Groovy：动态属性

Question

In Javascript you can define an object with properties a and b like so:

myObj={a:'a',b:'b'}

and then you can add a property c like so

myObj.c = 'c'

whats the equivalent of that in Groovy? Do I have to use metaClass?

Use case: JSON converters in Grails do not add transient properties to the response, i would like to just attach a random property to each element of my object list.

Answer 1

You can use a Map , which has similar syntax and behavior:

def myObj [a:'a', b:'b']
myObj.c = 'c'

You can also attach behavior with Closures, eg

myObj.sayHello = { -> println 'Hi' }

and then call it like a method:

myObj.sayHello()

Answer 2

Quoting from Using methodMissing and propertyMissing :

Groovy also supports propertyMissing for dealing with property resolution attempts. For a getter you use a propertyMissing definition that takes a String argument:

  class Foo {
       def propertyMissing(String name) { name }
    }
    def f = new Foo()

    assertEquals "boo", f.boo

For a setters you add a second propertyMissing definition that takes a value argument:

class Foo {
   def storage = [:]
   def propertyMissing(String name, value) { storage[name] = value }
   def propertyMissing(String name) { storage[name] }
}
def f = new Foo()
f.foo = "bar"

assertEquals "bar", f.foo

As with methodMissing you will likely want to dynamically register new properties at runtime to improve the performance of you code.