Spring3: Dependency Configuration In Detail(Part I)

Introduction:

    In this article, we focus on the configuration file beans.xml for IoC purpose.

 

1. A simple bean injected with simple property

<?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">

	<bean id="student" class="edu.xmu.domain.Student">
		<!-- collaborators and configuration for this bean go here -->
		<property name="id" value="1" />
	</bean>

</beans>

    1) Here we declare a simple bean whose name is student and type is edu.xmu.domain.Student.

    2) This instance has a property named id whose value we set as 1.

 

2. A simpe bean injected with constructor.

<?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">

	<bean id="student" class="edu.xmu.domain.Student">
		<constructor-arg type="Integer" value="1" />
		<constructor-arg type="String" value="Davy" />
		<constructor-arg type="Integer" value="23" />
	</bean>

</beans>

    1) The constructor-arg has to be ordered by declaration in constructor. As there is no name to identify the arg. The only reason to assign the value to a property is its type.

 

3. A simple bean injected with complex property.

        1) By refering to another bean.

<?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">

	<bean id="student" class="edu.xmu.domain.Student">
		<property name="address" ref="address"></property>
	</bean>
	
	<bean id="address" class="edu.xmu.domain.Address">
		<property name="country" value="China"></property>
		<property name="province" value="Shanghai"></property>
		<property name="city" value="Shanghai"></property>
		<property name="avenue" value="ChenhuiRD"></property>
		<property name="number" value="1000"></property>
	</bean>
	
</beans>

4. A simple bean injected with complex constructor

<?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">
	<bean id="student" class="edu.xmu.domain.Student">
		<constructor-arg type="Integer" value="1"></constructor-arg>
		<constructor-arg type="String" value="Davy"></constructor-arg>
		<constructor-arg type="Integer" value="23"></constructor-arg>
		<constructor-arg type="edu.xmu.domain.Address" ref="address1"></constructor-arg>
		<constructor-arg type="edu.xmu.domain.Address">
			<ref bean="address2"/>
		</constructor-arg>
	</bean>
	<bean id="address1" class="edu.xmu.domain.Address">
		<property name="country" value="China"></property>
	</bean>
	<bean id="address2" class="edu.xmu.domain.Address">
		<property name="country" value="Canada"></property>
	</bean>
</beans>

    1) Pay attention to the two different approaches in constructing instance

        (1) Assign as a property "ref"

        (2) Assign as a sub-element with tag <ref>

 

5. A simple bean injected with complex constructor using Factory method

<?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">
	<bean id="student" class="edu.xmu.domain.Student" factory-method="createInstance">
		<constructor-arg type="Integer" value="1"></constructor-arg>
		<constructor-arg type="String" value="Davy"></constructor-arg>
		<constructor-arg type="Integer" value="23"></constructor-arg>
		<constructor-arg type="edu.xmu.domain.Address" ref="address1"></constructor-arg>
		<constructor-arg type="edu.xmu.domain.Address">
			<ref bean="address2"/>
		</constructor-arg>
	</bean>
	<bean id="address1" class="edu.xmu.domain.Address">
		<property name="country" value="China"></property>
	</bean>
	<bean id="address2" class="edu.xmu.domain.Address">
		<property name="country" value="Canada"></property>
	</bean>
</beans>

 

	public Student(Integer id, String name, Integer age, Address address,
			Address homeAddress)
	{
		this.id = id;
		this.name = name;
		this.age = age;
		this.address = address;
		this.homeAddress = homeAddress;
	}

	public static Student createInstance(Integer id, String name, Integer age,
			Address address, Address homeAddress)
	{
		System.out.println("createInstance invoked");
		return new Student(id, name, age, address, homeAddress);
	}

    1) What's the purpose of using factory-method instead of simply using constructor?

        (1) The only benefit of using factory-method is return type can be sub-class of declared return type. But what's the point?

 

6. Refer to other beans

<?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">
           
    <import resource="edu/xmu/service/service.xml"/>
    <import resource="edu/xmu/dao/dao.xml"/>
</beans>

    1) Using <ref bean="***"> tag for the scope of whole xml including parent xml and children xml

    2) Using <ref local="***"> tag for the scope of only current xml

    3) Using <ref parent="***"> tag for the scope of only parent xml