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Enterprise Application Development
Sadegh Aliakbary
An Introduction to Spring Framework
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Outline Dependency Injection and IoC Aspect Oriented Programming Spring Framework Spring vs. EJB
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Introduction to Spring Framework
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An open source Java platform Initially written by Rod Johnson, first released
under the Apache 2.0 license in June 2003 Spring is lightweight: the basic version = 2MB The core features can be used in any Java
application But there are extensions for web applications on
top of Java EE platform Spring targets to make J2EE development easier to
use Promote good programming practice By enabling a POJO-based programming model
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About Spring
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Provides to create high performing, easily testable and
reusable code. is organized in a modular fashion simplifies java development
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Spring Modules
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Spring is modular Allowing you to choose which modules are
applicable to you Provides about 20 modules
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Spring Modules (cont’d)
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Two Key Components of Spring
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Dependency Injection (DI) Aspect Oriented Programming (AOP)
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Dependency Injection (DI)
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Inversion of Control (IoC) Object coupling is bound at run time The binding process is achieved through
dependency injection Some argue that a “service locator” also provides
IoC Dependency injection is a software design
pattern DI allows the removal of hard-coded
dependencies Makes it possible to change them at run-time E.g.
as a simple way to load plugins dynamically to choose stubs or mock objects in test
environments vs. real objects in production environments.
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Dependency Injection (cont’d)
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application classes should be as independent as possible To increase the possibility to reuse these classes and to test them independently
Dependency: an association between two classes E.g., class A is dependent on class B
Injection: class B will get injected into class A by the IoC
Dependency injection in the way of passing parameters to the constructor or by post-construction using setter methods
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Aspect Oriented Programming (AOP)
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cross-cutting concerns The functions that span multiple points of an application
cross-cutting concerns are conceptually separate from the application's business logic E.g., logging, declarative transactions, security, and
caching The key unit of modularity
in OOP: the class in AOP: the aspect.
DI helps you decouple application objects from each other
AOP helps you decouple cross-cutting concerns from the objects that they affect
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Spring vs. EJB
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Spring is light-weight And portable Offers many features of EJBs But simpler and easier No need to application server Core features: non-web applications Spring integrates many existing frameworks
ORM frameworks, logging frameworks, JEE, Quartz and JDK timers, other view technologies
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Spring vs. EJB (cont’d)
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Testing is simpler Testing in non-web contexts Injection of mock objects
Lightweight IoC containers a consistent transaction management
interface scale down to a local transaction
using a single database scale up to global transactions
using JTA
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What is Spring?
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Spring is the most popular application development framework for enterprise Java
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Trends: Spring vs. EJB
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Spring Setup
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Spring is some jar files Download from:
http://www.springsource.org/spring-community-download
And dependencies to some others Apache Common Logging API
Download from: http://commons.apache.org/logging/ AspectJ
aspectjrt.jar aspectjweaver.jar aspectj.jar Aopalliance.jar
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Spring – Hello World
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Create your java project Simple application Web application
Add required Jar libraries Create source files
Class of beans Create bean configuration file (XML) Retrieve beans
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Source: Bean Classes
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Bean Configuration File
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Retrieve Beans
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Spring Container
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Spring Configuration Metadata
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XML based configuration file. Annotation-based configuration Java-based configuration
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Spring IoC Containers (cont’d)
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Spring BeanFactory Container the simplest container providing basic support for
DI for the purposes of backward compatibility E.g.
XmlBeanFactory factory = new XmlBeanFactory (new ClassPathResource("Beans.xml"));
Spring ApplicationContext Container This container adds more enterprise-specific
functionality E.g.
ApplicationContext context = new FileSystemXmlApplicationContext ("C:/Beans.xml");
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Spring Bean Definition
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class name (id) scope constructor-arg properties autowiring mode lazy-initialization mode initialization method
A callback, invoked just after all properties on the bean have been set
For the sake of post-processing the bean creation destruction method
A callback, invoked when the container is destroyed.
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Spring Bean Scopes
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Common Scopes singleton prototype
container creates new bean instance of the object every time a request for that specific bean is made.
Web-aware applications request session global-session
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Hint
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Think about it: Spring bean container is not a web framework How a servlet container may prepare web-
contexts (request, session and global-session) for beans?
Listeners
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Note
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Singleton pattern: singleton per class-loader
Singleton in Spring: singleton per bean definition, per container
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Default initialization and destroy methods
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Bean Example
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Bean Definition Inheritance
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Parent property for beans
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Bean Definition Inheritance (cont’d)
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Abstract beans Bean Definition Template
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Note
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Relation of parent and abstract to OOP concepts?
