Check empty Strings while mapping to LocalDateTime

[karl....@googlemail.com]

Hi,

i am really impressed by mapstruct but i am facing a pretty simple mapping problem and dont know how to solve it. I hope you can help me.
I am working with Java 8 and MapStruct 1.1.0.Final

Here is my mapping from String to LocalDateTime:

@Mapping(target = "localDateTime", source = "dateString", dateFormat = "yyyy-MM-dd:HH:mm")
Target toTarget(Source src);

Unfortunately the source dateString can be an empty string and i dont know how to force mapstruct to not only check for null but for empty string either.


I hope you have a good hint for me.

[Gunnar Morling]

Hi Karl,

It'd probably make sense to have some kind of global option for
controlling how to deal with empty strings.

But for the time being you could try it like this:

public interface MyMapper {

@Mapping(
target = "localDateTime",
expression = "java(emptyToNull(src.getDateString()))",

dateFormat = "yyyy-MM-dd:HH:mm"
)
Target toTarget(Source src);

default String emptyToNull(String s) {
return s == null || s.isEmpty() ? null : s;
}
}

I.e. feed the input property through some property which converts
empty strings to null before applying the mapping.

--Gunnar



2017-03-02 11:25 GMT+01:00 karl.w.roth via mapstruct-users
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[karl....@googlemail.com]

Hi Gunnar,

thanks for the reply.
Your suggestion does not compile:
Here is my code:

@Mapper
public interface SourceTargetMapper {

    SourceTargetMapper INSTANCE = Mappers.getMapper(SourceTargetMapper.class);

    @Mapping(target = "localDateTime", expression = "java(emptyToNull(src.getDateString()))", dateFormat = "yyyy-MM-dd:HH:mm")
    Target toTarget(Source src);

    default String emptyToNull(String s) {

        return s == null || s.isEmpty() ? null : s;
    }
}

Unfortunately the generated Code does not do the conversion:
  

public class SourceTargetMapperImpl implements SourceTargetMapper {
 @Override

    public Target toTarget(Source src) {

        if ( src == null ) {

            return null;
        }

        Target target = new Target();

// no conversion here!
        target.setLocalDateTime( emptyToNull(src.getDateString()) );

        return target;
    }
}

But i picked up the idea and did it this way:

@Mapper
public interface SourceTargetMapper {

    SourceTargetMapper INSTANCE = Mappers.getMapper(SourceTargetMapper.class);

    @Mapping(target = "localDateTime", expression = "java(emptyToNull(src.getDateString()))")
    Target toTarget(Source src);

    default LocalDateTime emptyToNull(String s) {
        if (s == null || s.isEmpty()) return null;
        return LocalDateTime.parse(s, DateTimeFormatter.ofPattern("yyyy-MM-dd:HH:mm"));
    }
}

It works but i am not sure if this is what you meant.

[Gunnar Morling]

Ah yes, of course. I believed the expression value would be subject to
conversion, but it actually isn't.

Your last snippet looks good, you can omit the expression() altogether
though. If there is a custom method for mapping String to LocalDate
Time it will take precedence over the built-in conversion routine and
automatically invoked in the generated code.

--Gunnar

2017-03-02 13:01 GMT+01:00 karl.w.roth via mapstruct-users
<mapstru...@googlegroups.com>:

[karl....@googlemail.com]

Thanks Gunnar,

just to finish this issue.
This is what you are talking about:

@Mapping(target = "localDateTime", source = "dateString")
    abstract Target toTarget(Source src);

    LocalDateTime emptyToNull(String s) {
        if (s == null || s.isEmpty()) return null;
        return LocalDateTime.parse(s, DateTimeFormatter.ofPattern("yyyy-MM-dd:HH:mm"));
    }

 Its pretty much the same but alot more straight forward. And it works ;)

Am Donnerstag, 2. März 2017 11:25:47 UTC+1 schrieb karl....@googlemail.com: