Category: Grails

A DSL for deploying grails apps

Everytime I deploy my grails app I do the same steps over and over again:

  • get the latest build from our Hudson CI
  • extract the war file from the CI archive
  • scp the war to a gateway server
  • scp the war to the target server
  • run stop.sh to shutdown the jetty
  • run update.sh to update the web app in the jetty webapps dir
  • run start.sh to start the jetty

Reading the Productive Programmer I thought: “This should be automated”. Looking at the Rails world I found a tool named Capistrano which looked like a script library for deploying Rails apps. Using builders in groovy and JSch for SSH/scp I wrote a small script to do the tedious work using a self defined DSL for deploying grails apps:

Grapes grapes = new Grapes()
def script = grapes.script {
    set gateway: "gateway-server"
    set username: "schneide"
    set password: "************"
    set project: "my_ci_project"
    set ciType: "hudson"
    set target: "deploy_target.com"
    set ci_server: "hudson-schneide"
    set files: ["webapp.war"]

    task("deploy") {
        grab from: "ci"
        scp to: "target"
        ssh "stop.sh"
        ssh "update.sh"
        ssh "start.sh"
    }
}

script.tasks.deploy.execute()

This is far from being finished but a starting point and I think about open sourcing it. What do you think: may it help you? What are your experiences with deploying grails apps?

Deploying a Grails app on an Oracle DB

Running our new grails app on HSQL and a Postgresql everything went fine. But the production DB was decided to be an Oracle. And suddenly the app crashed several times. Here’s a list of what problems we encountered:

  • ORA-00972: identifier is too long
  • want to store a null value in a non null column

Oracle identifiers are limited to 30 characters. So we thought using a mapping for the table should do the trick. But grails uses the table names to construct the n:m relations and their id column names between the domain classes. Looking at the grails docs we found a joinTable mapping:

static mapping = {
    table 'PROP'
    tablePerHierarchy false
    instrumentInfos joinTable: [name:'PROP_INS', key:'id', column:'instrumentInfos_id']
}

This worked most of the time but in some cases grails just didn’t want to take our definitions. The problem was a bug in grails. The workaround we took was to shorten the domain classes names.
The second problem arose as we tried to store empty strings into the database. Oracle stores empty strings as null values which causes a constraint violation exception. The solution was to declare the string columns nullable or not nullable and not blank but you cannot use a not nullable and blank string with an Oracle DB.

Global error pages with Jetty and grails

We wanted to configure global error pages for our grails app. Using your favorite search engine you quickly find the following info.

At the bottom it says that in order to support global error pages you have to forward to a context because error pages can only be handled within contexts/webapps.
So I started adding a context to the contexts dir which looked like this:

<Configure class="org.mortbay.jetty.webapp.WebAppContext">
      <Set name="contextPath">/</Set>
      <Set name="war"><SystemProperty name="jetty.home" default="."/>/webapps/mywebapp.war</Set>
      <Set name="extractWAR">false</Set>
...

This caused an “IllegalArgumentException: name” at startup. The solution was to set extractWAR to true. JSPs or other resources (like GSPs) cannot be used inside a war when extractWAR is set to false. But this way got another pitfall: using localhost:8080/mywebapp won’t work. So why not just forward all requests from / to /mywebapp. Said and done:

<Set name="handler">
  <New id="Handlers" class="org.mortbay.jetty.handler.RewriteHandler">
    <Set name="rewriteRequestURI">false</Set>
    <Set name="rewritePathInfo">false</Set>
    <Set name="originalPathAttribute">requestedPath</Set>
    <Call name="addRewriteRule"><Arg>/mywebapp/*</Arg><Arg></Arg></Call>
    <Call name="addRewriteRule"><Arg>/*</Arg><Arg>/mywebapp</Arg></Call>
    <Set name="handler">
here the old handlers are inserted...

