Java 如何在 Jackson 中将 JSON 字符串解析为 JsonNode？
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How to parse a JSON string into JsonNode in Hymanson?
提问by fadmaa
It should be so simple, but I just cannot find it after being trying for an hour #embarrasing.
它应该如此简单，但我尝试了一个小时后找不到它#embarrasing。
I need to get a JSON string, for example, {"k1":v1,"k2":v2}, parsed as a JsonNode.
我需要获取一个 JSON 字符串，例如{"k1":v1,"k2":v2}，解析为JsonNode.
JsonFactory factory = new JsonFactory();
JsonParser jp = factory.createJsonParser("{\"k1\":\"v1\"}");
JsonNode actualObj = jp.readValueAsTree();
gives
给
java.lang.IllegalStateException: No ObjectCodec defined for the parser, can not deserialize JSON into JsonNode tree
java.lang.IllegalStateException: No ObjectCodec defined for the parser, can not deserialize JSON into JsonNode tree
采纳答案by slashnick
A slight variation on Richards answer but readTreecan take a string so you can simplify it to:
理查兹答案略有变化，但readTree可以采用字符串，因此您可以将其简化为：
ObjectMapper mapper = new ObjectMapper();
JsonNode actualObj = mapper.readTree("{\"k1\":\"v1\"}");
回答by Richard Fearn
You need to use an ObjectMapper:
您需要使用一个ObjectMapper：
ObjectMapper mapper = new ObjectMapper();
JsonFactory factory = mapper.getJsonFactory(); // since 2.1 use mapper.getFactory() instead
JsonParser jp = factory.createJsonParser("{\"k1\":\"v1\"}");
JsonNode actualObj = mapper.readTree(jp);
Further documentation about creating parsers can be found here.
可以在此处找到有关创建解析器的更多文档。
回答by StaxMan
Richard's answer is correct. Alternatively you can also create a MappingJsonFactory(in org.codehaus.Hymanson.map) which knows where to find ObjectMapper. The error you got was because the regular JsonFactory(from corepackage) has no dependency to ObjectMapper(which is in the mapperpackage).
理查德的回答是正确的。或者，您也可以创建一个MappingJsonFactory(in org.codehaus.Hymanson.map)，它知道在哪里可以找到ObjectMapper. 您得到的错误是因为常规JsonFactory（来自core包）不依赖于ObjectMapper（在mapper包中）。
But usually you just use ObjectMapperand do not worry about JsonParseror other low level components -- they will just be needed if you want to data-bind parts of stream, or do low-level handling.
但通常你只是使用ObjectMapper而不用担心JsonParser其他低级组件——如果你想对流的部分进行数据绑定，或者进行低级处理，它们将是必需的。
回答by qerub
A third variant:
第三种变体：
ObjectMapper mapper = new ObjectMapper();
JsonNode actualObj = mapper.readValue("{\"k1\":\"v1\"}", JsonNode.class);
回答by pdxleif
import com.github.fge.Hymanson.JsonLoader;
JsonLoader.fromString("{\"k1\":\"v1\"}")
== JsonNode = {"k1":"v1"}
