< h：selectManyListbox JSF和Enums Class Cast错误 [英] <h:selectManyListbox JSF and Enums Class Cast error

问题描述

这让我疯狂，找不到错误。

This drives me crazy, cannot find the error.

这里是xhtml页面：

Here the xhtml page:

...
<h:selectManyListbox style="width: 207px" size="10" value="#{reportBean.selectedSeverities}">
                            <f:selectItems value="#{reportBean.severities}"/>
                        </h:selectManyListbox>
...

报表Bean：

...
private List<Severity> severities;
private List<Severity> selectedSeverities = new ArrayList<Severity>();
...
public List<Severity> getSeverities() {
   if (this.severities == null) {
        this.severities = new ArrayList<Severity>();
        this.severities.add(Severity.LOW);
        this.severities.add(Severity.HIGH);
        this.severities.add(Severity.UNDEFINED);
        this.severities.add(Severity.MEDIUM);
    }
        return severities;
}

对于命令按钮，我有以下操作方法：

For a command Button I have the following action method:

if (!selectedSeverities.isEmpty()) {
    Severity s = selectedSeverities.get(0);
}
return;

Wenn我选择一个严重性（枚举）并点击命令按钮我得到以下堆栈跟踪： p>

Wenn I select a severity(enum) and hit the commandbutton I get the following stack trace:

...
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to securityscan.util.Severity
...

我没有得到它。

任何帮助都非常感谢。

BR Reen

推荐答案

您不能使用枚举与 h：selectMany *** 组合而不使用转换器。 JSF / EL看不到/知道每个单独的列表项的通用类型。换句话说，它只看到一个列表而不是列表< Severity> ，并将每个项目视为 String ，除非你以其他方式告诉它。

You can't use enums in combination with h:selectMany*** components without using a converter. JSF/EL does not see/know the generic type of each of the separate list items. In other words, it only sees a List and not List<Severity> and treats every item as a String, unless you tell it to do otherwise.

你需要自己创建和指定一个转换器。对于枚举，最好扩展JSF提供的 EnumConverter 。

You need to create and specify a converter yourself. For enums, it's the best to extend the JSF-provided EnumConverter.

package com.example;

import javax.faces.convert.EnumConverter;
import javax.faces.convert.FacesConverter;

@FacesConverter(value="severityConverter")
public class SeverityConverter extends EnumConverter {

    public SeverityConverter() {
        super(Severity.class);
    }

}

（注意当您仍然在使用旧的JSF 1.2，您应该在 faces-config.xml < converter> c>而不是通过 @FacesConverter ）

(note that when you're still using the old JSF 1.2, you should be declaring this as <converter> in faces-config.xml instead of by @FacesConverter)

您使用的内容如下：

<h:selectManyListbox converter="severityConverter">

另请参见：

• 如何在选择的许多菜单中使用枚举？



See also:

• How to use enums in select many menus?

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