That old Spring magic has me in its SpEL

That old Spring magic has me in its SpEL

Craig Walls

SpringOne 2GX 2009. All rights reserved. Do not distribute without permission.

About me


About me

• Java, Spring, and OSGi fanatic


About me


• Principal consultant with Improving Enterprises


About me



• Author


About me



• Author


Agenda

3


Agenda

• Introducing SpEL

3


Agenda


• Using SpEL

3


Agenda


• Using SpEL

• SpEL Essentials

3


Agenda


• Using SpEL

• SpEL Essentials

• A few SpEL incantations

3


Agenda


• Using SpEL

• SpEL Essentials

• A few SpEL incantations

• Q & A

3


Download the examples

Approximately the same code...

http://spring.habuma.com/examples/SpEL-examples.zip

4




Introducing SpEL


What is SpEL

6


What is SpEL

• New in Spring 3.0

6


What is SpEL

• New in Spring 3.0– Originally conceived in Spring.NET

6


What is SpEL


• The Spring Expression Language

6


What is SpEL



• Much like Unified EL, OGNL, JBoss EL, and others

6


What is SpEL




• Will be used across entire Spring portfolio

6


What is SpEL





• Succinctly express complex concepts

6


What is SpEL






• Can be used to wire bean properties

6


What is SpEL






• Can be used to wire bean properties

• Can be used outside of Spring

6


Using SpEL


Configuring beans with SpEL (XML)


Configuring beans with SpEL (XML)

<bean id="appConfigurer" class="com.habuma.spel.tests.Witch"> <property name="name" value="#{systemProperties['WITCH_NAME']}" /></bean>


Configuring beans with SpEL (@Value)


Configuring beans with SpEL (@Value)

@Componentpublic class Wizard { @Value("#{systemEnvironment['WIZARD_NAME']}") private String name;

// ...}


Programming with SpEL


Programming with SpEL

ExpressionParser parser = new SpelAntlrExpressionParser();

StandardEvaluationContext context = new StandardEvaluationContext(rootObject);

Expression ex = parser.parseExpression("witches.^[isWicked()]");

Witch wickedWitch = (Witch) ex.getValue(context);


Essential SpEL


Literal expressions


Literal expressions

#{'abracadabra'}


Literal expressions

#{'abracadabra'}

#{42}


Literal expressions

#{'abracadabra'}

#{42} #{3.1415926}


Literal expressions

#{'abracadabra'}

#{42} #{3.1415926}

#{1e4}


Literal expressions

#{'abracadabra'}

#{true}

#{42} #{3.1415926}

#{1e4}


Literal expressions

#{'abracadabra'}

#{true} #{false}

#{42} #{3.1415926}

#{1e4}


Literal expressions

#{'abracadabra'}

#{true} #{false}

#{42} #{3.1415926}

#{null}

#{1e4}


Ready-to-use variables



#{systemProperties['WIZARD_NAME']}




#{systemProperties.WIZARD_NAME}





#{systemEnvironment['WIZARD_NAME']}






#{systemEnvironment.WIZARD_NAME}







#{wizardBean.name}







#{wizardBean.name}

Only available when using SpEL in Spring configuration





#{request.getParameter('wizardId')}




#{session.getAttribute('wizard')}




#{session.getAttribute('wizard')}

Can only be used to configure appropriately-scoped beans


Constructors


Constructors

#{new com.habuma.spel.tests.Wizard('Gandalf')}


Constructors

#{new com.habuma.spel.tests.Wizard('Gandalf')}

#{new String('hokus pokus')}


Accessing object members



#{elf.name}



#{elf.name}

#{elf.Name}



#{elf.name}

#{elf.Name}

#{elf.getName()}



#{elf.name}

#{elf.Name}

#{elf.getName()}

#{elf.name?.length()}


Mixing expressions and text


Mixing expressions and text

The wizard’s name is #{wizard.name}

Embeds the wizard’s name in some text


Arithmetic operators



#{'Harry' + ' ' + 'Potter'}




#{25 + 52}




#{25 + 52} #{2.19 + 2.02}




#{25 + 52} #{2.19 + 2.02}

#{77 - 25}




#{25 + 52} #{2.19 + 2.02}

#{77 - 25} #{52 - -25}




#{25 + 52} #{2.19 + 2.02}

#{77 - 25} #{52 - -25}

#{6 * 7}




#{25 + 52} #{2.19 + 2.02}

#{77 - 25} #{52 - -25}

#{6 * 7} #{42 / 6}




#{25 + 52} #{2.19 + 2.02}

#{77 - 25} #{52 - -25}

#{6 * 7} #{42 / 6}

#{44 % 7}


Relational operators



#{42 > 7}



#{42 > 7} #{7 > 42}



#{42 > 7} #{7 > 42}

#{10000 == 1e4}



#{42 > 7} #{7 > 42}

#{10000 == 1e4}

#{‘Apple’ == ‘Apple’}



#{42 > 7} #{7 > 42}

#{10000 == 1e4}


#{‘Apple’ < ‘Orange’}



#{42 > 7} #{7 > 42}

#{10000 == 1e4}


#{‘Apple’ < ‘Orange’} #{‘Orange’ > ‘Apple’}


Logical operators


Logical operators

#{witch.isWicked() and witch.name == 'Elphaba'}


Logical operators


#{witch.isWicked() or witch.name == 'Tattypoo'}


Logical operators


#{witch.isWicked() or witch.name == 'Tattypoo'}

#{!witch.isWicked()}


Ternary and Elvis operator



#{wizard.isGood() ? 'Gandalf' : 'Saruman'}



#{wizard.isGood() ? 'Gandalf' : 'Saruman'}

#{wizard.name ?: 'unknown'}


The type operator : T()



