That old Spring magic has me in its SpEL

Craig Walls

About me

• Java, Spring, and OSGi fanatic

About me

• Principal consultant with Improving Enterprises

About me

• Author

About me

• Author

Agenda

• Introducing SpEL

Agenda

• Using SpEL

Agenda

• Using SpEL

• SpEL Essentials

Agenda

• Using SpEL

• SpEL Essentials

• A few SpEL incantations

Agenda

• Using SpEL

• SpEL Essentials

• A few SpEL incantations

• Q & A

Download the examples

Approximately the same code...

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

Introducing SpEL

What is SpEL

• New in Spring 3.0

What is SpEL

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

What is SpEL

• The Spring Expression Language

What is SpEL

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

What is SpEL

• Will be used across entire Spring portfolio

What is SpEL

• Succinctly express complex concepts

What is SpEL

• Can be used to wire bean properties

What is SpEL

• Can be used to wire bean properties

• Can be used outside of Spring

Using SpEL

Configuring beans with SpEL (XML)

Configuring beans with SpEL (@Value)

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

// ...}

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

#{'abracadabra'}

Literal expressions

#{'abracadabra'}

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}

Only available when using SpEL in Spring configuration

#{request.getParameter('wizardId')}

#{session.getAttribute('wizard')}

Can only be used to configure appropriately-scoped beans

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.getName()}

#{elf.name}

#{elf.Name}

#{elf.getName()}

#{elf.name?.length()}

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}

#{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}

#{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

#{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.name ?: 'unknown'}

The type operator : T()

#{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).PI}

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

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

Regular expressions

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

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)'}

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

#{wizards.![name]}

Get the names of all wizards

The #this variable

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

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

Adding a custom function

Only available with programmatic SpEL

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);

A few SpEL incantations

Wiring in a system property (with a default)

Wiring bean references

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

...or...

Don’t do this!

...or...

Don’t do this!However...

...or...

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>

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

Parting thoughts

• SpEL expressions are great for doing Spring configuration magic

Parting thoughts

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

Parting thoughts

• Don’t abuse SpEL

Parting thoughts

– Remember Goethe’s Sorcerer’s Apprentice

Parting thoughts

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

Parting thoughts

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

• Write tests!!!

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

That old Spring magic has me in its SpEL

Technology

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