instructions are ridiculously vague, and seem more centered on plugins rather than just a webapp.

I finally managed to work it out, and I wanted to show the source code involved for posterity, and anyone else who might stumble upon this solution.

First off, create your filter in /src/main/java/myPackage:

package myPackage;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

 * @author Nathan Crause <>
@WebFilter(filterName = "testFilter", urlPatterns = {"/*"})
public class TestFilter implements Filter {

	private FilterConfig filterConfig;

	public TestFilter() {

	 * @param request The servlet request we are processing
	 * @param response The servlet response we are creating
	 * @param chain The filter chain we are processing
	 * @exception IOException if an input/output error occurs
	 * @exception ServletException if a servlet error occurs
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		HttpServletRequest httpRequest = (HttpServletRequest) request;
		HttpServletResponse httpResponse = (HttpServletResponse) response;

		for (int i = 0; i < 100; ++i) {
			for (int c = 0; c < 80; ++c) {

		chain.doFilter(request, response);

	 * Destroy method for this filter
	public void destroy() {		

	 * Init method for this filter
	 * @param filterConfig
	public void init(FilterConfig filterConfig) {		
		this.filterConfig = filterConfig;


Now the really poorly documented part – where the hell do you tell Grails to load the damned thing? Turns out you just use /grails-app/conf/spring/resources.groovy:

import org.springframework.core.Ordered
import org.springframework.boot.web.servlet.FilterRegistrationBean
import myPackage.TestFilter

beans = {
	testFilter(FilterRegistrationBean) {
		filter = bean(TestFilter)
		urlPatterns = ['/*']
		// we want all other Grails filters to have loaded first
		order = Ordered.LOWEST_PRECEDENCE

Now, I originally opted for using pure Java for the speed, but it did expose the problem that none of my domain classes were accessible, which I did require. So, I re-implemented the filter as a Groovy class in the /grails-app/controllers/myPackage directory.

It’s also worth noting that you will be required to create a new hibernate session in order to perform queries.

package myPackage

import javax.servlet.Filter
import javax.servlet.FilterChain
import javax.servlet.FilterConfig
import javax.servlet.ServletException
import javax.servlet.ServletRequest
import javax.servlet.ServletResponse
import javax.servlet.http.HttpServletRequest
import javax.servlet.http.HttpServletResponse

 * @author Nathan Crause <>
class TestFilter implements Filter {
	FilterConfig filterConfig
	void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
		for (int i = 0; i < 10; ++i) {
			println("-" * 80)

		Account.withNewSession {

		chain.doFilter(request, response)
	void destroy() {		
	void init(FilterConfig filterConfig) {		
		this.filterConfig = filterConfig

Project: Kalliope

Last year, I set myself the task of trying to actually produce a bunch of smaller web projects for s few reasons:

  • To learn some new frameworks
  • To illustrate my ability to learn there different frameworks
  • To showcase my skills in development in general

To that end, I thought I’d explain each project here in my blog, and the motivation behind each.

First up is Kalliope –

This is a “font server” with two primary end-goals – be able to arbitrarily upload a true type font, and have it produce web downloadable fonts, or to actively serve unlicensed fonts (in the same vein as Google Fonts).

The latter end-goal (as detailed above) was actually the primary goal on project inception – I wanted to have the ability to use a variety of fonts, but I didn’t want Google snooping the traffic on my sites (e.g. cookies, etc.). You can think of it as a replace for Google Fonts, really.

The other end-goal came about when the place where I worked had a client who had purchased some proprietary font, and wanted it used on their website. I didn’t want this font directly in the font server itself (as it requires a license), but all the leg-work had already been done to perform the conversion.

Interestingly enough, the original work on this was actually done for a completely different project – I had implemented a lot of the code within a project for generating print materials using SVGs. Since the SVGs needed to be displayable in all browsers, as well as the final PDF, I decided to use “FontForge” to do all the heavy lifting. It was only years later when developing a website where it occurred to me to break out the functionality into a separate web service.

It’s also a good project to learn and showcase the Grails framework.

Grails/Spring service autowiring

While working on a Grails project, I came across 2 interesting things:

  1. autowiring for domain classes doesn’t work, even if you follow all the instructions on how to enable it (either globally, or in the domain class definition itself)
  2. autowiring on abstract service classes doesn’t work (so if you’re implementing a data service with some custom functionality, your services won’t get autowired)

I’ve been able to fix both of these issues using a very simple utility class:

import grails.util.Holders

 * Since Grails doesn't seem capable of autowiring into abstract classes, this
 * causes a bit of an issue when creating data services which do more than
 * just get/save.
 * All those context beans are available, so we just need to fudge the idea of
 * autowiring, and this class helps by providing a quick reference to the
 * singe long line required to get those Spring beans.
 * This also helps with domain classes, which have autowiring disabled, and
 * despite all the documentation saying the contrary, into which you cannot
 * autowire.
 * That said, this might prove to be a faster solution for use within domain
 * classes anyway since we don't have to worry about autowiring happening on
 * every object instantiation, but rather we just have a reference to the
 * singular instance with in the main context.
class Beans {
	static def get(String name) {
	static def $static_propertyMissing(String name) {

Now, instead of setting up a service like this:

def myService

You instead define a getter method like this:

def getMyService() {

You can then use “myService” as you would’ve expected to under normal autowiring circumstances.

