Copy Groovy class properties

Question

I want to copy object properties to another object in a generic way (if a property exists on target object, I copy it from the source object).

My code works fine using ExpandoMetaClass, but I don't like the solution. Are there any other ways to do this?

class User {
    String name = 'Arturo'
    String city = 'Madrid'
    Integer age = 27
}

class AdminUser {
    String name
    String city
    Integer age
}

def copyProperties(source, target) {
    target.properties.each { key, value ->
        if (source.metaClass.hasProperty(source, key) && key != 'class' && key != 'metaClass') {
            target.setProperty(key, source.metaClass.getProperty(source, key))
        }
    }
}

def (user, adminUser) = [new User(), new AdminUser()]
assert adminUser.name == null
assert adminUser.city == null
assert adminUser.age == null

copyProperties(user, adminUser)
assert adminUser.name == 'Arturo'
assert adminUser.city == 'Madrid'
assert adminUser.age == 27

Answer 1

I think the best and clear way is to use InvokerHelper.setProperties method

Example:

import groovy.transform.ToString
import org.codehaus.groovy.runtime.InvokerHelper

@ToString
class User {
    String name = 'Arturo'
    String city = 'Madrid'
    Integer age = 27
}

@ToString
class AdminUser {
    String name
    String city
    Integer age
}

def user = new User()
def adminUser = new AdminUser()

println "before: $user $adminUser"
InvokerHelper.setProperties(adminUser, user.properties)
println "after : $user $adminUser"

Output:

before: User(Arturo, Madrid, 27) AdminUser(null, null, null)
after : User(Arturo, Madrid, 27) AdminUser(Arturo, Madrid, 27)

Note: If you want more readability you can use category

use(InvokerHelper) {
    adminUser.setProperties(user.properties) 
}

Answer 2

I think your solution is quite good and is in the right track. At least I find it quite understandable.

A more succint version of that solution could be...

def copyProperties(source, target) {
    source.properties.each { key, value ->
        if (target.hasProperty(key) && !(key in ['class', 'metaClass'])) 
            target[key] = value
    }
}

... but it's not fundamentally different. I'm iterating over the source properties so I can then use the values to assign to the target :). It may be less robust than your original solution though, as I think it would break if the target object defines a getAt(String) method.

If you want to get fancy, you might do something like this:

def copyProperties(source, target) {
    def (sProps, tProps) = [source, target]*.properties*.keySet()
    def commonProps = sProps.intersect(tProps) - ['class', 'metaClass']
    commonProps.each { target[it] = source[it] }
}

Basically, it first computes the common properties between the two objects and then copies them. It also works, but I think the first one is more straightforward and easier to understand :)

Sometimes less is more.

Answer 3

Another way is to do:

def copyProperties( source, target ) {
  [source,target]*.getClass().declaredFields*.grep { !it.synthetic }.name.with { a, b ->
    a.intersect( b ).each {
      target."$it" = source."$it"
    }
  }
}

Which gets the common properties (that are not synthetic fields), and then assigns them to the target

---

You could also (using this method) do something like:

def user = new User()

def propCopy( src, clazz ) {
  [src.getClass(), clazz].declaredFields*.grep { !it.synthetic }.name.with { a, b ->
    clazz.newInstance().with { tgt ->
      a.intersect( b ).each {
        tgt[ it ] = src[ it ]
      }
      tgt
    }
  }
}


def admin = propCopy( user, AdminUser )
assert admin.name == 'Arturo'
assert admin.city == 'Madrid'
assert admin.age == 27

So you pass the method an object to copy the properties from, and the class of the returned object. The method then creates a new instance of this class (assuming a no-args constructor), sets the properties and returns it.

---

Edit 2

Assuming these are Groovy classes, you can invoke the Map constructor and set all the common properties like so:

def propCopy( src, clazz ) {
  [src.getClass(), clazz].declaredFields*.grep { !it.synthetic }.name.with { a, b ->
    clazz.metaClass.invokeConstructor( a.intersect( b ).collectEntries { [ (it):src[ it ] ] } )
  }
}

Answer 4

Spring BeanUtils.copyProperties will work even if source/target classes are different types. http://docs.spring.io/autorepo/docs/spring/3.2.3.RELEASE/javadoc-api/org/springframework/beans/BeanUtils.html