Dependency Injection in Spring?

Question

How can we know if spring framework is using constructor based dependency injection or setter method based dependency injection, when both the constructor and setter method is defined?

for example.. I have two java classes as follows.. TextEditor.java

public class TextEditor {
    private SpellChecker spellChecker;

    TextEditor(SpellChecker spellChecker){

       this.spellChecker = spellChecker;
    }


    public void setSpellChecker(SpellChecker spellChecker) {

      this.spellChecker = spellChecker;
    }

   // a getter method to return spellChecker
    public SpellChecker getSpellChecker() {
      return spellChecker;
    }

    public void spellCheck() {
      spellChecker.checkSpelling();
    }
}

and SpellChecker.java

public class SpellChecker {
   public SpellChecker(){
      System.out.println("Inside SpellChecker constructor." );
   }

   public void checkSpelling(){
      System.out.println("Inside checkSpelling." );
   }
}

in configuration file, pom.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <!-- Definition for textEditor bean using inner bean -->
   <bean id="textEditor" class="com.tutorialspoint.TextEditor">
      <property name="spellChecker">
         <bean id="spellChecker" class="SpellChecker"/>
       </property>
   </bean>

</beans>

now, how can we know that spring has added dependency using Constructor or using Setter method?

Where are the `@Autowired` or `@Inject` annotations? Show your code. — JB Nizet, Jul 15 '15 at 09:10
I am asking about using annotations. I am using XML file configuration based structure. — Prashant, Jul 15 '15 at 09:15
possible duplicate of [How does Spring @Autowired work](http://stackoverflow.com/questions/3536674/how-does-spring-autowired-work) — Seb, Jul 15 '15 at 09:18

score 2 · Accepted Answer · edited May 29 '18 at 17:40

2

When using a <property>, spring injects dependencies via setter.

If you want to inject it via constructor, you use <constructor-arg>.

Also see: http://docs.spring.io/spring/docs/current/spring-framework-reference/html/beans.html#beans-factory-collaborators

edited May 29 '18 at 17:40

Carl Walsh

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answered Jul 15 '15 at 09:35

Seb

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score 0 · Answer 2 · answered Jul 15 '15 at 09:10

It is all about developer choice how does he/she configure spring to inject dependency.

Since everyone could write big wall of text about how Dependency Injection works you should see/read this:

http://www.journaldev.com/2410/spring-dependency-injection-example-with-annotations-and-xml-configuration

Dependency Injection in Spring?

2 Answers2