03 spring core2

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2008 coreservlets.com

Core Capabilities Part 2

Originals of Slides and Source Code for Examples:

http://courses.coreservlets.com/Course-Materials/spring.html

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Topics in This Section

Bean naming

Bean scoping

Dependency injection

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Review




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General Approach Review

Define and create service interfaces

Implement service interfaces

Add bean definitions

Access and use container-managed beans



Name




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Bean Definition Example

Adapts names from client contexts

beanFactor . etBean "beanAlias"

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Naming Convention

Establish a convention in order to predictbean names

Identify objects according to the interface

se unqua e c ass names

Start name with a lower-case letter



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Naming Convention

Conventions are guidelinesWhen necessary, it is okay to depart from the convention

This may demonstrate the need to refactor ,


Naming Convention Example

Bean interface

BookLibrary bookLibrary = (BookLibrary)

beanFactory.getBean("bookLibrary");



Convention coordinates naming within aean e n on ocumen

Bean name

" "

Bean reference

class="coreservlets.JavaBookLibrary" />


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Convention coordinates naming acrosssepara e ean e n on es

Bean name


16

Bean reference


Coordinating names across contextsTest

Production



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Bean Naming Summary

Establish a naming conventionUnqualified class name

Name starting with a lower-case letter

Use the convention to predict names across

Use the XML bean id attribute for declaringthe bean name

Rely on the same conventions for

referencing other beans




Implement services interfaces

Add the bean definitionsEstablish bean identifiers using the id attribute

Aliases can be established using name attribute oralias

elementDevelop bean names consistently using a convention

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



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Bean Scope



Bean Scope

Bean scopes control bean creation and storage

The Spring IoC container defines five beanscopes

prototype

* session*

globalSession*

*Only available in web application environments

Bean scope configuration is exposed through


the XML bean attribute scope

21


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Singleton Scope

The default bean scope Explicitly specifying singleton is allowed but redundant

Caches and distributes the same bean instance

BeanFactorybean access requests

Re laces sin leton im lementations


Singleton Scope Example

BeanFactory beanFactory =

new ClassPathXmlApplicationContext(

Bean scope

"/applicationContext.xml");

Object a = beanFactory.getBean("bookLibrary");

" ".

Object c = beanFactory.getBean("bookLibrary");

Object d = beanFactory.getBean("bookLibrary");

System.out.printf("%s, %s, %s%n",

a == b, b == c, c == d);

Bean references


Standard output

true, true, true


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Prototype Scope

Prototype scope caches and distributes a newean ns ance or var ous ypes o ean

requests Collaborative references

BeanFactorybean access requests


Prototype Scope Example

BeanFactory beanFactory = new ClassPathXmlApplicationContext(


Bean scope

Object a = beanFactory.getBean("bookLibrary");

Object b = beanFactory.getBean("bookLibrary");

" " .

Object d = beanFactory.getBean("bookLibrary");

System.out.printf("%s, %s, %s%n", Bean references

a == b, b == c, c == d);


Standard output

false, false, false


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Externally-Stored Bean Scopes

Java Servlet scope support

Spring scope name Java Servlet

request request

globalSession application

n/a page





Add the bean definitionsEstablish identifiers using the id attribute



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

Access and use container-managed beans -


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epen ency



Dependency Injection Targetpublic class BookReader {

private BookLibrary bookLibrary;

public BookReader() {

}

public BookReader(BookLibrary bookLibrary) {this.bookLibrary = bookLibrary;

}

pu c vo setBoo L rary Boo L rary oo L rary

this.bookLibrary = bookLibrary;

}


...

}

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Property Setter DI Target

public class BookReader {



}

public BookReader(BookLibrary bookLibrary) {


}



}


...

}

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Property Setter DI Example

< =" "

class="coreservlets.JavaBookLibrary"/>



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Property Setter DI Details

Matches on qualified setter methods by name

Based on JavaBean conventions

The property setter has no relationship to a class field

set

e.g., property foo as the setter method setFoo

Configuration fails with private, protected, or package-private

modifiers

Incompatible with chaining setter methods

Must accept exactly one parameter


Must e enc ose y a c ass t at as a no-args constructor No requirements on the access modifier

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Property Setter DI Implications

Forces the class to be mutable

Includes the property name in the DIdeclaration



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Property Setter DI Bean

Configuration is exposed by the XML elementypeproperty

child to the XML element bean re uires a value for the XML element attribute name

Supports shorthand configuration value attribute for directly specifying a value

ref attribute for referring to beans defined elsewhere

Supports child references , , ,


Property Setter DI Process

Verify the presence of a no-args constructor

Verify the method signature public access modifier

void return type

bean-oriented name

Create the nested XMLproperty element

Identif the ro ert usin the name attribute

Identify the value to be passed into the setter method as aparameter value



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}


No-args constructor


}



} Bean-oriented name Single parameter


...

