I currently have a Map<String, String>
that contains values in the form key = value
and I would like to "expand" those into a real object.
Is it possible to automate that with MapStruct and how would I do that?
To clarify: The code I would write by hand would look something like this:
public MyEntity mapToEntity(final Map<String, String> parameters) {
final MyEntity result = new MyEntity();
result.setNote(parameters.get("note"));
result.setDate(convertStringToDate(parameters.get("date")));
result.setCustomer(mapIdToCustomer(parameters.get("customerId")));
// ...
return result;
}
MapStruct is an open-source Java-based code generator which creates code for mapping implementations. It uses annotation-processing to generate mapper class implementations during compilation and greatly reduces the amount of boilerplate code which would regularly be written by hand.
Yes, it works on a Java 11 / Spring Boot 2 project at work, and we use Mapstruct without issues.
To do this, we use the MapStruct unmappedTargetPolicy to provide our desired behavior when there is no source field for the mapping: ERROR: any unmapped target property will fail the build – this can help us avoid accidentally unmapped fields. WARN: (default) warning messages during the build. IGNORE: no output or ...
In general, mapping collections with MapStruct works the same way as for simple types. Basically, we have to create a simple interface or abstract class, and declare the mapping methods. Based on our declarations, MapStruct will generate the mapping code automatically.
Method 1
The MapStruct repo gives us useful examples such as Mapping from map.
Mapping a bean from a java.util.Map would look something like :
@Mapper(uses = MappingUtil.class )
public interface SourceTargetMapper {
SourceTargetMapper MAPPER = Mappers.getMapper( SourceTargetMapper.class );
@Mappings({
@Mapping(source = "map", target = "ip", qualifiedBy = Ip.class),
@Mapping(source = "map", target = "server", qualifiedBy = Server.class),
})
Target toTarget(Source s);
}
Notice the use of the MappingUtil class to help MapStruct figuring out how to correctly extract values from the Map :
public class MappingUtil {
@Qualifier
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.SOURCE)
public @interface Ip {
}
@Qualifier
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.SOURCE)
public static @interface Server {
}
@Ip
public String ip(Map<String, Object> in) {
return (String) in.get("ip");
}
@Server
public String server(Map<String, Object> in) {
return (String) in.get("server");
}
}
Method 2
As per Raild comment on the issue related to this post, it is possible to use MapStruct expressions to achieve similar results in a shorter way :
@Mapping(expression = "java(parameters.get(\"name\"))", target = "name")
public MyEntity mapToEntity(final Map<String, String> parameters);
No note on performance though and type conversion may be trickier this way but for a simple string to string mapping, it does look cleaner.
Since version 1.5.0.Beta1 (Jul 2021) MapStruct supports mapping from Map to POJO.
Example:
@Mapper
public interface CustomerMapper {
@Mapping(target = "name", source = "customerName")
Customer toCustomer(Map<String, String> map);
}
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With