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Spring auto-wiring mode byType


If you specify auto-wiring by type, then the injection will be based on data type of the bean and should be compatible with assigning bean property data type.

In spring, auto-wiring by type allows a property to be autowired if there is exactly one bean of the property type in the container. If there is more than one, a fatal exception is thrown, and this indicates that you may not use byType autowiring for that bean. If there are no matching beans, nothing happens; the property is not set. If this is not desirable, setting the dependency-check= "objects" attribute value specifies that an error should be thrown in this case.

package com.java2novice.beans;

public class PaymentGateway {

	private Order order;
	
	public void setOrder(Order ord){
		this.order = ord;
	}
	 
	public Order getOrder() {
		return order;
	}

	@Override
	public String toString(){
		return "ordering "+this.order.getItem()+" | price: "+this.order.getPrice();
	}
}

package com.java2novice.beans;

public class Order {

	private String item;
	
	private String price;
	
	public String getItem() {
		return item;
	}
	public void setItem(String item) {
		this.item = item;
	}
	public String getPrice() {
		return price;
	}
	public void setPrice(String price) {
		this.price = price;
	}
}

Here is the xml based configuration file, which shows normal way of injecting dependencies:

<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">

    <bean id="paymentGateway" class="com.java2novice.beans.PaymentGateway" >
		<property name="order" ref="orderBean" />
	</bean>
	
    <bean id="orderBean" class="com.java2novice.beans.Order" >
		<property name="item" value="Java Book" />
		<property name="price" value="RS 225" />
	</bean>
</beans>

Here is the xml based configuration file, which shows injection by type using auto-wiring. We are using bean property called autowire to specify auto-wire by type:

<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">

    <bean id="paymentGateway" class="com.java2novice.beans.PaymentGateway"
    								 autowire="byType" />
	
    <bean id="orderBean" class="com.java2novice.beans.Order" >
		<property name="item" value="Java Book" />
		<property name="price" value="RS 225" />
	</bean>
</beans>

Spring bean demo class:

package com.java2novice.test;

import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.java2novice.beans.PaymentGateway;

public class SpringDemo {

	public static void main(String a[]){
		String confFile = "applicationContext.xml";
		ConfigurableApplicationContext context 
						= new ClassPathXmlApplicationContext(confFile);
		PaymentGateway paymentGateway = (PaymentGateway) context.getBean("paymentGateway");
		System.out.println(paymentGateway.toString());
	}
}

Output:
ordering Java Book | price: RS 225
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Spring framework examples

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  2. Spring bean java based configuration using @Configuration and @Bean
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  6. Spring Dependency Injection and Types
  7. Spring Dependency Injection via setter method
  8. Spring Dependency Injection via Constructor
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  12. Spring bean tag properties
  13. Differen types of spring bean scopes
  14. How to inject inner bean in spring?
  15. Set spring bean scope using annotation
  16. How to invoke spring bean init and destroy methods?
  17. Spring bean initialization callback
  18. Spring bean destruction callback
  19. Configure default initialization and destroy method in all spring beans
  20. Spring bean init and destroy methods using annotations
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  22. How to read property file in spring using xml based configuration file?
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  24. How to inject date into spring bean property?
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  27. Spring dependency checking with @Required annotation
  28. How to define a custom Required-style annotation for dependency checking?
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  30. How to inject Set into spring bean?
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  44. Spring auto-wiring mode byType
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Knowledge Centre
String Vs StringBuffer
We know that String is immutable object. We can not change the value of a String object once it is initiated. If we try to change the value of the existing String object then it creates new object rather than changing the value of the existing object. So incase, we are going to do more modificatios on String, then use StringBuffer. StringBuffer updates the existing objects value, rather creating new object.
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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