04 spring core3

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2008 coreservlets.com

Core Capabilities Part 3

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Topics in This Section

Referencing other beans

Plain values

Properties integration

Resource integration

Collection mapping

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e erenc ng er




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Bean Collaborator Reference

CollaboratorPeer bean in a bean interaction

Configuration e erence ot er eans w t n a common pr ng o

container

Define collaborators usin local eneral or inner beanreferences


Inner Bean Reference

Fulfills a single dependency injectioninstance

Analogous to anonymous classes



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Inner Bean Process

Nested for XML constructor or propertysetter DI

XML element type bean y -

Nested reference for XML collection element ,

Do not specify identifiers or scope


Inner Bean Example

-

-

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General Collaborator Reference

Reference other beans in the Spring IoCcontainer

Favor as the default method for specifying


General Collaborator Process

Nested reference for XML constructor orproperty setter DIXML element type ref and attribute bean

-

Short-hand reference for XML constructor

Declare as XML attribute type ref

Nested reference for XML collection elementFor example, XML list child



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General Collaborator Example

" "=


12

General Collaborator

Flexible approach Supports collaborator relationships across multiple contexts

Compatible with parent/child containers or splitting andmer in contexts

Practical for large multi-module projects

Fragile configuration Bean references could identify collaborator definitionssupplied at runtime or errors

o XML parser validation support

Configuration error discovery can be delayed further if beansare lazily initialized


Risks can be mitigated through a basic and automated

integration test13


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Local Collaborator Reference

Reference other beans in the Spring IoCcontainer

Leverage XML parser validation m te to co a orator eans w t n t e same ean

definitions document


Local Collaborator Process

Nested reference for XML constructor orproperty setter DIXML element type ref and attribute local

-

No short-hand equivalent

For example, XML list child



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Local Collaborator Example

< -


Local Collaborator

Reduces flexibility Presents an additional configuration constraint

Bean reference must identify a bean within the same document

Mitigates the benefits of using multiple bean definition files Less practical for large multi-module projects

Improves validation parser ver ca on suppor

Bean references are verified in advance of constructing andinitializing beans



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Bean Identifier Reference

Reference a literal bean identifier value

Inject into application context support

beans or examp e, pr ng proxy actory eans nee ng to

acquire the names of advisor beans


Bean Identifier Process

Nested reference for XML constructor orproperty setter DI XML element type idref and attribute local orbean

bean collaborator concepts local values must correlate to a bean in the same

container

Nested reference for XML collection elementFor example, XML list child



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Bean Identifier Example

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General Approach Review

Define and create service interfaces

Implement services interfaces

Add the bean definitionsEstablish identifiers using the id attribute

Aliases can be established using name attribute oralias

elementDevelop bean names consistently using a convention

Default to singleton beans verr e ean crea on an cac ng us ng scope a r u e

Specify bean inter-dependencies using DI mechanisms Property setter, constructor, lookup-method, autowiring


Reference collaborators by referencing general, inner orlocal beans

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Access and use container-managed beansThe access and integration method is context-dependent



Plain Value




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Null Value Declaration Example


< proper y>

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Value Type Conversion

Converts values from java.lang.String Uses JavaBean PropertyEditors

Converts to implied or explicitly defined type

explicit declarations

Converts to multiple types Primitive and wrapper types

Enum types

java.io.File

java.io.InputStream


java.lang.Class

java.util.Properties29


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Value Type Conversion Example

public class SimpleValues {

Red, Yellow, Blue;

}

public void setInteger(Integer integer) {

}

public void setColor(Color color) {

}

public void setFile(File file) {

}

pu c vo setNum er Num er e

}

public void setProperties(Properties properties) {


public void setInputStream(InputStream inputStream) {

}

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Value Type Conversion Example

< =" "

100

name00=value00

name01=value01


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Custom Type Conversion

Implement java.beans.PropertyEditorExtend default implementation

java.beans.PropertyEditorSupport

setAsText(text:String):void

implementationSee CustomEditorConfigurer from package

org.springframework.beans.factory.config

See PropertyEditorRegistrar from packageorg.springframework.beans






Aliases can be established using name attribute oralias

elementDevelop bean names consistently using a convention




Reference collaborators by referencing inner beans orgeneral or local beans

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Add the bean definitions continued Inject plain values using thevalue attribute or element

Access and use container-managed beans e access an ntegrat on met o s context- epen ent



Properties Integration




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Injects Configuration properties directly into bean definitions

