如何将此JSON响应解析为POJO

Question

我有以下测试类：

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.ibm.cio.cloud.cost.model.ElasticResponse;
import com.jayway.jsonpath.JsonPath;
@JsonIgnoreProperties(ignoreUnknown = true)
public class TestJSONPaths {
private static final String json = "{"hits":{"total":1,"hits":[{"_id":"oEE4j2QBXCNPxFWHqq3i","_score":1.0,"_source":{"status":"SUCCESSFUL","reason":"OK, Single ACTIVE status can process"}}]}}";
public static void main(String[] args) {
List<String> strippedJSON = JsonPath.read(json, "$.hits.hits._source");
ElasticResponse response = null;
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.configure(DeserializationFeature.USE_JAVA_ARRAY_FOR_JSON_ARRAY, true);
try {
System.out.println("From this json string:" + strippedJSON + "n");
response = mapper.readValue(strippedJSON.toString(), ElasticResponse.class);
System.out.println("ElasticDocument=" + mapper.writerWithDefaultPrettyPrinter().writeValueAsString(response.getDocuments()));
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

这是ElasticResponse类def:

public class ElasticResponse {
private List<ElasticDocument> documents;
public List<ElasticDocument> getDocuments() {
return documents;
}
public void setDocuments(List<ElasticDocument> documents) {
this.documents = documents;
}
}
public class ElasticDocument {
private String _id;
private String status;
private String reason;
... getters/setters
}

我试图从给定的JSON中获取一个ElasticDocument对象，但它在下面抛出了以下错误。我试图将JSON过滤掉，使其简单地为：[｛_source document values｝]。这个错误发生在Main类的第一行。我该如何绘制Json的地图？

[DEBUG] Evaluating path: $['hits']['hits']['_source']
Exception in thread "main" com.jayway.jsonpath.PathNotFoundException: Expected to find an object with property ['_source'] in path $['hits']['hits'] but found 'net.minidev.json.JSONArray'. This is not a json object according to the JsonProvider: 'com.jayway.jsonpath.spi.json.JsonSmartJsonProvider'.
at com.jayway.jsonpath.internal.path.PropertyPathToken.evaluate(PropertyPathToken.java:71)
at com.jayway.jsonpath.internal.path.PathToken.handleObjectProperty(PathToken.java:81)
at com.jayway.jsonpath.internal.path.PropertyPathToken.evaluate(PropertyPathToken.java:79)
at com.jayway.jsonpath.internal.path.PathToken.handleObjectProperty(PathToken.java:81)
at com.jayway.jsonpath.internal.path.PropertyPathToken.evaluate(PropertyPathToken.java:79)
at com.jayway.jsonpath.internal.path.RootPathToken.evaluate(RootPathToken.java:62)
at com.jayway.jsonpath.internal.path.CompiledPath.evaluate(CompiledPath.java:53)
at com.jayway.jsonpath.internal.path.CompiledPath.evaluate(CompiledPath.java:61)
at com.jayway.jsonpath.JsonPath.read(JsonPath.java:187)
at com.jayway.jsonpath.internal.JsonContext.read(JsonContext.java:102)
at com.jayway.jsonpath.internal.JsonContext.read(JsonContext.java:89)
at com.jayway.jsonpath.JsonPath.read(JsonPath.java:502)
at com.ibm.cio.cloud.cost.TestJSONPaths.main(TestJSONPaths.java:18)

Answer 1

异常是由于jsonpath返回的是数组而不是对象，因此如果您将jsonpath修复为如下所示：

$.hits.hits[*]._source

然后它将进行适当的评估。然而，这可能仍然不能实现您希望它做的事情。JsonPath.read()将为您取消JSON的序列化。但你必须注意这个：

public class Test {
private static final String json = "{"hits":{"total":1,"hits":[{"_id":"oEE4j2QBXCNPxFWHqq3i","_score":1.0,"_source":{"status":"SUCCESSFUL","reason":"OK, Single ACTIVE status can process"}}]}}";

public static void main(String[] args) {
List<ElasticDocument> docs = JsonPath.read(json, "$.hits.hits[*]._source");
System.out.println("elasticDoc: " + docs.get(0));
}
public static class ElasticDocument {
public String _id;
public String status;
public String reason;
@Override
public String toString() {
return "ElasticDocument{" +
"_id='" + _id + ''' +
", status='" + status + ''' +
", reason='" + reason + ''' +
'}';
}
}
}

看起来它可以工作，但是docsList现在实际上是Maps的List。显然，可以向Jackson注册JsonPath，但我无法使其工作

或者，您可以使用Jackson来取消JSON的序列化，然后您应该创建一个与JSON结构匹配的对象模型，然后您可以使用ObjectMapper来执行取消序列化

public class Test {
private static final String json = "{"hits":{"total":1,"hits":[{"_id":"oEE4j2QBXCNPxFWHqq3i","_score":1.0,"_source":{"status":"SUCCESSFUL","reason":"OK, Single ACTIVE status can process"}}]}}";
public static void main(String[] args) {
System.out.println("From this json string:" + json + "n");
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.configure(DeserializationFeature.USE_JAVA_ARRAY_FOR_JSON_ARRAY, true);
try {
HitsResource hitsResource = mapper.readValue(json, HitsResource.class);
System.out.println("jackson elasticDoc: " + hitsResource.hitsParent.hits.get(0).source);
} catch (Exception e) {
e.printStackTrace();
}
}
public static class HitsResource {
@JsonProperty("hits")
public HitsParent hitsParent;
@Override
public String toString() {
return "HitsResource{" +
"hitsParent=" + hitsParent +
'}';
}
}
public static class HitsParent {
@JsonProperty("total")
public Long total;
@JsonProperty("hits")
public List<Hits> hits;
@Override
public String toString() {
return "HitsParent{" +
"total=" + total +
", hits=" + hits +
'}';
}
}
public static class Hits {
@JsonProperty("_id")
public String id;
@JsonProperty("_score")
public BigDecimal score;
@JsonProperty("_source")
public ElasticDocument source;
@Override
public String toString() {
return "Hits{" +
"id='" + id + ''' +
", score=" + score +
", source=" + source +
'}';
}
}
public static class ElasticDocument {
@JsonProperty("_id")
public String _id;
@JsonProperty("status")
public String status;
@JsonProperty("reason")
public String reason;
@Override
public String toString() {
return "ElasticDocument{" +
"_id='" + _id + ''' +
", status='" + status + ''' +
", reason='" + reason + ''' +
'}';
}
}
}