How to copy properties from one Java bean to another?

Question

I have a simple Java POJO that I would copy properties to another instance of same POJO class.

I know I can do that with BeanUtils.copyProperties() but I would like

Answer 1

I had the same problem when developing an app for Google App Engine, where I couldn't use BeanUtils due to commons Logging restrictions. Anyway, I came up with this solution and worked just fine for me.

public static void copyProperties(Object fromObj, Object toObj) {
    Class<? extends Object> fromClass = fromObj.getClass();
    Class<? extends Object> toClass = toObj.getClass();

    try {
        BeanInfo fromBean = Introspector.getBeanInfo(fromClass);
        BeanInfo toBean = Introspector.getBeanInfo(toClass);

        PropertyDescriptor[] toPd = toBean.getPropertyDescriptors();
        List<PropertyDescriptor> fromPd = Arrays.asList(fromBean
                .getPropertyDescriptors());

        for (PropertyDescriptor propertyDescriptor : toPd) {
            propertyDescriptor.getDisplayName();
            PropertyDescriptor pd = fromPd.get(fromPd
                    .indexOf(propertyDescriptor));
            if (pd.getDisplayName().equals(
                    propertyDescriptor.getDisplayName())
                    && !pd.getDisplayName().equals("class")) {
                 if(propertyDescriptor.getWriteMethod() != null)                
                         propertyDescriptor.getWriteMethod().invoke(toObj, pd.getReadMethod().invoke(fromObj, null));
            }

        }
    } catch (IntrospectionException e) {
        e.printStackTrace();
    } catch (IllegalArgumentException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    }
}

Any enhancements or recomendations are really welcome.

Answer 2

There is no simple way to do it. Introspector and the Java beans libraries are monolithic - BeanUtils is a simple wrapper around this and works well. Not having libraries just to not have libraries is a bad idea in general - there's a reason it's commons to begin with - common functionality that should exist with Java, but doesn't.

Answer 3

Have a look at the JavaBeans API, in particular the Introspector class. You can use the BeanInfo metadata to get and set properties. It is a good idea to read up on the JavaBeans specification if you haven't already. It also helps to have a passing familiarity with the reflection API.

Answer 4

Another alternative is MapStruct which generates mapping code at build time, resulting in type-safe mappings which don't require any dependencies at runtime (Disclaimer: I'm the author of MapStruct).

Answer 5

You can achieve it using Java Reflection API.

public static <T> void copy(T target, T source) throws Exception {
    Class<?> clazz = source.getClass();

    for (Field field : clazz.getDeclaredFields()) {
        if (Modifier.isPrivate(field.getModifiers()))
            field.setAccessible(true);
        Object value = field.get(source);
        field.set(target, value);
    }
}

Answer 6

I guess if you look at the source code of BeanUtils, it will show you how to do this without actually using BeanUtils.

If you simply want to create a copy of a POJO (not quite the same thing as copying the properties from one POJO to another), you could change the source bean to implement the clone() method and the Cloneable interface.