includeViewParams = true将null模型值转换为查询字符串中的空字符串

Question

给出<p:selectOneMenu>如下.

<f:metadata>
    <f:viewParam name="id" value="#{testManagedBean.id}" converter="javax.faces.Long"/>
</f:metadata>

<p:selectOneMenu value="#{localeBean.language}" onchange="changeLanguage();">
    <f:selectItem itemValue="en" itemLabel="English" />
    <f:selectItem itemValue="hi" itemLabel="Hindi" />
</p:selectOneMenu>

<p:remoteCommand action="#{testManagedBean.submitAction}"
                 name="changeLanguage"
                 process="@this"
                 update="@none"/>

相应的托管bean:

@ManagedBean
@RequestScoped
public final class TestManagedBean {

    private Long id; //Getter and setter.

    public TestManagedBean() {}

    public String submitAction() {
        return FacesContext.getCurrentInstance().getViewRoot().getViewId() + "?faces-redirect=true&includeViewParams=true";
    }
}

指示的参数<f:viewParam>是可选的.例如,使用URL访问页面,如下所示.

https://localhost:8181/Project-war/private_resources/Test.jsf

由于id是可选参数,<p:selectOneMenu>因此如果未按如下方式提供,则将空参数附加到URL(更改语言时).

https://localhost:8181/Project-war/private_resources/Test.jsf?id=

这不应该发生.如果未提供空参数,则不应附加空参数,并且URL应与第一个类似.

有没有办法防止空参数被传递到URL时没有传递？

---

这仅与<f:viewParam>- 指定的转换器相关联javax.faces.Long.

如果删除此转换器,则在未提供参数的情况下,参数不会附加到URL.

虽然完全没有必要指定转换器,但我有如下所示的转换器将id通过URL作为查询字符串参数传递给JPA实体.

@ManagedBean
@RequestScoped
public final class ZoneConverter implements Converter {

    @EJB
    private final SharableBeanLocal sharableService = null;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {
        try {
            long parsedValue = Long.parseLong(value);

            if (parsedValue <= 0) {
                throw new ConverterException(new FacesMessage(FacesMessage.SEVERITY_ERROR, "Message Summary", "Message"));
            }

            ZoneTable entity = sharableService.findZoneById(parsedValue);
            if (entity == null) {
                throw new ConverterException(new FacesMessage(FacesMessage.SEVERITY_WARN, "Message Summary", "Message"));
            }

            return entity;
        } catch (NumberFormatException e) {
            throw new ConverterException(new FacesMessage(FacesMessage.SEVERITY_ERROR, "Message Summary", "Message"), e);
        }
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {
        return value instanceof ZoneTable ? ((ZoneTable) value).getZoneId().toString() : "";
    }
}

现在需要明确指定此转换器<f:viewParam>,如下所示.

<f:viewParam name="id" 
             value="#{testManagedBean.id}"
             converter="#{zoneConverter}"
             rendered="#{not empty param.id}"/>

并且需要按如下方式更改关联的托管bean.

@ManagedBean
@RequestScoped
public final class TestManagedBean {

    private ZoneTable id;  //Getter and setter.

    public TestManagedBean() {}

    public String submitAction() {
        return FacesContext.getCurrentInstance().getViewRoot().getViewId() + "?faces-redirect=true&includeViewParams=true";
    }
}

Answer 1

这可能是对Mojarra默认实现的疏忽,UIViewParameter#getStringValueFromModel()其源代码可供参考,如下所示:

384    public String getStringValueFromModel(FacesContext context)
385        throws ConverterException {
386        ValueExpression ve = getValueExpression("value");
387        if (ve == null) {
388            return null;
389        }
390
391        Object currentValue = ve.getValue(context.getELContext());
392
393        // If there is a converter attribute, use it to to ask application
394        // instance for a converter with this identifer.
395        Converter c = getConverter();
396
397        if (c == null) {
398            // if value is null and no converter attribute is specified, then
399            // return null (null has meaning for a view parameters; it means remove it).
400            if (currentValue == null) {
401                return null;
402            }
403            // Do not look for "by-type" converters for Strings
404            if (currentValue instanceof String) {
405                return (String) currentValue;
406            }
407
408            // if converter attribute set, try to acquire a converter
409            // using its class type.
410
411            Class converterType = currentValue.getClass();
412            c = context.getApplication().createConverter(converterType);
413
414            // if there is no default converter available for this identifier,
415            // assume the model type to be String.
416            if (c == null) {
417                return currentValue.toString();
418            }
419        }
420
421        return c.getAsString(context, this, currentValue);
422    }

在为查询字符串构建期间,为每个UIViewParameter(后面的UI组件<f:viewParam>)调用此方法includeViewParams=true.我们看到无论它调用转换器的源currentValue是null或不是.换句话说,即使模型值是null,它仍然用它来调用转换器.

根据转换器的javadoc,Converter#getAsString()如果值为null:返回零长度字符串所需的规范:

符getAsString

...

返回:值为零的长度字符串null,否则为转换的结果

因此,转换器实际上应该不会再回来null的getAsString().然后他们返回一个空字符串.在查询字符串中的视图参数的情况下,这是非常不期望的.空字符串值与查询字符串中完全缺失之间的差异非常重要.

我已经向Mojarra家伙报告了问题3288.然后他们应该解决这个问题如下:

391        Object currentValue = ve.getValue(context.getELContext());
392
393        if (currentValue == null) {
394            return null;
395        }

在此期间,我致力于解决OmniFaces.在<o:viewParam>已扩展与此修复程序.它可以按照今天的1.8快照获得.

<f:metadata>
    <o:viewParam name="id" value="#{testManagedBean.id}" converter="javax.faces.Long"/>
</f:metadata>

更新:他们决定不解决它.无论如何,有OmniFaces.