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>
How to do using annotations
wow! thank you! did not know if there are wrong and correct ways
This works great for and style syntax. Any clue when using c: or p: namespaces?
Are u using Setter Injection then go for tag and are using constructor injection go for tag
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!
Nishant, because null is interpreted, as String with value “null”.
Actually it will start searching for a bean named null and we haven’t declared so it will give an error bean not found.
Also if you are using c schema you cannot write null or an empty string.
I have a question how to inject null values using c: schema ??