Java Tech & Tools | Grails in the Java Enterprise | Peter Ledbrook

Grails in the Java Enterprise

Peter Ledbrook / VMware

Tuesday, 1 November 11

What is Grails?

Rapid Web Application Development Framework• for the JVM• with first-class Java integration

Inspired by Ruby on Rails, Django and others• Convention over Configuration• Don’t Repeat Yourself (DRY)

Grails

What is Grails?

Web MVC GSP (Views)

GORM(Data Access)

Doc Engine

Servlet Container

Test Support

Database I18n

Grails

What is Grails?

Web ControllersThe Domain Model

Business Logic Custom View Tags

Views & LayoutsLibraries (JARs)

Additional Sources

Web Resources

i18n bundles

Build Commands

Say bye-bye to the plumbing!

Enterprise requirements

Web App

Messaging

Legacy Databases Services

Is this a problem for Grails apps?

Integration Points

BuildDependenciesDatabaseDeploymentSpring

Integration Points

Remember the Grails project structure?• add in build events and...

Can’t build natively with other build tools!

Grails Build System

Ant GradleMaven

Ant Integration

An Ant task built in (grails.ant.GrailsTask)Template Ant build: grails integrate-with --ant

• Uses Ivy for dependency management• Not compatible with Ant 1.8

...or use ‘java’ task to call Grails command• Grails manages dependencies• Use ‘grails’ for build

Maven Grails Plugin: https://github.com/grails/grails-mavenUse Maven 2 or 3 to build Grails projectsDeclare dependencies in POMWorks for both applications and plugins!Integration test framework:

https://github.com/grails/grails_maven_plugin_testing_tests

Getting Started

mvn archetype-generate ...

mvn initialize

Set MAVEN_OPTS

Optional: add ‘pom true’ to dependency DSL

e.g. -Xmx256m -XX:MaxPermSize=256m

Packaging Types

‘war’• Must configure execution section• Works with plugins that depend on ‘war’

‘grails-app’• Less configuration

‘grails-plugin’• For plugins!

Maven & Grails Plugins

> grails release-plugin

> mvn deploy

<dependency> <groupId>org.grails.plugins<groupId> <artifactId>hibernate</artifactId> <type>grails-plugin</type></dependency>

Either:

Use ‘mvn deploy’ or Release plugin!

And ‘pom: false’

grails.project.dependency.resolution = { ... plugins { compile ":hibernate:1.3.6" } ...}

Customise the Build

Create new commands in <proj>/scriptsPackage the commands in a plugin!Create <proj>/scripts/_Events.groovy

• Interact with standard build steps• Add test types• Configure embedded Tomcat

What the future holds...

Grails 3.0 will probably move to Gradle• More powerful and more flexible• Standard, well documented API• Ant & Maven support

Integration Points

Dependencies are JARs

Use any Java library you like!Full support for Maven-compatible repositoriesDeclarative dependenciesPlugins can be declared the same way

Dependency DSL

grails.project.dependency.resolution = { inherits "global" log "warn" repositories { grailsHome() mavenCentral() mavenRepo "http://localhost:8081/..." } ...}

Dependency DSL

grails.project.dependency.resolution = { inherits "global" log "warn" ... dependencies { compile "org.tmatesoft.svnkit:svnkit:1.3.3" test "org.gmock:gmock:0.8.1" } ...}

Integration Points

‘Legacy’ Databases

Grails can create a database from your domain model......but what if you don’t own the database?

• DBA determines structure• Company conventions• Existing ‘legacy’ database

class Book { ... static mapping = { table "books" title type: "books" author column: "author_ref" }}

No existing domain modelSchema not too far off the beaten track

Option 1: Custom ORM mapping

Option 2: JPA annotations

<?xml version='1.0' encoding='UTF-8'?><!DOCTYPE ...><hibernate-configuration> <session-factory> <mapping class="org.ex.Book"/> <mapping class="org.ex.Author"/> ... </session-factory></hibernate-configuration>

