javascript Java Jackson：反序列化复杂的多态对象模型：JsonMappingException：意外的令牌（START_OBJECT），预期的VALUE_STRING
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Java Hymanson: deserialize complex polymorphic object model: JsonMappingException: Unexpected token (START_OBJECT), expected VALUE_STRING
提问by Giovanni Bitliner
I have this tree of objects
我有这棵对象树
A
一个
B extends A
B 扩展 A
C extends B
C 扩展 B
D extends B
D 扩展 B
E extends C
E 扩展 C
F extends A and has one reference to A
F 扩展了 A 并且有一个对 A 的引用
A has the following annotation
A 有以下注释
@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS,include=JsonTypeInfo.As.PROPERTY,property="@class")
@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS,include=JsonTypeInfo.As.PROPERTY,property="@class")
If i try to deserialize a JSON array of objects that extends A, it throws the following error
如果我尝试反序列化扩展 A 的 JSON 对象数组，则会引发以下错误
org.codehaus.Hymanson.map.JsonMappingException: Unexpected token (START_OBJECT), expected VALUE_STRING: need JSON String that contains type id (for subtype of java.util.Collection)
org.codehaus.Hymanson.map.JsonMappingException：意外的令牌（START_OBJECT），预期的 VALUE_STRING：需要包含类型 id 的 JSON 字符串（用于 java.util.Collection 的子类型）
The json string is generated by toString() method of a set and the set is parametric to type A where A is serialized in JSON with the following code:
json 字符串由集合的 toString() 方法生成，该集合参数为类型 A，其中 A 使用以下代码在 JSON 中序列化：
ObjectMapper objectMapper=new ObjectMapper();
objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_CONCRETE_AND_ARRAYS);
String res="";
try {
res = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(t);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return res;
The code to deserialize the json array (that is the set described above) is:
反序列化 json 数组（即上面描述的集合）的代码是：
ObjectMapper mapper = new ObjectMapper();
mapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_CONCRETE_AND_ARRAYS);
Collection<T> results=null;
try {
results = mapper.readValue(json, TypeFactory.defaultInstance().constructParametricType(Collection.class, clazz ) );
} catch (JsonParseException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (JsonMappingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return results;
The json sample that it parses is like:
它解析的 json 示例如下：
"[{
"@class" : "pack1.pack2.MyClass",
"id" : null,
"f1" : "",
"f2" : 0.9933817827,
"f3" : 6.883261E-4,
"f4" : 0.001375699,
"f5" : {
"@class" : "pack1.pack2.MyClass2",
"id" : null,
"f1" : "",
"f2" : 0.0,
"f3" : 0.0,
"f4" : 0.0,
"f5" : [ "java.util.HashSet", [ 0 ] ],
"f6" : [ "java.util.HashSet", [ 2 ] ],
"f7" : [ "java.util.ArrayList", [ "scelta", "brani", "buona" ] ],
"f8" : [ null, "NOM", null ],
"f9" : false
},
"f10" : [ "java.util.HashMap", {
"2" : "ADJ"
} ],
"f11" : [ "java.util.HashSet", [ 0 ] ],
"f12" : [ "java.util.HashSet", [ 2 ] ],
"f13" : [ "java.util.ArrayList", [ "scelta", "brani", "buona" ] ],
"featureIndicator" : false
}]"
Here the json string includes only some objects of my sample of java Set
这里的 json 字符串只包括我的 java Set 样本的一些对象
回答by Pascal Gélinas
I believe the problem is with the default typing. The start of your JSON is not generated as what Hymanson expect with default typing. The begining of the JSON should be:
我相信问题出在默认类型上。JSON 的开头不是按照 Hymanson 期望的默认类型生成的。JSON 的开头应该是：
["java.util.HashSet", [{
and the end should have an extra closing bracket }]].
并且最后应该有一个额外的结束括号}]]。
That's because you generate the JSON using the toString()method of your set. You should instead use the ObjectMapper, that's configured with default typing, like so:
那是因为您使用toString()集合的方法生成了 JSON 。您应该改为使用ObjectMapper, 配置为默认类型，如下所示：
res = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(yourSet);