Inheritance in Spring is different from OOP inheritance Parent has a different meaning
Abstract in Spring is different from OOP abstract
Parent and abstract is defined for beans (objects) not for classes
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Dependency Injection
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Every java based application has a few objects that work together
In a complex Java application, application classes should be as independent as possible
To increase the possibility to reuse these classes
and to test them independently Dependency Injection (or sometime called
wiring) helps in gluing these classes together and same time keeping them independent.
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Example of a Dependency:
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What is wrong with this code? we have created a dependency between the
TextEditor and the SpellChecker concrete class
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Solution
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inversion of control like this:
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Dependency Injection Types
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Constructor-based dependency injection Setter-based dependency injection
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Constructor-based dependency injection
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Constructor-based dependency injection (2)
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Constructor-based dependency injection (3)
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Constructor-based dependency injection (4)
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Perhaps the best way
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Setter-based
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XML Configuration using p-namespace
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Injecting Collections (list)
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Injecting Collections (set)
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Injecting Collections (map)
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Injecting Collections (properties)
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Injecting references in Collections
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Inner Beans
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Defined within the scope of another bean a <bean/> element inside the <property/>
or <constructor-arg/> elements Similar to inner classes, but: It is all about the scope of beans, nothing
about OOP
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Injecting null and empty string values
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Auto-wiring
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We can autowire relationships between collaborating beans
Without using <constructor-arg> or <property> elements
Decreases the amount of XML configuration you write
Use the autowire attribute of the <bean/> element no byName byType constructor
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Auto-wiring : byName
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Autowiring by property name. Spring looks at the properties of the beans on
which autowire attribute is set to byName Tries to match and wire its properties with the
beans defined by the same names If matches are not found, it will throw
exceptions
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Auto-wiring : byType
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Autowiring by property datatype Spring looks at the properties of the beans on
which autowire attribute is set to byType Tries to match and wire a property if its type
matches with exactly one of the beans If more than one such beans exists, a fatal
exception is thrown
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Auto-wiring : constructor
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Similar to byType but type applies to constructor arguments If there is not exactly one bean of the
constructor argument type in the container, a fatal error is raised
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Limitations with autowiring
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Annotation Based Configuration
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Since Spring 2.5 to configure the dependency injection using
annotations instead of using XML to describe a bean wiring move the bean configuration into the
component class itself by using annotations
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Annotation-based Configuration Examples
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Spring Java Based Configuration
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To write most of your Spring configuration without XML
But with few Java-based annotations @Configuration: the class can be used by
the Spring IoC container as a source of bean definitions Instead of writing xml files
@Bean: the annotated method will return an object that should be registered as a bean in the Spring application context Instead of writing <bean> tags
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Example
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Above code will be equivalent to the following XML configuration:
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Creating the Context
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Injecting Bean Dependencies
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AOP with Spring Framework
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Aspect oriented programming cross-cutting concerns
logging, auditing, declarative transactions, security, and caching
The key unit of modularity in OOP is the class in AOP the unit of modularity is the aspect Dependency Injection helps you decouple your
application objects from each other AOP helps you decouple cross-cutting concerns from the
objects that they affect AOP is like triggers Spring AOP module provides interceptors
for example, when a method is executed you can add extra functionality before or after the method
execution
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AOP Terminology
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Aspect A module which has APIs providing cross-cutting
requirements E.g., a logging module
Join point the actual place in the application where an action will be
taken E.g., before deposit() method
Advice the actual action to be taken
Point-cut a set of one or more join-points where an advice should be
executed Expressed using expressions or patterns
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AOP Terminology (2)
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Introduction to add new methods or attributes to existing classes
Target object The object being advised by one or more aspects will always be a proxied object Also referred to as the advised object
Weaving The process of linking aspects with other application
types or objects, to create an advised object This can be done at compile time, load time, or at
runtime.
