h:inputText绑定到String属性正在提交空字符串而不是null | inputText绑定到String属性正在提交空字符串而不是n

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问题描述

我在Tomcat上有一个JSF 2.0应用程序，其中有许多<h:inputText>字段用于在数据库中输入数据.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会设置空字符串""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解决此问题

How can I fix this behavior without checking every String with

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

推荐答案

您可以将JSF 2.x配置为通过web.xml中的以下context-param将空提交的值解释为null(名称很长，即也将是为什么我不记得它的原因;)):

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>

对于参考和感兴趣的人，在JSF 1.2(因此不是1.1或更低版本，因为在设计上不可能为java.lang.String使用Converter)，这可以通过以下Converter解决: /p>

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中进行以下注册:

...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>

如果您尚未使用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.

空字符串疯狂

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