How to use a java Hashmap as variable in JasperReport

I want to use a java.util.HashMap as variable in JasperReport to save group names of my report in it.

I have tired and declared a variable of开发者_高级运维 type java.util.HashMap and its expression field is:

$V{variable1}.put($F{GROUPCOLUMNVALUE}, $F{GROUPCOLUMNVALUE})

but it does not works and gives null when I print it on report's group footer.

I am using iReport 3.7.3

You wrote that Variable expression: new java.util.HashMap() I think it might be initial value expression instead of variable expression

I tried it there and got it working.

I set the following properties on the variable:

• Variable class: java.util.HashMap()
• Reset type: None
• Calculation: System
• Variable expression: new java.util.HashMap()