Spring MVC Dependency Injection Understanding

Question

I am new to Spring MVC.I am learning the concept of dependency Injection.I am following this link for the code example of Spring using dependency Injection.

Spring Example

In that example i was very clear of the concept of dependency Injection. But i have a small question on how to tell Spring that i want to use multiple shapes. In that First example (Constructor based) he gave a reference to a Circle Object so that it draws a circle.

<bean id="geometryExample1" class="com.boraji.tutorail.spring.GeometryExample1">
    <constructor-arg ref="circleShape"/>
</bean>

But what if want to draw both Circle,Rectangle and other Shapes? how do i tell or configure in Spring that depending on what shape i have provided it should use the approriate shape to draw the shape.

Any help is appreciated. Thanks in advance. Any suggestions?

Your question has nothing to do with Spring. The logic how to draw a shape is encapsulated in each of its subclasses. `GeometryExample1` does not and should not know how to draw a shape, it only calls the `draw` method that has different implementation based on the `Shape` instance passed to it. — tsolakp, Dec 13 '17 at 16:53

score 1 · Answer 1 · answered Dec 13 '17 at 16:36

1

Please find a tutorial that uses Java config instead of XML config. Your life will be much easier if you learn to use Java config.

When autowiring you can specify a @Qualifier and reference the bean by the id, e.g.

// This is your circle object
@Autowired
@Qualifier("geometryExample1")
public GeometryExample1 circleShape;

If you had

<bean id="squareExample" class="com.boraji.tutorail.spring.GeometryExample1">
    <constructor-arg ref="squareShape"/>
</bean>

...then in your code you'd have this:

// This is your square object
@Autowired
@Qualifier("squareExample")
public GeometryExample1 squareShape;

See How to autowire by name in Spring with annotations? for a little more detail and an example of instantiating a bean using Java config.

answered Dec 13 '17 at 16:36

Paul

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Hi @Paul thanks a lot for the suggestion. i will learn annotation based configuration too. But Can you please help how can i pass Multiple shapes here instead of one please? – Stack Dec 13 '17 at 18:46
also how can i configure in spring in sucha way that it accepts multiple shapes? @Paul – Stack Dec 13 '17 at 20:01
The answer by @KamilNoster seems complete - please try that and comment if it doesn't work. – Paul Dec 14 '17 at 14:54

Kamil Noster · Answer 2 · 2017-12-14T07:12:38.257

Implement your classes:

class CircleShape implements Shape {
    void draw() {
        // TODO implementation
    }
}

class RectangleShape implements Shape {
    void draw() {
        // TODO implementation
    }
}

Declare beans:

<bean id="rectangleShape" class="com.boraji.tutorail.spring.RectangleShape" />
<bean id="rectangleShape" class="com.boraji.tutorail.spring.CircleShape" />

<bean id="geometryExample1" class="com.boraji.tutorail.spring.GeometryExample1">
    <constructor-arg ref="rectangleShape"/>
</bean>

Java methods are virtual, so draw() from RectangleShape is called. Change geometryExample1 bean constructor arg back to CircleShape:

<bean id="geometryExample1" class="com.boraji.tutorail.spring.GeometryExample1">
    <constructor-arg ref="circleShape"/>
</bean>

Now draw() from CircleShape is called.

Read more about virtual methods here. And use annotations, please.

I hope I understood your problem correctly.

EDIT: Example class:

class GeometryExample1 {
    private Set<Shape> shapes;

    void example() {
        shapes.foreach(Shape::draw);
    }

    public void setShapes(Set<Shape> shapes) {
         this.shapes = shapes;
    }

    public Set<Shape> getShapes() {
        return shapes;
    }
 }

And bean declaration:

<bean id="geometryExample1" class="com.boraji.tutorail.spring.GeometryExample1">
    <property name="shapes">
        <set>
            <ref bean="circleShape" />
            <ref bean="rectangleShape" />
        </set>
    </property>
</bean>

In this case, annotation config should be way more clear.

Thanks. But what if i want to draw a circle and rectangle one after other? We can not go back and change the configuration for each shape . So Can you please exaplain how will be the configuration and using them ? — Stack, Dec 13 '17 at 17:00
Thanks for the answer. But there can be special scenario's right? Like What if i just want to draw rectangle once and both rectangle and circle once? So i should make changes in this case in cnfiguration. So is there a dynamic way just to pass it to the Shape object and can pass multiple shapes to the same object ? — Stack, Dec 13 '17 at 18:45

Spring MVC Dependency Injection Understanding

2 Answers2