具有泛型类型的 WebFlux WebClient

Question

我正在尝试使用 Spring WebFlux 中的 WebClient 创建一个客户端库。

服务器返回类似 JSON 的响应：

{
  "result": [
    {
      "parent": "",
      "made_sla": "true",
      "watch_list": "",
      "upon_reject": "cancel",
      "sys_updated_on": "2016-01-19 04:52:04",
      "approval_history": "",
      "number": "PRB0000050",
      "sys_updated_by": "glide.maint",
      "opened_by": {
        "link": "https://instance.service-now.com/api/now/table/sys_user/glide.maint",
        "value": "glide.maint"
      },
      "user_input": "",
      "sys_created_on": "2016-01-19 04:51:19",
      "sys_domain": {
        "link": "https://instance.service-now.com/api/now/table/sys_user_group/global",
        "value": "global"
      },
      "state": "4",
      "sys_created_by": "glide.maint",
      "knowledge": "false",
      "order": "",
      "closed_at": "2016-01-19 04:52:04",
      "cmdb_ci": {
        "link": "https://instance.service-now.com/api/now/table/cmdb_ci/55b35562c0a8010e01cff22378e0aea9",
        "value": "55b35562c0a8010e01cff22378e0aea9"
      },
      "delivery_plan": "",
      "impact": "3",
      "active": "false",
      "work_notes_list": "",
      "business_service": "",
      "priority": "4",
      "sys_domain_path": "/",
      "time_worked": "",
      "expected_start": "",
      "rejection_goto": "",
      "opened_at": "2016-01-19 04:49:47",
      "business_duration": "1970-01-01 00:00:00",
      "group_list": "",
      "work_end": "",
      "approval_set": "",
      "wf_activity": "",
      "work_notes": "",
      "short_description": "Switch occasionally drops connections",
      "correlation_display": "",
      "delivery_task": "",
      "work_start": "",
      "assignment_group": "",
      "additional_assignee_list": "",
      "description": "Switch occasionally drops connections",
      "calendar_duration": "1970-01-01 00:02:17",
      "close_notes": "updated firmware",
      "sys_class_name": "problem",
      "closed_by": "",
      "follow_up": "",
      "sys_id": "04ce72c9c0a8016600b5b7f75ac67b5b",
      "contact_type": "phone",
      "urgency": "3",
      "company": "",
      "reassignment_count": "",
      "activity_due": "",
      "assigned_to": "",
      "comments": "",
      "approval": "not requested",
      "sla_due": "",
      "comments_and_work_notes": "",
      "due_date": "",
      "sys_mod_count": "1",
      "sys_tags": "",
      "escalation": "0",
      "upon_approval": "proceed",
      "correlation_id": "",
      "location": ""
    },
    {
      "parent": "",
      "made_sla": "true",
      "watch_list": "",
      "upon_reject": "cancel",
      "sys_updated_on": "2016-01-19 04:52:04",
      "approval_history": "",
      "number": "PRB0000050",
      "sys_updated_by": "glide.maint",
      "opened_by": {
        "link": "https://instance.service-now.com/api/now/table/sys_user/glide.maint",
        "value": "glide.maint"
      },
      "user_input": "",
      "sys_created_on": "2016-01-19 04:51:19",
      "sys_domain": {
        "link": "https://instance.service-now.com/api/now/table/sys_user_group/global",
        "value": "global"
      },
      "state": "4",
      "sys_created_by": "glide.maint",
      "knowledge": "false",
      "order": "",
      "closed_at": "2016-01-19 04:52:04",
      "cmdb_ci": {
        "link": "https://instance.service-now.com/api/now/table/cmdb_ci/55b35562c0a8010e01cff22378e0aea9",
        "value": "55b35562c0a8010e01cff22378e0aea9"
      },
      "delivery_plan": "",
      "impact": "3",
      "active": "false",
      "work_notes_list": "",
      "business_service": "",
      "priority": "4",
      "sys_domain_path": "/",
      "time_worked": "",
      "expected_start": "",
      "rejection_goto": "",
      "opened_at": "2016-01-19 04:49:47",
      "business_duration": "1970-01-01 00:00:00",
      "group_list": "",
      "work_end": "",
      "approval_set": "",
      "wf_activity": "",
      "work_notes": "",
      "short_description": "Switch occasionally drops connections",
      "correlation_display": "",
      "delivery_task": "",
      "work_start": "",
      "assignment_group": "",
      "additional_assignee_list": "",
      "description": "Switch occasionally drops connections",
      "calendar_duration": "1970-01-01 00:02:17",
      "close_notes": "updated firmware",
      "sys_class_name": "problem",
      "closed_by": "",
      "follow_up": "",
      "sys_id": "04ce72c9c0a8016600b5b7f75ac67b5b",
      "contact_type": "phone",
      "urgency": "3",
      "company": "",
      "reassignment_count": "",
      "activity_due": "",
      "assigned_to": "",
      "comments": "",
      "approval": "not requested",
      "sla_due": "",
      "comments_and_work_notes": "",
      "due_date": "",
      "sys_mod_count": "1",
      "sys_tags": "",
      "escalation": "0",
      "upon_approval": "proceed",
      "correlation_id": "",
      "location": ""
    },
    {
      "parent": "",
      "made_sla": "true",
      "watch_list": "",
      "upon_reject": "cancel",
      "sys_updated_on": "2016-01-19 04:52:04",
      "approval_history": "",
      "number": "PRB0000050",
      "sys_updated_by": "glide.maint",
      "opened_by": {
        "link": "https://instance.service-now.com/api/now/table/sys_user/glide.maint",
        "value": "glide.maint"
      },
      "user_input": "",
      "sys_created_on": "2016-01-19 04:51:19",
      "sys_domain": {
        "link": "https://instance.service-now.com/api/now/table/sys_user_group/global",
        "value": "global"
      },
      "state": "4",
      "sys_created_by": "glide.maint",
      "knowledge": "false",
      "order": "",
      "closed_at": "2016-01-19 04:52:04",
      "cmdb_ci": {
        "link": "https://instance.service-now.com/api/now/table/cmdb_ci/55b35562c0a8010e01cff22378e0aea9",
        "value": "55b35562c0a8010e01cff22378e0aea9"
      },
      "delivery_plan": "",
      "impact": "3",
      "active": "false",
      "work_notes_list": "",
      "business_service": "",
      "priority": "4",
      "sys_domain_path": "/",
      "time_worked": "",
      "expected_start": "",
      "rejection_goto": "",
      "opened_at": "2016-01-19 04:49:47",
      "business_duration": "1970-01-01 00:00:00",
      "group_list": "",
      "work_end": "",
      "approval_set": "",
      "wf_activity": "",
      "work_notes": "",
      "short_description": "Switch occasionally drops connections",
      "correlation_display": "",
      "delivery_task": "",
      "work_start": "",
      "assignment_group": "",
      "additional_assignee_list": "",
      "description": "Switch occasionally drops connections",
      "calendar_duration": "1970-01-01 00:02:17",
      "close_notes": "updated firmware",
      "sys_class_name": "problem",
      "closed_by": "",
      "follow_up": "",
      "sys_id": "04ce72c9c0a8016600b5b7f75ac67b5b",
      "contact_type": "phone",
      "urgency": "3",
      "company": "",
      "reassignment_count": "",
      "activity_due": "",
      "assigned_to": "",
      "comments": "",
      "approval": "not requested",
      "sla_due": "",
      "comments_and_work_notes": "",
      "due_date": "",
      "sys_mod_count": "1",
      "sys_tags": "",
      "escalation": "0",
      "upon_approval": "proceed",
      "correlation_id": "",
      "location": ""
    }
  ]
}

