JSF自定义转换器未调用null值 [英] JSF Custom Converter not called on null value

问题描述

我在输出java.math.BigDecimal时创建了自定义Converter。当BigDecimal为0.00或 null 时，我想输出一个破折号。

I've created custom Converter for when I output java.math.BigDecimal. When the BigDecimal is 0.00 or null I want output a dash.

这是我的XHTML

<p:dataTable value="#{bean.data}" var="item">
    <p:column>
        <h:outputText value="#{item.currentValue}">
            <f:converter converterId="my.bigDecimalConverter" />
        </h:outputText>
    </p:column>
</p:dataTable>

我遇到的问题是＃{item.currentValue}是 null 转换器中的 getAsString 方法未被调用。

The problem I have is when #{item.currentValue} is null the getAsString method in the Converter is not called.

@FacesConverter("my.bigDecimalConverter")
public class BigDecimalConverter implements Converter {

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {
        if (context == null || component == null) {
            throw new NullPointerException();
        }                

        if (value == null) {
            System.out.println("null=");
            return "--";
        }

        System.out.print("Class=" + value.getClass());

        if (value instanceof String) {
            System.out.println("Str=" + value);
            return (String) value;
        }

        if (value instanceof BigDecimal) {
            BigDecimal bd = (BigDecimal)value;
            if (bd.equals(new BigDecimal("0.00"))) {
                return "--";
            } else {
                return bd.toPlainString();
            }
        }

        return "";
    }
}

我说它没有被叫，因为我没有当BigDecimal为 null 时，错误并且没有 println 语句输出。当BigDecimal不是 null 时，它按预期工作，并且 Class = class java.math.BigDecimal打印出来，当BigDecimal为0.00时我在页面上输出 - 。

I'm saying its not called because I get no errors and no println statement output when the BigDecimal is null. When the BigDecimal is not null it works as expected and "Class=class java.math.BigDecimal" gets printed out and when the BigDecimal is 0.00 I do get -- outputted on the page.

我正在使用JSF 2.1，Mojarra 2.1.27

I'm using JSF 2.1, Mojarra 2.1.27

我还使用以下方法测试我的转换器。

I also using the following to test my converter.

<h:outputText value="#{null}">
    <f:converter converterId="my.bigDecimalConverter" />
</h:outputText>

阅读这个问题似乎转换器应该使用 null 价值。
https://stackoverflow.com/a/19093197/50262

Reading over this question it would seem that a converter should work with a null value. https://stackoverflow.com/a/19093197/50262

推荐答案

你发布的链接说转换器应该使用null，但是不要说在每种情况下都会调用转换器。

The link you posted says that a converter should work with a null but doen't say a converter will be called in every situation with null values.

具体地说，当在 h里面时，它不会说转换器会被调用h：outputText ，且值为空。

Concretely it don't says a converter will be called when it is inside a h:outputText and the value is null.

如果你深入了解Mojarra来源，你会看到：

If you dig in the Mojarra sources you'll see:

//Line 355 -- com.sun.faces.renderkit.html_basic.HtmlBasicRenderer
//method getCurrentValue

    Object currentObj = getValue(component);
    if (currentObj != null) {
        currentValue = getFormattedValue(context, component, currentObj);
    }

很明显，永远不会转换空值！而且我找不到解决方法。

It's clear that a null value will never be converted! And I couldn't find a workaround.

然后如果你确实需要你的值为null（你可以返回0或者其他）我认为您唯一的机会是制作自定义渲染器。这很简单：

Then if you really need your value to be null (you could return 0 or something) I think your only chance is making a custom renderer. It is very easy:

你编写的渲染器会覆盖重要的方法：

You write a renderer that overrides the method that matters:

package my;

import javax.faces.component.UIComponent;
import javax.faces.component.UIInput;
import javax.faces.context.FacesContext;

import com.sun.faces.renderkit.html_basic.TextRenderer;

public class HtmlCustomRenderer extends TextRenderer {

    @Override
    public String getCurrentValue(FacesContext context, UIComponent component) {

        if (component instanceof UIInput) {
            Object submittedValue = ((UIInput) component).getSubmittedValue();
            if (submittedValue != null) {
                // value may not be a String...
                return submittedValue.toString();
            }
        }

        String currentValue = null;
        Object currentObj = getValue(component);
        //Remove the 'if' to call getFormattedValue even if null
        currentValue = getFormattedValue(context, component, currentObj);
        return currentValue;

    }

}

然后我们在faces-config.xml中声明渲染器：

And then we declare the renderer in faces-config.xml:

<render-kit>
    <renderer>
        <component-family>javax.faces.Output</component-family>
        <renderer-type>javax.faces.Text</renderer-type>
        <renderer-class>my.HtmlCustomRenderer</renderer-class>
    </renderer>
</render-kit>

现在您的转换器将被调用为空值！

Now your converter will be called with null values!

我希望它会有所帮助！

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