How to merge two maps in a single map

Question

i have two maps existing. i want to merge both the maps into a single map through coding. do we have any function which can solve this problem. If not then please provide me some suggestions to solve this problem.
thanks,
amit

Answer 1

Amit,
I did this once using the HashMapUtils found in the apache myfaces code...
package se.inserve.util;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.Iterator;
public class HashMapUtils
    //~ Constructors -------------------------------------------------------------------------------
    protected HashMapUtils()
        // block public access
    //~ Methods ------------------------------------------------------------------------------------
     * Calculates initial capacity needed to hold <code>size</code> elements in
     * a HashMap or Hashtable without forcing an expensive increase in internal
     * capacity. Capacity is based on the default load factor of .75.
     * <p>
     * Usage: <code>Map map = new HashMap(HashMapUtils.calcCapacity(10));<code>
     * </p>
     * @param size the number of items that will be put into a HashMap
     * @return initial capacity needed
    public static final int calcCapacity(int size)
        return ((size * 4) + 3) / 3;
     * Creates a new <code>HashMap</code> that has all of the elements
     * of <code>map1</code> and <code>map2</code> (on key collision, the latter
     * override the former).
     * @param map1 the fist hashmap to merge
     * @param map2 the second hashmap to merge
     * @return new hashmap
    public static HashMap merge(Map map1, Map map2)
        HashMap retval = new HashMap(calcCapacity(map1.size() + map2.size()));
        retval.putAll(map1);
        retval.putAll(map2);
        return retval;
     * spit out each name/value pair
    public static String mapToString(Map map){
        Set entries = map.entrySet();
        Iterator iter = entries.iterator();
        StringBuffer buff = new StringBuffer();
        while (iter.hasNext())
            Map.Entry entry = (Map.Entry) iter.next();
            buff.append("[" + entry.getKey() + "," + entry.getValue() + "]\n");
        return buff.toString();
}Then then just calling the methods from within a rule in XPRESS.
<Rule name='Inserve - mergeHashMap'>
  <RuleArgument name='map1'/>
  <RuleArgument name='map2'/>
  <block>
    <set name='map1'>
      <map>
        <s>A</s>
        <s>1</s>
        <s>B</s>
        <s>2</s>
      </map>
    </set>
    <set name='map2'>
      <map>
        <s>C</s>
        <s>3</s>
        <s>D</s>
        <s>4</s>
      </map>
    </set>
    <invoke name='merge' class='se.inserve.util.HashMapUtils'>
      <ref>map1</ref>
      <ref>map2</ref>
    </invoke>
  </block>
  <MemberObjectGroups>
    <ObjectRef type='ObjectGroup' id='#ID#Top' name='Top'/>
  </MemberObjectGroups>
</Rule>This gives the output:
<Map>
  <MapEntry key='A' value='1'/>
  <MapEntry key='B' value='2'/>
  <MapEntry key='C' value='3'/>
  <MapEntry key='D' value='4'/>
</Map>I typically create a jar-file with my custom classes which i place in $WSHOME/WEB-INF/lib.
Good luck and hope this helps. Im sure there are better ways to do this, but this did the trick for me.
/Anders