Spring深入分析讲解BeanUtils的实现

//DO是源数据对象,DTO是目标对象,把源类的数据拷贝到目标对象
BeanUtils.copyProperties(DO,DTO);

/**
 * Copy the property values of the given source bean into the target bean.
 * <p>Note: The source and target classes do not have to match or even be derived
 * from each other, as long as the properties match. Any bean properties that the
 * source bean exposes but the target bean does not will silently be ignored.
 * <p>This is just a convenience method. For more complex transfer needs,
 * consider using a full BeanWrapper.
 * @param source the source bean
 * @param target the target bean
 * @throws BeansException if the copying failed
 * @see BeanWrapper
 */
public static void copyProperties(Object source, Object target) throws BeansException {
  copyProperties(source, target, null, (String[]) null);
}

private static void copyProperties(Object source, Object target, @Nullable Class<?> editable,
    @Nullable String... ignoreProperties) throws BeansException {
  Assert.notNull(source, "Source must not be null");
  Assert.notNull(target, "Target must not be null");
  //目标Class
  Class<?> actualEditable = target.getClass();
  if (editable != null) {
    if (!editable.isInstance(target)) {
      throw new IllegalArgumentException("Target class [" + target.getClass().getName() +
          "] not assignable to Editable class [" + editable.getName() + "]");
    }
    actualEditable = editable;
  }
    //1.获取目标Class的属性描述
  PropertyDescriptor[] targetPds = getPropertyDescriptors(actualEditable);
  List<String> ignoreList = (ignoreProperties != null ? Arrays.asList(ignoreProperties) : null);
  //2.遍历源Class的属性
  for (PropertyDescriptor targetPd : targetPds) {
        //源Class属性的写方法,setXXX
    Method writeMethod = targetPd.getWriteMethod();
        //3.如果存在写方法,并且该属性不忽略,继续往下走,否则跳过继续遍历
    if (writeMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) {
            //4.获取源Class的与目标属性同名的属性描述
      PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName());
      //5.如果源属性描述不存在直接跳过,否则继续往下走
            if (sourcePd != null) {
                //获取源属性描述的读方法
        Method readMethod = sourcePd.getReadMethod();
                //6.如果源属性描述的读防范存在且返回数据类型和目标属性的写方法入参类型相同或者派生
                //继续往下走,否则直接跳过继续下次遍历
        if (readMethod != null &&
            ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) {
          try {
                        //如果源属性读方法修饰符不是public,那么修改为可访问
            if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) {
              readMethod.setAccessible(true);
            }
                        //7.读取源属性的值
            Object value = readMethod.invoke(source);
                        //如果目标属性的写方法修饰符不是public,则修改为可访问
            if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) {
              writeMethod.setAccessible(true);
            }
                        //8.通过反射将源属性值赋值给目标属性
            writeMethod.invoke(target, value);
          }
          catch (Throwable ex) {
            throw new FatalBeanException(
                "Could not copy property '" + targetPd.getName() + "' from source to target", ex);
          }
        }
      }
    }
  }
}

//获取目标bean属性描述
PropertyDescriptor[] targetPds = getPropertyDescriptors(actualEditable);
//获取源bean指定名称的属性描述
PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName());

/**
 * Retrieve the JavaBeans {@code PropertyDescriptor}s of a given class.
 * @param clazz the Class to retrieve the PropertyDescriptors for
 * @return an array of {@code PropertyDescriptors} for the given class
 * @throws BeansException if PropertyDescriptor look fails
 */
public static PropertyDescriptor[] getPropertyDescriptors(Class<?> clazz) throws BeansException {
  CachedIntrospectionResults cr = CachedIntrospectionResults.forClass(clazz);
  return cr.getPropertyDescriptors();
}

@SuppressWarnings("unchecked")
static CachedIntrospectionResults forClass(Class<?> beanClass) throws BeansException {
  //1.从强缓存获取beanClass的内省结果,如果有数据直接返回
    CachedIntrospectionResults results = strongClassCache.get(beanClass);
  if (results != null) {
    return results;
  }
    //2.如果强缓存中不存在beanClass的内省结果,则从软缓存中获取beanClass的内省结果,如果存在直接返回
  results = softClassCache.get(beanClass);
  if (results != null) {
    return results;
  }
  //3.如果强缓存和软缓存都不存在beanClass的自省结果,则创建一个
  results = new CachedIntrospectionResults(beanClass);
  ConcurrentMap<Class<?>, CachedIntrospectionResults> classCacheToUse;
  //4.如果beanClass是缓存安全的,或者beanClass的类加载器是配置可接受的,缓存引用指向强缓存
  if (ClassUtils.isCacheSafe(beanClass, CachedIntrospectionResults.class.getClassLoader()) ||
      isClassLoaderAccepted(beanClass.getClassLoader())) {
    classCacheToUse = strongClassCache;
  }
  else {
        //5.如果不是缓存安全,则将缓存引用指向软缓存
    if (logger.isDebugEnabled()) {
      logger.debug("Not strongly caching class [" + beanClass.getName() + "] because it is not cache-safe");
    }
    classCacheToUse = softClassCache;
  }
  //6.将beanClass内省结果放入缓存
  CachedIntrospectionResults existing = classCacheToUse.putIfAbsent(beanClass, results);
  //7.返回内省结果
    return (existing != null ? existing : results);
}

public static void main(String[] args) {

    Demo1 demo1 = new Demo1(Arrays.asList("1","2","3"));

    Demo2 demo2 = new Demo2();
    BeanUtils.copyProperties(demo1,demo2);
    for (Integer integer : demo2.getList()) {
        System.out.println(integer);
    }
    for (String s : demo1.getList()) {
        demo2.addList(Integer.valueOf(s));
    }
}
@Data
static class Demo1 {
    private List<String> list;
    public Demo1(List<String> list) {
        this.list = list;
    }
}
@Data
static class Demo2 {
    private List<Integer> list;
    public void addList(Integer target) {
        if(null == list) {
            list = new ArrayList<>();
        }
        list.add(target);
    }
}

for (Object obj : demo2.getList()) {
    System.out.println(obj);
}