如何解析来自 HTTP JSON 响应负载的值

Question

我对 Apama 比较陌生。我正在使用 v10.3.1。我正在按照以下代码片段在监视器中执行 REST 请求：

http://www.apamacommunity.com/documents/10.3.1.1/apama_10.3.1.1_webhelp/apama-webhelp/#page/apama-webhelp%2Fco-ConApaAppToExtCom_httpclient_using_predefined_generic_event_definitions.html%23wwconnect_header

当前处理响应的操作如下所示：


action handleResponse(Response response){
        if response.isSuccess(){
            print "###The response payload is :" + response.payload.toString();
        }

        else {
            print "###Request failed. Response status is: " + response.statusCode.toString() + " | " + response.statusMessage;
        }
    }

我正在寻找在 JSON 响应负载中提取以下属性值的最佳方法：

assetparents.references[0].managedObject.name (here “SOME”).

我尝试了不同的方法，但总是运行出错。

打印语句为响应负载提供以下输出：



###The response payload is :com.apama.util.AnyExtractor(any(string,"

{"owner":"some@one.com","additionParents":{
    "self":"https://somebaseurl/inventory/managedObjects/5706999/additionParents","references":[]
},
"childDevices":{
    "self":"https://somebaseurl/inventory/managedObjects/5706999/childDevices","references":[]
},

"childAssets":{
    "self":"https://somebaseurl/inventory/managedObjects/5706999/childAssets","references":[]
},
"creationTime":"2019-05-09T11:36:10.197Z",
"lastUpdated":"2019-05-10T05:28:07.893Z",
"childAdditions":{
    "self":"https://somebaseurl/inventory/managedObjects/5706999/childAdditions",
    "references":[{
        "managedObject":{"name":"Escalate alarmtest",
        "self":"https://somebaseurl/inventory/managedObjects/5706698",
        "id":"5706698"},
        "self":"https://somebaseurl/inventory/managedObjects/5706999/childAdditions/5706698"
    }
]},
"name":"SOME Test Device",
"deviceParents":{
    "self":"https://somebaseurl/inventory/managedObjects/5706999/deviceParents",
    "references":[]
},
"assetParents":{
    "self":"https://somebaseurl/inventory/managedObjects/5706999/assetParents",
    "references":[{
        "managedObject":{
            "additionParents":{
                "self":"https://somebaseurl/inventory/managedObjects/5706682/additionParents",
                "references":[]
            },
            "childDevices":{
                "self":"https://somebaseurl/inventory/managedObjects/5706682/childDevices",
                "references":[]
            },
            "childAssets":{
                "self":"https://somebaseurl/inventory/managedObjects/5706682/childAssets",
                "references":[]
            },
            "childAdditions":{
                "self":"https://somebaseurl/inventory/managedObjects/5706682/childAdditions",
                "references":[]
            },
            "name":"SOME",
            "deviceParents":{
                "self":"https://somebaseurl/inventory/managedObjects/5706682/deviceParents",
                "references":[]
            },
            "assetParents":{
                "self":"https://somebaseurl/inventory/managedObjects/5706682/assetParents",
                "references":[]
            },
            "self":"https://somebaseurl/inventory/managedObjects/5706682",
            "id":"5706682"
        },
        "self":"https://somebaseurl/inventory/managedObjects/5706999/assetParents/5706682"
    }]
},
"self":"https://somebaseurl/inventory/managedObjects/5706999",
"id":"5706999",
"c8y_ActiveAlarmsStatus":{
    "minor":0,
    "critical":1
},
"c8y_IsDevice":{},
"ax_Customer":"SOME CUSTOMER",
"c8y_SupportedMeasurements":["c8y_Temperature"]}"))

除了解析单个属性之外，将整个对象映射到 Apama 事件的推荐方法是什么？

如果您能提供代码片段，我们将不胜感激。

非常感谢马蒂亚斯

Answer 1

回答你的第一个问题。

打印语句的输出非常有帮助。它表明响应有效负载是原始 JSON 字符串而不是经过解析的 JSON object。这意味着 JOSN 编解码器跳过了对 JSON srting 的解码。如果 contentType header 不完全是 application/json，则在使用 "JSON with generic request/response event definitions" plug-in 时会发生这种情况。使用 Cumulocity 进行的测试表明，header 的值并不总是 application/json，而是可能类似于 application/vnd.com.nsn.cumulocity.managedobject+json 或 application/vnd.com.nsn.cumulocity.measurementcollection+json，而当前的 JSON 编解码器不能处理。

在 JSON 编解码器中没有任何更改的情况下，您可以通过两种方式处理它。

1) 禁用 JSON 编解码器

的消息过滤

"JSON with generic request/response event definitions" plug-in 使用的 JSON 编解码器配置为跳过未将 contentType header 设置为 [=12= 的解码消息].这可以通过编辑 Designer 项目中 "Connectivity and Adapters/HTTP Client/HTTPClient" 节点下的 HTTPClient.yaml 文件来禁用。将 filterOnContentType 属性设置为 false。这将导致所有响应都被处理为 JSON；如果负载不是 JSON，解析将失败并且消息将被丢弃。因此，仅当您确定所有响应都是 JSON.

