访问 bean 的嵌套/索引属性时如何防止 NPE

发布于 2024-08-31 08:50:15 字数 266 浏览 7 评论 0原文

使用 commons-beanutils 访问嵌套 bean 时，有什么方法可以防止 NPE 吗？这是我的代码：

new BeanUtilsBean().getProperty(human, "parent.name");

在这种情况下，我希望 getProperty() 当 human.getParent() == null 时返回空字符串 ("") 或在除了抛出 NPE 之外的其他方式。

原文

Is there any way to prevent NPE when accessing a nested bean using commons-beanutils?
Here is my code:

new BeanUtilsBean().getProperty(human, "parent.name");

In this case I want getProperty() to either return empty string ("") when human.getParent() == null or handle it in a way other that throwing an NPE.

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梦里梦着梦中梦 2024-09-07 08:50:15

他们正在考虑添加语言功能JDK7，但是最终它们没有被添加

现在你必须手动检查。你可以破解它并创建一个类似

public static void propertyHack(Object bean, String property, String nullreplace){
  try{
    return new BeanUtilsBean().getProperty(bean, property);
  }
  catch(NullPointerException npe){
    return nullreplace;
  }
}

“有点糟糕”的函数，但它会起作用。

They were thinking of adding language features to JDK7, but ultimately they weren't added

For now you'll have to manually check. You can just hack it and create a function like

public static void propertyHack(Object bean, String property, String nullreplace){
  try{
    return new BeanUtilsBean().getProperty(bean, property);
  }
  catch(NullPointerException npe){
    return nullreplace;
  }
}

Kind of sucks, but it will work.

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染柒℉ 2024-09-07 08:50:15

PropertyUtils 有一个用于嵌套属性 getNestedProperty(...) 的特定方法，它通过抛出 NestedNullException 来处理 NPE，这可能（？）更好为了眼睛。

这是 Javadoc。

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萧瑟寒风 2024-09-07 08:50:15

如果其他人正在寻找答案

    Guia g = new Guia();
    GuiaParticipante gp = new GuiaParticipante(1);
    g.setTbGuiaParticipanteCollection(Collections.singletonList(gp));//comment this line to test
    String name = "tbGuiaParticipanteCollection[0].codParticipante";//the expression itself
    Resolver resolver = new DefaultResolver();//used to "clean" the expression
    if (resolver.isIndexed(name)) {
        String property = resolver.getProperty(name);//remove the [0].codParticipante

        if (PropertyUtils.getProperty(g, property) != null) { //get the collection object, so you can test if is null
            String cod = BeanUtils.getNestedProperty(g, name); //get the value if the collection isn't null
            System.out.println(cod);
        }
    }

If someone else is searching the answer

    Guia g = new Guia();
    GuiaParticipante gp = new GuiaParticipante(1);
    g.setTbGuiaParticipanteCollection(Collections.singletonList(gp));//comment this line to test
    String name = "tbGuiaParticipanteCollection[0].codParticipante";//the expression itself
    Resolver resolver = new DefaultResolver();//used to "clean" the expression
    if (resolver.isIndexed(name)) {
        String property = resolver.getProperty(name);//remove the [0].codParticipante

        if (PropertyUtils.getProperty(g, property) != null) { //get the collection object, so you can test if is null
            String cod = BeanUtils.getNestedProperty(g, name); //get the value if the collection isn't null
            System.out.println(cod);
        }
    }

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