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https://issues.apache.org/jira/browse/VELOCITY-444?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Henning Schmiedehausen closed VELOCITY-444.
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> Allow evaluation of Java expressions that does not return text or value!
> ------------------------------------------------------------------------
>
> Key: VELOCITY-444
> URL: https://issues.apache.org/jira/browse/VELOCITY-444
> Project: Velocity
> Issue Type: Improvement
> Components: Engine
> Affects Versions: 1.4
> Environment: WindowsXP
> Reporter: Colbert Philippe
> Priority: Critical
>
> I have started to use Velocity as a file preprocessor with my own macros in
> separate files. I quickly realized that there are some features missing in
> Velocity.
> I want to create Velocity macros with optional parameters, which is essential
> for my application. When a user calls my macros, she/he should not be
> obliged to pass all the necessary parameters to my macro. The macro should
> be callable with no parameter or with partial or full set of parameters.
> All parameters will have default values.
> I think the best way to do this is to have a Map (like a java.util.Map as in
> HashMap). As far as I know, Velocity does not support a Map objects
> directly. Such object as a Map has to be created in Java and used from the
> Velocity macro language. Therein lies the problem.
> Velocity does not have a reserved word for evaluating a Java expression
> without returning a value or text. In the documentation, using #set(
> $result = $myObj.method() ), method() can have side effects but it must
> return a value. I want to be able to call methods that return nothing
> (void). I have tried many things to try circumventing this but nothing
> works. Velocity always outputs the text of the expression without evaluating
> it.
> The solution would be to have a reserve construct similar like #set(....) but
> it would be called #eval(....). Such expression #eval(....) would take a
> Java expression and would evaluate it without generating any text. The
> #eval(....) would be used to set the value of my Map.
> // Utility Java class that creates and keeps HashMap(s)
> public static class Utility {
> public static final byte MAP_COUNT = 16;
> private final Stack<Map<String,String>> maps =
> new Stack<Map<String,String>>();
> public Utility() { this(MAP_COUNT); }
> public Utility(int count) {
> for(int i=0;i<count;i++) {
> maps.push(new HashMap<String,String>());
> }
> }
> public Map<String,String> createMap() { return maps.pop(); }
> public void discardMap(Map<String,String> map) { map.clear();
> maps.push(map); }
> }
> protected final Utility util = new Utility();
> engine.setProperty("util", util); // ...later passed as property of
> VelocityEngine
> ##=======================
> ## Macro to create a Map and use it inside the macro
> ##=======================
> #set( $myMap = $util.createMap() )
> $myMap.size()
> #$myMap.put("first", "alpha")
> #$myMap.put("second", "beta")
> #$myMap.put("third", "kapa")
> #$myMap.put("fourth", "gamma")
> #foreach( $myKey in [ "first", "second", "third", "fourth" ] )
> $myKey ${myMap.get($myKey)}
> #end
> ##=======================
> ## Output text file ...DOES NOT WORK AS PLANNED!!
> ##=======================
> $myMap.size()
> #$myMap.put("first", "alpha")
> #$myMap.put("second", "beta")
> #$myMap.put("third", "kapa")
> #$myMap.put("fourth", "gamma")
> first ${myMap.get($myKey)}
> second ${myMap.get($myKey)}
> third ${myMap.get($myKey)}
> fourth ${myMap.get($myKey)}
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