[ 常見問題 ] Deep copy Map in Groovy

Source From Here
Question
How can I deep copy a map of maps in Groovy? The map keys are Strings or Ints. The values are Strings, Primitive Objects or other maps, in a recursive way.

How-To
An easy way is this:

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1. // standard deep copy implementation  
2. def deepcopy(orig) {  
3.     def bos = new ByteArrayOutputStream()  
4.     def oos = new ObjectOutputStream(bos)  
5.     oos.writeObject(orig); oos.flush()  
6.     def bin = new ByteArrayInputStream(bos.toByteArray())  
7.     def ois = new ObjectInputStream(bin)  
8.     return ois.readObject()  
9. }  

One testing sample code as below:

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1. def deepcopy(orig) {  
2.     def bos = new ByteArrayOutputStream()  
3.     def oos = new ObjectOutputStream(bos)  
4.     oos.writeObject(orig); oos.flush()  
5.     def bin = new ByteArrayInputStream(bos.toByteArray())  
6.     def ois = new ObjectInputStream(bin)  
7.     return ois.readObject()  
8. }  
9.   
10. def map1 = ['name':'john', 'age':20]  
11. printf("Original map1=%s\n", map1)  
12. def map2 = map1  
13. map2['name']='bob'  
14. printf("map2=%s\n", map2)  
15. printf("map1=%s\n", map1)  // map1 will be affected by modification on map2  
16. def map3 = deepcopy(map1)  
17. map3['name']='ken'  
18. printf("map3=%s\n", map3)  
19. printf("map1=%s\n", map1)  // map1 won't be affected by modification on map3   

Execution result:

Original map1={name=john, age=20}
map2={name=bob, age=20}
map1={name=bob, age=20}
map3={name=ken, age=20}
map1={name=bob, age=20}

Supplement
* Java HashMap - deep copy

Take a look at Deep Cloning, on Google Code you can find a library. You can read it on https://github.com/kostaskougios/cloning.

How it works is easy. This can clone any object, and the object doesn't have to implement any interfaces, like serializable.