Properties file with a list as the value for an individual key

Question

For my program I want to read a key from a properties file and an associated List of values for the key.
Recently I was trying like that

public static Map<String,List<String>>categoryMap = new Hashtable<String, List<String>>();       Properties prop = new Properties();       try {          prop2.load(new FileInputStream(/displayCategerization.properties));         Set<Object> keys = prop.keySet();         List<String> categoryList = new ArrayList<String>();         for (Object key : keys) {             categoryList.add((String)prop2.get(key));             LogDisplayService.categoryMap.put((String)key,categoryList);         }         System.out.println(categoryList);         System.out.println("Category Map :"+LogDisplayService.categoryMap);          keys = null;         prop = null;      } catch (Throwable e) {         e.printStackTrace();     } 

and my properties file is like below -

A=APPLE A=ALPHABET A=ANT B=BAT B=BALL B=BUS 

I want for key A there should be a list which contain [APPLE, ALPHABET,ANT] and B contain [BAT,BALL,BUS].
So Map should be like this {A=[APPLE, ALPHABET,ANT], B=[BAT,BALL,BUS]} but I get
{A=[ANT], B=[BUS]}
I searched on the internet for such a way but found nothing. I wish there should be a way. Any help?

Answer 1

Try writing the properties as a comma separated list, then split the value after the properties file is loaded. For example

a=one,two,three b=nine,ten,fourteen 

You can also use org.apache.commons.configuration and change the value delimiter using the AbstractConfiguration.setListDelimiter(char) method if you're using comma in your values.

Answer 2

The comma separated list option is the easiest but becomes challenging if the values could include commas.

Here is an example of the a.1, a.2, ... approach:

for (String value : getPropertyList(prop, "a")) {     System.out.println(value); }  public static List<String> getPropertyList(Properties properties, String name)  {     List<String> result = new ArrayList<String>();     for (Map.Entry<Object, Object> entry : properties.entrySet())     {         if (((String)entry.getKey()).matches("^" + Pattern.quote(name) + "\\.\\d+$"))         {             result.add((String) entry.getValue());         }     }     return result; }