bean wiring - training prez new

7/31/2019 Bean Wiring - Training Prez New

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Spring202 Bean Wiring23-Sep-2011


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2 COPYRIGHT 2011 SAPIENT CORPORATION | CONFIDENTIAL

Prerequisites

Why Spring? Spring benefits Spring architecture Dependency Injection Spring Container BeanFactory and ApplicationContext Defining beans in the configuration file Explicit Bean Wiring Setter and Constructor based Injection


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Agenda

Bean Life Cycle Bean Scoping

Autowiring Parent-Child Beans Injecting Non-Spring Beans Externalizing Configuration Properties Annotation based dependency injection


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Let us revise

Why Spring? Dependency Injection

Spring Container BeanFactory and ApplicationContext Defining beans in the configuration file Explicit Bean Wiring Setter and Constructor based Injection


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Spring Bean Lifecycle


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Spring bean Lifecycle

Steps a bean goes through within Spring container

Called only if the bean is instantiated

within ApplicationContext container.


7/677 COPYRIGHT 2011 SAPIENT CORPORATION | CONFIDENTIAL

Bean Instantiation and Populating Properties

Let us revise (if not done already)

Bean Instantiationo BeanFactory Lazily Loaded

o ApplicationContext Preloaded

Populating Propertieso Constructor Injection

o Setter Method Injection



Constructor Injection vs. Setter Method Injection

Constructor Injection

Enforces the objects to be created with somestate initialized.

Enforces strong dependency contract. No need for superfluous setter methods. Helps in making the properties immutable.

Setter Method Injection

Amenable to reconfiguration. If several dependencies, constructors

parameter list can be quite lengthy. Several ways of constructing valid objects

Difficult to come up with uniqueconstructors.

Parameters to super() method need to be

passed manually in beans constructor.

Best Practice:

No hard and fast rule. Constructor based injection - Use type attribute than indexattribute

Usage:

Constructor Database Connection (should be initialized before use).

Setter Singleton, Abstract classes etc.



Wiring Collections

Four types of collection configuration elements:o - Wiring a list of values, allowing duplicates.

o - Wiring a set of values, ensuring no duplicates.

o - Name-value pair where name and value can be of any type.

o - Name-value pair where name and value are both strings.



Exercise | Investment Portal | Wiring

PaisaControl.com is a famous investment portal and it offers many products like insurance, loans,deposits etc. to its customers. Design the order management system (OMS) component of this

portal. OMS is responsible for accepting the order having order and payment details, authorizingthe payment with credit card authorization class and then approving/rejecting the order.

Following classes need to be designed:o Order (Attributes: orderId, productCode, itemName, amount)

o Payment (Attributes: cardNumber, userId, password)

o OrderManager (Attributes: CreditCardAuthorizer, Method: placeOrder(Order,Payment))

o CreditCardAuthorizer (Method: authorize(cardNumber, userId, password))

o CreditCardAuthorizerImpl (Implementation of the CreditCardAuthorizer)

o Spring-Context.xml (Bean Configuration)

o Main (Load the container)

Wire the above dependencies using Springs dependency injection and start the container.

Solution: Refer com.sapient.wiring package



Exercise | Investment Portal | Collection

Create a new class OrderBasket that stores the collection of orders. This orderBasket along withPayment details are passed to the Ordermanager.

Following additional classes need to be designed:o OrderBasket(Attributes: orderBasket: Map)

o OrderManager (Method: placeOrder(OrderBasket,Payment))

o Main (Load the container)

Populate the orderBasket attribute in OrderBasket class through DI.

Solution: Refer com.sapient.collection package



Setting the bean name

Bean needs to implement BeanNameAware interface.

Usage:

Useful in debugging when a number of beans are instantiated using the same class with eachconfigured in a different way.

Limitations:

Class becomes Spring interface dependant.



Setting the bean factory name

Bean needs to implement BeanFactoryAware interface.

Implement setBeanFactorymethod. Beans can look up collaborating beans via the factory.

Usage:

Required when singleton bean needs to use non-singleton bean.



Setting the application context

Bean needs to implementApplicationContextAware interface.

Similar to BeanFactoryAware but some additional methods.

Usage:

Access to parameterized text message in a message source. Publish application events.


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Bean Post Processor

Bean needs to implement BeanPostProcessor interface.

