Combining Groovy, Grails, MySQL, and the Java Persistence API

Combining Groovy, Grails, MySQL, and the Java Persistence API

by Carol McDonald

With the addition of support for scripting
languages in the Java platform
, there has been a lot of interest
in combining into web applications scripting languages such as Groovy, Java technologies such as the Java Persistence
API (JPA), and databases such as MySQL. Last year I wrote a Tech Tip titled
Combining JavaServer Faces
Technology, Spring, and the Java Persistence API
that showed how you can use JavaServer Faces
Technology, Spring, and the JPA to create an application that displays an online catalog of pets.
In this tip, I'll show you how to create an online catalog application using the Groovy language, the Grails framework,
the MySQL database, and the Java Persistence API.

A package that contains the code for the sample application
accompanies the tip. The code examples
in the tip are taken from the source code of the sample (which is included in the package). In this tip, you'll use
NetBeans IDE 6.5 Milestone 1
to build the application and deploy it on the GlassFish
application server. The NetBeans IDE is a modular, standards-based, integrated development environment (IDE) written
in the Java programming language. The latest NetBeans IDE offering, NetBeans IDE 6.5 Milestone 1 (or M1 for short),
offers many new features including support for Groovy and Grails.
GlassFish is a free, open source application server that implements the newest features in the Java EE 5 platform.

A Summary of the Languages, Technologies, and Frameworks in the Sample Application

If you're not familiar with Groovy, Grails, MySQL, or the Java Persistence API, here are brief descriptions:

Groovy
is an agile and dynamic language for the
Java Virtual Machine1

. It compiles to Java bytecode and combines popular features from
languages such as Smalltalk, Python, and Ruby.

Grails
is an open-source web application framework that leverages
the Groovy language and complements Java Web development. It aims to bring the "coding by convention" paradigm
to Groovy. Grails is a Model-View-Controller based framework that simplifies the development of web applications by
reducing the need for configuration files and by generating a lot of the things needed in a database-backed web application.

MySQL
is the world's most popular open-source database. It offers
consistently fast performance, high reliability and ease of use.

The Java Persistence API
provides a (plain old
Java object) POJO-based persistence model for Java EE and Java SE applications. It handles the details of how relational
data is mapped to Java objects, and it standardizes Object/Relational (O/R) mapping.

The Sample Application

The sample application displays an online catalog of pets sold in a pet store. Figure 1
shows the
Catalog Listing page, which allows a user to page through a list of items in a store.

Figure 1. Catalog Listing Page

Examining the Application

Earlier I mentioned that Grails is a Model-View-Controller based framework that simplifies the development of web applications.
The online catalog application uses Grails and so it follows the MVC pattern, that is, the application isolates its data,
the "Model", from the user interface, the "View", and from the code that manages the communication
between the model and the view, the "Controller". Let's first look at the Model for the application.

The Model

The Model not only represents the data for the application, but it also represent persistent data, that is, data
that persists beyond the life of the application. In other words, the Model represents an application's persistent
business domain objects. The application uses JPA to manage that persistence. In JPA, an entity instance -- an instance of
an entity object -- represents a row of data in a database table.

If you examine the source code for the application, you'll find the following two classes in the

model

directory:

Item

and

Address

.

Item

is an entity class -- a typical JPA entity object -- that
maps to an

item

table in a database. The table stores information about items in the catalog. Here is part
of the source code for the

Item

class:

package model;

import java.io.Serializable;

...

@Entity

@Table(name = "item")

public class Item implements Serializable {

private static final long serialVersionUID = 1L;

@Id

private Long id;

private String name;

private String description;

private String imageurl;

private String imagethumburl;

private BigDecimal price;

@ManyToOne(optional = false)

@JoinColumn(name = "address_id")

private Address address;

// getters and setters

...

}

Address

is an entity class that maps to an

address

table in the database. The table stores
addresses associated with items in the catalog. Here is part of the source code for the

Address

class:

package model;

import java.io.Serializable;

...

