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解決feign接口返回泛型設(shè)置屬性為null的問題

 更新時間:2021年06月24日 14:59:37   作者:PolarisHuster  
這篇文章主要介紹了解決feign接口返回泛型設(shè)置屬性為null的問題,具有很好的參考價值,希望對大家有所幫助。如有錯誤或未考慮完全的地方,望不吝賜教

簡介

feign是一種聲明式http請求調(diào)用方式,工作原理就是根據(jù)FeignClient注解生成新的接口(也就是傳說中的動態(tài)代理),常見使用方式如下所示:

@FeignClient(name="UserFeignService",url="${auth.url}",
        fallbackFactory = OrgFeignServiceFallback.class,
        configuration = FeignErrorDecoderConfiguration.class)
public interface OrgFeignService {
 
    /**
     * 
     * @param org
     * @return
     */
    @PostMapping(value="Tenant/AddTenantOrg", consumes="application/json; charset=UTF-8")
    APIResultTO<TenantOrg> addOrg(OrgDto org, @RequestHeader("token")String token);
}

應(yīng)用場景

1、序列化以及反序列化采用jackson

2、調(diào)用第三方采用feign注解式接口

問題分析

APIResultTO是一個api通用接口返回泛型類,TenantOrg為傳入的具體泛型類,咱們來看下出問題的類:

@Getter
@Setter
@NoArgsConstructor
public class TenantOrg {
    /**
     */
    @JsonProperty("Id")
    private String Id;
    /**
     * 父級Id
     */
    @JsonProperty("PId")
    private String PId;
    /**
     * 租戶代碼
     */
    @JsonProperty("Tenant")
    private String tenant;
    /**
     * 組織架構(gòu)名字
     */
    @JsonProperty("Name")
    private String name;
}

必須要用@JsonProperty("Id")或者@JsonSetter("Id")注解來顯示聲明屬性名字,尤其是首字母為大寫的情況,否則反序列化后的數(shù)據(jù)就為空值。

為什么TenantOrg類中的Id等其他屬性跟第三方服務(wù)返回的json數(shù)據(jù)字段完全一致,卻沒有成功設(shè)置對應(yīng)的屬性呢,這個就要看下BeanDeserializer類的deserializeFromObject方法,從其名字上我們可以看出這是將請求返回的數(shù)據(jù)反序列化成對應(yīng)的類對象:

public Object deserializeFromObject(JsonParser p, DeserializationContext ctxt) throws IOException
    {
        /* 09-Dec-2014, tatu: As per [databind#622], we need to allow Object Id references
         *   to come in as JSON Objects as well; but for now assume they will
         *   be simple, single-property references, which means that we can
         *   recognize them without having to buffer anything.
         *   Once again, if we must, we can do more complex handling with buffering,
         *   but let's only do that if and when that becomes necessary.
         */
        if ((_objectIdReader != null) && _objectIdReader.maySerializeAsObject()) {
            if (p.hasTokenId(JsonTokenId.ID_FIELD_NAME)
                    && _objectIdReader.isValidReferencePropertyName(p.getCurrentName(), p)) {
                return deserializeFromObjectId(p, ctxt);
            }
        }
        if (_nonStandardCreation) {
            if (_unwrappedPropertyHandler != null) {
                return deserializeWithUnwrapped(p, ctxt);
            }
            if (_externalTypeIdHandler != null) {
                return deserializeWithExternalTypeId(p, ctxt);
            }
            Object bean = deserializeFromObjectUsingNonDefault(p, ctxt);
            if (_injectables != null) {
                injectValues(ctxt, bean);
            }
            /* 27-May-2014, tatu: I don't think view processing would work
             *   at this point, so commenting it out; but leaving in place
             *   just in case I forgot something fundamental...
             */
            /*
            if (_needViewProcesing) {
                Class<?> view = ctxt.getActiveView();
                if (view != null) {
                    return deserializeWithView(p, ctxt, bean, view);
                }
            }
            */
            return bean;
        }
        final Object bean = _valueInstantiator.createUsingDefault(ctxt);
        // [databind#631]: Assign current value, to be accessible by custom deserializers
        p.setCurrentValue(bean);
        if (p.canReadObjectId()) {
            Object id = p.getObjectId();
            if (id != null) {
                _handleTypedObjectId(p, ctxt, bean, id);
            }
        }
        if (_injectables != null) {
            injectValues(ctxt, bean);
        }
        if (_needViewProcesing) {
            Class<?> view = ctxt.getActiveView();
            if (view != null) {
                return deserializeWithView(p, ctxt, bean, view);
            }
        }
        if (p.hasTokenId(JsonTokenId.ID_FIELD_NAME)) {
            String propName = p.getCurrentName();
            do {
                p.nextToken();
                //如果要跟蹤測試的話,直接定位到該位置就可以,你就會發(fā)現(xiàn)如果沒有
                //JSONProperty之類的注解定義屬性名字的話,Id、PId屬性在_beanProperties都成了小寫的屬性
                SettableBeanProperty prop = _beanProperties.find(propName);
                if (prop != null) { // normal case
                    try {
                        prop.deserializeAndSet(p, ctxt, bean);
                    } catch (Exception e) {
                        wrapAndThrow(e, bean, propName, ctxt);
                    }
                    continue;
                }
                handleUnknownVanilla(p, ctxt, bean, propName);
            } while ((propName = p.nextFieldName()) != null);
        }
        return bean;
    }

