> For the complete documentation index, see [llms.txt](https://manual.docs.microstream.one/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://manual.docs.microstream.one/2.2/data-store/customizing/custom-legacy-type-handler.md).

# Custom Legacy Type Handler

{% hint style="warning" %}
**This is the manual for older MicroStream versions (Version < 5.0).**

**The new documentation (Version >= 5.0) is located at:**

[https://docs.microstream.one/](https://docs.microstream.one/manual)
{% endhint %}

In addition to the methods for legacy type mapping described in chapter [Legacy Type Mapping](/2.2/data-store/legacy-type-mapping.md) there is also the possibility to implement custom legacy type handlers. Those handlers are the most flexible way to do the mapping from old to new types.

The basic interface that has to be implemented is `one.microstream.persistence.types.PersistenceLegacyTypeHandler.`

Fortunately the standard persistence implementation provides the abstract class `one.microstream.persistence.binary.types.BinaryLegacyTypeHandler.AbstractCustom` that should be sufficient to start with a custom implementation in most cases.

{% hint style="info" %}
See the example **customLegacyTypeHandler** on [GitHub](https://github.com/microstream-one/examples/tree/2.2/customLegacyTypeHandler)
{% endhint %}

{% hint style="info" %}
Please note the this example requires manual code modifications as described in it's main class.
{% endhint %}


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