How can I determine if a variable exists from within the Groovy code running in the Scripting Engine?

问题

How can I determine if a variable exists from within the Groovy code running in the Scripting Engine?

The variable was put by ScriptEngine's put method

回答1:

In the groovy.lang.Script there is a method public Binding getBinding(). See also groovy.lang.Binding with method public boolean hasVariable(String name).

Thus you can simple check variable existence like

if (binding.hasVariable('superVariable')) {
// your code here
}

回答2:

// Example usage: defaultIfInexistent({myVar}, "default")
def defaultIfInexistent(varNameExpr, defaultValue) {
    try {
        varNameExpr()
    } catch (exc) {
        defaultValue
    }
}

回答3:

Variables injected by the Scripting Engine are held within binding.variables, so you can e.g. check for variable named xx:

if (binding.variables["xx"]) ...

来源：https://stackoverflow.com/questions/42465028/how-can-i-determine-if-a-variable-exists-from-within-the-groovy-code-running-in