Type Handler

Type handlers are applied to entity class fields for assignment and conversion.

Note

• For example, if the field type is InputStream, the content needs to be converted to byte[] for storage, and when querying, the Binary class returned by MongoDB should be converted back to InputStream.
• Type handlers have higher priority than converters and mappers because TypeHandler operates at the field level.
• When using a type handler on an entity class, you need to implement two methods of the type handler. If it returns null, MongoPlus processing continues; otherwise, the data returned by the type handler's methods is used directly.
• Pass the type handler through the typeHandler property of the CollectionField annotation on the entity class field, e.g., @CollectionField(typeHandler = InputStreamTypeHandler.class).

com.mongoplus.handlers.TypeHandler

• This interface defines a type handler. All type handlers should implement this interface and its methods.
• setParameter: Sets the value.
• getResult: Retrieves the result.

Example

First, implement the TypeHandler interface in your type handler class and set the generic type to the field type. Pass it via the typeHandler property of the CollectionField annotation.

// Example using InputStream
public class InputStreamHandler implements TypeHandler<InputStream> {}

Next, implement the mapping methods of the TypeHandler interface to define the mapping strategy.

public class InputStreamHandler implements TypeHandler<InputStream> {

    @Override
    public Object setParameter(String fieldName, InputStream obj) {
        try(ByteArrayOutputStream bos = new ByteArrayOutputStream()){
            byte[] b = new byte[1024];
            int len;
            while ((len = obj.read(b)) != -1) {
                bos.write(b, 0, len);
            }
            // Convert InputStream to byte[] and return
            return bos.toByteArray();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public InputStream getResult(Object obj) {
        // After setParameter, the retrieved data will be of type Binary
        // Cast to Binary, get byte[], then convert to InputStream
        return new ByteArrayInputStream(((Binary)obj).getData());
    }
}

Finally, apply it in the entity class.

@CollectionName(value = "user")
public class User {

    @ID(type = IdTypeEnum.ASSIGN_ID)
    private String userId;

    @CollectionField(typeHandler = InputStreamHandler.class) // Set the typeHandler property and pass in our custom type handler
    private InputStream file;

}