Provides two callback methodso Before initializing a bean (postProcessBeforeInitialization)

o After initializing a bean (postProcessAfterInitialization)

Usage:

Used to log, update, perform the validations on the bean members. Example Logging the pre-init and post-init values of fields annotated with Log. ApplicationContextAwareProcessor is a bean post processor.


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Initializing Bean

init-methodis an attribute in bean element.

Advantages:

Purpose same as InitializingBean except bean has no dependency on Spring class.


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Other lifecycle Steps

Self Study the following bean lifecycle stepso DisposableBean

o Destroy-method

o Default-init-method

o Default-destroy-method

o BeanFactoryPostProcessor


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Exercise | Investment Portal | Lifecycle

Implement the following bean lifecycle steps in the portal classes:o BeanNameAware

o BeanFactoryAwareo ApplicationContextAware

o BeanPostProcessor

o InitializingBean

o Init-method

Solution: Refer com.sapient.lifecycle package


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Bean Scoping, Factory Method & Inner Bean


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Bean Scoping | Singleton

Single instance of the bean is created in the container. By default, all spring beans are singleton (per application context).

Usage:

Stateless beans are always made Singleton.


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Bean Scoping | Prototype

Creation of a new bean instance every time a request for that specific bean is made.

Usage:

Stateful beans are made Prototype.

Other scopes - request, session, global-session (only valid when used within a web-capablespring or portlet context. Covered in detail later)


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Bean Scoping | Prototype (Contd..)

Best Practice:

Non-Singleton Beans (Prototype Beans)o Avoid or design carefully if uses resources like database, network connection etc.

o Similar to creating newobjects in Java.

o Useful for factory bean to create new bean instances or when a new object is required per request.


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Bean creation fromfactorymethods

Calling factory method to get bean instance. Factory method has to be static.

Usage:

Instantiating Third-Party Singleton Classes (with constructors private)o Java.lang.RunTime

o Java.awt.GraphicEnvironment


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Bean creation from instancefactorymethod

Instance Factory method Factory method non-static


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Inner Beans

Self Study Inner Beanso Anonymous bean configuration inside another bean configuration.

Link: Spring Inner Bean
http://www.javabeat.net/tips/95-inner-beans-in-spring-ioc.htmlhttp://www.javabeat.net/tips/95-inner-beans-in-spring-ioc.html


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Exercise | Investment Portal | Scope & Factory Method

Implement the following in the portal classes:o Make the Orderbean with scope Prototype.

o Create a LogFactorysingleton class and call its getInstance method to instantiate a bean.

Instantiate a FoodFactory class to return the FoodProduct object. (factory instanceimplementation)

Solution: Refer com.sapient.scoping package


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Autowiring


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Autowiring

Container determines how to wire a beans properties.

If matching bean not found, property remains unwired.

Limitations:

Hard to debug. Reduces XML code at the cost of readability. Either all attributes or none. (Only XML based Autowiring)

Types:


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Autowiring | byName

Name of the property matches with the name of the bean that is to be wired.

Autowiring and Explicit (Manual) wiring can be combined.o Autowiring will try to wire the properties not wired through explicit wiring.

Limitations:o Sometimes not possible to make the name of the target bean the same as the property.

o If multiple orderManagerdefined then same creditCardAuthorizerinstance will be wired. (if this is therequirement, then its not a limitation)


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Autowiring | byType

Spring finds out beans whose type is assignable to propertys type.

Limitations:o Exception thrown if Spring finds more than one bean whose type is assignable to autowired property.


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Autowiring | constructor

Finds beans whose types satisfy the arguments of one of the constructor.

Limitations:o Must wire all constructor argumentscant mix with constructor autowiring.

o Exception thrown if Spring finds more than one bean whose type is assignable to a constructorparameter.

o Exception thrown if dependencies of more than one constructor is satisfied by autowiring.


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Autowiring | Best Practices

Best Practices:

AvoidXML basedautowiringo Sacrifices the explicitness and maintainability of the configurations.

o Hard to debug.

o Prefer Annotation based autowiring (covered later) as it is easier to maintain and saves space and time.

Self Study

o autodetectautowiring

o default-autowire attribute in the beans element in spring configuration


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Exercise | Investment Portal | Autowiring

Wire the creditCardAuthorizer property ofOrderManagerclasso Use XML based autowiring.

o Use byType, byName and constructor type to wire the above property.