Now /mywebapp points to my webapp. / gives a 500 and other invalid urls give a 404.
To use your custom error pages inside a grails app just add the error codes you want to map inside the UrlMappings.groovy file:

class UrlMappings {
  ...
  static mappings = {
    "500"(view:'/error')
    "404"(view:'/error404')
  }
}

Using grails projects in Hudson

Being an agile software development company we use a continuous integration (CI) server like Hudson.
For our grails projects we wrote a simple ant target -call-grails to call the batch or the shell scripts:

    <condition property="grails" value="${grails.home}/bin/grails.bat">
        <os family="windows"/>
    </condition>
    <property name="grails" value="${grails.home}/bin/grails"/>

    <target name="-call-grails">
		<chmod file="${grails}" perm="u+x"/>
        <exec dir="${basedir}" executable="${grails}" failonerror="true">
            <arg value="${grails.task}"/>
            <arg value="${grails.file.path}"/>
            <env key="GRAILS_HOME" value="${grails.home}"/>
        </exec>
    </target>

Calling it is as easy as calling any ant target:

  <target name="war" description="--> Creates a WAR of a Grails application">
        <antcall target="-call-grails">
            <param name="grails.task" value="war"/>
            <param name="grails.file.path" value="${target.directory}/${artifact.name}"/>
        </antcall>
    </target>

One pitfall exists though, if your target takes no argument(s) after the task you have to use a different call:

	<target name="-call-grails-without-filepath">
		<chmod file="${grails}" perm="u+x"/>
        <exec dir="${basedir}" executable="${grails}" failonerror="true">
            <arg value="${grails.task}"/>
            <env key="GRAILS_HOME" value="${grails.home}"/>
        </exec>
    </target>

Multipage Flows with Grails Part One – The traditional way

When you are developing web apps once in a while you need a flow of multiple pages just like a shopping cart at Amazon. Since there are different ways to implement such a multipage flow in Grails I thought of recording our experiences here.

The scenario

We model the process of submission of a proposal for different kinds of technologies. First you have to decide which type of proposal (once, long-term, in house) you want to submit. On the second page you give your personal infos and a general description of your intentions using the chosen technologies. Here you also choose the technologies you want. This has an impact on the following page which holds the information for the different technologies. Last but not least you save the proposal and show it to the user so he can see what data he entered. This flow could look like this:

-> chooseType -> enterGeneralInfo -> enterSpecificInfo -> save -> show

In each of the steps we need different parts of the full proposal. So we decided to use Command Objects in Grails. These objects are filled and are validated automatically by Grails. To use them you just have to delare them as parameter to the closure:

def enterSpecificInfo = {GeneralPartCommand cmd ->
  if (!cmd.hasErrors()) {
    Proposal proposal = new Proposal(cmd.properties)
    proposal.specificInfos = determineSpecificInfos(proposal.technologies)
    render(view: 'enterSpecificInfo', model: ['proposal': proposal])
  }
  else {
    render(view: 'enterGeneralInfo', model: ['proposal': cmd])
  }
}

You can then bind the properties in the command object to the proposal itself. The GeneralPartCommand has the properties and constraints which are needed for the general information of the proposal. This imposes a violation of the DRY (Don’t Repeat Yourself) principle as the properties and the constraints are duplicated in the proposal and the command object but more about this in another post.

How to collect all the data needed

Since you can only and possibly want to save the proposal at the end of the flow when it is complete you have to track the information entered in the previous steps. Here hidden form fields come in handy. These have to store the information of all previous steps taken so far. This can be a burden to do by hand and is a place where bugs arise.

How to go from one state to another

To transition from one state to the next you just validate the command object (or the proposal in the final state) to see if all data required is there. If you have no errors you render the view of the next state. When something is missing you just re-render the current view:

if (!cmd.hasErrors()) {
  Proposal proposal = new Proposal(cmd.properties)
  proposal.specificInfos = determineSpecificInfos(proposal.technologies)
  render(view: 'enterSpecificInfo', model: ['proposal': proposal])
}
else {
  render(view: 'enterGeneralInfo', model: ['proposal': cmd])
}

The errors section in the view takes the errors and prints them out. The forms in the views then use the next state for the action parameter.

Summary

An advantage of this solution is you can use it without any add-ons or plugins. Also the URLs are simple and clean. You can use the back button and jump to almost every page in the flow without doing any harm. Almost – the transition which saves the proposal causes the same proposal to be saved again. This duplicates the proposal because the only key is the internal id which is set in the save action.
Besides the DRY violation sketched above another problem arises from the fact that the logic of the states and the transitions are scattered between several controller actions and the action parameters in the forms. Also you have to remember to track every data in hidden form fields.
In a future post we take a look at how Spring (WebFlow) solves some of these problems and also introduces others.