java - Spring MVC 绑定(bind)嵌套对象

Question

我有一个以下类的实例，我想从中编辑它，然后将其保存回后端。

public class NestedClass {
    List<InnerClass> inners = new LinkedList<InnerClass>();

    //getter and setter

    public class InnerClass {
        private String innerField;

        //getter and setter
   }
}

编辑:编辑示例代码以满足@Slava Semushin 的建议。

当我实例化类并将其传递给模型时，我可以使用以下 jsp 片段读取值:

<form:input path="inners[0].innerField" /><br/>
<form:input path="inners[1].innerField" /><br/>

但是当我把它传回去时，我得到以下异常:

Invalid property 'inners[0]' of bean class [com.sodacrm.webapp.forms.NestedClass]: Illegal attempt to get property 'inners' threw exception; nested exception is org.springframework.beans.NullValueInNestedPathException: Invalid property 'inners' of bean class [com.sodacrm.webapp.forms.NestedClass]: Could not instantiate property type [com.sodacrm.webapp.forms.NestedClass$InnerClass] to auto-grow nested property path: java.lang.InstantiationException: com.sodacrm.webapp.forms.NestedClass$InnerClass
org.springframework.beans.InvalidPropertyException: Invalid property 'inners[0]' of bean class [com.sodacrm.webapp.forms.NestedClass]: Illegal attempt to get property 'inners' threw exception; nested exception is org.springframework.beans.NullValueInNestedPathException: Invalid property 'inners' of bean class [com.sodacrm.webapp.forms.NestedClass]: Could not instantiate property type [com.sodacrm.webapp.forms.NestedClass$InnerClass] to auto-grow nested property path: java.lang.InstantiationException: com.sodacrm.webapp.forms.NestedClass$InnerClass

我正在使用的真实类是 3 层深，我不想将内部类放在单独的文件中，因为它们强烈属于它们的外部类...

Answer 1

如何为 inners 成员定义 getter？检查它是否始终返回有效列表:

List<InnerClass> inners = new LinkedList<InnerClass>();

或

public List<InnerClass> getInners() {
    if (inners == null) {
        inners = new LinkedList<InnerClass>();
    }
    return inners;
}