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

给出一个<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";
    }
}

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

The parameter as indicated by <f:viewParam> is optional. A page, for example is accessed using a URL as follows.

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

由于id是可选参数，因此在未提供以下内容的情况下，会将URL附加空参数(当语言从<p:selectOneMenu>更改时).

Since id is an optional parameter, an empty parameter is attached to the URL (when a language is changed from <p:selectOneMenu>), in case it is not supplied as follows.

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看起来应该像第一个一样.

This should not happen. An empty parameter should not be appended, if it is not supplied and the URL should look like the first one.

有没有一种方法可以防止在不传递空参数时将其附加到URL?

Is there a way to prevent an empty parameter from being appended to the URL, when it is not passed?

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

This is only associated with the converter as specified with <f:viewParam> - javax.faces.Long.

如果删除了此转换器，则在不提供任何参数的情况下，不会将参数附加到URL.

If this converter is removed then, parameters are not appended to the URL, in case no parameters are supplied.

尽管完全没有必要像此处演示的那样指定转换器，但我具有如下所示的转换器，可以将通过URL传递的id作为查询字符串参数转换为JPA实体.

Although specifying a converter as demonstrated here is completely unnecessary, I have converters as shown below to convert an id passed though the URL as a query-string parameter to a JPA entity.

@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() : "";
    }
}

现在需要使用<f:viewParam>明确指定此转换器，如下所示.

This converter is now required to be specified explicitly with <f:viewParam> as follows.

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

关联的受管Bean需要进行如下更改.

And the associated managed bean needs to be changed as follows.

@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";
    }
}