Question

I have a macro taking several parameters. Some of these are optional and if a parameter is left empty it will replaced with default.

Now the question is how to make this as easy as possible for ordinary web designer. Is there any other possibity apart from my examples to handle this case?

Example 1:

The obvious problem here is the optional values.

#macro (myTag $param1 $param2 $param3) ... #end 

Example 2:

And here the problem is a possible issue when same macro is used more than once and all variables are not set again.

#set ($param1='value1')  #set ($param2='value2')  #set ($param3='value3')   #macro (myTag) ... #end 

Answer 1

As of Velocity 1.6, optional or named parameters are not supported. There was a recent patch submitted with this feature so we might see it available in a future release.

In the meantime, consider passing in a list or a map of values. For example you can pass in a map of params as follows (requires Velocity 1.5 or greater):

#macro(myMacro $p)   item 1: $p.param1   item 2: $p.param2 #end  #set($params = {'param1' : 'val1', 'param2':'val2'}) #myMacro($params) 

displays:

item 1: val1 item 2: val2 

To handle optional parameters, use an #if within the macro to check for the parameter. Adding new elements to the map is a little messy. Since the Java method ‘put’ returns a value, you have to use #set to dispose of the return value. (Otherwise it’s displayed in the resulting text).

#macro(myMacro $p)   #if(!$p.param1)#set($dummy = $p.put('param1', 'default1'))#end   #if(!$p.param2)#set($dummy = $p.put('param2', 'default2'))#end   #if(!$p.param3)#set($dummy = $p.put('param3', 'default3'))#end    item 1: $p.param1   item 2: $p.param2   item 3: $p.param3 #end  #set($params = {'param1' : 'val1', 'param2':'val2'}) #myMacro($params) 

displays

item 1: val1 item 2: val2 item 3: default3