Gradle deployment script for Grails webapp

Please note the “Update” section below.

I haven’t had much success with finding useful deployment strategies and/or scripts for Grails anywhere. The extent of the documentation I’ve been able locate for deployment simply tells you to create a WAR and upload it to the servlet container.

Not terribly helpful if you want to run a formal process.

So, for my Grails webapps, I came up with this. I create a file in the “gradle” directory named “deploy.gradle” containing the following:

buildscript {
	repositories {
	dependencies {
		classpath 'org.hidetake:gradle-ssh-plugin:2.9.0'

apply plugin: 'org.hidetake.ssh'

// the below is in it's own ext block because it can potentially be
// overridden by .deployrc.gradle in the user's home directory, and the scmUser
// might be required in the following ext block (where the repository is
// set up)
ext {
	scmUser = project.hasProperty('user') ? project.getProperty('user') :['']

// please note that the file must end in ".gradle" or Gradle won't know how
// to process it, and you'll get a "String index out of bounds: 0" error
def rcFile = new File("${['user.home']}/.deployrc.gradle")
if (rcFile.exists()) {
	apply from: rcFile.absolutePath

ext {
	timeNow = new Date().format('yyyyMMddHHmmss')
	// TODO: the below should use a repository directly associated with the individual user
	scmRepository = "${project.scmUser}${}.git"
	runEnvironment = project.hasProperty('env') ? project.getProperty('env') : 'production'
	scmBranch = project.hasProperty('branch') ? project.getProperty('branch') : 'master'
	tmpDir = System.getProperty('') + "${}/${timeNow}"

apply from: "${project.projectDir}/gradle/deploy/${project.runEnvironment}.gradle"

task deploy {
	group 'Remote Deployment'
	description 'Deploys a branch from your SCM to a target environment on a remote server'
	doLast {
		println "Deploying from branch ${project.scmBranch} to environment ${project.runEnvironment}" {
			session(remotes.role('webserver')) {
				// upload the WAR to the target server(s)
				println 'Uploading WAR file'
				put from: "${project.buildDir}/libs/mercury.war", into: "mercury/mercury-${timeNow}.war"
				// stop Tomcat so we can get this party started
				println 'Stopping Tomcat'
				execute 'sudo service tomcat8 stop'
				// if a pre-existing link exists to "current", remove it
				println 'Symlinking'
				execute 'if [ -f mercury/mercury-current.war ]; then rm mercury/mercury-current.war; fi'
				// link our new WAR to the name "current"
				execute "cd mercury; ln -s mercury-${timeNow}.war mercury-current.war"
				// Tomcat doesn't clean up extracted WAR file directories, so we must flush out the /var/lib/tomcat8/webapps directory
				execute 'if [ -d /var/lib/tomcat8/mercury ]; then sudo rm -rf /var/lib/tomcat8/mercury; fi'
				// Fire tomcat back up
				println 'Starting Tomcat'
				execute 'sudo service tomcat8 start'

task deployBuild << {
	println "Building WAR for ${project.runEnvironment} environment"
	exec {
		workingDir project.tmpDir
		environment 'TERM', 'dumb'	// this prevents grails+gradle for displaying a second progress bar during the following invocation
		commandLine 'grails', "-Dgrails.env=${project.runEnvironment}", 'war', 'mercury.war'

task deployCheckout << {
	println "Cloning ${project.scmRepository}#${project.scmBranch} for user ${project.scmUser} into ${project.tmpDir}"
	exec {
		commandLine 'git', 'clone', '-b', project.scmBranch, project.scmRepository, project.tmpDir

task deployCleanup << {
	println "Removing temporary directory ${project.tmpDir}"

	exec {
		commandLine 'rm', '-rf', project.tmpDir

deployBuild.dependsOn deployCheckout
deploy.dependsOn deployBuild
deploy.finalizedBy deployCleanup

Also in the “gradle” directory is a subdirectory named “deploy” where I have the files specific to the environments to which I can deploy, such as “staging.gradle”:

remotes {
	web {
		role 'webserver'
		host = ''
		user = 'webapps'
		identity = file("${['user.home']}/.ssh/webapps")

Now, you will need to make some modifications to your main “build.gradle” script. First, add in the SSH plugin dependency, immediately after the “buildscript” section:

plugins {
    id 'org.hidetake.ssh' version '2.10.1'

And then in the area where you have all the “apply” instructions:

apply from: "${project.projectDir}/gradle/deploy.gradle"

Using the script above, I can deploy a particular branch from within my git repository to a specific environment thus:

gradle -Penv=staging -Pbranch=hotfix/ deploy

It’s probably not perfect, but since I’m new to Gradle and Grails, I think it’s a pretty good start!


Alas the “org.hidetake.ssh” plugin has not kept up to date with the latest updates to SSH, and as such the above scripts no longer work, and I have abandoned any attempts to use Gradle to effect deployments. Instead, I have switched over to using Ansible to deal with all of this.