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?

Solution 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.

Solution 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;
}

Solution 3

If this is for some configuration file processing, consider using Apache configuration. https://commons.apache.org/proper/commons-configuration/javadocs/v1.10/apidocs/index.html?org/apache/commons/configuration/PropertiesConfiguration.html It has way to multiple values to single key- The format is bit different though

key=value1,value2,valu3 gives three values against same key.

Solution 4

Your logic is flawed... basically, you need to:

1. get the list for the key
2. if the list is null, create a new list and put it in the map
3. add the word to the list

You're not doing step 2.

Here's the code you want:

Properties prop = new Properties();
prop.load(new FileInputStream("/displayCategerization.properties"));
for (Map.Entry<Object, Object> entry : prop.entrySet())
{
    List<String> categoryList = categoryMap.get((String) entry.getKey());
    if (categoryList == null)
    {
        categoryList = new ArrayList<String>();
        LogDisplayService.categoryMap.put((String) entry.getKey(), categoryList);
    }
    categoryList.add((String) entry.getValue());
}

Note also the "correct" way to iterate over the entries of a map/properties - via its entrySet().

Solution 5

Create a wrapper around properties and assume your A value has keys A.1, A.2, etc. Then when asked for A your wrapper will read all the A.* items and build the list. HTH

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