神奇的 beanUtils.copyProperties 目标与源对象属性类型不一致但可以 set 成功

V2EX = way to explore

V2EX 是一个关于分享和探索的地方

现在注册

已注册用户请登录

这是一个创建于 833 天前的主题，其中的信息可能已经有所发展或是发生改变。

public class CourseCategoryResponse {

    private String id;
    @ApiModelProperty("分类名称")
    private String name;
    @ApiModelProperty("分类图标")
    private String image;

    @ApiModelProperty("英文名称")
    private String nameEn;

    @ApiModelProperty("子分类")
    private List<CourseCategoryResponse> children;
    @ApiModelProperty("课程列表")
    private List<CourseSimpleResponse> coures;
}

public class Category {

    @Id
    @Column(length = 37)
    @GeneratedValue(generator = "jpa-uuid")
    private String id;

    @ApiParam("主体")
    @Column(length = 32)
    private String subject;


    @ApiParam("分类名称")
    @Column(length = 32)
    private String name;
   
    private List<Category> children;
    
 }
 
 ==========调用代码=====================
 
  PropertyDescriptor propertyDescriptors = BeanUtils.getPropertyDescriptor(CourseCategoryResponse.class,"children");
        CourseCategoryResponse courseCategoryResponse = new CourseCategoryResponse();
        Category category = new Category();
        category.setName("123");
        Category children = new Category();
        children.setName("234");
        category.setChildren(List.of(children));
        PropertyDescriptor source = BeanUtils.getPropertyDescriptor(Category.class,"children");

        Object value = source.getReadMethod().invoke(category);
       propertyDescriptors.getWriteMethod().invoke(courseCategoryResponse,value);
       System.out.println(courseCategoryResponse);
       
       
 打印结果 courseCategoryResponse 的 children 是有值的，我想这个为什么可以 set 进去

第 1 条附言 · 2022-08-04 17:15:32 +08:00

经过一段源码阅读，很好奇fastjson是怎样序列化,它是怎样判断children类型,先通过反射类的方法和属性，然后生成一堆拼接json的代码,为什么要这样，生成一个类就可以重用，不用每次都反射，效率太慢，mapStuct也是这样原理其中这段代码

 List var13 = (List)var10.getChildren();

通过asm





public class ASMSerializer_1_CourseCategoryResponse extends JavaBeanSerializer implements ObjectSerializer {
    public Type children_asm_fieldType = ASMUtils.getMethodType(CourseCategoryResponse.class, "getChildren");
    public ObjectSerializer children_asm_list_item_ser_;
    public ObjectSerializer children_asm_ser_;
    public Type coures_asm_fieldType = ASMUtils.getMethodType(CourseCategoryResponse.class, "getCoures");
    public ObjectSerializer coures_asm_list_item_ser_;
    public ObjectSerializer coures_asm_ser_;

    public ASMSerializer_1_CourseCategoryResponse(SerializeBeanInfo var1) {
        super(var1);
    }

    public void write(JSONSerializer var1, Object var2, Object var3, Type var4, int var5) throws IOException {
        if (var2 == null) {
            var1.writeNull();
        } else {
            SerializeWriter var9 = var1.out;
            if (!this.writeDirect(var1)) {
                this.writeNormal(var1, var2, var3, var4, var5);
            } else if (var9.isEnabled(32768)) {
                this.writeDirectNonContext(var1, var2, var3, var4, var5);
            } else {
                CourseCategoryResponse var10 = (CourseCategoryResponse)var2;
                if (!this.writeReference(var1, var2, var5)) {
                    if (var9.isEnabled(2097152)) {
                        this.writeAsArray(var1, var2, var3, var4, var5);
                    } else {
                        SerialContext var11 = var1.getContext();
                        var1.setContext(var11, var2, var3, 0);
                        char var12 = '{';
                        String var6 = "children";
                        List var13 = (List)var10.getChildren();

第 2 条附言 · 2022-09-12 14:42:06 +08:00

这个还有补充一点，beanUtis.copyPropertites里面是有判断类型是否能够赋值的

	for (PropertyDescriptor targetPd : targetPds) {
			Method writeMethod = targetPd.getWriteMethod();
			if (writeMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) {
				PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName());
				if (sourcePd != null) {
					Method readMethod = sourcePd.getReadMethod();
					if (readMethod != null &&
							ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) {
						
					}
				}
			}
		}

public static boolean isAssignable(Class<?> lhsType, Class<?> rhsType) {
        Assert.notNull(lhsType, "Left-hand side type must not be null");
        Assert.notNull(rhsType, "Right-hand side type must not be null");
        if (lhsType.isAssignableFrom(rhsType)) {
            return true;
        } else {
            Class resolvedPrimitive;
            if (lhsType.isPrimitive()) {
                resolvedPrimitive = (Class)primitiveWrapperTypeMap.get(rhsType);
                if (lhsType == resolvedPrimitive) {
                    return true;
                }
            } else {
                resolvedPrimitive = (Class)primitiveTypeToWrapperMap.get(rhsType);
                if (resolvedPrimitive != null && lhsType.isAssignableFrom(resolvedPrimitive)) {
                    return true;
                }
            }

            return false;
        }
    }

关键是上面的 isAssignable 方法，当List<Category> 赋给 List<CategoryResponse>,他们比较的是List类型，绝对不会比较List里面的类型，实在也是坑之一，所以就会能够产生上述结果

private