Question

springframework.beans.BeanUtils is very useful to copy objects, and I use the “ignoreProperties” option frequently. However, sometimes I want to copy only specific objects (basically, the opposite of “ignore Properties”). Does anyone know how can I do that? Any help will be appreciated.

import org.springframework.beans.BeanUtils;

public class Sample {    
    public static void main(String[] args) {    
        DemoADto demoADto = new DemoADto();
        demoADto.setName("Name of Demo A");
        demoADto.setAddress("Address of Demo A");

        DemoBDto demoBDto = new DemoBDto();

        // This is "ignoreProperties" option
        // But I want to know how I can copy only name field by using BeanUtils or something.
        BeanUtils.copyProperties(demoADto, demoBDto, new String[] {"address"});

        System.out.println(demoBDto.getName());
        System.out.println(demoBDto.getAddress());    
    }    
}

public class DemoADto {    
    private String name;    
    private String address;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }    
}

public class DemoBDto {    
    private String name;    
    private String address;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }    
}

Answer 1

You can use the BeanWrapper technology. Here’s a sample implementation:

public static void copyProperties(Object src, Object trg, Iterable<String> props) {

    BeanWrapper srcWrap = PropertyAccessorFactory.forBeanPropertyAccess(src);
    BeanWrapper trgWrap = PropertyAccessorFactory.forBeanPropertyAccess(trg);

    props.forEach(p -> trgWrap.setPropertyValue(p, srcWrap.getPropertyValue(p)));

}

Or, if you really, really want to use BeanUtils, here’s a solution. Invert the logic, gather excludes by comparing the full property list with the includes:

public static void copyProperties2(Object src, Object trg, Set<String> props) {
    String[] excludedProperties = 
            Arrays.stream(BeanUtils.getPropertyDescriptors(src.getClass()))
                  .map(PropertyDescriptor::getName)
                  .filter(name -> !props.contains(name))
                  .toArray(String[]::new);

    BeanUtils.copyProperties(src, trg, excludedProperties);
}