constructor-arg and property together in bean definition
<bean id="cObject" scope="request" class="x.y.z.CClass"/>
<bean id="bObject" scope="request" class="x.y.z.BClass"/>
<bean id="aObject" scope="request" class="x.y.z.AClass">
<constructor-arg ref="bObject" />
<property name="c开发者_JS百科Ref" ref="cObject" />
</bean>
aObject.cRef is not getting set for some reason. Note that constructor-arg and property are used in the same definition. I have not seen an example / post with similar feature.
On same sources my colleague discover:
Caused by: org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'service.MenuService#0'
defined in class path resource [spring-beans/integrator.xml]:
Could not resolve matching constructor (hint: specify index/type/name
arguments for simple parameters to avoid type ambiguities)
while my host, test and production servers have no such error.
With:
<bean class="service.MenuService">
<constructor-arg index="0" type="java.lang.String" value="#{user}"/>
<constructor-arg index="1" type="java.lang.String" value="#{password}"/>
<constructor-arg index="2" type="java.lang.String" value="#{uri}"/>
<property name="system" value="OPRT"/>
<property name="client" value="OPRT"/>
</bean>
while there are only one 3-args constructor in bean.
The reason to use constructor - it perform some additional actions on non-Spring library by invoking init()
method. And set args as fields.
So I change spring-beans.xml
to:
<bean class="service.MenuService" init-method="init">
<property name="login" value="#{user}"/>
<property name="password" value="#{password}"/>
<property name="httpsUrl" value="#{uri}"/>
<property name="system" value="OPRT" />
<property name="client" value="OPRT" />
</bean>
Take attention to init-method=
part.
UPDATE After all I wrote simple XML config and step through Spring source code in debugger. Seems that with Spring 3.x it's possible to combine constructor-arg and property in XML bean definition (check doCreateBean in AbstractAutowireCapableBeanFactory.java
, which call createBeanInstance and populateBean next).
See also https://softwareengineering.stackexchange.com/questions/149378/both-constructor-and-setter-injection-together-in-spring/
Mixing <constructor-arg>
and <property>
is generally a bad idea.
There is only one good reason for using <constructor-arg>
, and that is to create immutable objects.
However, your objects are not immutable if you can set their properties. Don't use <constructor-arg>
. Redesign the class, use an initializer method annotated with @PostConstruct
if you need to apply some logic at bean creation time.
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