Spring是否要求所有bean都有默认构造函数？ [英] Does Spring require all beans to have a default constructor?

问题描述

我不想为我的 auditRecord 类创建默认构造函数。

I don't want to create a default constructor for my auditRecord class.

但是Spring似乎坚持：

But Spring seems to insist on it:

org.springframework.beans.factory.BeanCreationException: 
Error creating bean with name 'auditRecord' defined in ServletContext resource
[/WEB-INF/applicationContext.xml]: 
Instantiation of bean failed; 
nested exception is org.springframework.beans.BeanInstantiationException: 
Could not instantiate bean class [com.bartholem.AuditRecord]: 
No default constructor found; 
nested exception is 
java.security.PrivilegedActionException:
java.lang.NoSuchMethodException: 
com.bartholem.AuditRecord

这真的有必要吗？

推荐答案

不，你不是需要使用默认（无arg）构造函数。

No, you are not required to use default (no arg) constructors.

你是如何定义bean的？听起来你可能告诉Spring将你的bean实例化为以下其中一种：

How did you define your bean? It sounds like you may have told Spring to instantiate your bean something like one of these:

<bean id="AuditRecord" class="com.bartholem.AuditRecord"/>

<bean id="AnotherAuditRecord" class="com.bartholem.AuditRecord">
  <property name="someProperty" val="someVal"/>
</bean>

你没有提供构造函数参数的地方。前一个将使用默认（或没有arg）构造函数。如果你想使用一个接受参数的构造函数，你需要用 constructor-arg 元素指定它们，如下所示：

Where you did not provide a constructor argument. The previous will use default (or no arg) constructors. If you want to use a constructor that takes in arguments, you need to specify them with the constructor-arg element like so:

<bean id="AnotherAuditRecord" class="com.bartholem.AuditRecord">
  <constructor-arg val="someVal"/>
</bean>

如果要在应用程序上下文中引用另一个bean，可以使用<$ c来完成$ c> ref constructor-arg 元素的属性，而不是 val 属性。

If you want to reference another bean in your application context, you can do it using the ref attribute of the constructor-arg element rather than the val attribute.

<bean id="AnotherAuditRecord" class="com.bartholem.AuditRecord">
  <constructor-arg ref="AnotherBean"/>
</bean>

<bean id="AnotherBean" class="some.other.Class" />

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