使用BeanUtils或类似方法将非空属性从一个对象复制到另一个对象 [英] Copy non-null properties from one object to another using BeanUtils or similar

问题描述

我的目标是将一个对象的字段复制到另一个对象中，但只复制那些不为null的字段.我不想明确分配它.更为通用的解决方案将非常有用且易于维护，例如，在REST API中实现PATCH时，您只允许提供特定的字段即可.

my aim is to copy fields of one object into another, but only those that aren't null. I don't want to assign it explicitly. A more generic solution would be very useful and easier to maintain i.e. for implementing PATCH in REST API where you allow providing only specific fields.

我看到了类似的线程，我正在尝试从此处实施一些想法:

I saw this similar thread and I'm trying to implement some of the ideas from here: Helper in order to copy non null properties from object to another ? (Java)

但是程序执行后，对象没有任何改变.

But the objects aren't altered in any way after the program execution.

这是我创建的示例类，例如:

So here are my example classes created for example:

class Person {
    String name;
    int age;
    Pet friend;

    public Person() {
    }

    public Person(String name, int age, Pet friend) {
        this.name = name;
        this.age = age;
        this.friend = friend;
    }

    // getters and setters here
}

class Pet {
    String name;
    int age;

    public Pet(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // getters and setters here
}

这是我覆盖的copyProperty方法:

Here is my overridden copyProperty method:

import org.apache.commons.beanutils.BeanUtilsBean;
import java.lang.reflect.InvocationTargetException;

public class MyBeansUtil extends BeanUtilsBean {

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

...，这是我要在一些示例上对其进行测试的地方:

... and here is the place I'm trying to test it on some examples:

public class SandBox {
    public static void main(String[] args) {
        Person db = new Person("John", 36, new Pet("Lucy", 3));
        Person db2 = new Person("John", 36, new Pet("Lucy", 2));
        Person db3 = new Person("John", 36, new Pet("Lucy", 4));

        Person in = new Person();
        in.age = 17;
        in.name = "Paul";
        in.friend = new Pet(null, 35);

        Person in2 = new Person();
        in2.name = "Damian";

        Person in3 = new Person();
        in3.friend = new Pet("Lup", 25);

        try {
            BeanUtilsBean notNull  =new MyBeansUtil();
            notNull.copyProperties(db, in);
            notNull.copyProperties(db2, in2);
            notNull.copyProperties(db3, in3);

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

不幸的是，原始对象db，db1，db2保持不变.我在这里做错什么了吗?

Unfortunately, the original objects db, db1, db2 stay the same as they were. Am I doing something wrong here?

推荐答案

我最终使用了Spring BeanUtils库.这是我的工作方法:

I ended up using Spring BeanUtils library. Here is my working method:

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

import java.lang.reflect.Field;
import java.util.Collection;

public class MyBeansUtil<T> {
    public T copyNonNullProperties(T target, T in) {
        if (in == null || target == null || target.getClass() != in.getClass()) return null;

        final BeanWrapper src = new BeanWrapperImpl(in);
        final BeanWrapper trg = new BeanWrapperImpl(target);

        for (final Field property : target.getClass().getDeclaredFields()) {
            Object providedObject = src.getPropertyValue(property.getName());
            if (providedObject != null && !(providedObject instanceof Collection<?>)) {
                trg.setPropertyValue(
                        property.getName(),
                        providedObject);
            }
        }
        return target;
    }
}

它工作正常，但是请注意，它会忽略属于集合的字段.那是故意的，我分开处理.

It works fine, but notice that it ignores fields that are collections. That's on purpose, I handle them separately.

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