Convert Boolean True/False to Yes/No

[jkrfs]

Greetings,

I'm sorry if this is common knowledge, I've done a couple of searches and have not been able to find anything on this topic.

I want to convert all the booleans that are displayed on my pages from true/false to Yes/No. I tried using the Custom Boolean property editor but either I am doing it wrong or I am completely far off.

What is the best solution to make this happen? Any help would be greatly appreciated.

Thanks!

[Keith Donald]

If you're using Spring 3, have a look at the Converters section of the MVC Showcase here: http://blog.springsource.com/2010/07...vc-3-showcase/. Converters are superior to PropertyEditors in many respects.

Specifically, the showcase demonstrates how to implement and plug in a custom Converter. org.springframework.samples.mvc.convert.Conversion ServiceFactoryBean is used to register the converter and it is plugged into the Spring MVC infrastructure in /WEB-INF/spring/appServlet/servlet-context.xml as a bean ref from the mvc:annotation-driven element. You could simply use that example as a base and register your own BooleanToStringConverter that does the following:

public BooleanToStringConverter implements Converter<Boolean, String> {
    public String convert(Boolean bool) {
        return bool ? "Yes" : "No";
    }
}

public class CustomConversionServiceFactoryBean extends FormattingConversionServiceFactoryBean {

	@Override
	protected void installFormatters(FormatterRegistry registry) {
		// register the default formatters in superclass
		super.installFormatters(registry);
		// install my custom ones
		registry.addConverter(new BooleanToStringConverter());
	}	
}

Remember, for this converter to kick-in you need to wire the custom conversionService into mvc:annotation-driven AND you either need to use a spring:form tag such as spring:input that applies conversion, or spring:eval that also applies conversion. Just doing a c:out or JSTL ${var} won't apply the conversion logic. We're looking at being able to plug in our EL system as the default EL in Spring 3.1.

Keith

[Enrico Pizzi]

If you use Spring 3 and yours is a web application, you need to:

- Write a custom formatter for the Boolean type:

public class MyCustomBooleanFormatter implements Formatter<Boolean> {
    public String print (Boolean fieldValue, Locale locale) {
        if (fieldValue.booleanValue()) return "Yes";
        else return "No";
    }

    public Boolean parse (String clientValue, Locale locale) {
        if ("Yes".equals(clientValue)) return new Boolean(true);
        else if ("No".equals(clientValue)) return new Boolean(false);
        else //throw some parsing exception or do what you like
    }
}

- register this formatter using FormattingConversionServiceFactoryBean:

<mvc:annotation-driven conversion-service="conversionService"/>

<bean id="conversionService"
class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
    <property name="converters">
        <set>
          <bean class="com.example.MyCustomBooleanFormatter"/>
        </set>
    </property>
</bean>

and that's it.

[Keith Donald]

Enrico,

Have you tested this? Looking at the code, the "converters" property only accepts Converter implementations, not Formatter implementations. It would be nice if it worked this way for Formatters, too, but it doesn't at the moment. The only way to register a custom Formatter using FormattingConversionServiceFactoryBean is to subclass and override installFormatters.

FYI: for an explanation of the differences between the Converter and Formatter SPIs, see the reference documentation in this area.

Keith

[Enrico Pizzi]

My apology, I actually tested something similar but with Converters...I thought it would work also with Formatters since somewhere in the documentation I read that Formatters are just a more specialized type of converters (just String/Object instead of Object/Object converters).

It would be nice if that worked also for formatters, maybe adding a "formatters" property to FormattingConversionServiceFactoryBean and implementing the same logic used for converters would be a nice add-on for future releases (I generally prefer not to "hack" my way into Spring by extending its classes and overriding its methods).

Best regards,

Enrico

[jkrfs]

Thank you Keith! I read your original post and rummaged through the MVC Showcase code (conveniently already checked out, a valuable source!) and was able to get it running right after I read your update/edit about switching the tags to spring:eval.

Again, thank you, you're a gentleman and a scholar!

[Keith Donald]

I opened a JIRA to make registering Formatters easier, vote it up at: https://jira.springframework.org/browse/SPR-7732

[jkrfs]

I fell into a little issue. How are we suppose to handle null values?

A page that has all of its Boolean values set to true/false loads perfectly fine, however if I try to load a page that holds onto a Boolean with a null value I get this:

java.lang.NullPointerException at org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:97) at
org.springframework.web.servlet.tags.EvalTag.doEndTag(EvalTag.java:113) at
org.apache.jsp.WEB_002dINF.jsp.operatingDetails.show_jsp._jspx_meth_spring_005feval_005f0(show_jsp.java:3540) at
org.apache.jsp.WEB_002dINF.jsp.operatingDetails.show_jsp._jspService(show_jsp.java:442) at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) at
javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377) at
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at

Thanks

[Keith Donald]

You may have hit a bug in Spring 3.0.x--try upgrading to 3.0.5.RELEASE, the latest maintenance version.

[jkrfs]

I upgraded to 3.0.5 last night and I am still running into the same error. I have two test cases, one with all values filled out, the page loads fine. The other with some null values where the page breaks with that error.