与杰克逊一起读取 json 时出现空指针异常

Question

本质上，我有一个 json 对象，我想用杰克逊解析它。我试图将我的测试归结为一个简单的 json 对象和一些示例杰克逊解析代码。例如，我有以下用于读取 json 的模型：

import java.util.Set;
import com.fasterxml.jackson.annotation.JsonAlias;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
public class HateoasSet<C> {
private HateoasEmbedded<C> embedded;
public Set<C> get() {
return embedded.content;
}
@JsonAlias("_embedded")
private void set(HateoasEmbedded<C> embedded) {
this.embedded = embedded;
}
private static class HateoasEmbedded<C> {
@JsonIgnore
private Set<C> content;
@JsonAnySetter
public void setContent(String name, Set<C> content) {
this.content = content;
}
}
}

我正在通过以下方式测试解析：

public static void main(String args[]) throws JsonParseException, JsonMappingException, IOException {
String json = "{n" + 
"    "_embedded": {n" + 
"        "endpoints": [n" + 
"            {n" + 
"                "createdAt": "2020-06-29T17:25:18.000+00:00",n" + 
"                "updatedAt": "2020-06-29T17:25:30.000+00:00",n" + 
"                "name": "Test User",n" + 
"                "networkId": "net2",n" + 
"                "endpointType": "CL",n" + 
"                "clientType": null,n" + 
"                "clientVersion": null,n" + 
"                "source": "IMPORT",n" + 
"                "syncId": null,n" + 
"                "registrationKey": "registrationkey",n" + 
"                "registrationAttemptsLeft": 5,n" + 
"                "status": 300,n" + 
"                "currentState": 100,n" + 
"                "stateLastUpdated": "2020-06-29T17:25:18.000+00:00",n" + 
"                "endpointProtectionRole": null,n" + 
"                "haEndpointType": null,n" + 
"                "o365BreakoutNextHopIp": null,n" + 
"                "gatewayClusterId": null,n" + 
"                "clientMfaEnable": "NO",n" + 
"                "ownerIdentityId": null,n" + 
"                "countryId": null,n" + 
"                "geoRegionId": "geo1",n" + 
"                "dataCenterId": "data1",n" + 
"                "sessionIdentityId": null,n" + 
"                "sessionStatus": 100,n" + 
"                "id": "myId",n" + 
"                "componentId": "componentId",n" + 
"                "_links": {n" + 
"                    "self": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "network": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "appWans": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "services": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "endpointGroups": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "geoRegion": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "dataCenter": {n" + 
"                        "href": "www.google.com"n" + 
"                    }n" + 
"                }n" + 
"            }n" + 
"        ]n" + 
"    },n" + 
"    "_links": {n" + 
"        "first": {n" + 
"            "href": "www.google.com"n" + 
"        },n" + 
"        "last": {n" + 
"            "href": "www.google.com"n" + 
"        }n" + 
"    },n" + 
"    "page": {n" + 
"        "size": 2000,n" + 
"        "totalElements": 1,n" + 
"        "totalPages": 1,n" + 
"        "number": 1n" + 
"    }n" + 
"}";
ObjectMapper mapper = new ObjectMapper().configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

HateoasSet<Endpoint> result = mapper.readValue(json, HateoasSet.class);
System.out.println(result.get());

}

HateoasSet 与 main 方法位于同一包中。有人可以告诉我为什么当我尝试解析此 json 时总是收到空指针异常吗？

Answer 1

我能够通过将类更改为

public class HateoasSet<C> {
private HateoasEmbedded<C> embedded;
public Set<C> get() {
return embedded.content;
}
@JsonAlias("_embedded")
private void setEmbedded(HateoasEmbedded<C> embedded) {
this.embedded = embedded;
}
private static class HateoasEmbedded<C> {
@JsonIgnore
private Set<C> content;
@JsonAnySetter
public void setContent(String name, Set<C> content) {
this.content = content;
}
}
}

以及测试部分：

public static void main(String args[]) throws JsonParseException, JsonMappingException, IOException {
String json = "{n" + 
"    "_embedded": {n" + 
"        "endpoints": [n" + 
"            {n" + 
"                "createdAt": "2020-06-29T17:25:18.000+00:00",n" + 
"                "updatedAt": "2020-06-29T17:25:30.000+00:00",n" + 
"                "name": "Test User",n" + 
"                "networkId": "net2",n" + 
"                "endpointType": "CL",n" + 
"                "clientType": null,n" + 
"                "clientVersion": null,n" + 
"                "source": "IMPORT",n" + 
"                "syncId": null,n" + 
"                "registrationKey": "registrationkey",n" + 
"                "registrationAttemptsLeft": 5,n" + 
"                "status": 300,n" + 
"                "currentState": 100,n" + 
"                "stateLastUpdated": "2020-06-29T17:25:18.000+00:00",n" + 
"                "endpointProtectionRole": null,n" + 
"                "haEndpointType": null,n" + 
"                "o365BreakoutNextHopIp": null,n" + 
"                "gatewayClusterId": null,n" + 
"                "clientMfaEnable": "NO",n" + 
"                "ownerIdentityId": null,n" + 
"                "countryId": null,n" + 
"                "geoRegionId": "geo1",n" + 
"                "dataCenterId": "data1",n" + 
"                "sessionIdentityId": null,n" + 
"                "sessionStatus": 100,n" + 
"                "id": "myId",n" + 
"                "componentId": "componentId",n" + 
"                "_links": {n" + 
"                    "self": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "network": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "appWans": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "services": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "endpointGroups": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "geoRegion": {n" + 
"                        "href": "www.google.com"n" + 
"                    },n" + 
"                    "dataCenter": {n" + 
"                        "href": "www.google.com"n" + 
"                    }n" + 
"                }n" + 
"            }n" + 
"        ]n" + 
"    },n" + 
"    "_links": {n" + 
"        "first": {n" + 
"            "href": "www.google.com"n" + 
"        },n" + 
"        "last": {n" + 
"            "href": "www.google.com"n" + 
"        }n" + 
"    },n" + 
"    "page": {n" + 
"        "size": 2000,n" + 
"        "totalElements": 1,n" + 
"        "totalPages": 1,n" + 
"        "number": 1n" + 
"    }n" + 
"}";
ObjectMapper mapper = new ObjectMapper().configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

HateoasSet<EndpointGroup> result = mapper.readValue(json, new TypeReference<HateoasSet<EndpointGroup>>(){});
System.out.println(result.get());

}