@Entity

public class Address implements Serializable {

private static final long serialVersionUID = 1L;

@Id

private Long id;

private String street1;

private String street2;

private String city;

private String state;

private String zip;

private BigDecimal latitude;

private BigDecimal longitude;

private BigInteger version;

@OneToMany(fetch = FetchType.EAGER,

cascade = { CascadeType.ALL },

mappedBy = "address")

private Collection<Item>items = new ArrayList();

// getters and setters

...

}

The

Item

class has a many-to-one relationship with the

Address

class, meaning that
there can be multiple items in the catalog associated with the same address, but multiple addresses cannot be associated
with the same item. This relationship is specified by the

@ManyToOne

annotation in the

Item

class
and the

@OneToMany(mappedBy = "address")

annotation in the

Address

entity class.

Using JPA Entities With Grails and MySQL

To use the JPA entities for the application with Grails and MySQL, you first need to create a Grails application
and then modify some files in the Grails application directory structure.

We'll use NetBeans IDE 6.5 M1 to create a Grails application. If you haven't already done so,
download NetBeans IDE 6.5 Milestone 1
and download Grails
.

Start NetBeans IDE 6.5 Milestone 1. Select New Project from the File menu. Then select Groovy in the Categories
window and Grails in the Projects window as shown in Figure2
.

Figure 2. Creating a Grails Project in NetBeans IDE 6.5 M1

Click the Next button and name the project, for instance,

MyGrailsApp

. Accept the default project location
or browse to select a different location. Leave the Set as Main Project checkbox checked and click the Finish button.

In response, NetBeans creates the Grails project and a standard directory structure for a Grails application.
Figure 3
shows the Grails directory structure for the online catalog application.

Figure 3. Grails Directory Structure for the Online Catalog Application

After you have your directory structure in place, do the following:

Put your entity files in the app_name
/src/java directory, where app_name
is the name of your Grails
application. The

Item

and

Address

entity files for the online catalog application are in the

catalog/src/java/model

directory.

Get the MySQL jdbc driver,

mysql-connector-java-5.1.6-bin.jar
and put it in the

app_name
/lib

directory.
You can find the

mysql-connector-java-5.1.6-bin.jar

file for the online catalog application in the

catalog/lib

directory.

Modify the

DataSource.groovy

file in the

app_name
/grails-app/conf

directory to use MySQL
as the database and specify the

GrailsAnnotationConfiguration

configuration class to use the annotations
in the JPA entities. The code marked in bold in the following code example shows the additions and modification that I made
to the

DataSource.groovy

file for the online catalog application.

import org.codehaus.groovy.grails.orm.hibernate.cfg.GrailsAnnotationConfiguration

dataSource {

configClass = GrailsAnnotationConfiguration.class

pooled = false

driverClassName = "com.mysql.jdbc.Driver

"

username = "root

"

password =  ""

dialect = "org.hibernate.dialect.MySQL5InnoDBDialect

"

}

hibernate {

cache.use_second_level_cache=true

cache.use_query_cache=true

cache.provider_class='com.opensymphony.oscache.hibernate.OSCacheProvider'

}

// environment specific settings

environments {

development {

dataSource {

dbCreate = "create-drop" // one of 'create', 'create-drop','update'

url = "jdbc:mysql://localhost/petcatalog

"

}

}

test {

dataSource {

dbCreate = "update"

url = "jdbc:mysql://localhost/petcatalog

"

}

}

production {

dataSource {

dbCreate = "update"

url = "jdbc:mysql://localhost/petcatalog

"

}

}

}

For Grails to recognize the JPA entities as domain classes, you need to add
the

hibernate.cfg.xml

file to the

app_name
/grails-app/conf/hibernate

directory.
Here is the

hibernate.cfg.xml

file for the online catalog application. You can find it in the

catalog/grails-app/conf/hibernate

directory.

