In Spring,you can use dependency checking feature to make sure the required properties have been set or injected.

Dependency checking modes

4 dependency checking modes are supported:

  • none – No dependency checking.
  • simple – If any properties of primitive type (int, long,double…) and collection types (map, list..) have not been set, UnsatisfiedDependencyException will be thrown.
  • objects – If any properties of object type have not been set, UnsatisfiedDependencyException will be thrown.
  • all – If any properties of any type have not been set, an UnsatisfiedDependencyException
    will be thrown.

P.S The default mode is none

Example

A Customer and Person object for the demonstration.


package com.mkyong.common;

public class Customer 
{
	private Person person;
	private int type;
	private String action;

	//getter and setter methods
}

package com.mkyong.common;

public class Person 
{
	private String name;
	private String address;
	private int age;
	
	//getter and setter methods	
}

1. none dependency checking

Spring bean configuration file with ‘none’ dependency checking mode.


<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-2.5.xsd">

	<bean id="CustomerBean" class="com.mkyong.common.Customer" >
		<property name="action" value="buy" />
	</bean>

	<bean id="PersonBean" class="com.mkyong.common.Person">
		<property name="name" value="mkyong" />
		<property name="address" value="address ABC" />
		<property name="age" value="29" />
	</bean>

</beans>

If you did not explicitly define the dependency checking mode, it’s default to ‘none’. No dependency checking will perform.

2. simple dependency checking

Spring bean configuration file with ‘simple’ dependency checking mode.


<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-2.5.xsd">

	<bean id="CustomerBean" class="com.mkyong.common.Customer" 
         dependency-check="simple">

		<property name="person" ref="PersonBean" />
		<property name="action" value="buy" />
	</bean>

	<bean id="PersonBean" class="com.mkyong.common.Person">
		<property name="name" value="mkyong" />
		<property name="address" value="address ABC" />
		<property name="age" value="29" />
	</bean>

</beans>

The ‘type’ property (primitive type or collection types) have not been set, an UnsatisfiedDependencyException will throw.


org.springframework.beans.factory.UnsatisfiedDependencyException: 
Error creating bean with name 'CustomerBean' 
defined in class path resource [config/Spring-Customer.xml]: 
Unsatisfied dependency expressed through bean property 'type': 
Set this property value or disable dependency checking for this bean.

3. objects dependency checking

Spring bean configuration file with ‘objects’ dependency checking mode.


<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-2.5.xsd">

	<bean id="CustomerBean" class="com.mkyong.common.Customer" 
         dependency-check="objects">

		<property name="action" value="buy" />
		<property name="type" value="1" />
	</bean>

	<bean id="PersonBean" class="com.mkyong.common.Person">
		<property name="name" value="mkyong" />
		<property name="address" value="address ABC" />
		<property name="age" value="29" />
	</bean>
	
</beans>

The ‘person’ property (objects type) have not been set, an UnsatisfiedDependencyException will throw.


org.springframework.beans.factory.UnsatisfiedDependencyException: 
Error creating bean with name 'CustomerBean' 
defined in class path resource [config/Spring-Customer.xml]: 
Unsatisfied dependency expressed through bean property 'person': 
Set this property value or disable dependency checking for this bean.

4. all dependency checking

Spring bean configuration file with ‘all’ dependency checking mode.


<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-2.5.xsd">

	<bean id="CustomerBean" class="com.mkyong.common.Customer" 
         dependency-check="all">

		<property name="action" value="buy" />
	</bean>

	<bean id="PersonBean" class="com.mkyong.common.Person">
		<property name="name" value="mkyong" />
		<property name="address" value="address ABC" />
		<property name="age" value="29" />
	</bean>

</beans>

The combination of ‘simple’ and ‘objects’ mode, if any properties of any type (primitive, collection and object) have not been set, an UnsatisfiedDependencyException will be thrown.

Global default dependency checking

Explicitly define the dependency checking mode for every beans is tedious and error prone, you can set a default-dependency-check attribute in the <beans> root element to force the entire beans declared within <beans> root element to apply this rule. However, this root default mode will be overridden by a bean’s own mode if specified.


<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-2.5.xsd" 
	default-dependency-check="all">

	<bean id="CustomerBean" class="com.mkyong.common.Customer">
		<property name="action" value="buy" />
		<property name="type" value="1" />
	</bean>

	<bean id="PersonBean" class="com.mkyong.common.Person">
		<property name="name" value="mkyong" />
		<property name="address" value="address ABC" />
		<property name="age" value="29" />
	</bean>
	
</beans>

All beans declared in this configuration file are default to ‘all’ dependency checking mode.

@Required Annotation
In most scenarios, you just need to make sure a particular property has been set, but not all properties of a certain types (primitive, collection or object). The @Required Annotation can enforce this checking, see detail.