That old Spring magic has me in its SpEL

That old Spring magic
has me in its SpEL
Craig Walls

About me

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

About me

• Java, Spring, and OSGi fanatic


About me


• Principal consultant with
Improving Enterprises


About me


• Principal consultant with
Improving Enterprises

• 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

– 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)

@Component
public 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'}

#{42} #{3.1415926}

#{1e4}

#{true}


Literal expressions

#{'abracadabra'}

#{42} #{3.1415926}

#{1e4}

#{true} #{false}


Literal expressions

#{'abracadabra'}

#{42} #{3.1415926}

#{1e4}

#{true} #{false}

#{null}


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

Embeds the wizard’s
name in some text
The wizard’s name is #{wizard.name}


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




#{1.23 instanceof T(Double)}

#{true instanceof T(Boolean)}


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)'}


Regular expressions


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

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


Setting variables


Setting variables

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


Setting variables

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

name = 'Broomhilda'


Accessing collection members



Arrays
#{wizards[0]}



Arrays
#{wizards[0]}

Maps and Properties
#{magicWords['abracadabra']}


Collection selection



Select all witches that aren’t wicked
#{witches.?[!isWicked()]}




Select the first wicked witch
#{witches.^[isWicked()]}




Select the first wicked witch
#{witches.^[isWicked()]}

Select the last wicked witch
#{witches.$[isWicked()]}


Collection projection


Collection projection

Get the names of all wizards

#{wizards.![name]}


The #this variable


The #this variable

Get the names of all wizards whose
name is lexically ordered after ‘G’
#{wizards.![name].?[#this > 'G']}


Adding a custom function

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);

31

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;



...or...

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



...or...


Don’t do this!



...or...


Don’t do this!
However...


Selective bean wiring


Selective bean wiring

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


Selective collection wiring



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



<util:list id="taxRules">
public interface TaxRule { <ref id="revenueTax" />
boolean appliesToState(String state); <ref id="carpetTax" />
double calculateTax(double base); <ref id="existenceTax" />
} <ref id="justBecauseTax" />
</util:list>



<util:list id="taxRules">
public interface TaxRule { <ref id="revenueTax" />
boolean appliesToState(String state); <ref id="carpetTax" />
double calculateTax(double base); <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>


Parting thoughts

38

Parting thoughts

• SpEL expressions are great for doing Spring
configuration magic

38

Parting thoughts

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

38

Parting thoughts

configuration magic
• Don’t abuse SpEL

38

Parting thoughts

configuration magic
– Remember Goethe’s Sorcerer’s Apprentice

38

Parting thoughts

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

38

Parting thoughts

configuration magic
– 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!!!


That old Spring magic has me in its SpEL

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