Existing Java/JPA domain model

grails-app/conf/hibernate/hibernate.cfg.xml

<?xml version='1.0' encoding='UTF-8'?><!DOCTYPE ...><hibernate-configuration> <session-factory> <mapping resource="org.ex.Book.hbm.xml"/> <mapping resource="org.ex.Author.hbm.xml"/> ... </session-factory></hibernate-configuration>

You have Java model + Hibernate mapping filesSchema is way off the beaten track

Option 3: Hibernate XML Mappings

grails-app/conf/hibernate/hibernate.cfg.xml

constraints = { title blank: false, unique: true ...}

ConstraintsGiven domain class:

org.example.myapp.domain.Book

src/java/org/example/myapp/domain/BookConstraints.groovy

GORM layer over JPAUse your own JPA providerUseful for cloud services that only work with JPA, not

Hibernate

Option 4: GORM JPA Plugin

Option 5: Remote service back-endDon’t have to use GORMUse only controllers and services

• Grails services back onto remote services

Web App

Invoice Log Service ...

SOAP, RMI, HTTP Invoker, etc.

Share your model!

Database Management

Hibernate ‘update’+

Production data=

Database Migration Plugin

Pre-production, Hibernate ‘update’ or ‘create-drop’

dbm-generate-changelogdbm-changelog-sync

Change domain model

dbm-gorm-diffdbm-update

Reverse Engineering Plugin

class Person { String name Integer age ...}

Database Management

Database Migration

http://grails.org/plugin/database-migration

Reverse Engineering

http://grails.org/plugin/database-migration

Integration Points

grails war

Build properties:• grails.war.copyToWebApp• grails.war.dependencies• grails.war.resources• grails.project.war.file

Control of JARsgrails.project.dependency.resolution = { defaultDependenciesProvided true inherits "global" log "warn" ...}

grails war --nojars => WEB-INF/lib/<empty>

=> No Grails JARs in WEB-INF/lib

Data Source

dataSource { jndiName = "java:comp/env/myDataSource"}

dataSource { url = System.getProperty("JDBC_STRING")}

System property:

Data Source

grails.config.locations = [ "file:./${appName}-config.groovy", "classpath:${appName}-config.groovy" ]

Config.groovy:

For run-app: ./<app>-config.groovy

For Tomcat: tomcat/lib/<app>-config.groovy

Integration Points

Grails is Spring

Spring MVC under the hoodGrails provides many useful beans

• e.g. grailsApplicationDefine your own beans!

• resources.xml/groovy• In a plugin

Exampleimport ...beans = { credentialMatcher(Sha1CredentialsMatcher) { storedCredentialsHexEncoded = true }

sessionFactory(ConfigurableLocalSessionFactoryBean) { dataSource = ref("dataSource") hibernateProperties = [ "hibernate.hbm2ddl.auto": "create-drop", "hibernate.show_sql": true ] }}

Enterprise Integration

Spring opens up a world of possibilities• Spring Integration/Camel• Messaging (JMS/AMQP)• ESB• RMI, HttpInvoker, etc.

Web services & REST

Grails Plugins

RoutingJMS, RabbitMQCXF, Spring-WS, WS-ClientREST

JMS Plugin Example

dependencies { compile 'org.apache.activemq:activemq-core:5.3.0'}

Add any required dependencies (BuildConfig.groovy)

jmsConnectionFactory(org.apache.activemq.ActiveMQConnectionFactory) { brokerURL = 'vm://localhost'}

Configure JMS factory (resources.groovy)

JMS Plugin Example

import javax.jms.Message

class SomeController { def jmsService

def someAction = { jmsService.send(service: 'initial', 1) { Message msg -> msg.JMSReplyTo = createDestination(service: 'reply') msg } }}

Send messages

JMS Plugin Example

class ListeningService { static expose = ['jms']

def onMessage(message) { assert message == 1 }}

Listen for messages

SummaryVarious options for integrating Grails with:

• Development/build• Deployment processes

Works with many external systems• Solid support for non-Grailsy DB schemas• Flexible messaging & web service support

More info

w: http://grails.org/f: http://grails.org/Mailing+Lists

e: pledbrook@vmware.comt: pledbrookb: http://blog.springsource.com/author/peter-ledbrook/

Java Tech & Tools | Grails in the Java Enterprise | Peter Ledbrook

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