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How to merge two complex objects in java

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佛祖请我去吃肉
佛祖请我去吃肉 2021-01-01 23:23

I have two java objects and I want to merge them into single object. Problem is the two objects does not contain plain primitive type properties(fields) they contain complex

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  • 半阙折子戏
    半阙折子戏 (楼主)
    2021-01-02 00:05

    Its pretty easy to do using the org.springframework.beans.BeanUtils class provided by spring. Or the Apache Commons BeanUtils library which I believe Springs version is either based on or is the same as.

    public static  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;
}

    if you cant or dont have a noargs constructor maybe you just pass in the result

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

    If you dont want null properties being copied you can use something like this:

    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);
}

    Nested object solution

    Heres a bit more robust solution. It supports nested object copying, objects 1+ level deep will no longer be copied by reference, instead Nested objects will be cloned or their properties be copied individually.

    /**
 * 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  dest
 * @return
 * @throws IllegalAccessException
 * @throws InvocationTargetException
 */
public static  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 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;
}



    Its kinda quick and dirty but works well. Since it does use recursion and the potential is there for infinite recursion I did place in a safety against.
    
    
    
             
    
                                                        
    
            
            
    
              
                
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