java hashmap with List as value to property

Question

I have a HashMap in the following format.

HashMap<String, List<String>> map

I'm trying without any luck to find the best way to write this out to a property file, is this possible? I had no problem with a HashMap<String, String> hashmap, but when the value is a List I can't figure out the best way to store this out. I Don't care if it's out in xml format or any other format, just so I can easily open the file and have it serialized or whatever back into a hashmap.

Thanks for any direction

Properties are strings. Concat the List to comma separated. e.g. value1,value2,value3,value4 and add it to your Properties object. — Brian Roach
– Brian Roach, Commented Oct 10, 2011 at 20:31
@BrianRoach that would assume that the values Strings do not contain commas. — John B
– John B, Commented Oct 10, 2011 at 21:23
@John - Well, yes. And if they did you could quote the values, use pipe instead of comma, etc ... not rocket science :) — Brian Roach
– Brian Roach, Commented Oct 10, 2011 at 21:44

C. K. Young · Accepted Answer · 2011-10-10 20:35:49Z

4

First, you might want to consider using a ListMultimap from Guava. It implements a Map<Key, List<Value>>.

Next, I would set up an XML Schema where each element has a name and a list of values. Use JAXB to marshall the data to a file.

edited Oct 10, 2011 at 20:35

C. K. Young

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answered Oct 10, 2011 at 20:31

John B

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Comments

ratchet freak · Accepted Answer · 2011-10-10 20:39:02Z

1

I'm not sure what you are currently doing, but you can always just get a set of the Map.Entry<String,List<String>> instances that compose the map and write them out any way you want. See this.

The psuedo code would look something like

for (Map.Entry<String,List<String>> entry : map.entrySet()) {
    String key = entry.getKey();
    List<String> value = entry.getValue();

    // now loop over value, which will be of type List<String>
}

edited Oct 10, 2011 at 20:39

ratchet freak

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answered Oct 10, 2011 at 20:29

hvgotcodes

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Tobias · Accepted Answer · 2011-10-10 20:29:58Z

0

A HashMap is Serializable; so you can do this by default.

FileOutputStream fileStream = new FileOutputStream("map.map");
ObjectOutputStream os = new ObjectOutputStream(fileStream);
os.writeObject(map);
os.close();

answered Oct 10, 2011 at 20:29

Tobias

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1 Comment

Green Over a year ago

This is what I was hoping to do, my value that is a List is a subList and that is causing a problem, but not sure the best way around it yet.

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