时才启用此功能

2) 解析 EPL

中的 JSON 个字符串

其他选项可能是在 EPL 本身中将字符串解析为 JSON，然后将 JSON object 包装到 AnyExtractor 中以提取所需的值。你可以使用类似下面的东西来做到这一点。

using com.apama.json.JSONPlugin;
using com.apama.util.AnyExtractor;
...
action handleResponse(Response res) {
    if res.isSuccess() {
        log "Response is: " + res.toString();
        // Check if payload is string. A string payload could suggest raw JSON string
        switch (res.payload.data as payload) {
            case string: {
                // Parse the JSON string manually
                AnyExtractor extractor := AnyExtractor(JSONPlugin.fromJSON(payload));
                string name := extractor.getString("assetparents.references[0].managedObject.name");
            }
            default: { 
                // probably already parsed to JSON - use AnyExtractor to work on it
            }
        }
    } else {
        log "Failed: " + res.statusMessage at ERROR;
    }
}

Answer 2

回答你的第二个问题，即"what is the recommended way to map the entire object to an Apama event?":

我已经定义了几个事件，这些事件将映射到您提供的 JSON：

event Reference {
    string self;
    any managedObject;
}

event Object {
    string self;
    sequence<Reference> references;
}

event ActiveAlarmsStatus {
    integer minor;
    integer critical;
}
event IsDevice {}

event ManagedObject {
    string owner;
    string self;
    string id;
    string name;
    string creationTime;
    string lastUpdated;
    Object additionParents;
    Object childDevices;
    Object childAssets;
    Object childAdditions;
    Object deviceParents;
    Object assetParents;
    ActiveAlarmsStatus c8y_ActiveAlarmsStatus;
    IsDevice c8y_IsDevice;
    string ax_Customer;
    sequence<string> c8y_SupportedMeasurements;
}

因为 ManagedObject 包含一个 Object，而该对象又包含一个 Reference，而 Reference 本身又包含一个 ManagedObject，由于递归类型，EPL 无法编译。因此，在 Reference 中我们使用 any 类型来屏蔽 ManagedObject。这允许 EPL 编译。

但是，因为 any 隐藏了类型，我们不知道将它转换成什么类型，所以我们有一个包含字典的 any。不过这很好，因为我们可以使用一些辅助函数来提取我们想要的信息：

action GetSequenceReference(sequence<any> s) returns sequence<Reference> {
    sequence<Reference> ret := new sequence<Reference>;
    any r := new any;
    for r in s {
        ret.append(<Reference>r);
    }
    return ret;
}
action GetSequenceString(sequence<any> s) returns sequence<string> {
    sequence<string> ret := new sequence<string>;
    any r := new any;
    for r in s {
        ret.append(<string>r);
    }
    return ret;
}

action GetObject(any a) returns Object {
    log "Getting object from: " + a.toString() at INFO;
    dictionary<any,any> dict := <dictionary<any,any> >a;

    Object ret := new Object;

    ret.self := <string>dict.getDefault( "self", "" );
    ret.references := GetSequenceReference( <sequence<any> >dict.getDefault( "references", new sequence<any> ) );

    return ret;
}

action GetActiveAlarmsStatus(any a) returns ActiveAlarmsStatus {
    log "Getting active alarms status from: " + a.toString() at INFO;
    dictionary<any,any> dict := <dictionary<any,any> >a;

    ActiveAlarmsStatus ret := new ActiveAlarmsStatus;

    ret.minor := <integer>dict.getDefault( "minor", 0 );
    ret.critical := <integer>dict.getDefault( "critical", 0 );

    return ret;
}
action GetIsDevice(any a) returns IsDevice {
    log "Getting is device from: " + a.toString() at INFO;
    dictionary<any,any> dict := <dictionary<any,any> >a;

    IsDevice ret := new IsDevice;

    return ret;
}
action GetManagedObject(any a) returns ManagedObject {

    log "Getting managed object from: " + a.toString() at INFO;
    dictionary<any,any> dict := <dictionary<any,any> >a;

    ManagedObject ret := new ManagedObject;
    ret.owner := <string>dict.getDefault( "owner", "" );
    ret.self := <string>dict.getDefault( "self", "" );
    ret.id := <string>dict.getDefault( "id", "" );
    ret.name := <string>dict.getDefault( "name", "" );
    ret.creationTime := <string>dict.getDefault( "creationTime", "" );
    ret.lastUpdated := <string>dict.getDefault( "lastUpdated", "" );
    ret.additionParents := GetObject( dict.getDefault( "additionParents", new dictionary<any,any> ) );
    ret.childDevices := GetObject( dict.getDefault( "childDevices", new dictionary<any,any> ) );
    ret.childAssets := GetObject( dict.getDefault( "childAssets", new dictionary<any,any> ) );
    ret.childAdditions := GetObject( dict.getDefault( "childAdditions", new dictionary<any,any> ) );
    ret.deviceParents := GetObject( dict.getDefault( "deviceParents", new dictionary<any,any> ) );
    ret.assetParents := GetObject( dict.getDefault( "assetParents", new dictionary<any,any> ) );
    ret.c8y_ActiveAlarmsStatus := GetActiveAlarmsStatus( dict.getDefault( "c8y_ActiveAlarmsStatus", new dictionary<any,any> ) );
    ret.c8y_IsDevice := GetIsDevice( dict.getDefault( "c8y_IsDevice", new dictionary<any,any> ) );
    ret.ax_Customer := <string>dict.getDefault( "ax_Customer", "" );
    ret.c8y_SupportedMeasurements := GetSequenceString( <sequence<any> >dict.getDefault( "c8y_SupportedMeasurements", new sequence<any> ) );
    return ret;
}

使用这些辅助函数，我们可以从原始事件中提取信息：

action handleResponse(Response response){
    if response.isSuccess(){
        ManagedObject mo := GetManagedObject( response.payload.toDictionary() );
        log "###The response payload is :" + mo.toString() at INFO;
    }

    else {
        log "###Request failed. Response status is: " + response.statusCode.toString() + " | " + response.statusMessage at INFO;
    }
}

给你！一个完全映射的事件。

如何解析来自 HTTP JSON 响应负载的值

How to parse value from HTTP JSON response payload

apama

1) 禁用 JSON 编解码器

2) 解析 EPL