具體如下圖所示:

正如上面所示,用@JsonProperty注解配置的屬性,在反序列化時就按照@JsonProperty注解定義的屬性名相同,至于為什么在TenantOrg中定義的PId屬性在使用時怎么變成了pid,

具體可以看下POJOPropertiesCollector類的_removeUnwantedProperties方法以及_renameProperties方法:

    protected void _removeUnwantedProperties(Map<String, POJOPropertyBuilder> props)
    {
        Iterator<POJOPropertyBuilder> it = props.values().iterator();
        while (it.hasNext()) {
            POJOPropertyBuilder prop = it.next();
 
            // 去除private屬性,PId屬性會在這里移除
            if (!prop.anyVisible()) {
                it.remove();
                continue;
            }
            // Otherwise, check ignorals
            if (prop.anyIgnorals()) {
                // first: if one or more ignorals, and no explicit markers, remove the whole thing
                if (!prop.isExplicitlyIncluded()) {
                    it.remove();
                    _collectIgnorals(prop.getName());
                    continue;
                }
                // otherwise just remove ones marked to be ignored
                prop.removeIgnored();
                if (!prop.couldDeserialize()) {
                    _collectIgnorals(prop.getName());
                }
            }
        }
    }
protected void _renameProperties(Map<String, POJOPropertyBuilder> props)
    {
        // With renaming need to do in phases: first, find properties to rename
        Iterator<Map.Entry<String,POJOPropertyBuilder>> it = props.entrySet().iterator();
        LinkedList<POJOPropertyBuilder> renamed = null;
        while (it.hasNext()) {
            Map.Entry<String, POJOPropertyBuilder> entry = it.next();
            POJOPropertyBuilder prop = entry.getValue();
 
            //被@JsonProperty注解的屬性會找到對應(yīng)的屬性名
            Collection<PropertyName> l = prop.findExplicitNames();
 
            // no explicit names? Implicit one is fine as is
            if (l.isEmpty()) {
                continue;
            }
            it.remove(); // need to replace with one or more renamed
            if (renamed == null) {
                renamed = new LinkedList<POJOPropertyBuilder>();
            }
            // simple renaming? Just do it
            //在這里使用@JsonProperty注解里面定義的屬性名,比如PId、Id等
            //所以使用了@JsonProperty注解后,我們就無需關(guān)注類里面屬性的大小寫,設(shè)置不用關(guān)注屬性名
            if (l.size() == 1) {
                PropertyName n = l.iterator().next();
                renamed.add(prop.withName(n));
                continue;
            }
            // but this may be problematic...
            renamed.addAll(prop.explode(l));
 
            /*
            String newName = prop.findNewName();
            if (newName != null) {
                if (renamed == null) {
                    renamed = new LinkedList<POJOPropertyBuilder>();
                }
                prop = prop.withSimpleName(newName);
                renamed.add(prop);
                it.remove();
            }
            */
        }
        
        // and if any were renamed, merge back in...
        if (renamed != null) {
            for (POJOPropertyBuilder prop : renamed) {
                String name = prop.getName();
                POJOPropertyBuilder old = props.get(name);
                if (old == null) {
                    props.put(name, prop);
                } else {
                    old.addAll(prop);
                }
                // replace the creatorProperty too, if there is one
                _updateCreatorProperty(prop, _creatorProperties);
                // [databind#2001]: New name of property was ignored previously? Remove from ignored
                // 01-May-2018, tatu: I have a feeling this will need to be revisited at some point,
                //   to avoid removing some types of removals, possibly. But will do for now.
                if (_ignoredPropertyNames != null) {
                    _ignoredPropertyNames.remove(name);
                }
            }
        }
    }

springcloud feign請求:數(shù)據(jù)返回null

問題描述

調(diào)用方調(diào)用服務(wù),DEBUG被調(diào)用方服務(wù)得到正確數(shù)據(jù),但調(diào)用方返回的數(shù)據(jù)對象屬性全為null

在這里插入圖片描述

原因及解決方法:

在feign調(diào)用接口中與被調(diào)用方接口返回類型不一致。

以上為個人經(jīng)驗,希望能給大家一個參考,也希望大家多多支持腳本之家。

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