<?xml version=""1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-configuration PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">

<hibernate-configuration>

<session-factory>

<mapping package="model" />

<mapping class="model.Item" />

<mapping class="model.Address" />

</session-factory>

</hibernate-configuration>

The Controller

NetBeans IDE 6.5 M1 enables you to create domain classes and controllers, but I haven't found the menu option to generate
controllers, so for now, let's use the command line as follows to generate a controller:

Open a command prompt and navigate to the project directory for your Grails application. If you've forgotten where this
is, you can find it in the project's Properties dialog.

Generate a controller for a domain class by entering the following command:

grails generate-controller domain-class

where domain-class
is the domain class name. For example, to generate a controller for the

Item

domain class in the online catalog application, I entered the following command:

grails generate-controller model.Item

In response, the command generates a file named

domain-class
Controller.groovy

in the

grails-app/controllers

directory. For the

Item

class, the generated controller is in

grails-app/controllers/ItemController.groovy

.

Figure 4
shows the controller,

ItemController.groovy

, in the NetBeans IDE 6.1 M1 Groovy
editor window.

Figure 4. A Controller Listed in the Grails Directory Structure for the Online Catalog Application

Controllers handle incoming HTTP requests, interact with the model to get data and process requests, invoke the correct
view, and direct domain data to the view for display. In Grails, HTTP requests are handled by controller classes that contain
one or more action methods that are executed on request. The action methods either render
a Groovy Server Page
(GSP)
or redirect to another action. Grails routes requests to the controller action that corresponds to the URL mapping for
the request. In Grails, the default mapping from URL to action method follows the convention http://host /app_name
/controller
/action
/id
where host
is the host name,
app_name
is the name of the Grails
application, controller
is the controller class, action
is the action method, and id
is the id of a passed parameter. For example, the URL http://host/catalog/item/list calls the

list

action method in the item controller class. Here is code snippet in

ItemController.groovy

that shows the

list

method:

import model.Item

class ItemController {

def index = { redirect(action:list,params:params) }

// the delete, save and update actions only accept POST requests

def allowedMethods = [delete:'POST', save:'POST', update:'POST']

def list = {

if(!params.max) params.max = 10

[ itemList: Item.list( params ) ]

}

Grails scaffolding
provides a series of standardized controller
action methods for listing, showing, creating, updating, and deleting objects of a class. These standardized actions come
with both controller logic and default view Groovy Server Pages. The

list

action in

ItemController

renders a view with a paginated list of item objects.

If a URL has a controller but no action, as is the case for http://localhost:8080/catalog/item/, Grails defaults to the

index

action. In the

ItemController

code, the

index

action method redirects to the

list

action method. The

list

action method calls the

Item.list()

method, which
returns an

ArrayList

of

item

objects retrieved from the

item

table in the
database. If there are more objects in the table than the number specified in

params.max

(in this case, 10),
Grails automatically creates next and previous pagination links. The Grails framework automatically makes the

itemList

variable available to the view.

After executing code, actions usually render a GSP in the

views

directory corresponding to the name of the
controller and action. For example the

list

action renders the GSP,

list.gsp

, in the

grails-app/views/item

directory.

The View

The view layer uses data from domain objects provided by the controller to generate a web page. In Grails, the view is
rendered using Groovy Server Pages. To generate the view, open a command prompt, navigate to the project directory for
your Grails application, and enter the following command:

grails generate-views domain-class

where domain-class
is the domain class. For example, to generate a view for the

Item

domain class in the online catalog application, I entered the following command:

grails generate-views model.Item

In response, the command generates GSPs for the domain class. For example, it generates

create.gsp

,

edit.gsp

,

list.gsp

, for the

model.Item

entity.

Here is part of the

list.gsp

file for the online catalog application. Note that I modified the HTML
table format that is generated by default to display the pet images.

