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## How to map a map/hashtable of elements

Intended Audience
Prerequisites
Simple Maps
Basic concept
Mapping file
XML output
Nested Maps
References

## Intended Audience

Anyone who wants to map a Map/Hashtable of elements.

This document helps people to get familiar with the basic concepts of mapping and shows an example.

## Prerequisites

None.

## Simple Maps

### Basic concept

Assume you have two classes Items and Item, where an Items instance holds a Map/Hashtable of Item instances.

        public class Items {

            private Map itemlist;

            public Map getItemlist() {
                return itemlist;
            }

            public void setItemlist(Map itemlist) {
                this.itemlist = itemlist;
            }
        }

        public class Item {

            private String id;
            private String description;
            private String supplier;
            private String contact;

            public String getContact() {
                return contact;
            }
            public void setContact(String contact) {
                this.contact = contact;
            }
            public String getSupplier() {
                return supplier;
            }
            public void setSupplier(String supplier) {
                this.supplier = supplier;
            }
            public String getDescription() {
                return description;
            }
            public void setDescription(String description) {
                this.description = description;
            }
            public String getId() {
                return id;
            }
            public void setId(String id) {
                this.id = id;
            }
        }

As shown above, the Items instance has a field 'itemList' to hold a Map of `Item` instances.

### Mapping file

Here's the mapping file to instruct Castor XML about the relation of those two classes, `Items` and `Item` respectively:

        <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
        <mapping>
          <class name="nl.vodafone.castorbinding.demo.Items">
              <map-to xml="Items"/>
              <field name="Itemlist" collection="hashtable">
                  <bind-xml name="MyItem">
                      <class name="org.exolab.castor.mapping.MapItem">
                          <field name="key" type="java.lang.String">
                              <bind-xml name="id" node="attribute"/>
                          </field>
                          <field name="value" type="nl.vodafone.castorbinding.demo.Item">
                              <bind-xml name="Item"/>
                          </field>
                      </class>
                  </bind-xml>
              </field>
          </class>
          <class name="nl.vodafone.castorbinding.demo.Item">
              <map-to xml="Item"/>
              <field name="Id" type="java.lang.String">
                  <bind-xml name="id" node="element"/>
              </field>
              <field name="Description" type="java.lang.String">
                  <bind-xml name="description" node="element"/>
              </field>
              <field name="Supplier" type="java.lang.String">
                  <bind-xml name="supplier" node="element"/>
              </field>
              <field name="Contact" type="java.lang.String">
                  <bind-xml name="contact" node="element"/>
              </field>
          </class>
        </mapping>

Please note the use of the org.exolab.castor.mapping.MapItem definition within the <bind-xml> element in above mapping to map the elements contained in the Map/Hashtable.

### XML output

Using the Castor XML marshaller with the mapping file shown above, the XML generated by Castor XML might look as follows:

        <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
        <Items>
           <MyItem id="1">
              <Item>
                <id>1</id>
                <description>desc1</description>
                <supplier>supp1</supplier>
                <contact>cont1</contact>
              </Item>
           </MyItem>
           <MyItem id="2">
              <Item>
                 <id>2</id>
                 <description>desc2</description>
                 <supplier>supp2</supplier>
                 <contact>cont2</contact>
              </Item>
           </MyItem>
           <MyItem id="3">
              <Item>
                 <id>3</id>
                 <description>desc3</description>
                 <supplier>supp3</supplier>
                 <contact>cont3</contact>
              </Item>
           </MyItem>
        </Items>

## Nested Maps

It is equally possible to nest Collections/Arrays within Maps, incl. Maps within Maps. The following Java class has a member 'map' of type `java.util.Map`.

    public class MapOfArrays {

        private Map map;

        public Map getMap() {
            return this.map;
        }

        public void setMap(Map map) {
            this.map = map;
        }

    }

The following code shows how this `Map` instance is filled with `String` arrays before marshalling.

    this.map.put("key1", new String[] { "key1_value1", "key1_Value2" });
    this.map.put("key2", new String[] { "key2_value1", "key2_Value2" });

Based upon the following mapping file, ...

    <class name="MapOfArrays">
        <field name="map" collection="map">
            <bind-xml name="map">
                <class name="org.exolab.castor.mapping.MapItem">
                    <field name="key" type="java.lang.String">
                        <bind-xml name="string1" node="attribute" />
                    </field>
                    <field name="value" collection="array" type="java.lang.String">
                        <bind-xml name="nested" />
                    </field>
                </class>
            </bind-xml>
        </field>
    </class>

the following XML will be generated during marshalling.

    <?xml version="1.0" encoding="UTF-8"?>
    <map-of-arrays>
      <map string1="key1">
        <nested>key1_value1</nested>
        <nested>key1_Value2</nested>
      </map>
      <map string1="key2">
        <nested>key2_value1</nested>
        <nested>key2_Value2</nested>
      </map>
    </map-of-arrays>

## References

- | XML mapping

<notice> Copyright © 1999-2005 ExoLab Group, Intalio Inc., and Contributors. All rights reserved. </notice>
<notice> Java, EJB, JDBC, JNDI, JTA, Sun, Sun Microsystems are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and in other countries. XML, XML Schema, XSLT and related standards are trademarks or registered trademarks of MIT, INRIA, Keio or others, and a product of the World Wide Web Consortium. All other product names mentioned herein are trademarks of their respective owners. </notice>