Cannot construct instance of 的错误解决

错误描述

: Cannot construct instance of (no Creators, like default constructor, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information

虽然该类实现了序列化 但是这个集合不能被解析

其实就是在spring security 权限集合反序列化失败

   @Override
    public Collection<? extends GrantedAuthority> getAuthorities() {
        List<SimpleGrantedAuthority> authorities = new ArrayList<>();
        for (Role role : roles) {
            SimpleGrantedAuthority authority = new SimpleGrantedAuthority(role.getName());
            authorities.add(authority);
        }
        return authorities;
    }

这时候我们就需要自定义一个反序列化的类

public class CustomAuthorityDeserializer extends JsonDeserializer {
    @Override
    public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        ObjectMapper mapper = (ObjectMapper) p.getCodec();
        JsonNode jsonNode = mapper.readTree(p);
        LinkedList<GrantedAuthority> grantedAuthorities = new LinkedList<>();
        Iterator<JsonNode> elements = jsonNode.elements();
        while (elements.hasNext()) {
            JsonNode next = elements.next();
            JsonNode authority = next.get("authority");
            //将得到的值放入链表 最终返回该链表
            grantedAuthorities.add(new SimpleGrantedAuthority(authority.asText()));
        }
        return grantedAuthorities;
    }
}

同时加上一个注解 自定义解析即可生效
@JsonDeserialize(using = )

    @Override
    @JsonDeserialize(using = CustomAuthorityDeserializer.class)
    public Collection<? extends GrantedAuthority> getAuthorities() {
        List<SimpleGrantedAuthority> authorities = new ArrayList<>();
        for (Role role : roles) {
            SimpleGrantedAuthority authority = new SimpleGrantedAuthority(role.getName());
            authorities.add(authority);
        }
        return authorities;
    }