<div dir="ltr" style="text-align: justify;">
<div dir="ltr" style="text-align: justify;">
<div style="color: #274e13;">In Spring <b>&#8220;Autowiring by Constructor means&#8221;</b> autowiring is actually <b><a href="https://dineshonjava.com/2012/06/spring-autowiring-by-type.html">autowiring by type</a></b> it means if data type of a bean is same as the data type of other bean constructor argument, auto wire it.<a href="https://dineshonjava.com/2012/06/spring-ioc-container.html">Spring container</a> looks at the properties of the beans on which <i><b>autowire </b></i>attribute is set to <i><b>constructor</b></i>in the XML configuration file. It then tries to match and wire its <b>properties with the beans defined by the same data type</b> of constructor argument in the configuration file.</div>
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<div style="color: #274e13;">For example, if a &#8220;<b>circle</b>&#8221; bean exposes an &#8220;<b>center</b>&#8221; constructor argument of <b>Point data type</b>, Spring will find these &#8220;<b>center</b>&#8221; in current <a href="https://dineshonjava.com/2012/06/spring-ioc-container.html">container</a> and wire it automatically. And if no matching found, just do nothing.</div>
<p> ;</p>
<div style="color: #274e13;">You can enable this feature via <i><b>autowire=&#8221;constructor&#8221; </b></i>like below :</div>
<p> ;</p>
<div style="color: #274e13;">
<p>Normally, you wire the bean explicitly, via ref attribute like this :</p>
</div>
<pre class="highlight"><;bean class="com.dineshonjava.sdnext.autoWiring.tutorial.Circle" id="circle">; 
 <;constructor-arg>;<;ref bean="center">;<;/ref>; 
 <;/constructor-arg>;<;/bean>; <;bean class="com.dineshonjava.sdnext.autoWiring.tutorial.Point" id="center">; <;property name="x" value="0">;<;/property>; <;property name="y" value="0">;<;/property>; <;/bean>;</pre>
<div style="color: #274e13;">
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<p>With autowire <b><i>by constructor </i></b>enabled, you do not need to declares the property tag anymore. As long as the &#8220;<b>center</b>&#8221; beans are same data type as the constructor argument of <b>&#8220;circle&#8221;</b> bean, which is &#8220;<b>center</b>&#8220;, Spring will wire it automatically.</p>
</div>
<p><b>Lets see Exaple</b><br />
<b><br />
</b> <b>Circle.java</b></p>
<pre class="highlight">package com.dineshonjava.sdnext.autoWiring.tutorial; 
 
public class Circle 
{ 
 private Point center; 
 
 /** 
 * @param center the center to set 
 */ 
 public Center(Point center) { 
 this.center = center; 
 } 
 
 public void draw() 
 { 
 System.out.println("Center of circle is ("+center.getX()+", "+center.getY()+")"); 
 } 
} 
</pre>
<p><b><br />
</b> <b>Point.java</b></p>
<pre class="highlight">package com.dineshonjava.sdnext.autoWiring.tutorial; 
 
public class Point 
{ 
 private int x; 
 private int y; 
 /** 
 * @return the x 
 */ 
 public int getX() { 
 return x; 
 } 
 /** 
 * @param x the x to set 
 */ 
 public void setX(int x) { 
 this.x = x; 
 } 
 /** 
 * @return the y 
 */ 
 public int getY() { 
 return y; 
 } 
 /** 
 * @param y the y to set 
 */ 
 public void setY(int y) { 
 this.y = y; 
 } 
} 
</pre>
<p><b><br />
</b> <b>spring.xml</b></p>
<pre class="highlight"><;beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.springframework.org/schema/beans" xsi:schemalocation="http://www.springframework.org/schema/beans 
 http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">; 
 
<;bean autowire="constructor" class="com.dineshonjava.sdnext.autoWiring.tutorial.Circle" id="circle">; 
 <;/bean>; 
 <;bean class="com.dineshonjava.sdnext.autoWiring.tutorial.Point" id="center">; 
 <;property name="x" value="0">;<;/property>; 
 <;property name="y" value="0">;<;/property>; 
 <;/bean>; 
<;/beans>; 
</pre>
<p><b><br />
</b> <b>DrawingApp.java</b></p>
<pre class="highlight">package com.dineshonjava.sdnext.autoWiring.tutorial; 
 
import org.springframework.context.ApplicationContext; 
import org.springframework.context.support.ClassPathXmlApplicationContext; 
 
 
/** 
 * @author Dinesh Rajput 
 * 
 */ 
public class DrawingApp 
{ 
 /** 
 * @param args 
 */ 
 public static void main(String[] args) 
 { 
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml"); 
 Circle circle = (Circle) context.getBean("circle"); 
 circle.draw(); 
 } 
}</pre>
<p> ;</p>
<div style="color: #274e13;">
<p>Now run this application and get following output on the console.</p>
</div>
<div style="background-color: #ff99cc; border-width: thin; border: solid;">
<div style="color: blue;"><b>Output:</b></div>
<div style="color: red;">Jun 25, 2012 7:55:23 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions</div>
<div style="color: red;">INFO: Loading XML bean definitions from class path resource [spring.xml]</div>
<div style="color: red;">Jun 25, 2012 7:55:24 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons</div>
<div style="color: red;">INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1592174: defining beans [circle ,center]; root of factory hierarchy</div>
<p><b>Center of Circle is (0, 0)</b></p>
</div>
</div>
<p> ;</p>
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