how to autowire a bean without default constructor

[tong123123]

How to use @Autowired on a field whose constructor need argument?

if the class RelationalDataSource has default constructor, the @Autowired function properly as follow

Class CustomerService

package com.cybelink.ioc;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Controller;


/**
 *
 * This class uses the DataSource to load Customer data 
 */

@Component
public class CustomerService {
	@Autowired
	// can switch between relationDataSource or xmlDataSource
	@Qualifier("relationalDataSource")
	//@Qualifier("xmlDataSource")
	private DataSource dataSource;
	private Customer customer;
	
	public static void main(String[] args){
		ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
		// don't create the customerService using new, should use spring method to make
		// customerService a spring managed bean!!
		//CustomerService customerService = new CustomerService();
		
		CustomerService customerService = (CustomerService)ctx.getBean("customerService");
		customerService.method1();		
	}
	
	public void method1(){		
		if (dataSource == null)
			System.out.println("dataSource == null");
		customer=(Customer)dataSource.retrieveObject();
		System.out.println(getCustomerName());
	}
	
	
	public CustomerService() {
		super();
		System.out.println("CustomerService Constructor is called");
	}
// unrelated code here
	
}

Interface DataSource

package com.cybelink.ioc;

/**
 *
 * Interface that must be implemented by all types of DataSource 
 */
public interface DataSource {
	public Object retrieveObject();
	public void setDataSourceName(String name);
	public String getDataSourceName();
	public void storeObject(Object object);
}

Class implement interface DataSource

package com.cybelink.ioc;

import org.springframework.stereotype.Component;

/**
 *
 * This class will be used to load the Customer from a Relational Database. 
 */

@Component("relationalDataSource")
public class RelationalDataSource implements DataSource {
	private String name;	
	
	public RelationalDataSource() {
		super();
	}

	/**
	 * Using the DataSource retrieve data for Customer and build a 
	 * Customer object to return it to the caller
	 */
	public Object retrieveObject() {
		//get data for Customer object from DB and create a 
		//Customer object
		return new Customer("Relational",10);
	}

	/**
	 * Set the DataSource name
	 */
	public void setDataSourceName(String name) {
		this.name=name;		
	}

	/**
	 * Return the name of the DataSource
	 */
	public String getDataSourceName() {
		return name;
	}

	/**
	 * Store Customer into relatioanl DB
	 */
	public void storeObject(Object object) {
		//store the customer data into Relatioanl DB
		
	}

}

the applicationContext.xml is as follow

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

<beans xmlns="http://www.springframework.org/schema/beans"
		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xmlns:context="http://www.springframework.org/schema/context"
		xmlns:aop="http://www.springframework.org/schema/aop"
		xmlns:tx="http://www.springframework.org/schema/tx"
		xsi:schemaLocation="
			http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
			http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
			http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd
			http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">


	<!-- ========================= GENERAL DEFINITIONS ========================= -->	
	<context:annotation-config/>
	
	
	<!-- To allow autodetect and register of beans under com.cybelink.ioc package -->
	<context:component-scan base-package="com" />
	
	
 
	<!-- Velocity Engine for email template -->
	<bean id="velocityEngine" class="org.springframework.ui.velocity.VelocityEngineFactoryBean">
      <property name="velocityProperties">
         <value>
         		input.encoding=UTF-8
            resource.loader=class
            class.resource.loader.class=org.apache.velocity.runtime.resource.loader.ClasspathResourceLoader
         </value>
      </property>
   </bean>
  
</beans>

but if I change the no-args constructor of relationalDataSource to

public RelationalDataSource(int a) {
		super();
	}

error occur as

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'customerService': Autowiring of fields failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.cybelink.ioc.DataSource com.cybelink.ioc.CustomerService.dataSource; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'relationalDataSource' defined in file [C:\workspace\workspace1\Test\bin\com\cybelink\ioc\RelationalDataSource.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.cybelink.ioc.RelationalDataSource]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.cybelink.ioc.RelationalDataSource.<init>()

[Justin Botelle]

see previous thread
http://forum.springsource.org/showthread.php?t=52810

[tong123123]

see previous thread
http://forum.springsource.org/showthread.php?t=52810

but the problem is how to assign value to the int a (the constructor parameter) ?

I add @Autowired in the constructor

@Autowired
	public RelationalDataSource(int a) {
		super();
	}

now, I get the error as follow:

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'customerService': Autowiring of fields failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.cybelink.ioc.DataSource com.cybelink.ioc.CustomerService.dataSource; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'relationalDataSource' defined in file [C:\workspace\workspace1\Test\bin\com\cybelink\ioc\RelationalDataSource.class]: Unsatisfied dependency expressed through constructor argument with index 0 of type [int]: : No unique bean of type [int] is defined: Unsatisfied dependency of type [int]: expected at least 1 matching bean; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [int] is defined: Unsatisfied dependency of type [int]: expected at least 1 matching bean

[tong123123]

if using xml method (not annotation method), there is something like

<constructor-arg> <value>100</value>
    	</constructor-arg>

but how to do this using @Autowired annotation?

[Justin Botelle]

So, I modified your constructor to take in another object (and that way you can switch out the value of a in your example by modifying this passed in object).

@Repository("relationalDataSource")
public class DataSource {

    private int a;
    
    @Autowired
    public DataSource(DataSourceSupplier d) {
        super();
        a = d.getA();
    }

and then introducing this new object:

@Component("dataSupplier")
public class DataSourceSupplier {
   
    public int getA() {return 1; }
    

}

Presumably you'd make DataSourceSupplier an interface and use different implementations per your pattern, distinguishing them by bean name.

[tong123123]

your example of using another object DataSourceSupplier d work.
But when I try to use Integer as constructor args (not primitive this time)

@Autowired
public RelationalDataSource(Integer d) {
	super();
	a = d.intValue();
}

I got the following exception

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [java.lang.Integer] is defined: Unsatisfied dependency of type [class java.lang.Integer]: expected at least 1 matching bean

so is it not allow to use java standard class as constructor args?

I try to add the following statement in applicationContext.xml

<bean id="Integer" class="java.lang.Integer"/>

and then the following exception prompted:

Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [java.lang.Integer]: No default constructor found; nested exception is java.lang.NoSuchMethodException: java.lang.Integer.<init>()

Also, another problem, in annotation like
@Component("relationalDataSource")
what is the exact meaning of the ("relationalDataSource") after @Component?
I use it because there are 2 class (named RelationalDataSource and XMLDataSource) implement the same interface named DataSource and so I use ("relationalDataSource") as @Qualifier, but if fact I do not know the exact meaning of ("relationDataSource") after @Component, especially if there is only one class inplement the interface DataSource.

[Justin Botelle]

If you want to do it all with annotations, then you couldn't have the ctor take an Integer e.g. (how would you specify the value). The name after Qualifier is to disambiguate different classes of the same type.

If you autowired based on an interface name (as is proper), and you had two different beans that implemented that interface, if you give them a name which you put in quotes after the service declaration, etc., then you can refer to that specific name with a qualifier declaration.