Spring properties dependency checking

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.

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.