How to convert Map to Map in java?

Question

I have the Map of type Object, i need to convert this map into the type String.

Map<String, String> map = new HashMap<String, String>();    
Properties properties = new Properties();    
properties.load(instream);

Can any body please tell me, how to assign the properties to above map?

Thanks & Regards, Msnaidu

@TimothyGroote - I think it's very likely ot be a `java.util.Properties`. — Andrzej Doyle, Jun 20 '13 at 08:15
possible duplicate of [Converting java.util.Properties To HashMap](http://stackoverflow.com/questions/17209260/converting-java-util-properties-to-hashmapstring-string) — Dave Jarvis, Jan 15 '15 at 00:08

dkateros · Answer 1 · 2013-06-20T08:31:20.597

3

Map<String, String> properties2Map(Properties p) {
            Map<String, String> map = new HashMap<String, String>();
            for(Map.Entry<Object, Object> entry : p.entrySet()) {
                String key = (String) entry.getKey(); //not really unsafe, since you just loaded the properties
                map.put(key, p.getProperty(key));
            }
            return map;
}

I also like to use utility methods with type arguments to walk around generic type invariance and do some "downcasting" or "upcasting" (when I KNOW it is safe to do so). In this case:

@SuppressWarnings("unchecked")
<A, B extends A> Map<B, B> downCastMap(Map<A,A> map) {
    return (Map<B, B>)map;
}

Then you can write

Properties p = ...
Map<String, String> map = downCastMap(p);

edited Jun 20 '13 at 08:31

answered Jun 20 '13 at 08:13

dkateros

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can i put it like Map map = (Map) properties; – M.S.Naidu Jun 20 '13 at 08:17
Yes, suppressing rawtypes and unchecked. However, the utility method is more code documenting for anyone else (and yourself) reading the code. – dkateros Jun 20 '13 at 08:37

Andrzej Doyle · Accepted Answer · 2013-06-20T10:03:43.703

3

The cleanest way to add the properties to the map would be (following on from your example):

for (String propName : properties.stringPropertyNames()) {
    map.put(propName, properties.getProperty(propName));
}

This works nicely in this particular case, because the Properties object is really a map containing String keys and values, as the getProperty method makes clear. It's only declared as Map<Object, Object> for horrible backwards-compatibility reasons.

By using the Properties-specific methods, rather than treating this as just a Map<Object, Object>, you can populate your Map<String, String> with perfect type-safety (rather than having to cast).

edited Jun 20 '13 at 10:03

answered Jun 20 '13 at 08:20

Andrzej Doyle

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I was curious about the reasons for Properties extending HashMap – JohnEye Nov 14 '13 at 13:05

score 3 · Answer 3 · answered Jun 20 '13 at 08:26

3

You can directly convert:

Properties properties = new Properties();
Map<String, String> map = new HashMap<String, String>((Map)properties);

answered Jun 20 '13 at 08:26

Tardis Xu

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score 1 · Answer 4 · answered Jun 20 '13 at 08:24

1

Because we know that the Properties are a String-to-String mapping already, it's save to do it with rawtype and unchecked conversion. Just leave a comment:

    Properties properties = new Properties();    
    properties.load(instream); 

    @SuppressWarnings({ "rawtypes", "unchecked" })
    // this is save because Properties have a String to String mapping
    Map<String, String> map = new HashMap(properties);

answered Jun 20 '13 at 08:24

Andreas Dolk

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Yes, but why create a new HashMap instance in the process? – dkateros Jun 20 '13 at 08:45
Because we can't *change* or *cast* an instance of Properties to the type `Map` because it implements the interface `Map – Andreas Dolk Jun 20 '13 at 08:48
Have a look at my answer above and the comments. – dkateros Jun 20 '13 at 08:50

score 1 · Answer 5 · answered May 07 '18 at 12:08

With Java 8 and the addition of Streams, I would suggest you to use the APIs Steam provides

Here, we assuming that each of the values actually are String objects, the cast to String should be safe:

Map<String,Object> map = new HashMap<>();

Map<String,String> stringifiedMapSafe = map.entrySet().stream()
     .collect(Collectors.toMap(Map.Entry::getKey, e -> (String)e.getValue()));

Now, in case we not sure that all the element are String, and we want to filter the key/values with null:

Map<String,Object> map = new HashMap<>();

Map<String,String> stringifiedMapNotSafe = map.entrySet().stream()
             .filter(m -> m.getKey() != null && m.getValue() !=null)
             .collect(Collectors.toMap(Map.Entry::getKey, e -> (String)e.getValue()));

score 0 · Answer 6 · answered Jun 20 '13 at 08:11

Map<String,String> getPropInMap(Properties prop){       
    Map<String, String> myMap = new HashMap<String, String>();
    for (Object key : prop .keySet()) {
        myMap.put(key.toString(), prop .get(key).toString());
    }       
    return myMap;
}

ovi · Answer 7 · 2017-08-07T17:07:47.163

0

Iterate over Map Object, take k v, make them string and put it to a Map String.

Map<Object,Object> map1; // with object k,v
Map<String, String> mapString = new HashMap<String, String>();
for (Object key : map1.keySet()) {
                String k = key.toString();
                String v = mmap1.get(key).toString();
                mapString.put(k, v);
            }

edited Aug 07 '17 at 17:07

answered Oct 20 '16 at 09:50

ovi

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How to convert Map to Map in java?

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