Helper in order to copy non null properties from o

问题:

See the following class

public class Parent {

    private String name;
    private int age;
    private Date birthDate;

    // getters and setters   

}

Suppose i have created a parent object as follows

Parent parent = new Parent();

parent.setName("A meaningful name");
parent.setAge(20);

Notice according to code above birthDate property is null. Now i want to copy ONLY non null properties from parent object to another. Something like

SomeHelper.copyNonNullProperties(parent, anotherParent);

I need it because i want to update anotherParent object without overrides its non null with null values.

Do you know some helper like this one ?

I accept minimal code as answer whether no helper in mind

regards,

回答1:

I supose you already have a solution, since a lot of time has happened since you asked. However, it is not marked as solved, and maybe I can help other users.

Have you tried by defining a subclass of the BeanUtilsBean of the org.commons.beanutils package? Actually, BeanUtils uses this class, so this is an improvement of the solution proposed by dfa.

Checking at the source code of that class, I think you can overwrite the copyProperty method, by checking for null values and doing nothing if the value is null.

Something like this :

package foo.bar.copy;
import java.lang.reflect.InvocationTargetException;
import org.apache.commons.beanutils.BeanUtilsBean;

public class NullAwareBeanUtilsBean extends BeanUtilsBean{

    @Override
    public void copyProperty(Object dest, String name, Object value)
            throws IllegalAccessException, InvocationTargetException {
        if(value==null)return;
        super.copyProperty(dest, name, value);
    }

}

Then you can just instantiate a NullAwareBeanUtilsBean and use it to copy your beans, for example:

BeanUtilsBean notNull=new NullAwareBeanUtilsBean();
notNull.copyProperties(dest, orig);

回答2:

Using PropertyUtils (commons-beanutils)

for (Map.Entry<String, Object> e : PropertyUtils.describe(parent).entrySet()) {
         if (e.getValue() != null && !e.getKey().equals("class")) {
                PropertyUtils.setProperty(anotherParent, e.getKey(), e.getValue());
         }
}

in Java8:

    PropertyUtils.describe(parent).entrySet().stream()
        .filter(e -> e.getValue() != null)
        .filter(e -> ! e.getKey().equals("class"))
        .forEach(e -> {
        try {
            PropertyUtils.setProperty(anotherParent, e.getKey(), e.getValue());
        } catch (Exception e) {
            // Error setting property ...;
        }
    });

回答3:

Simply use your own copy method:

void copy(Object dest, Object source) throws IntrospectionException, IllegalArgumentException, IllegalAccessException,
        InvocationTargetException {
    BeanInfo beanInfo = Introspector.getBeanInfo(source.getClass());
    PropertyDescriptor[] pdList = beanInfo.getPropertyDescriptors();
    for (PropertyDescriptor pd : pdList) {
        Method writeMethod = null;
        Method readMethod = null;
        try {
            writeMethod = pd.getWriteMethod();
            readMethod = pd.getReadMethod();
        } catch (Exception e) {
        }

        if (readMethod == null || writeMethod == null) {
            continue;
        }

        Object val = readMethod.invoke(source);
        writeMethod.invoke(dest, val);
    }
}

回答4:

If your setter's return type is not void, BeanUtils of Apache will not work, spring can. So combine the two.

package cn.corpro.bdrest.util;

import org.apache.commons.beanutils.BeanUtilsBean;
import org.apache.commons.beanutils.ConvertUtilsBean;
import org.apache.commons.beanutils.PropertyUtilsBean;
import org.springframework.beans.BeanUtils;

import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;

/**
 * Author: [e-mail]
 * DateTime: 2016/10/20 10:17
 */
public class MyBeanUtils {

    public static void copyPropertiesNotNull(Object dest, Object orig) throws InvocationTargetException, IllegalAccessException {
        NullAwareBeanUtilsBean.getInstance().copyProperties(dest, orig);
    }

    private static class NullAwareBeanUtilsBean extends BeanUtilsBean {

        private static NullAwareBeanUtilsBean nullAwareBeanUtilsBean;

        NullAwareBeanUtilsBean() {
            super(new ConvertUtilsBean(), new PropertyUtilsBean() {
                @Override
                public PropertyDescriptor[] getPropertyDescriptors(Class<?> beanClass) {
                    return BeanUtils.getPropertyDescriptors(beanClass);
                }

                @Override
                public PropertyDescriptor getPropertyDescriptor(Object bean, String name) throws IllegalAccessException, InvocationTargetException, NoSuchMethodException {
                    return BeanUtils.getPropertyDescriptor(bean.getClass(), name);
                }
            });
        }

        public static NullAwareBeanUtilsBean getInstance() {
            if (nullAwareBeanUtilsBean == null) {
                nullAwareBeanUtilsBean = new NullAwareBeanUtilsBean();
            }
            return nullAwareBeanUtilsBean;
        }

        @Override
        public void copyProperty(Object bean, String name, Object value) throws IllegalAccessException, InvocationTargetException {
            if (value == null) return;
            super.copyProperty(bean, name, value);
        }
    }
}

回答5:

you can use Apache Common BeanUtils, more specifically the copyProperties helper in BeanUtils class:

 BeanUtils.copyProperties(parent, anotherParent);   

however why do you want copy only non-null properties? if a property in parent is null, by simply copying it you have null also in anotherParent right?

Just guessing... you want to update a bean with another bean?

回答6:

I know the fact that this question is pretty old, but I thought the below answer may be useful for someone.

If you use Spring, you may try the below option.

import java.beans.PropertyDescriptor;
import java.util.HashSet;
import java.util.Set;

import org.springframework.beans.BeanWrapper;
import org.springframework.beans.BeanWrapperImpl;

/**
 * Helper class to extract property names from an object.
 * 
 * @Threadsafe
 * 
 * @author arun.bc
 * 
 */
public class PropertyUtil {

    /**
     * Gets the properties which have null values from the given object.
     * 
     * @param - source object
     * 
     * @return - String array of property names.
     */
    public static String[] getNullPropertiesString(Object source) {
        Set<String> emptyNames = getNullProperties(source);
        String[] result = new String[emptyNames.size()];

        return emptyNames.toArray(result);
    }


    /**
     * Gets the properties which have null values from the given object.
     * 
     * @param - source object
     * 
     * @return - Set<String> of property names.
     */
    public static Set<String> getNullProperties(Object source) {
        final BeanWrapper src = new BeanWrapperImpl(source);
        PropertyDescriptor[] pds = src.getPropertyDescriptors();

        Set<String> emptyNames = new HashSet<String>();
        for (PropertyDescriptor pd : pds) {
            Object srcValue = src.getPropertyValue(pd.getName());
            if (srcValue == null)
                emptyNames.add(pd.getName());
        }
        return emptyNames;
    }

    /**
     * Gets the properties which are not null from the given object.
     * 
     * @param - source object
     * 
     * @return - Set<String> array of property names.
     */
    public static Set<String> getNotNullProperties(Object source) {
        final BeanWrapper src = new BeanWrapperImpl(source);
        PropertyDescriptor[] pds = src.getPropertyDescriptors();

        Set<String> names = new HashSet<String>();
        for (PropertyDescriptor pd : pds) {
            Object srcValue = src.getPropertyValue(pd.getName());
            if (srcValue != null)
                names.add(pd.getName());
        }

        return names;
    }
}

Again you may use PropertyDescriptor and the Set from the above methods to modify the object.