Spring Framework Annotation- Part 1

To make the annotation work, you need to

<context:component-scan
base-package="com.xxx.bar">
</context:component-scan>

The <context:component-scan> element
does everything that <context:annotation-config> does, plus it configures
Spring to automatically discover beans and declare them for you. What this means is
that most (or all) of the beans in your Spring application can be declared and wired
without using <bean>.




Spring's very own annotation:
@Autowired
@Qualifier
@Value

The @Inject annotation from JSR-000330 Dependency Injection for Java 


The @Resource annotation from JSR-000250 Common Annotations for the Java(tm) Platform ("Specification") : The Resource annotation is used to declare a reference to a resource. It can be specified on a class, methods or on fields. When the annotation is applied on a field or method, the container will inject an instance of the requested resource into the application when the application is initialized. If the annotation is applied to a class, the annotation declares a resource that the application will look up at runtime.

• Usage of @Autowired

Accessor

@Autowired

public voidsetInstrument(Instrument instrument){

this.instrument=instrument;

}

Now you can get rid of the <property> element that wires the Instrumentalist with

an instrument

 Method 

@Autowired

public void heresYourInstrument(Instrument instrument){

      this.instrument=instrument;

}

 Constructor

@Autowired

public Instrumentalist(Instrument instrument){

this.instrument=instrument;

}

Properties

@Autowired

private Instrument instrument;

you can directly annotate properties and do away with the setter

methods altogether;

@Autowired(required=false)

private Instrument instrument;

Here, Spring will try to wire the instrument property. But if no bean of type

Instrument can be found, then no problem. The property will be left null.

• Usage of @Qualifier

@Autowired

@Qualifier("guitar")

private Instrument instrument;

As shown here, the @Qualifier annotation will try to wire in a bean whose ID matches

guitar. It’s important to know that @Qualifier is really about narrowing the selection of autowire candidate beans.

• Usage of @Value

@Value("Eruption")

private String song;

Here we’re wiring a String value into a String property

• Usage of @Inject

@Inject

private Instrument instrument;

Just like @Autowired, @Inject can be used to autowire properties, methods, and con-

structors. Unlike @Autowired, @Inject doesn’t have a required attribute. Therefore,

@Inject-annotated dependencies are expected to be fulfilled, failing with an excep-

tion if they’re not.

• QUALIFYING @INJECTED PROPERTIES

@Inject

@Named("guitar")

private Instrumentinstrument;

The key difference between Spring’s @Qualifier and JSR-330’s @Named is one of

semantics.