Yaml Parsing from a config file

Question

This is the first time i am using a YAML parser and I am currently stuck at this point

I have a config file which goes something like

Users
 -Name:A
  Id : x
  Addr:10.0.0.1
 -Name:B
  Id  :y
  Addr:10.0.0.2

HomeAddress
 City:bla bla
 Country:bla bla

Office Address
 City:abchd
 Country:bha bha ba

So I thought the best way to parse it would be to have a list like this.

List<Map<String, obj>> Object = (List<Map<String, obj>>) yaml.load(input);

Objective was to access the object by specifying a string. Like Username A, I shld be able to obtain his id and IPAddr (This is the most important to me at the moment). But when I tried this declaration, I got an error like this

Exception in thread "main" java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to java.util.List
    at Message.MessagePasser.<init>(MessagePasser.java:34)

Can someone please help me debug this. I am running by a deadline!!:(

Solution 1

The YAML parser seems to be returning a Map. So you should use it like this:

Map config = (Map) yaml.load(input);
Map usersConfig = config.get("Users");

Also what particular YAML parser are you using?

Update 1: If you look at the documentation, the load method either returns a List or Map depending on the contents of your YAML file. As your YAML file starts with a key-value mapping (Users) and not an array (-), the load method returns a Map which is the appropriate type to be returned in this case.

Solution 2

1) check the validity of your YAML here: http://instantyaml.appspot.com/

2) Your document should look like this: (mind the spaces !)

Users : 
 - Name : A
   Id : x
   Addr : 10.0.0.1
 - Name : B
   Id   : y
   Addr : 10.0.0.2

Comments

[ExceptionHandler]

I am using a SnakeYaml Parser

[ExceptionHandler]

Thank you for the clarification. Taking your tip on this one, I modified my code to something like Map<String,nodeIP> obj = (Map<String,nodeIP>) yaml.load(input); But inspite of this, I have an error which says it cannot cast java.util.ArrayList to NodeIP type (which is a class defined by me). So Can you suggest some change on this?

[Behrang]

@ExceptionHandler Have a look at this test case (especially testLoadMap) and its accompanying YAML file to see how that would work. In short, SnakeYaml needs some extra information regarding how a JavaBeans maps to a YAML element and back.

[GreenAsJade]

Your Update1 is a fantastic tidbit. I just spent an hour trying to work out why code that worked before stopped working ... it's because I ignorantely put a thingo: into my YAML, changing the return value type of the load!!

[Alex]

Your validator does not work anymore, here is another one : yamllint.com . Also, the good formatting seems to remove spaces between keywords and ':' and '-' should be on a empty line, with the attributes coming on CR LF.