java - 如何在Java中合并两个复杂的对象

我有两个Java对象，我想将它们合并为一个对象。问题是这两个对象不包含普通的原始类型属性(字段)，而它们包含复杂的类型属性(例如其他类型的对象和其他类型的对象列表)。

对象1:通过设置一些属性(字段)返回

对象2:通过设置一些属性(字段)返回，或者它可以返回其持有但类型不为对象1返回的新对象。

对象1和对象2属于同一类型。

结果对象3 = obj1属性+如果与obj1类型相同，则从obj 2更新属性+从obj2更新新对象

最佳答案

使用spring提供的org.springframework.beans.BeanUtils类非常容易做到。或Apache Commons BeanUtils library(我认为Springs版本基于或与之相同)。

public static <T> T combine2Objects(T a, T b) throws InstantiationException, IllegalAccessException {
    // would require a noargs constructor for the class, maybe you have a different way to create the result.
    T result = (T) a.getClass().newInstance();
    BeanUtils.copyProperties(a, result);
    BeanUtils.copyProperties(b, result);
    return result;
}

如果您不能或没有noargs构造函数，也许您只是传入结果

public static <T> T combine2Objects(T a, T b, T destination) {
    BeanUtils.copyProperties(a, destination);
    BeanUtils.copyProperties(b, destination);
    return destination;
}

如果您不希望复制空属性，则可以使用以下方法:

public static void nullAwareBeanCopy(Object dest, Object source) throws IllegalAccessException, InvocationTargetException {
    new BeanUtilsBean() {
        @Override
        public void copyProperty(Object dest, String name, Object value)
                throws IllegalAccessException, InvocationTargetException {
            if(value != null) {
                super.copyProperty(dest, name, value);
            }
        }
    }.copyProperties(dest, source);
}

嵌套对象解决方案

这里是一个更强大的解决方案。它支持嵌套对象复制，不再通过引用复制1级以上的对象，而是将克隆嵌套对象或单独复制其属性。

/**
 * Copies all properties from sources to destination, does not copy null values and any nested objects will attempted to be
 * either cloned or copied into the existing object. This is recursive. Should not cause any infinite recursion.
 * @param dest object to copy props into (will mutate)
 * @param sources
 * @param <T> dest
 * @return
 * @throws IllegalAccessException
 * @throws InvocationTargetException
 */
public static <T> T copyProperties(T dest, Object... sources) throws IllegalAccessException, InvocationTargetException {
    // to keep from any chance infinite recursion lets limit each object to 1 instance at a time in the stack
    final List<Object> lookingAt = new ArrayList<>();

    BeanUtilsBean recursiveBeanUtils = new BeanUtilsBean() {

        /**
         * Check if the class name is an internal one
         * @param name
         * @return
         */
        private boolean isInternal(String name) {
            return name.startsWith("java.") || name.startsWith("javax.")
                    || name.startsWith("com.sun.") || name.startsWith("javax.")
                    || name.startsWith("oracle.");
        }

        /**
         * Override to ensure that we dont end up in infinite recursion
         * @param dest
         * @param orig
         * @throws IllegalAccessException
         * @throws InvocationTargetException
         */
        @Override
        public void copyProperties(Object dest, Object orig) throws IllegalAccessException, InvocationTargetException {
            try {
                // if we have an object in our list, that means we hit some sort of recursion, stop here.
                if(lookingAt.stream().anyMatch(o->o == dest)) {
                    return; // recursion detected
                }
                lookingAt.add(dest);
                super.copyProperties(dest, orig);
            } finally {
                lookingAt.remove(dest);
            }
        }

        @Override
        public void copyProperty(Object dest, String name, Object value)
                throws IllegalAccessException, InvocationTargetException {
            // dont copy over null values
            if (value != null) {
                // attempt to check if the value is a pojo we can clone using nested calls
                if(!value.getClass().isPrimitive() && !value.getClass().isSynthetic() && !isInternal(value.getClass().getName())) {
                    try {
                        Object prop = super.getPropertyUtils().getProperty(dest, name);
                        // get current value, if its null then clone the value and set that to the value
                        if(prop == null) {
                            super.setProperty(dest, name, super.cloneBean(value));
                        } else {
                            // get the destination value and then recursively call
                            copyProperties(prop, value);
                        }
                    } catch (NoSuchMethodException e) {
                        return;
                    } catch (InstantiationException e) {
                        throw new RuntimeException("Nested property could not be cloned.", e);
                    }
                } else {
                    super.copyProperty(dest, name, value);
                }
            }
        }
    };


    for(Object source : sources) {
        recursiveBeanUtils.copyProperties(dest, source);
    }

    return dest;
}

它有点快速和肮脏，但效果很好。因为它确实使用了递归，并且存在无限递归的潜力，所以我确实避免了这种情况。