Sample Java code:

public class SomeClass {
...
@POST
public void someMethod(@FormParam("key") String[] values)

...
}

Sample Javascript code:

SomeClass.someMethod(

);

Sample HTTP request:

Request entity is "key=val1,val2,val3"

The AJAX client code concatenates the values of the Array and then sends a single form parameter with the concatenated string as the value. It should add multiple form parameters with the same name and each value of the array once.