how to retrieve nested properties in groovy

I'm wondering what is the best way to retrieve nested properties in Groovy, taking a given Object and arbitrary "property" String. I would like to something like this:

someGroovyObject.getProperty("property1.property2")

I've had a hard time finding an example of o开发者_如何学运维thers wanting to do this, so maybe I'm not understanding some basic Groovy concept. It seems like there must be some elegant way to do this.

As reference, there is a feature in Wicket that is exactly what I'm looking for, called the PropertyResolver: http://wicket.apache.org/apidocs/1.4/org/apache/wicket/util/lang/PropertyResolver.html

Any hints would be appreciated!

I don't know if Groovy has a built-in way to do this, but here are 2 solutions. Run this code in the Groovy Console to test it.

def getProperty(object, String property) {

  property.tokenize('.').inject object, {obj, prop ->       
    obj[prop]
  }  
}

// Define some classes to use in the test
class Name {
  String first
  String second
}

class Person {
  Name name
}

// Create an object to use in the test
Person person = new Person(name: new Name(first: 'Joe', second: 'Bloggs'))

// Run the test
assert 'Joe' == getProperty(person, 'name.first')

/////////////////////////////////////////
// Alternative Implementation
/////////////////////////////////////////
def evalProperty(object, String property) {
  Eval.x(object, 'x.' + property)
}

// Test the alternative implementation
assert 'Bloggs' == evalProperty(person, 'name.second')

Groovy Beans let you access fields directly. You do not have to define getter/setter methods. They get generated for you. Whenever you access a bean property the getter/setter method is called internally. You can bypass this behavior by using the .@ operator. See the following example:

class Person {
    String name
    Address address
    List<Account> accounts = []
}

class Address {
    String street
    Integer zip
}

class Account {
    String bankName
    Long balance
}

def person = new Person(name: 'Richardson Heights', address: new Address(street: 'Baker Street', zip: 22222)) 
person.accounts << new Account(bankName: 'BOA', balance: 450)
person.accounts << new Account(bankName: 'CitiBank', balance: 300)

If you are not dealing with collections you can simply just call the field you want to access.

assert 'Richardson Heights' == person.name
assert 'Baker Street' == person.address.street
assert 22222 == person.address.zip

If you want to access a field within a collection you have to select the element:

assert 'BOA' == person.accounts[0].bankName
assert 300 == person.accounts[1].balance​​​​​​​​​

You can also use propertyMissing. This is what you might call Groovy's built-in method.

Declare this in your class:

def propertyMissing(String name) {
    if (name.contains(".")) {
        def (String propertyname, String subproperty) = name.tokenize(".")
        if (this.hasProperty(propertyname) && this."$propertyname".hasProperty(subproperty)) {
            return this."$propertyname"."$subproperty"
        }
    }
}

Then refer to your properties as desired:

def properties = "property1.property2"
assert someGroovyObject."$properties" == someValue

This is automatically recursive, and you don't have to explicitly call a method. This is only a getter, but you can define a second version with parameters to make a setter as well.

The downside is that, as far as I can tell, you can only define one version of propertyMissing, so you have to decide if dynamic path navigation is what you want to use it for.

See

https://stackoverflow.com/a/15632027/2015517

It uses ${} syntax that can be used as part of GString