}

36 public access modifier

void return type


< =" "


BookReader property

Setter parameter value



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Alternative Property Setter DI

< =" "


BookReader property

Setter parameter value


Constructor DI Targetpublic class BookReader {



}

public BookReader(BookLibrary bookLibrary) {this.bookLibrary = bookLibrary;

}



}


...

}

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Constructor DI Example

< =" "



Constructor DI Details

Matches on a constructor using parameterypes

Must share matching quantities

Must share matchin t es

Must match while preserving parameter ordering

Constructor by type matching is ambiguous Multiple constructors may match the constructor-argconfiguration



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Constructor DI Implications

Supports an immutable class design

Does not support parameter naming

Requires multiple constructors for eachparame er parame er com na on


Constructor DI Bean Definition

Configuration is exposed by the XML element type-

Child of the XML element bean

Supports shorthand configuration value attribute for directl in ectin a value

ref for referring to beans defined elsewhere

Supports child references , , ,

Offers fine-tuned constructor matching options index

type



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Constructor DI Example





}

...Dependency injection interface

}


Implied Constructor DI

Implied index and type


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Explicit Constructor DI

Explicit index and type


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Implied Constructor Matching

Arguments can be automatically re-ordered

public class Values {

public Values(Integer integer, String string){

public Values(String string, Integer integer){

}


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Implied Constructor Matching

Implied matches are unreliable



}

" ".

Standard output


Exception in thread "main"

org.springframework.beans.factory.UnsatisfiedDependencyException

Failed to convert value of type [java.lang.String] to required

type [java.lang.Integer]


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Explicit Constructor Matching

Implied matches can be corrected byspec y ng e index an or type



}

}

" " " "-


Constructor Matching

Always specify index and type when youhave overloaded constructors



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Constructor DI Alternative

public class ValuesFactory {

private Integer integer;

private String string;

Factory method

public Values newValuesInstance() {

return new Values(integer, string);

}

Additional setter

public void setIntegerValueFromString(String string) {

this.integerValue = Integer.parseInt(string);

public void setIntegerValue(Integer integerValue) {


.

}

...

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Constructor DI Alternative

Target bean

Factory bean

Standard output


stringValue=123 integerValue=456


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DI Alternatives

Lookup Method

Autowiring

Annotation-driven autowiring


Lookup Method DI

Overrides or implements a factory method abstract keyword is optional

public modifier is required

Accommodates special use cases

specifies a more transient scope

Version of the abstract template pattern

Requires the cglib library



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Lookup Method DI

public abstract class AbstractBookLibraryVisitor

im lements BookLibrar Visitor

public int visitLibrary(int visitCount){

Setset = new HashSet();while(visitCount-- > 0){

set.add(getBookLibrary().hashCode());

}

return set.size();

public abstract BookLibrary getBookLibrary();

}


< ean>

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Lookup Method DIpublic class Main {

BeanFactory beanFactory = new

ClassPathXmlApplicationContext(


BookLibraryVisitor visitor = (BookLibraryVisitor)

beanFactory.getBean("bookLibraryVisitor");

System.out.println("BookLibraryVisitor class: %s%n",

visitor.getClass().getSimpleName());

}

Standard output

object from cglib generated class


BookLibraryVisitor class:

AbstractBookLibraryVisitor$$EnhancerByCGLIB$$9fec4bdc


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Autowiring DI

Enabled by specifying an autowiringstrategy

Autowiring is implied reso u on may qu e y a

Property setter dependency resolution


Autowiring DIpublic class BookReader {


}

...

}

< ean =" oo L rary"




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Annotation-Driven Autowiring

Uses annotations for specifyingdependencies

Reduces XML configuration n ro uces pr ng c ass mpor s n o source

code

Decentralizes application configuration

Implies dependencies



Declare an empty XML element,context:annotat on-conf g

Requirement depends on BeanFactory

Annotate dependency target

Method

Constructor



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import org.springframework.beans.factory.annotation.*;



@Autowired



}

...


Annotation-Driven Autowiringimport org.springframework.beans.factory.annotation.*;



@Autowired

public void setBookLibrary(BookLibrary bookLibrary) {this.bookLibrary = bookLibrary;

}

...



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Autowired Test Contexts

import org.springframework.beans.factory.annotation.*;

public class BookLibraryTest {

@Autowired

public BookLibrary bookLibrary;

@Test

public void verify() { ... }

...





Add the bean definitionsEstablish identifiers using the id attribute



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


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

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Wrap-up



Summary

Bean namingEstablish naming standards

Use id and/orname attributes or separate alias

Favorid attribute

Sim le bean confi urationUse constructor-arg elements

Complex bean configurationUseproperty elements

Consider using a separate factory bean withproperty


Target bean: factory-bean and factory-method

Factory bean: id and class69


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Summary Continued

Transient bean collaborator referenceAdd cglib library

Use nested lookup-method element with name

AutowiredMa re uire XML context element

annotation-config



ues ons

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