配置速度以使用toString以外的其他内容渲染对象？

Question

Is there a way to configure Velocity to use something other than toString() to convert an object to a string in a template? For example, suppose I'm using a simple date class with a format() method, and I use the same format every time. If all of my velocity code looks like this:

$someDate.format('M-D-yyyy')

is there some configuration I could add that would let me just say

$someDate

instead? (Assuming I'm not in a position to just edit the date class and give it an appropriate toString()).

I'm doing this in the context of a webapp built with WebWork, if that helps.

Answer 1

I faced this problem too and I was able to solve it based on Nathan Bubna answer .

I'm just trying to complete the answer providing the link to Velocity documentation which explains how to use EventHandlers.

In my case, I needed Velocity calls "getAsString" instead of toString method for all JsonPrimitive objects from gson library every time that a reference was inserted.

It was as simple as creating a

public class JsonPrimitiveReferenceInsertionEventHandler implements ReferenceInsertionEventHandler{

    /* (non-Javadoc)
     * @see org.apache.velocity.app.event.ReferenceInsertionEventHandler#referenceInsert(java.lang.String, java.lang.Object)
     */
    @Override
    public Object referenceInsert(String reference, Object value) {
        if (value != null && value instanceof JsonPrimitive){
            return ((JsonPrimitive)value).getAsString();
        }
        return value;
    }

}

And add the event to the VelocityContext

vec = new EventCartridge();
vec.addEventHandler(new JsonPrimitiveReferenceInsertionEventHandler());

...

context.attachEventCartridge(vec);

Answer 2

Velocity allows for a JSTL like utility called velocimacros:

http://velocity.apache.org/engine/devel/user-guide.html#Velocimacros

This would allow you to define a macro like:

#macro( d $date)
   $date.format('M-D-yyyy')
#end

And then call it like so:

#d($someDate)

Answer 3

您还可以创建自己的ReferenceInsertionEventHandler来监视日期并自动为您进行格式化。

Answer 4

Oh, and the 1.6+ versions of Velocity have a new Renderable interface. If you don't mind tying your date class to a Velocity API, then implement this interface and Velocity will use the render(context, writer) method (for your case, you just ignore the context and use the writer) instead of toString().