Spring MVC Injection
Dependency
Yet Another
Did SomeoneWeb
say:Framework
JNDI?
copyright 2009 Trainologic LTD
Spring MVC –Injection
Dependency part 1
• Introduction
What is Dependency Injection?
• Injection
The MVC Pattern
Types
• EJB
Spring
Timers
MVC Implementation
• Controllers
• Mapping Request Handlers
• Views
• I18N and Locale Resolvers
• Customizing Look & Feel using Themes
• File Uploading
• Error Handling
• Using Annotations copyright 2009 Trainologic LTD
Dependency Injection
Motivation
• Usually, EJBs need access to different types of
resources:
• DB connection pools.
• JMS resources.
• Environment entries.
• Timers.
• Etc…
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Dependency Injection
Use of JNDI
• In previous versions these resources were acquired
using the JNDI API.
• Here is how it was done in EJB 2.1:
public class MyBean implements SessionBean{
private DataSource myDS;
public void ejbCreate()
{
try
{
// connects to the JNDI
Context ctx = new InitialContext();
// lookup the DataSource
myDS = (DataSource)ctx.lookup("jdbc/myDS");
} catch (NamingException e)
{ // ... handle the exception somehow }
}
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Dependency Injection
JNDI Lookups
• Following are the disadvantages of JNDI lookups:
• Duplicate code.
• Can't unit-test (need JNDI service).
• Need to handle JNDI checked exceptions.
• Most projects use the “Service Locator” design
pattern to make JNDI lookups abstract.
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Dependency Injection
Enter Dependency Injection
• Dependency Injection is a new feature of EJB3.
• Obsoletes most of the JNDI calls.
• No more “Service Locator” design pattern.
• Eases unit-testing.
• OK, what is it?...
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Dependency Injection
No More “Service Locator”
• With EJB3 you can inject the dependencies directly into
the members.
• Use "push" approach instead of "pull" approach.
• Let’s see how it is done...
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Dependency Injection
@Resource
• The @Resource annotation specifies dependency
injection.
• It can be placed on a field like the following:
@Stateful
public class ShoppingCartBean implements ShoppingCart {
@Resource(name = "jdbc/productionDS”)
private DataSource myDS;
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Dependency Injection
@Resource
• Fields annotated with @Resource get their values
injected into them before any business method (and
before @PostConstruct).
• The field will be injected with the object from the JNDI
located by the name attribute.
• The name attribute of the annotation is optional and
defaults to the name of the field.
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Dependency Injection
Setter Methods
• Dependency injection can be specified on setter methods
instead of fields:
@Stateless
public class SomeBean {
@Resource // the lookup will be for productionDB
public void setProductionDB(DataSource ds1)
{
…
}
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Dependency Injection
• What is Dependency Injection?
• Injection Types
• EJB Timers
copyright 2009 Trainologic LTD
Dependency Injection
Injected Types
• The following types can be injected:
• Managed resources.
• Environment entries.
• EJBContext.
• Session Beans.
• UserTransaction.
• EntityManager.
• TimerService.
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Dependency Injection
Managed Resources
• All of the resources that the Application Server
managed, and which are stored in the JNDI can be
injected.
• This includes:
• DB connection pools.
• JMS connection factories.
• JMS destinations (queues & topics).
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Dependency Injection
Environment Entries
• An EJB may use a dedicated environment entries.
• These entries are per bean type.
• The type of the environment entry can be only one of
the following: String, Character, Integer, Boolean,
Double, Byte, Short, Long and Float.
• These entries are stored in a JNDI context which is
bean-specific and has the name of: java:comp/env.
• Let’s see an example…
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Dependency Injection
Example
@Stateless
public class SimpleSLSB implements Simple {
@Resource float vat;
@Override
public boolean getPriceWithVAT(String catalogNumber) {
return item.get(price) * (1.0f + vat);
}
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Dependency Injection
Setting Environment Entries
• Environment entries can be set in the deployment
descriptor (and thus customized at deployment).
• E.g.:
<enterprise-beans>
<session>
...
<ejb-name>Simple</ejb-name>
<ejb-class>com.trainologic.SimpleSLSB
</ejb-class>
...
<env-entry>
<description>The VAT</description>
<env-entry-name>vat</env-entry-name>
<env-entry-type>java.lang.Float</env-entry-type>
<env-entry-value>16.5</env-entry-value>
</env-entry>
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Dependency Injection
EJBContext
• Every EJB can communicate with the container (the
Application Server) through a special object called:
EJBConext.
• Session Beans use: SessionContext.
• Message Driven Beans use: MessageDrivenContext.
• We’ll discuss MDBs in a later chapter.
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Dependency Injection
EJBContext
• Using the EJBContext, the EJB can perform the following
operations:
• Use transactions API (discussed in the transactions
chapter).
• Retrieve the authenticated identity (discussed in the
security chapter).
• With Session Beans, the EJB can retrieve the
EJBObject associated with the bean (in order to pass
it to another bean).
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Dependency Injection
EJBContext Injection
• The @Resource annotation can be used to inject the
EJBConext:
@Resource
private SessionContext ctx;
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Dependency Injection
Injecting EJB References
• Dependency injection is also supported for EJB
references.
• In previous versions it was like with remote clients:
private StringCounter counter; // another EJB
public void ejbCreate() {
Context ctx = new InitialContext();
CounterHome home =
(CounterHome)ctx.lookup("ejb/otherEJBHome");
counter = home.create();
}
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Dependency Injection
@EJB
• Now, you should use the @EJB annotation:
@EJB(name=“StringCounterBean/local")
private StringCounter counter; // another EJB
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EJB 3.0
Persistence Context Injection
• Dependency injection is also used with the new
persistence framework (JPA).
• We will discuss it in the JPA chapter.
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Dependency Injection
• What is Dependency Injection?
• Injection Types
• EJB Timers
copyright 2009 Trainologic LTD
Dependency Injection
Scheduling
• Many applications need a scheduling infrastructure.
• E.g., perform a cleaning task every hour.
• EJBs support scheduling through EJB timers.
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Dependency Injection
EJB Timers
• Timers can be created for Stateless Session Beans and
Message Driven beans.
• The @Timeout annotation is used to declare a method
as the timer callback.
• The method must have the following signature:
void method-name (Timer)
• The method must not be final or static.
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Dependency Injection
Example
@Stateless
public class SomeBean implements SomeInterface {
@Resource
private TimerService timerService; // Dependency Injection
// a business method
public void createBeep() {
// start after 5 secs, then every 5 secs.
// The third parameter is a Serializable info object
timerService.createTimer(5000, 5000, null);
}
@Timeout
public void beep(Timer timer) {
System.out.println("BEEP!");
}
}
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