The Data Library Customizer tool provides a way to customize ICU's data library. There are two common scenarios to use this tool. You can remove data, and you can add data that is not in ICU by default. Once you have customized the data library, you may have to rebuild ICU, but under certain configurations, you will be able to use the generated data library directly. These instructions will help you to use this tool.
The data that comes from this tool will only work with a specific version of ICU. The data is compatible with the version of ICU with the same major and minor mentioned on the main Data Library Customizer page. This data will not work with any other version of ICU. When a new version of ICU is released, older versions of the data may not be available any more.
If you are using ICU in a memory constrained environment, you can use this tool to remove some data. For most people, only the groups need to be selected for removal. This is the easiest way to remove large chunks of data you may not be using. For example, if you only need Unicode based collation, you can deselect all the groups except the collation group. This will bring the data library down to a fraction of the original size.
ICU comes with a large set of data that meets the needs for the vast majority of ICU users. Under some circumstances, additional data is needed. For example, this tool provides some additional charset conversion tables that are not available under the default distribution of ICU. When you expand the "Charset Mapping Tables" group, you will see a set of mapping tables that are available for addition or removal. All items checked will be included in your customized data library. You can sort the description column, and related data items will usually sort together.
Before adding more charset mapping tables to ICU, you should consider using Unicode with your application instead. Many of these mapping tables are only needed for interacting with legacy systems that have not been upgraded to use Unicode yet. These mapping tables are not needed to support additional languages or countries. If there is a mapping table for the charset you need, then Unicode will support all the characters you need.
Sometimes fine grained customization is needed to add or remove a large number of specific data items. Instead of selecting many data items by hand, you can use the "Advanced Options" at the bottom of the page. You can expand all the groups or contract all the groups. You can also filter all the data items in the data library.
When you perform a filter operation with a regular expression, only those items will be visible under each group. Expanding all the groups will show you everything that has been filtered. The "Select All" and "Deselect All" buttons can be used to use to select or deselect the filtered items. When the filtering field is left blank, and the "Filter Items" button is pressed, all selectable items become visible for selection again.
For example, if you enter the expression mt.*res and click "Filter Items", the customizer will SHOW only the Maltese related items. If you click "Deselect All" next to the expression, it will deselect only those items, and clicking "Select All" will select those items, all without altering any items not matching the expression.
After the data library package has been downloaded there are two common ways to use the new package.
There are other ways to configure ICU's data, and many of those options are described in the Data Management chapter of the ICU User's Guide. For example, the icupkg tool that comes with ICU4C can help with managing the data on an end user's system, but your options may be limited if ICU is only set up to use its data from a shared or static library.
As of ICU4J 3.8, there is only one normal way to modify ICU4J's data. Place the icudata.jar into src/com/ibm/icu/impl/data in your copy of ICU4J's source code and rebuild ICU4J.
There are other ways to modify an existing ICU4J's data in a jar file, but it's not trivial to perform this update. It's usually easier to just rebuild ICU4J.