Unmarshal blank strings to null with BeanIO

Question

BeanIO reference guide states that for a fixed-length stream:

if required is set to false, spaces are unmarshalled to a null field value regardless of the padding character.

So if I understand this sentence correctly, it means that the test below should pass for this pojo:

@Record
public class Pojo {

    @Field(length = 5, required = false)
    String field;

    // constructor, getters, setters
}

The test:

@Test
public void test(){

    StreamFactory factory = StreamFactory.newInstance();
    factory.define(new StreamBuilder("pojo")
    .format("fixedlength")
    .addRecord(Pojo.class));

    Unmarshaller unmarshaller = factory.createUnmarshaller("pojo");

    Pojo pojo = (Pojo) unmarshaller.unmarshal("     "); // 5 spaces
    assertNull(pojo.field);

}

But it fails, the 5 spaces are unmarshalled as an empty string. What am I missing? How can I unmarshal spaces to a null String?

Answer 1

In the end, I managed this problem with the use of a type handler based on StringTypeHandler:

@Test
public void test(){

    StringTypeHandler nullableStringTypeHandler = new StringTypeHandler();
    nullableStringTypeHandler.setNullIfEmpty(true);
    nullableStringTypeHandler.setTrim(true);

    StreamFactory factory = StreamFactory.newInstance();
    factory.define(new StreamBuilder("pojo")
        .format("fixedlength")
        .addRecord(Pojo.class)
        .addTypeHandler(String.class, nullableStringTypeHandler)
    );


    Unmarshaller unmarshaller = factory.createUnmarshaller("pojo");

    Pojo pojo = (Pojo) unmarshaller.unmarshal("     ");
    assertNull(pojo.field);

}

Update: As a user on the beanio-users group suggested, one could also use trim=true, lazy=true on the @Field annotation:

    @Field(length = 5, trim = true, lazy = true) 
    String field;