Dubbo3.0.3的继承于MAP参数类型只能接受2目的解决方案

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我有一个restful返回数据类型，在各项目中应用一直没问题，但用在Dubbo上就出事了：

@Data
@NoArgsConstructor
@AllArgsConstructor
public class ResponseEntity<T> extends LinkedHashMap<String,Object> implements Serializable {private long id;private int errCode;private String message;private T result;public static <V> ResponseEntity<V> fromResult(long id, V val){ResponseEntity<V> ret = new ResponseEntity<>();ret.result = val;ret.id=id;return ret;}public static ResponseEntity fromErr(long id, int errCode, String message){ResponseEntity ret=new ResponseEntity(id,errCode,message,null);return ret;}@JsonIgnorepublic Map toMap(){Map map= JsonUtils.fromJson(JsonUtils.toJsonString(this), HashMap.class);return map;}

直接报错，

Caused by: java.lang.IllegalArgumentException: [ServiceDefinitionBuilder] Map type [com.freestyle.common.models.ResponseEntity<java.lang.String>] with unexpected amount of arguments [[Ljava.lang.reflect.Type;@3c1f2651].[class java.lang.String]at org.apache.dubbo.metadata.definition.builder.MapTypeBuilder.build(MapTypeBuilder.java:56)at org.apache.dubbo.metadata.definition.TypeDefinitionBuilder.build(TypeDefinitionBuilder.java:56)at org.apache.dubbo.metadata.definition.TypeDefinitionBuilder.build(TypeDefinitionBuilder.java:80)

报错代码

  ParameterizedType parameterizedType = (ParameterizedType) type;Type[] actualTypeArgs = parameterizedType.getActualTypeArguments();int actualTypeArgsLength = actualTypeArgs == null ? 0 : actualTypeArgs.length;if (actualTypeArgsLength != 2) {throw new IllegalArgumentException(MessageFormat.format("[ServiceDefinitionBuilder] Map type [{0}] with unexpected amount of arguments [{1}]."+ Arrays.toString(actualTypeArgs), type, actualTypeArgs));}

搞不懂它为什么只接受2目的泛型，已经submit issue看他们有什么说法，现在只能修改成2目用着

@Data
@NoArgsConstructor
@AllArgsConstructor
public class ResponseEntity<V,T> extends LinkedHashMap<String,V>  implements Serializable {private long id;private int errCode;private String message;private T result;public static <V,T> ResponseEntity<V,T> fromResult(long id, T val){ResponseEntity<V,T> ret = new ResponseEntity<>();ret.result = val;ret.id=id;return ret;}public static <V,T>ResponseEntity<V,T> fromErr(long id, int errCode, String message){ResponseEntity<V,T> ret=new ResponseEntity<>(id,errCode,message,(T)null);return ret;}@JsonIgnorepublic Map toMap(){Map map= JsonUtils.fromJson(JsonUtils.toJsonString(this), HashMap.class);return map;}
}

================
后续的解决：
今晚再查阅代码发现TypeBuilder官方有4个实现，具体请参考dubbo里面的META-INF\dubbo\internal\org.apache.dubbo.metadata.definition.builder.TypeBuilder

array=org.apache.dubbo.metadata.definition.builder.ArrayTypeBuilder
collection=org.apache.dubbo.metadata.definition.builder.CollectionTypeBuilder
map=org.apache.dubbo.metadata.definition.builder.MapTypeBuilder
enum=org.apache.dubbo.metadata.definition.builder.EnumTypeBuilder

它针对这四种类型写了TypeBuilder的实现，而因为我自定义的ResponseEntity是extends map的，所以就交由MapTypeBuilder处理，而阿里的老哥相当严谨地认为map必须就2目，没考虑到继承问题。所以只能通过SPI对ResponseEntity进行针对性的TypeBuilder注册：
在自己的模块里面的resources下相应地建立META-INF\dubbo\internal\org.apache.dubbo.metadata.definition.builder.TypeBuilder
里面填上它的实现类：

responseEntity=com.freestyle.common.support.ResponseEntityTypeBuilder

打开源代码org.apache.dubbo.metadata.definition.TypeDefinitionBuilder，在Statis节打个断点，你会发现这时候tbs装入的是5个实现，也就是成功装入responseEntity的type builder实现类了。
ResponseEntityTypeBuilder其实也很简单，就是复制MapTypeBuilder，把检查2目的代码删除即可。

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