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Types of Advice
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before before the a method execution
after around
before and after after-returning
only if method completes successfully after-throwing
only if method exits by throwing an exception
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XML Schema Based AOP with Spring
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AOP Needed jars:
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aspectjrt.jar aspectjweaver.jar aspectj.jar aopalliance.jar
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Example: AOP in Spring
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Annotation-based Aspects
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enabled by including <aop:aspectj-autoproxy/> inside XML Schema-based configuration file
The actual body of the businessService() is irrelevant should be empty
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Spring JDBC Framework
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Simplifies JDBC programming Takes care of all the low-level details
opening the connection prepare and execute the SQL statement process exceptions handle transactions finally close the connection
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DataSource
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<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" /><property name="url" value="jdbc:mysql://localhost:3306/test" /><property name="username" value="root" /><property name="password" value="123" />
</bean>
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JDBCTemplate Class
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executes SQL queries update statements stored procedure calls performs iteration over ResultSets and
extraction of returned parameter values
Instances of the JdbcTemplate class are threadsafe
single instance of a JdbcTemplate is sufficient safely inject this shared reference into
multiple DAOs
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JDBCTemplate Examples
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String SQL = "select count(*) from Student"; int rowCount = jdbcTemplateObject.queryForInt( SQL );
String SQL = "select age from Student where id = ?"; int age = jdbcTemplateObject.queryForInt(SQL,
new Object[]{10});
String SQL = "select name from Student where id = ?"; String name = jdbcTemplateObject.queryForObject(
SQL, new Object[]{10}, String.class);
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JDBCTemplate Examples (cont’d)
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String SQL = "select * from Student where id = ?";Student student = jdbcTemplateObject.queryForObject(SQL, new Object[]{10}, new StudentMapper());
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Data Access Object (DAO)
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DAOs provide a means to read/write data to the database
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Student DAO (Cont’d)
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Spring Transaction Management
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A database transaction is a sequence of actions that are treated as a single unit of work
four key properties described as ACID Atomicity Consistency Isolation Durability
Local vs. Global Transactions Programmatic vs. Declarative Declarative: annotations or XML based configuration
Declarative transaction management is preferable Spring supports declarative transaction management
through AOP
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Programmatic Transaction Management
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Declarative Transaction Management
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Use Advices which creates a transaction-handling advice <tx:advice /> tag
Define a pointcut that matches all methods we wish to make transactional
Reference the transactional advice If a method name has been included in the
transactional configuration then created advice will begin the transaction before calling the method
Target method will be executed in a try / catch block. If the method finishes normally, the AOP advice
commits the transaction successfully otherwise it performs a rollback
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Spring’s Declarative Transaction Management
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Bean Configuration for Transactions
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Using @Transactional
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<!-- enable the configuration of transactional behavior based on annotations -->
<tx:annotation-driven transaction-manager="txManager"/>
<!-- a PlatformTransactionManager is still required -->
<bean id="txManager" class="org.springframework.jdbc.datasource. DataSourceTransactionManager">
<property name="dataSource" ref="dataSource"/></bean>
You can use @Transactional for methods or Classes
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Spring Framework Alternatives
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Google Guice provides support for dependency injection using
annotations Java EE 6 new standards
Contexts and Dependency Injection (CDI) specified by JSR 299 JBoss Weld is its reference implementation
CDI: a JCP specification included in Java EE 6 (JSR 299) Weld: the reference implementation of CDI Seam 3: a set of modules which extend CDI to
provide functionality beyond that offered by Java EE 6 Red HatJBossSeam Framwork Weld
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Decision point
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Standards or (non-standard) frameworks? The benefits of standard technologies
Standards JSP, JSF, JPA, …
Non-standard technologies Spring, GWT, …
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JavaEE6’s Advocates Say:
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The Age of Frameworks is Over The J2EE platform had its shortcoming
Spring quickly became the most prominent framework for easily building enterprise-ready applications
Helping developers avoid many of the pitfalls of the old enterprise Java platform
But J2EE represents the past, and Java EE 6 represents the future!
Java EE 6 promises us the ability to go beyond frameworks.
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JavaEE6’s Advocates Say: (cont’d)
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Frameworks like Spring are really just a bridge between the mistakes of the J2EE past and the success of the Java EE 6 future.
Frameworks are out, and extensions to the Java EE 6 platform are in.
Now is the time to start looking past Spring, and looking forward to Seam and Weld and CDI technologies.
And to start shifting into a world of extensions, and moving away from frameworks,
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But, Spring’s Advocates Say:
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In fact, Spring is more than a DI framework Perhaps, it is still the most popular application
development framework for enterprise Java Many extensions for easy integration with
other frameworks
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Review a Real Application
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Beans for data access (DAO) E.g., Hibernate or JDBC classes
Beans for business logic Beans for presentation
E.g., GWT or JSF pages
How are the dependencies? How are the beans retrieved from bean container? How many beans:
Data-sources? DAOs? Logic classes? Presentation classes?
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Exercise
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Write a web application “Add” and “List” forms for telephone contacts With all layers
Dao Business logic Presentation
Define the beans and spring-enable your project
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References and Material
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Spring Framework Reference Documentation http://www.springsource.org/documentation
Spring Framework 3.1 Tutorial www.tutorialspoint.com/spring/spring_tutorial.pdf
