DiffUtils.java

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;

/**
 * Modified from {@link <a href="http://stackoverflow.com/a/32817115/5729581"/>}
 *
 * @author nekocode (nekocode.cn@gmail.com)
 */
public class DiffUtils {
    private static final HashMap<Class, ArrayList<GetterAndSetter>> methodMap = new HashMap<>();

    public static <T> void compareAndApplyDifferences(T target, T source) {
        final Class<?> c1 = target.getClass();
        final Class<?> c2 = source.getClass();

        if (!c1.equals(c2)) {
            return;
        }

        ArrayList<GetterAndSetter> getterAndSetters = methodMap.get(c1);

        if (getterAndSetters == null) {
            /*
              Cache Getters & Setters
             */
            final HashMap<String, Method> gettersMap = new HashMap<>();
            final ArrayList<Method> setters = new ArrayList<>();

            final Method[] methods = c1.getMethods();
            for (Method method : methods) {
                if (isGetter(method)) {
                    final String methodName = method.getName();
                    if (methodName.startsWith("is")) {
                        gettersMap.put(methodName.substring(2), method);
                    } else if (methodName.startsWith("get")) {
                        gettersMap.put(methodName.substring(3), method);
                    }
                } else if (isSetter(method)) {
                    setters.add(method);
                }
            }

            getterAndSetters = new ArrayList<>();

            if (gettersMap.size() > 0 && setters.size() > 0) {
                for (Method setter : setters) {
                    final Method getter = gettersMap.get(setter.getName().substring(3));
                    if (getter != null) {
                        getterAndSetters.add(new GetterAndSetter(getter, setter));
                    }
                }
            }

            methodMap.put(c1, getterAndSetters);
        }

        for (GetterAndSetter getterAndSetter : getterAndSetters) {
            final Method getter = getterAndSetter.getter;
            final Method setter = getterAndSetter.setter;
            Object getterResult1, getterResult2;

            try {
                getterResult1 = getter.invoke(target);
            } catch (Exception ignored) {
                getterResult1 = null;
            }

            try {
                getterResult2 = getter.invoke(source);
            } catch (Exception ignored) {
                getterResult2 = null;
            }

            if (getterResult2 != null && !getterResult2.equals(getterResult1)) {
                // Copy value
                try {
                    setter.invoke(target, getterResult2);
                } catch (Exception ignored) {
                }
            }
        }
    }

    private static boolean isGetter(Method method) {
        if (!(method.getName().startsWith("get") || method.getName().startsWith("is")))
            return false;
        if (method.getParameterTypes().length != 0)
            return false;
        if (void.class.equals(method.getReturnType()))
            return false;
        return true;
    }

    private static boolean isSetter(Method method) {
        if (!method.getName().startsWith("set"))
            return false;
        if (method.getParameterTypes().length != 1)
            return false;
        return true;
    }

    private static class GetterAndSetter {
        Method getter;
        Method setter;

        GetterAndSetter(Method getter, Method setter) {
            this.getter = getter;
            this.setter = setter;
        }
    }
}