无法从字符串值 ('{') 实例化 java.util.LinkedHashMap 类型的值；没有单字符串构造函数/工厂方法
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Cannot instantiate value of type java.util.LinkedHashMap from String value ('{'); no single-String constructor/factory method
提问by checklist
I have the following 2 classes:
我有以下两个类：
@JsonIgnoreProperties(ignoreUnknown = true)
public class ChangesJSON {
@JsonProperty("changes")
List<ChangeJSON> changes;
@JsonProperty("more")
Boolean more;
}
public class ChangeJSON {
@JsonProperty("epoch")
Long epoch;
@JsonProperty("payload")
Map<String, Object> payload;
}
When I try to deserialize using this test:
当我尝试使用此测试反序列化时：
String test = "{\"changes\":[{\"epoch\":1441556306522,\"payload\":\"{\"to\":1}\"},{\"epoch\":1441555481524,\"payload\":\"{\"to\":-1}\"}],\"more\":false}";
@Test
public void myTest() {
ObjectMapper mapper = new ObjectMapper();
ChangesJSON result = null;
try {
result = mapper.readValue(test, ChangesJSON.class);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
assertNotNull(result);
}
I get the following exception:
我收到以下异常：
com.fasterxml.Hymanson.databind.JsonMappingException: Can not instantiate value of type java.util.LinkedHashMap from String value ('{'); no single-String constructor/factory method at [Source: {"changes":[{"epoch":1441556306522,"payload":"{"to":1}"},{"epoch":1441555481524,"payload":"{"to":-1}"}],"more":false}; line: 1, column: 35] (through reference chain: demo.ChangesJSON["changes"]->java.util.ArrayList[0]->demo.ChangeJSON["payload"])
com.fasterxml.Hymanson.databind.JsonMappingException：无法从字符串值（'{'）中实例化 java.util.LinkedHashMap 类型的值；[Source: {"changes":[{"epoch":1441556306522,"payload":"{"to":1}"},{"epoch":1441555481524,"payload" 没有单字符串构造函数/工厂方法:"{"to":-1}"}],"more":false}; 行：1，列：35]（通过参考链：demo.ChangesJSON["changes"]->java.util.ArrayList[0]->demo.ChangeJSON["payload"]）
It seems that there is an issue with the map but I thought Hymanson should be able to handle maps. I get the same issue also when I change the map to Map. But I do need to support all sorts of classes as the values of the map.
地图似乎有问题，但我认为Hyman逊应该能够处理地图。当我将地图更改为 Map 时，我也遇到了同样的问题。但我确实需要支持各种类作为地图的值。
回答by Petter
You have quotes around the payloadobject. Try changing this part:
您在payload对象周围有引号。尝试更改此部分：
\"payload\":\"{\"to\":1}\"
into this:
进入这个：
\"payload\":{\"to\":1}
回答by mprivat
I think it's the JSON itself that has a problem. It unescapes to:
我认为是 JSON 本身有问题。它转义为：
{"changes":[{"epoch":1441556306522,"payload":"{"to":1}"},{"epoch":1441555481524,"payload":"{"to":-1}"}],"more":false}
It should probably be something like:
它可能应该是这样的：
{"changes":[{"epoch":1441556306522,"payload":{"to":1}},{"epoch":1441555481524,"payload":{"to":-1}}],"more":false}
So:
所以：
String test = "{\"changes\":[{\"epoch\":1441556306522,\"payload\":{\"to\":1}},{\"epoch\":1441555481524,\"payload\":{\"to\":-1}}],\"more\":false}";
