我有两个java对象，我想将它们合并到单个对象中。问题是两个对象不包含普通原始类型属性（字段），它们包含复杂类型属性（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）和
返回对象2：通过设置一些属性（字段）返回，或者它可以返回它所拥有但不被对象1返回的类型的新对象。
对象1和对象2都属于同一类型。
结果对象3 = obj1属性+如果类型与obj1相同，则更新obj 2中的属性+来自obj2的新更新对象
答案 0 :(得分：19)
使用spring提供的org.springframework.beans.BeanUtils类非常容易。或者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;
}
如果你不能或没有noargs构造函数，也许你只需传递结果
public static <T> T combine2Objects(T a, T b, T destination) {
BeanUtils.copyProperties(a, destination);
BeanUtils.copyProperties(b, destination);
return destination;
}
如果您不想复制null属性，可以使用以下内容：
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+级别的对象，而是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;
}
它快速而又脏，但效果很好。因为它确实使用了递归，并且潜在的是无限递归，所以我确实将其置于安全状态。
答案 1 :(得分：2)
尝试使用class.getFields
Field[] fields = YourClass.getFields();
for (Field field : fields) {
// get value
YourObject value = field.get(objectInstance);
// check the values are different, then update
field.set(objetInstance, value);
}
答案 2 :(得分：1)
下面的方法将忽略serialVersionUID，遍历所有字段，如果对象b中的null为null，则复制对象a->对象b中的非null值。换句话说，如果b中的任何字段为null，则从a中获取它，如果不为null。
public static <T> T combine2Objects(T a, T b) throws InstantiationException,IllegalAccessException{
T result = (T) a.getClass().newInstance();
Object[] fields = Arrays.stream(a.getClass().getDeclaredFields()).filter(f -> !f.getName().equals("serialVersionUID")).collect(Collectors.toList()).toArray();
for (Object fieldobj : fields) {
Field field = (Field) fieldobj;
field.set(result, field.get(b) != null ? field.get(b) : field.get(a));
}
return result;
}
答案 3 :(得分：1)
尝试
public <T> T objectMerge(T local, T remote, boolean toappend) throws Exception {
Class<?> clazz = local.getClass();
Object merged = clazz.newInstance();
for (Field field : clazz.getDeclaredFields()) {
field.setAccessible(true);
Object localValue = field.get(local);
Object remoteValue = field.get(remote);
if (localValue != null) {
String key = "";
if (localValue.getClass().getSimpleName().toLowerCase().contains("map")) {
key = "map";
} else if (localValue.getClass().getSimpleName().toLowerCase().contains("set")) {
key = "set";
} else if (localValue.getClass().getSimpleName().toLowerCase().contains("list")) {
key = "list";
} else {
key = localValue.getClass().getSimpleName();
}
switch (key) {
case "Default":
case "Detail":
case "String":
case "Date":
case "Integer":
case "Float":
case "Long":
case "Double":
case "Object":
field.set(merged, (remoteValue != null) ? remoteValue : localValue);
break;
case "map":
if (toappend) {
((Map) localValue).putAll((Map) remoteValue);
} else {
localValue = (remoteValue != null) ? remoteValue : localValue;
}
field.set(merged, localValue);
break;
case "list":
if (toappend) {
((List) localValue).addAll((List) remoteValue);
} else {
localValue = (remoteValue != null) ? remoteValue : localValue;
}
field.set(merged, localValue);
break;
case "set":
if (toappend) {
((Set) localValue).addAll((Set) remoteValue);
} else {
localValue = (remoteValue != null) ? remoteValue : localValue;
}
field.set(merged, localValue);
break;
default:
field.set(merged, this.objectMerge(localValue, remoteValue, toappend));
break;
}
}
}
return (T) merged;
}
答案 4 :(得分：0)
import java.util.Objects;
import java.util.function.Consumer;
import java.util.function.Supplier;
public final class PropertyMerger {
public static <T> void mergeProperty(
Supplier<T> sourceGetter,
Supplier<T> targetGetter,
Consumer<T> targetSetter
) {
var source = sourceGetter.get();
var target = targetGetter.get();
if (!Objects.equals(source, target)) {
targetSetter.accept(source);
}
}
}
代码中的某处：
PropertyMerger.mergeProperty(facebookOAuth2User::getId, existingFacebookOAuth2UserDB::getFacebookId, existingFacebookOAuth2UserDB::setFacebookId);
PropertyMerger.mergeProperty(facebookOAuth2User::getName, existingFacebookOAuth2UserDB::getName, existingFacebookOAuth2UserDB::setName);