# Custom 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 %}

Custom Type Handler allow taking control over the storing and loading procedure of specific java types. This is useful to optimize the performance for storing complex objects or in the rare case that it is not possible to store a type with the default type handlers.

### Implementation

Suitable base class to start the implementation of a custom type handler for the Microstream standard binary storage implementation are:

`one.microstream.persistence.binary.internal.AbstractBinaryHandlerCustomValue`\
for simpler custom type handling in case only value have to be stored\
or\
`one.microstream.persistence.binary.internal.AbstractBinaryHandlerCustom`  \
if the object own references that have to be persisted too.

{% hint style="info" %}
[Example on GitHub](https://github.com/microstream-one/examples/tree/2.1/customTypeHandler)

This example implements a custom type handler for the java.awt.image.BufferedImage class. Instead of storing the rather complex object structure of that class the image is serialized as png image format using javax.imageio.ImageIO into an byte array. This byte array is stored by microstream.
{% endhint %}

### Setup

The custom type handler must be registered in the CustomTypeHandlerRegistry to enable it:

```java
mbeddedStorageManager storage = EmbeddedStorage
     .Foundation(WORKINGDIR)
     .onConnectionFoundation(f->
          f.registerCustomTypeHandlers(new CustomBufferedImageHandler()))
     .start(ROOT);
```


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