Adding Custom Converter to ProxyProjectionFactory for Interface-based Projections

In this article, we will learn how to add a custom converter to the ProxyProjectionFactory for interface-based projections. This is an advanced feature that allows you to customize the way your data is projected and mapped in your application. But don't worry, we will take it step by step and make it easy to understand for entry level users.

What is a Projection?

In the context of data mapping and projection, a projection is a simplified representation of an entity or a collection of entities. Projections are used to reduce the amount of data that needs to be transferred between the database and the application, improving the performance and scalability of your application.

What is a ProxyProjectionFactory?

The ProxyProjectionFactory is a class in the MapStruct library that is used to create proxy-based projections for your entities. A proxy-based projection is a dynamic representation of an entity that is created at runtime, allowing you to customize the way your data is projected and mapped without the need to create separate classes for each projection.

Why would you need a Custom Converter?

There are many cases where the default mapping and projection capabilities of MapStruct are not sufficient for your needs. For example, you might need to convert a date or a number in a specific way, or you might need to perform some custom logic before mapping the data. In these cases, you can use a custom converter to extend the mapping and projection capabilities of MapStruct.

How to add a Custom Converter to ProxyProjectionFactory?

To add a custom converter to the ProxyProjectionFactory, you need to follow these steps:

1. Create a new class that implements the org.mapstruct.ap.spi.Converter interface.
2. Define the input and output types of your converter.
3. Implement the convert method to perform the conversion logic.
4. Register your converter with the ProxyProjectionFactory using the addConverter method.

Step 1: Create a new Converter class

The first step is to create a new class that implements the Converter interface. This interface defines a single method, convert, that you need to implement to perform the conversion logic. Here is an example of a custom converter that converts a String to an Integer:

@Component
public class StringToIntegerConverter implements Converter<String, Integer> {

    @Override
    public Integer convert(String source) {
        return Integer.parseInt(source);
    }
}

Step 2: Define the input and output types

The next step is to define the input and output types of your converter. In our example, the input type is String and the output type is Integer. You can define the types using generics, as shown in the previous example.

Step 3: Implement the convert method

The convert method is where you implement the conversion logic. In our example, the conversion logic is to parse the String to an Integer using the Integer.parseInt method. Here is the complete implementation of our custom converter:

@Component
public class StringToIntegerConverter implements Converter<String, Integer> {

    @Override
    public Integer convert(String source) {
        return Integer.parseInt(source);
    }
}

Step 4: Register the converter with ProxyProjectionFactory

The final step is to register your custom converter with the ProxyProjectionFactory. You can do this using the addConverter method. Here is an example of how to register the StringToIntegerConverter with the ProxyProjectionFactory:

ProxyProjectionFactory factory = new ProxyProjectionFactory();
factory.addConverter(new StringToIntegerConverter());

In this article, we have learned how to add a custom converter to the ProxyProjectionFactory for interface-based projections. This is an advanced feature that allows you to customize the way your data is projected and mapped in your application. By following the steps in this article, you can easily create your own custom converters and extend the mapping and projection capabilities of MapStruct.

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