如何使数字输入区域最初为空而不是0或0.00?

问题描述

我有一个应该输入数字的输入位置.我希望它显示为空.但是，当我运行程序时，默认值为0或0.00.如何将其清空?

I have an input place that should get a number. I want it to be displayed as empty. However when I run my program, I get 0 or 0.00 as default. How can I make it empty?

推荐答案

如果将值绑定到基本类型而不是其包装表示形式，则会发生这种情况.原语int始终默认为0，原语double始终默认为0.0.您想改用Integer或Double(或BigDecimal).

This will happen if you bound the value to a primitive instead of its wrapper representation. The primitive int always defaults to 0 and the primitive double always defaults to 0.0. You want to use Integer or Double (or BigDecimal) instead.

例如:

public class Bean {

    private Integer number;

    // ...
}

然后，在处理表单提交时还要考虑两件事.首先，您需要指示JSF将提交的空字符串的值解释为null，否则EL仍将把空字符串强制为0或0.0.可以通过web.xml中的以下上下文参数完成此操作:

Then there are two more things to take into account when processing the form submit. First, you need to instruct JSF to interpret empty string submitted values as null, otherwise EL will still coerce the empty string to 0 or 0.0. This can be done via the following context parameter in web.xml:

<context-param>
    <param-name>javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL</param-name>
    <param-value>true</param-value>
</context-param>

第二，如果您使用的是Tomcat/JBoss或任何在幕后使用Apache EL解析器的服务器，则需要指示其不要将null强制为0或0.0 >类型通过以下VM参数(它以直觉的方式对待Number类型，就像它们是原始类型一样):

Second, if you're using Tomcat/JBoss or any server which uses Apache EL parser under the covers, then you need to instruct it to not coerce null to 0 or 0.0 in case of Number types by the following VM argument (it's unintuitively dealing with Number types as if they are primitives):

-Dorg.apache.el.parser.COERCE_TO_ZERO=false

另请参见:

• 空字符串疯狂
• h:inputText绑定到Integer属性的值提交值为0而不是null
• h:inputText，它是绑定到String属性的是提交空字符串而不是null
• javax.faces自Java EE 7/EL 3.0起，.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL不再起作用

See also:

• The empty string madness
• h:inputText which is bound to Integer property is submitting value 0 instead of null
• h:inputText which is bound to String property is submitting empty string instead of null
• javax.faces.INTERPRET_EMPTY_STRING_SUBMITTED_VALUES_AS_NULL does not work anymore since Java EE 7 / EL 3.0

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