#{T(String)}



#{T(String)}

#{T(Math)}



#{T(String)}

#{T(Math)}

#{T(int)}



#{T(String)}

#{T(Math)}

#{T(int)}

#{T(java.util.Date)}


Accessing class members



#{T(Math).floor(42.56)}



#{T(Math).floor(42.56)}

#{T(Math).PI}


instanceof


instanceof

#{‘Sabrina’ instanceof T(String)}


instanceof


#{123 instanceof T(Integer)}


instanceof



#{123L instanceof T(Long)}


instanceof




#{1.23 instanceof T(Double)}


instanceof




#{true instanceof T(Boolean)}

#{1.23 instanceof T(Double)}


Regular expressions


Regular expressions

#{phoneNumber matches '\\d{3}-\\d{3}-\\d{4}'}


Regular expressions


#{websiteUrl matches 'http://www\\.[a-zA-Z0-9]*\\.(com|edu|net)'}

http://www

http://www


Regular expressions


#{customerEmail matches '[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,4}'}

#{websiteUrl matches 'http://www\\.[a-zA-Z0-9]*\\.(com|edu|net)'}

http://www

http://www


Setting variables


Setting variables

Assuming that the root object has a name property...


Setting variables

name = 'Broomhilda'

Assuming that the root object has a name property...


Accessing collection members



#{wizards[0]}

Arrays



#{wizards[0]}

#{magicWords['abracadabra']}

Arrays

Maps and Properties


Collection selection



#{witches.?[!isWicked()]}

Select all witches that aren’t wicked




#{witches.^[isWicked()]}


Select the first wicked witch




#{witches.^[isWicked()]}

#{witches.$[isWicked()]}


Select the first wicked witch

Select the last wicked witch


Collection projection


Collection projection

#{wizards.![name]}

Get the names of all wizards


The #this variable


The #this variable

#{wizards.![name].?[#this > 'G']}

Get the names of all wizards whose name is lexically ordered after ‘G’


Adding a custom function

31

Only available with programmatic SpEL



31

context = new StandardEvaluationContext();parser = new SpelAntlrExpressionParser();context.registerFunction("inEnglish", EnglishNumberInator.class.getDeclaredMethod( "translate", new Class[] {int.class}));




31

context = new StandardEvaluationContext();parser = new SpelAntlrExpressionParser();context.registerFunction("inEnglish", EnglishNumberInator.class.getDeclaredMethod( "translate", new Class[] {int.class}));

Expression ex = parser.parseExpression("#inEnglish(123)");String englishNumber = ex.getValue(context);



Demo


A few SpEL incantations


Wiring in a system property (with a default)


Wiring in a system property (with a default)

<bean class="Wizard"> <property name="name" value= "#{systemProperties['WIZARD_NAME'] ?: 'Gandalf'}" /></bean>


Wiring bean references



@Value("#{pricingService}")private PricingService pricingService;




<property name="pricingService" value="#{pricingService}" />

...or...





Don’t do this!

...or...





Don’t do this!However...

...or...


Selective bean wiring


Selective bean wiring

@Value("#{systemProperties['PRICING'] == 'aggressive'" + "? aggressivePricing : regularPricing}")private PricingService pricingService;


Selective collection wiring



public interface TaxRule { boolean appliesToState(String state); double calculateTax(double base);}




<util:list id="taxRules"> <ref id="revenueTax" /> <ref id="carpetTax" /> <ref id="existenceTax" /> <ref id="justBecauseTax" /></util:list>



<bean id="taxProcessor" class="TaxProcessor" scope="session"> <aop:scoped-proxy /> <property name="taxRules" value= "#{taxRules.?[appliesToState(session.getAttribute('user').state)]}" /></bean>


<util:list id="taxRules"> <ref id="revenueTax" /> <ref id="carpetTax" /> <ref id="existenceTax" /> <ref id="justBecauseTax" /></util:list>


Parting thoughts

38


Parting thoughts

• SpEL expressions are great for doing Spring configuration magic

38


Parting thoughts


• SpEL expressions are just Strings...no compile-time help to ensure type-safety, syntax, etc.

38


Parting thoughts



• Don’t abuse SpEL

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Parting thoughts




– Remember Goethe’s Sorcerer’s Apprentice

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Parting thoughts





– A little bit of magic in the wrong hands can be dangerous

38


Parting thoughts





– A little bit of magic in the wrong hands can be dangerous

• Write tests!!!

38


Q&A

Thank you!Don’t forget to turn in your evaluations!!!

Technology

That old Spring magic has me in its SpEL