Solution: Refer com.sapient.autowire package


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Parent-Child Beans


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Parent-Child Beans | constructor

Bean definitions in configuration xmls can show parent-child relationship. This cuts down redundant XML in context definition file.

element provides two attributes:o Parent Indicates the id of a bean which is the parent of the bean having the parentattribute.

o AbstractIf set to true, declaration is abstract and cant be instantiated by Spring.


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Abstracting a base bean type

Two beans with different ids but same class and properties.

The type(class) of all sub-beans is same as that of the parent bean. Overriding a property allowed. Parent bean does not have to be abstract. Possible to subclass a concrete bean.


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Abstracting common properties

Sub-beans dont have to share a common parent type. Two beans with different class attribute can just share the common set of attributes.

Overriding a property allowed. Parent bean does not have to be abstract. Possible to subclass a concrete bean.

Best Practice:

Reuse bean definitions whenever possible.


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Exercise | Investment Portal | Inheritance

Write the following classes to implement Inheritance in Investment Portalo Rename CreditCardAuthorizer interface to CardAuthorizer interface.

o CardAuthorizerImpl: Implements CardAuthorizerInterfaceo CardAuthorizerImpl: Attribute: externalAuthorizerURL, userId, password.

o DebitCardAuthorizerImpl extends CardAuthorizerImpl

o CreditCardAuthorizerImpl extends CardAuthorizerImpl

Define CardAuthorizerImpl, CreditCardAuthorizerImpl and DebitCardAuthorizerImpl beans inSpring config xml and set them through inheritance.

Solution: Refer com.sapient.inheritance package


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Injecting non-spring beans


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Injecting non-spring beans

Spring can also configure beans that it does not instantiate. Not all objects are instantiated by Spring.

o For ex. Domain objects by an ORM tool, custom tags by web container.

How to inject dependencies in non-spring beans?

Assume OrderManager is the bean instantiated outside the container scope. Set the bean attribute abstract=trueo This means Spring container should not instantiate the bean instantiated outside the

container.


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Injecting non-spring beans (Contd..)

Annotate the bean with @Configurable(). This means -o Bean configured by Spring though instantiated outside the container.

o Associate the class with bean id passed as parameter.

Configuration to let Spring know that it needs to configure few beans instantiated outside theSpring container.


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Injecting non-spring beans (Contd..)

Starting Aspect-J enabled JVM by passing instrument jar file as VM argument.

Add the following jars in the classpath:o Aspectjweaver.jar

o Aspectjrt.jar

o org.springframework.aspects-3.1.0.M2.jar


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Exercise | Investment Portal | Non-Spring Beans

Implement the necessary changes to instantiate OrderManager class outside the scope ofcontainer.

The property OrderManager.creditCardAuthorizershould be set through bean wiring.

Solution: Refer com.sapient.nonspring package


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External Configuration Properties & Property Editors


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Externalizing Configuration Properties

Application Specific Configurations vs. Deployment Specific Configurationso Application Specific Spring Configuration. For ex. Inter-objects dependencies

o Deployment Specific External properties file. For ex. Connection URL

PropertyPlaceholderConfigurero Pulls values from properties file into bean definitions.

Values in properties fileo =

o For ex. oms.authorizeduser=xyz


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Externalizing Configuration Properties

Syntax to fetch the propertieso ${placeholder-variable}


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Internationalization

Display text in users native language.

If resource bundle is omso oms.properties - Default

o oms_en_US.properties English speaking people in US

o oms_hi_IN.properties Hindi Speaking people in India

ResourceBundleMessageSourceo Id has to be messageSource

ApplicationContext.getMessageo Parameters Message key, argument and locale


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Property Editors

Wiring String value to non-String type or vice-versa. Simplifies bean wiring of some data types likejava.io.File, java.util.Date, java.lang.class etc.

Java.beans.PropertyEditorSupporto getAsText()Returns String representation of a propertys value.

o setAsText(String value) Sets a bean property value from the String value passed in.

Spring inbuilt PropertyEditorso FileEditor java.io.Fileo URLEditor java.net.URL

o LocaleEditor java.util.Locale

o CustomDateEditor java.util.Date

o ClassEditor java.lang.Class

o StringArrayPropertyEditor Comma delimited String to String array.

o Custom PropertyEditors can also be written by extending Java.beans.PropertyEditorSupport class.


