Merging two Config.yml Files in Java?

Question

While programming my bukkit plugin, i realized that i needed to have my own config file so i can add comments into the file. I also needed to be able to update the config (if it has been created and is old).

I had also recently finished a simple jQuery plugin, where I used jQuery.extend and i merged two settings arrays. I wanted to know if this was possible in java with config files.

My Question:

Is there a way i can merge the new default config with the one the user already has? (Removing non-needed values or changing the names of the same strings)

An Explanation of the question:

Here is an example config.yml i might have:

# Comment here....

myString: defaultString 

myBool: false

myList: 
  - Value
  - Value 2

Pretty simple. Lets say this is my default config. The plugin has copied this config (if it is not already there) inside the plugin folder. But, this brings up one issue:

What if i need to update my config? (Add/Remove a bool, string, etc.)

One day, i say "I no longer need that boolean myBool". I remove it from the default config.yml and the config looks something like this:

# Comment here....

myString: defaultString 

myList: 
  - Value
  - Value 2

Or, i might need to add an extra string myNewString:

# Comment here....

myString: defaultString
myNewString: string 

myList: 
  - Value
  - Value 2

If i rewrite the config yml to my new "Default" config file, i will lose all the user's configuration settings.

Is there a way i can merge the new default config with the one the user already has and just add the new string with the default values?

Answer 1

Bukkit has a built in YamlConfiguration class with methods which allow you to get a value or specify a default value to retrieve if none exist, such as getString(String path, String default).

Gets the requested String by path, returning a default value if not found.

If the String does not exist then the specified default value will returned regardless of if a default has been identified in the root Configuration.

However it does not have a way to remove values from the configuration. If the new configuration is so different from the previous one, you might consider creating the new configuration, deleting the old and renaming the new to take it's place. Though I wouldn't be too concerned about it unless it's significantly different.

Answer 2

If you are using Spring then you can make use of YamlPropertiesFactoryBean. It has built in support for reading multiple yaml files and merging them together. So that way you can obtain merged Map<String,Object> from your yaml files. Then if you wish you can make use of ObjectMapper to convert it to particular type.

eg.

YamlMapFactoryBean factory = new YamlMapFactoryBean();
factory.setResolutionMethod(ResolutionMethod.OVERRIDE_AND_IGNORE);
factory.setResources(...resources);
Map<String, Object> yamlValueMap = factory.getObject();

If multiple resources are provided the later ones will override entries in the earlier ones hierarchically; that is, all entries with the same nested key of type {@code Map} at any depth are merged. For example:

      <pre class="code">
      foo:
        bar:
         one: two
      three: four
      </pre>

      plus (later in the list)

      <pre class="code">
      foo:
        bar:
         one: 2
      five: six
      </pre>

      results in an effective input of

      <pre class="code">
      foo:
        bar:
         one: 2
      three: four
      five: six
      </pre>

      Note that the value of "foo" in the first document is not simply replaced
      with the value in the second, but its nested values are merged.