Constructor DI Pro ert setter DI

Collection element

Replaces Configuration management libraries

Calls from business logic to configuration management APIs

Iterative exposure over application settings

Clarifies


Distinctions between administerable application settings anddeveloper settings

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FeatureConfiguration mappings are supported by property editor

support

Limitation

Each container onl su orts one ro erties declaration



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Properties Integration Process

spring-context XML namespace spr ng-con ex namespace n orma on

property-placeholder XML element Add a property-placeholder declaration

location attr ute Reference a resource path such as a classpath or filesystem location

${name} expression Reference property file properties with the property key nested within the

expression format ${name}

Configuration management For projects requiring multiple bean definition files, isolate the property-

placeholder declaration in its own file

Merge the configuration file into the container with peer bean definition


i es

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Properties Integration Examplename.01=value

=

name.03=value

name.04=value



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Reference values sourced from application configurationfiles usin the ex ression format ${name}

Integrate properties files usingproperty-

placeholder elements supplied by

-

Access and use container-managed beansThe access and inte ration method is context-de endent



Resource Integration




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Resource Integration

Abstracts multiple resource typesFilesystem resource

Classpath resource

Context-specific resources For example, servlet context

Replaces URL schemesConventional JVM URL scheme registration system is

n ex e


Resource Integration Process

Identify the path to the I/O sourceFor example, classpath resource path

Rely on the default I/O context based on thepp ca on on ex

For instance, ClassPathXmlApplicationContext

ma s aths to resources located within the class ath Optionally, prefix the path with a custom

scheme file:/path

classpath:/path



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Resource Integration Example

< =" "

value="classpath:/log4j.xml" />

public class SimpleValues {

public void setInputStream(InputStream inputStream) {

}

}



Collections




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Collections

Enables list or set data structuredeclarations in bean definitions

Supports data structure type conversion to

Provides element type conversion to


Collections

ConfigurationXML element type list or set

Collection type conversion ava.u . o ec on

java.util.List

java.util.SetArray types

Element type conversionGenerics

Array type


bean, ref, idref,value, null, list, set,map,props49


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Collections Process

Identify the DI targetFor example, property setter or constructor

Verify the parameter type ust e an array type, ava.ut l.Collect on, orjava.util.List, orjava.util.Set

Declare the collection elements as XMLchild elements


Collection Examplepublic class CollectionValues {

public void setVarargs(String... values) {

}

public void setArray(String[] values) {

}

public void setList(List values) {

}

pu c vo setSet Set va ues

}


}

}

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List Collection Example

< =" "

abc

abc

abc


...

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Set Collection Example

< =" "

abc

abc

abc


...

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Collection Type Conversion

100

/etc/hosts

java.lang.String


< s >

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Dictionary Collections

Enables dictionary data structuredeclarations in bean definitions

Supports data structure type conversion to

Provides element type conversion to



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Map Collections

Configuration

Data structure

XML element typemap

XML element type entry and key elements

Collection t e conversion java.util.Map

Element type conversion

Generics

Array type


c e emen ypes bean, ref, idref,value, null, list, set,map,props58

Map Collections Process


Verify the parameter type ust e an array type, ava.ut l.Map

Declare the XML elementmap

element type entry



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Map Collections Example

< =" "

01

02

< ey> < va ue>< ey>

03


60

Map Collections Example



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Properties Collections

Enables simple dictionary data structuredeclarations in bean definitions to be

Provides simplied interface for configuring

No type conversion support


Properties Collections

Configuration

ata structure XML element typeprops

Elements XML element typeprop and key attribute

Property value is specified as theprop element content body

Collection type conversion java.util.Map

java.util.Properties

Element t e conversion

None

XML child element types


one

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Properties Collections Process


Verify the parameter type ust e an array type, ava.ut l.Map orjava.util.Properties

Declare the XML element ro s

Declare the map elements using XML childelement typeprops


Properties Collections Example

< =" "

value



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Aliases can be established using name attribute oraliaselement

Develop bean names consistently using a convention




Reference collaborators by referencing inner beans orgeneral or local beans

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Reference values sourced from application configurationfiles usin the ex ression format ${name}

Integrate properties files usingproperty-

placeholder elements supplied by

-

Inject collections by defining data structures directlywithin the bean definitions configuration

List, set, map, or properties structures

Access and use container-managed beans


-

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rap-up



Summary

General collaborator referencesFlexible but fragile

Process

XML attribute ref

Local collaborator references Improved validation but inflexible

Process re oca

XML attribute ref



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Summary Continued

Plain valuesXML element typevalue or attributevalue

XML attribute type to override implied conversion

XML elementproperty-placeholder declaration

from the s rin -context names ace

Requires the additional spring-context namespacedeclaration


Summary Continued

Resource integrationFacilitated inline when specifying path information using

scheme prefixes file, classpath, http

behavior

CollectionsXML parent element types list, set,map, andproperty



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