<table>

<thead>

<tr>

<g:sortableColumn property="name" title="Name" />

<g:sortableColumn property="imagethumburl" title="Photo" />

<g:sortableColumn property="price" title="Price" />

</tr>

</thead>

<tbody>

<g:each in="${itemList}" status="i" var="item">

<tr class="${(i % 2) == 0 ? 'odd' : 'even'}">

<td>

<g:link action="show" id="${item.id}">

${item.name?.encodeAsHTML()}</g:link>

</td>

<td>

<img src="${createLinkTo(dir:'images',file:item.imagethumburl)}"/>

</td>

<td>${item.price?.encodeAsHTML()}</td>

</tr>

</g:each>

</tbody>

</table>

</div>

<div class="paginateButtons">

<g:paginate total="${Item.count()}" />

</div>

The view uses instance variables set by the controller to access the data it needs to render the GSP. Groovy Server Pages
use a GroovyTagLib that is similar to the JSP tag library. Notice the tags that start with

<g:

in the

list.gsp

code. These are GroovyTags. Here is a brief summary of the GroovyTags and some other
elements in the

list.gsp

code:

<g:sortableColumn>

Renders a sortable column to support sorting in tables.

<g:each in="${itemList}" status="i" var="item">

Loops through each object in the

itemList

variable, which is an ordered

ArrayList

of

Item

model objects, and assigns each

Item

model object to the

item

variable.

<g:link
action="show" id="${item.id}">${item.name?.encodeAsHTML()}</g:link>

Creates an HTML anchor tag

href

based on the specified action, id, and controller parameters specified.
In this example, it generates a link to the

item/show/id

action. This action will display the
corresponding item details. Here, the line generates the following HTML for the variable

item

:

<a href="/catalog/item/show/2">Friendly Cat</a>

<img src="${createLinkTo
(dir:'images',file:item.imagethumburl)}"/>

Generates an HTML link for the item's attribute.

${item.price?.encodeAsHTML()}

Displays the value of the item 's price attribute as escaped HTML text.

<g:paginate
total="${Item.count()}" />

Creates next/previous buttons and a breadcrumb trail to allow pagination of results using the
domain method.

The Show Action Method

Recall that in Grails, the default mapping from URL to action method follows the convention http://host/app_name /controller
/action
/id
where host
is the host name,
app_name
is the name of the Grails
application, controller
is the controller class, action
is the action method, and id
is the id of the passed parameter. This means that in the online catalog application, a URL of http://host/item/show/1 will route to the show action in the

ItemController

, passing 1 to the method as the id of the parameter.
The

show

action of the

ItemController

class is shown below. The

ItemController

show

action renders a view showing the details of the

item

object corresponding to the

id

parameter.

def show = {

def item = Item.get( params.id )

if(!item) {

flash.message = "Item not found with id ${params.id}"

redirect(action:list)

}

else { return [ item : item ] }

}

The

show

action method calls the

Item.get()

method. That method, in turn, queries
the

items

table, and returns an

item

instance variable that corresponds to the

item

whose attribute id (that is, its primary key) is equal to the

id

parameter.
This is the equivalent to the following SQL statement:

select * from items where id='1'

The Grails framework automatically makes the

item

variable available to the

Show

view.

The Show Item GSP

After executing the appropriate code, the

show

action renders the

show.gsp

file
in the applications's

views/item

directory. Here is the part of the

show.gsp

file
for the online catalog application, presenting the item show view:

<table>

<tbody>

<tr class="prop"">

<td valign="top" class="name">Name:</td>

<td valign="top" class="value">${item.name}</td>

</tr>

<tr class="prop">

<td valign="top" class="name">Description:</td>

<td valign="top" class="value">${item.description}</td>

</tr>

<tr class="prop">

<td valign="top" class="name">Imageurl:</td>

<td valign="top" class="value">

<img src="${createLinkTo(dir:'images',file:item.imageurl)}" />

</td>

</tr>

<tr class="prop">

<td valign="top" class="name">Price:</td>

<td valign="top" class="value"> ${item.price}</td>

</tr>

<tr class="prop">

<td valign="top" class="name">Seller's Address:</td>

<td valign="top" class="value">${item?.address?.street1},

${item?.address?.city}, ${item?.address?.state}</td>

</tr>

</tbody>

</table>

Here are some important parts of the item show view:

${item.description}

Displays the value of the item 's description attribute.

