java 构造函数参数和属性一起在 bean 定义中
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constructor-arg and property together in bean definition
提问by anthos
<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="cRef" 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.
aObject.cRef 由于某种原因未设置。请注意，构造函数参数和属性在同一定义中使用。我还没有看到具有类似功能的示例/帖子。
回答by Sean Patrick Floyd
Mixing <constructor-arg>and <property>is generally a bad idea.
混合<constructor-arg>和<property>通常是一个坏主意。
There is only one good reason for using <constructor-arg>, and that is to create immutable objects.
使用 的原因只有一个<constructor-arg>，那就是创建不可变对象。
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 @PostConstructif you need to apply some logic at bean creation time.
但是，如果您可以设置它们的属性，您的对象就不是不可变的。不要使用<constructor-arg>. 重新设计类，@PostConstruct如果需要在 bean 创建时应用一些逻辑，请使用带有注释的初始化方法。
回答by gavenkoa
On same sources my colleague discover:
我的同事在同一来源发现：
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.
而我的主机、测试和生产服务器没有这样的错误。
With:
和：
<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.
而 bean 中只有一个 3-args 构造函数。
The reason to use constructor - it perform some additional actions on non-Spring library by invoking init()method. And set args as fields.
使用构造函数的原因 - 它通过调用init()方法对非 Spring 库执行一些额外的操作。并将 args 设置为字段。
So I change spring-beans.xmlto:
所以我改成spring-beans.xml：
<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.
注意init-method=部分。
UPDATEAfter 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-argand propertyin XML beandefinition (check doCreateBeanin AbstractAutowireCapableBeanFactory.java, which call createBeanInstanceand populateBeannext).
更新毕竟我编写了简单的 XML 配置并在调试器中逐步执行 Spring 源代码。似乎使用 Spring 3.x 可以在 XML bean定义中组合构造函数参数和属性（检查doCreateBeanin ，接下来调用createBeanInstance和populateBean）。AbstractAutowireCapableBeanFactory.java