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Exercise | Investment Portal | External Config

Add a new attribute threadCount in OrderManager and read its value from oms.properties filepresent in the same package.

Make the above threadCount locale dependant and read its local specific value from theproperties file.

Solution: Refer com.sapient.externalconfig package


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P namespace and util schema


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P-Namespace

Shortcut for defining properties.


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Util Schema

Utility configuration issueso Referencing constants

o Configuring collectionso Etc

o Set a constant value(e.g. 'java.sql.Connection.TRANSACTION_SERIALIZABLE) to a property value.

o Creating a bean having the value equal to the x property of y bean.

o Instantiate java.util.Properties instance with the values loaded from Resource location.

o Explicity control the exact type of list which will be instantiated.

Refer: com.sapient.beanwiring.util package


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Loading Resources

Reading External Resources (e.g. Text files, XML, Properties, Images etc) From Remote Locations (e.g. File system, classpath, URL)

ApplicationContext.getResource Prefixes: file, classpath


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Exercise | Util Schema

Write LoginDao and LogoutDao with the following properties

LoginDaoo isolationLevel Set the value java.sql.Connection.TRANSACTION_SERIALIZABLEo propertySet - java.util.Properties Populate the properties from jdbc.properties

LogoutDaoo

isolationLevel Set the value LoginDao. isolationLevelo logoutPages logoutPages: List - Populate set of three pages in the LinkedList

Solution: Refer com.sapient.util


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Annotation based dependency injection


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@Autowired

XML Based Wiring Limitationso Wires all properties What if you like to wire a specific property only?

o Only by type or name What if neither strategy suits you?

DI through Annotation is solution.

@Autowired and @Autowired (required=false) Autowiring by Type. Target Setters, Methods, Constructors, Attributes

RegisteringAutowiredAnnotationBeanPostProcessor


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@Qualifier

Specifying a candidate bean name when more than one bean with compatible type incontainer

Target Fields, Parameters, Type, Annotation Type

Best Practice:

Prefer Annotation based Autowiring over XML based. Add @Qualifier annotation wherever required to make the code more readable.


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Component Scanning

Limitation:

Every bean declared manually in configuration file.

What if Spring automatically detects the components?

Spring supports:o @Component Basic Annotation

o @Repository Components in Persistence Layer

o @Service Components in Service Layer

o @Controller Components in Presentation Layer

( )


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Component Scanning (Contd..)

Naming Convention: Default: Same as class name but the first alphabet in lowercase.

Name: Bean name can be passed as parameter to annotations. For ex: @Service()

Scanning can be customized by applying include/exclude filters. Scanning Annotations not required if a class is defined in include-filter. Types

o Annotation Annotation type

o Assignable - Class/Interface for filtering

o Regex Regular Expression

o Aspectj Pointcut expression matching the classes

| l |


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Exercise | Investment Portal | Annotations

Modify the Spring configuration file to Autowire the property of OrderManager class throughAnnotation.

Scan all the bean definitions in the given package than manually defining them in the config file.

Solution: Refer com.sapient.autowire.annotation


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Additional Best Practices

Additi l B t P ti


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Additional Best Practices

Prefer ApplicationContext over BeanFactoryo ApplicationContext supports i18n, Resource Loading and Eventso

BeanFactory preferred when there is limitation on resources and size of application. For ex.Applets, Mobile Applications.

Bean Naming Conventiono Use clear, descriptive naming convention for beanso Recommendation: CamelCase.o Use Java naming convention for classes with first alphabet in lowercase

Inner Beanso Use when bean only available to a parent bean

Use or null propertyo Leaving blank may set some other default values in the properties.

Split the configuration in different xml files.o Minimal one xml file per architectural layer.

Prefer assembling beans (multiple xmls) through ApplicationContext over imports.

B t P ti


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Best Practices

Every bean must have an id or name.o

No anonymous bean.o Id attribute makes XML parsers validate the bean.

Update Config files(if required) after making Java changes.


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Appendix - A

E i | S l ti


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Exercises | Solution

Steps to Import the solutions in Eclipse STS.

Open Spring Source Tool Suite.

Select File->Import.

Select General->Existing Projects into Workspace.

Select the Select Archive File and open the attachedzip.

Click Finish.


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Thank You!

bean wiring - training prez new

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