绑定到 String 属性的 h:inputText 提交的是空字符串而不是 null [英] h:inputText which is bound to String property is submitting empty string instead of null

问题描述

我在 Tomcat 上有一个 JSF 2.0 应用程序，其中有许多 字段用于在我的数据库中输入数据.某些字段不是必需的.

I have a JSF 2.0 application on Tomcat with many <h:inputText> fields to input data in my database. Some fields are not required.

<h:inputText value="#{registerBean.user.phoneNumber}" id="phoneNumber">
    <f:validateLength maximum="20" />
</h:inputText>

当用户将此字段留空时，JSF 设置空字符串 "" 而不是 null.

When the user leave this field empty JSF sets empty string "" instead of null.

如何在不检查每个字符串的情况下修复此行为

How can I fix this behavior without checking every String with

if (string.equals("")) { string = null; }

推荐答案

您可以通过 web.xml 中的以下 context-param 配置 JSF 2.x 以将空提交的值解释为 null.xml(它的名字很长，这也是我想不起来的原因；)):

You can configure JSF 2.x to interpret empty submitted values as null by the following context-param in web.xml (which has a pretty long name, that'll also be why I couldn't recall it ;) ):

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

---

供参考和对 JSF 1.2 感兴趣的人使用(因此不是 1.1 或更早版本，因为设计上不可能有 java.lang.StringConverter 的Convertercode>) 这可以通过以下 Converter 解决:

---

For reference and for ones who are interested, in JSF 1.2 (and thus not 1.1 or older because it's by design not possible to have a Converter for java.lang.String) this is workaroundable with the following Converter:

public class EmptyToNullStringConverter implements Converter {

    public Object getAsObject(FacesContext facesContext, UIComponent component, String submittedValue) {
        if (submittedValue == null || submittedValue.isEmpty()) {
            if (component instanceof EditableValueHolder) {
                ((EditableValueHolder) component).setSubmittedValue(null);
            }

            return null;
        }

        return submittedValue;
    }

    public String getAsString(FacesContext facesContext, UIComponent component, Object modelValue) {
        return (modelValue == null) ? "" : modelValue.toString();
    }

}

...需要在faces-config.xml中注册如下:

...which needs to be registered in faces-config.xml as follows:

<converter>
    <converter-for-class>java.lang.String</converter-for-class>
    <converter-class>com.example.EmptyToNullStringConverter</converter-class>
</converter>

如果您还没有使用 Java 6，请将 submittedValue.empty() 替换为 submittedValue.length() == 0.

In case you're not on Java 6 yet, replace submittedValue.empty() by submittedValue.length() == 0.

• 空字符串的疯狂

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