How to inject null value in Spring

In Spring, you can uses this special <null /> tag to pass a “null” value into constructor argument or property.

1. Constructor Argument

The wrong way to inject a null into constructor argument, a really common mistake, and nice try :)


  <bean id="defaultMongoTypeMapper1"
	 class="org.springframework.data.mongodb.core.convert.DefaultMongoTypeMapper">
	 <constructor-arg name="typeKey" value="null" />
  </bean>

Correct way.


  <bean id="defaultMongoTypeMapper"
	class="org.springframework.data.mongodb.core.convert.DefaultMongoTypeMapper">
	<constructor-arg name="typeKey">
		<null />
	</constructor-arg>
  </bean>

2. Property

The wrong way to inject null value into property.


  <bean id="myConverter"
	class="com.mkyong.convert.MoneyConverter">
	<property name="typeMapper" value="null" />
  </bean>

Correct way.


  <bean id="myConverter"
	class="com.mkyong.convert.MoneyConverter">
	<property name="typeMapper"><null/></property>
  </bean>

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mkyong
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Chinmoy Anand
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Chinmoy Anand

How to do using annotations

Dhruva Mist
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Dhruva Mist

wow! thank you! did not know if there are wrong and correct ways

gjbaxter
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gjbaxter

This works great for and style syntax. Any clue when using c: or p: namespaces?

Ravi Ch
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Ravi Ch

Are u using Setter Injection then go for tag and are using constructor injection go for tag

Nishant
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Nishant

Hi, Pretty nice article. I have one question though.
The article explains the wrong way and correct way to pass null values, but it does not explain “why” a particular approach is wrong.
Why kind of issues I might face going with the wrong approach.
Basically, I want to understand why passing null as “null” is wrong.

Thanks!

Dmitry
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Dmitry

Nishant, because null is interpreted, as String with value “null”.