spring integration spel 表达式从消息有效负载中提取字段

Question

对于消息有效负载，我无法理解 SPEL。我想从我的消息有效负载的某些字段中提取数据，这些字段本质上是将以下 JSON 转换为 Map<String, Object> 并传递给 @Transformer

{
  "expand":"renderedFields,names,schema,transitions,operations,editmeta,changelog,versionedRepresentations",
  "id":"14730",
  "self":"https://jira.foo.com/rest/api/2/issue/14730",
  "key":"SDP-145",
  "fields":{
    "issuetype":{
      "self":"https://jira.foo.com/rest/api/2/issuetype/10200",
      "id":"10200",
      "description":"gh.issue.epic.desc",
      "iconUrl":"https://jira.foo.com/ghanghor/viewkaka?size=xsmall&kakaId=10501&kakaType=issuetype",
      "name":"Epic",
      "subtask":false,
      "kakaId":10501
    },
    "priority":{
      "self":"https://jira.foo.com/rest/api/2/priority/3",
      "iconUrl":"https://jira.foo.com/images/icons/priorities/major.svg",
      "name":"Major",
      "id":"3"
    },
    "labels":[
      "Lizzy",
      "kanban",
      "rughani"
    ],
    "updated":"2021-01-21T10:33:38.000+0000",
    "status":{
      "self":"https://jira.foo.com/rest/api/2/status/1",
      "description":"The issue is open and ready for the assignee to start work on it.",
      "iconUrl":"https://jira.foo.com/images/icons/statuses/open.png",
      "name":"Open",
      "id":"1",
      "statusCategory":{
        "self":"https://jira.foo.com/rest/api/2/statuscategory/2",
        "id":2,
        "key":"new",
        "colorName":"blue-gray",
        "name":"To Do"
      }
    },
    "summary":"new epic for Tazzy",
    "creator":{
      "self":"https://jira.foo.com/rest/api/2/user?username=skadmin",
      "name":"skadmin",
      "key":"skadmin",
      "emailAddress":"Lizzy.t@foo.com",
      "displayName":"Lizzy Rughani",
      "active":true,
      "timeZone":"Asia/Kolkata"
    },
    "subtasks":[

    ],
  }
}

我对这里的三个嵌套值感兴趣，我试图通过以下表达式获取它们

issueDataMap = {LinkedHashMap@4867}  size = 3
 "name" -> "#payload['fields']['summary']"
 "description" -> "#payload['description']"
 "text3" -> "#payload['key']"

应用表达式时出现此错误

org.springframework.expression.spel.SpelEvaluationException: EL1012E: Cannot index into a null value

这是我如何在我的转换器的 as 参数中获取有效负载

@Transformer
public Map<String, Object> generateCardData(Map<String, Object> payload,
                                            @Header("X-UPSTREAM-WEBHOOK-SOURCE") String projectId) {

紧随其后

StandardEvaluationContext evaluationContext = evaluationContextFactory.getObject();

我是这样评价的

new SpelExpressionParser().parseExpression(issueDataMap.get(key)).getValue(
                            evaluationContext, payload, String.class)));

我有使用@SpringBootApplication 和@EnableInegration 注释的应用程序，并且我自动装配IntegrationEvaluationContextFactoryBean 的实例以获取StandardEvaluationContext

我也试过变种

issueDataMap = {LinkedHashMap@4867}  size = 3
 "name" -> "payload['fields']['summary']"
 "description" -> "payload['description']"
 "text3" -> "payload['key']"

然后我明白了

EL1008E: Property or field 'payload' cannot be found on object of type 'java.util.LinkedHashMap' - maybe not public or not valid?

Answer 1

首先，当您拥有对对象的完全访问权限时，为什么要在代码中手动使用 SpEL 尚不清楚。另外，您应该记住，创建StandardEvaluationContext、解析表达式并在每次调用时对其进行评估对性能来说是一种开销。您可能只需要更改您的 generateCardData() 签名以接受表达式的结果而不是整个地图。请参阅@Payload.expression 属性。

无论如何，对于您的问题，这不是您想听到的。它在这里： getValue(evaluationContext, payload, String.class)))。根评估对象是您的payload - Map。因此，您只需要在表达式定义中假设您可以访问该根对象。因此表达式必须是这样的：fields.summary、description、key。

您通常会在文档中看到 payload（或 header）作为表达式中的第一个标记。这只是因为 Spring Integration 使用 Message 作为表达式求值的根对象。

现在关于性能。即使您的逻辑是在运行时通过某个键选择表达式 (issueDataMap.get(key))，您仍然只能解析一次。