Hi everyone , recently I came accross a usecase where I had to map multiple keys against one value. So Juggling with this I came to know about MultiKeyMap of apache.<\/p>\n
MultikeyMap is used to map multiple keys against one value . The purpose of this class is to avoid the need to write code to handle maps of maps. It simply implements java.io.Serializable, java.util.Map and IterableMap.<\/p>\n
These provide get(), containsKey(), put() and remove() methods for individual keys which operate without extra object creation.This map is implemented as a decorator of a AbstractHashedMap which enables extra behaviour to be added easily.<\/p>\n
[java]
\nimport org.apache.commons.collections.map.MultiKeyMap<\/p>\n
MultiKeyMap.decorate(new LinkedMap()) \/\/creates an ordered map
\nMultiKeyMap.decorate(new LRUMap()) \/\/creates an least recently used map.
\nMultiKeyMap.decorate(new ReferenceMap()) \/\/creates a garbage collector sensitive map.
\n[\/java]<\/p>\n
Lets take an example for this:-<\/p>\n
[java]<\/p>\n
MultiKeyMap multiKeyMap=MultiKeyMap.decorate(new LinkedHahMap())<\/p>\n
multiKeyMap.put("key1","key2","key3","value1") \/\/ Last parameter is value against defined keys.
\nmultiKeyMap.put("key11","key22","key33","key44","value11")
\nmultiKeyMap.put("key111","key222","key333","value111")
\nmultiKeyMap.put("key1111","key2222","value1111")<\/p>\n
[\/java]<\/p>\n
This is how we create a map with multiple keys. Now let’s see how to fetch value out of multiKeyMap for one combination of keys.<\/p>\n
PS :- One point to note is you have to provide combination of key in the same sequence that you provided while puting into map.<\/p>\n
[java]
\nString value1 = multiKeyMap.get("key1","key2","key3")
\nString value2 = multiKeyMap.get("key11","key22","key33","key44")
\n[\/java]<\/p>\n
During this learning I came to know about MultiKey which is again an another way to solve above use case.A MultiKey allows multiple map keys to be merged together. Example of MultiKeyMap With MultiKey :-<\/p>\n
[java]
\nimport org.apache.commons.collections.keyvalue.MultiKey<\/p>\n
MultiKey multiKey=new MultiKey("key1","key2","key3")
\nMultikeyMap multiKeyMap=MultiKeyMap.decorator(new LinkedHashMap())<\/p>\n
\/\/Map map = new HashMap(); you can also use simple Map while using Multikey.
\nmultiKeyMap.put(multiKey,"value1")<\/p>\n
\/\/To fetch value from map using multikey, we simply do as follows :-
\nmultiKeyMap.get(multiKey)
\n[\/java]<\/p>\n
You can also access each key using index of key within MultiKey object. For Example :-<\/p>\n
[java]
\nmultikey.getKey(0) \/\/ output is ‘key1’
\n[\/java]<\/p>\n
I hope this blog was helpful and added useful content to your knowledge. For any queries you can comment below.<\/p>\n","protected":false},"excerpt":{"rendered":"
Hi everyone , recently I came accross a usecase where I had to map multiple keys against one value. So Juggling with this I came to know about MultiKeyMap of apache. MultikeyMap is used to map multiple keys against one value . The purpose of this class is to avoid the need to write code […]<\/p>\n","protected":false},"author":72,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"iawp_total_views":68,"footnotes":""},"categories":[7,446],"tags":[1729],"class_list":["post-18699","post","type-post","status-publish","format-standard","hentry","category-grails","category-java","tag-grails-java-maps-multikeymap-nestedmap"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t