<img src="${createLinkTo(dir:'images',file:item.imageurl)}" /> ${item.description}

Generates an HTML image tag for the item's

imageurl

attribute.

${item?.address?.city}

Displays the value of the item's address city attribute.

Running the Sample Code

These instructions assume that you have
NetBeans IDE 6.1
,
GlassFish v2ur2
, and
MySQL
installed.
You can download all three
in a single bundle
. Another option is to download a bundle that includes

Sun Java System Application Server 9.1 Update 1 with MySQL Community Server
.

Install the GlassFish v2 plugin for Grails as follows:

Start the GlassFish Update Center by issuing the following command:

GF_install
/updatecenter/bin/updatetool

Check the GlassFish Support for Grails Framework checkbox in the GlassFish Update Center and click Install.

If you haven't already done so, download and install
NetBeans IDE 6.5 M1
.

Download the sample code
and extract its contents. You should now see the newly extracted directory
as

<sample_install_dir>/catalog

, where

<sample_install_dir>

is the directory
where you unzipped the sample package. For example, if you extracted the contents to

C:/

on a Windows machine,
then your newly created directory should be at

C:/catalog

.

Start NetBeans IDE 6.5 Milestone 1.

Start the MySQL database as follows:

Click the Services tab in the NetBeans IDE.

Expand the databases node. You should see the MySQL server database in the list of databases.

Right-mouse click on the MySQL server database and select Start.

Create the petcatalog database as follows:

Right-mouse click on the MySQL server database and select Create Database.

Enter the database name petcatalog.
This will open a New Database Connection window. Click O.K. to accept the displayed settings.

Create the tables in the MySQL pet-catalog database as follows:

Expand the Drivers node. You should a driver for the petcatalog database in the list of drivers.

Right-mouse click on the petcatalog driver and select Connect.

Right-mouse click on the petcatalog driver and select Execute Command. This will open up a SQL command window.

Copy the contents of the

catalog.sql

file in the

catalog

directory
and paste the contents into the SQL command window.

Click the Run SQL icon



(Ctrl+Shift+E) above the SQL command window.

Create a WAR file as follows:

Ensure that the username and password settings in the

catalog/grails-app/conf/DataSource.groovy

file are the same as the corresponding property settings in NetBeans
IDE 6.5 M1 for the MySQL server database.

Right- click the catalog node in the Projects window.

Select Grails, then Create war file. This will create a

catalog-0.1.war

file in your the catalog project
directory. You might need to change the level of Grails expected by the application -- this is the

app.grails.version

setting in the

catalog/application.properties

file -- to align it
with the level of Grails you have installed.

Copy the

catalog-0.1.war

file to the

GF_install
/domains/domain1/autodeploy

directory, where GF_install
is the directory where you installed GlassFish.

Start GlassFish if you haven't already.

Enter the URL

http://localhost:8080/catalog-0.1/

in your browser. You should see the home page of the
sample application.

Further Reading

Sample Store Catalog using Groovy and Grails and the Java Persistence API on Glassfish with MySQL

Developing Grails with NetBeans

GlassFish and Scripting

TOTD #31: CRUD
Application using Grails - Hosted on GlassFish and MySQL

Grails

Groovy

mysql Commands

About the Author

Carol McDonald is a Java Technology Evangelist at Sun Microsystems. As a software developer since 1986, Carol's experience
has been in the technology areas of distributed network applications and protocols, including Java EE technology, XML,
Internet/Intranet applications, LDAP, Distributed Network Management (CMIP,SNMP) and Email (X.400,X.500). Besides Java,
Carol is also fluent in French and German.

1

As used on this web site, the terms "Java virtual machine"
or "JVM" mean a virtual machine for the Java platform.