result 字段包含元素数组，这些元素可能因所使用的 API 而异。

有关该 API 的更多信息是来自 ServiceNow 产品的Table API。

正如您在文档中看到的那样，API 路径类似于：GET /now/table/{tableName}，其中 tableName 可能是不同的值，结果元素拓扑将取决于获取的表。

因此结果字段中的响应元素可以由不同的名称或不同数量的属性组成。基本上它是一个通过 HTTP 公开的数据库，因此每个表都可以由不同数量的列组成。

我的 GET 实现：

public Mono<Result> get(){
    return client.get()
            .uri(uriBuilder -> uriBuilder
                    .path(this.tablePath)
                    .queryParam("active", "true")
                    .queryParam("state", "1")
                    .build())
            .accept(MediaType.APPLICATION_JSON)
            .retrieve()
            .bodyToMono(Result.class);
}

POJO

@Data
public class ProjectTask {

    private String project;

}

@Data
public class Result <T> {

    List<T> result;

}

获取错误的简单用法：

List<ProjectTask> projectTasks = Objects.requireNonNull(
        client.table("pm_project_task")
                .get().block())
        .getResult();

for (ProjectTask task : projectTasks){
    System.out.println("========PROJECT=============== "+task.getProject());
}

for (ProjectTask task : projectTasks){ 行我的运行时错误

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to my.namespace.api.services.servicenow.model.ProjectTask

响应需求：

• 结果 POJO 必须使用通用类型来管理不同的响应元素类型。
• 如果无法完成第一点，请尝试提供一种解决方案，通过针对不同表类型的可重用 GET 实现来获取该 API。
• 我不想从客户端返回 List，我的想法是这个库只返回 Mono 或 Flux 对象。

Answer 1

您需要使用 parameterizedtypereference 将 json 反序列化为 Result 的确切类型。否则 Spring 将任何未知类型反序列化为 LinkedHashMap。 例如。

  public Mono<Result<ProjectTask>> get(){
    return client.get()
        .uri(uriBuilder -> uriBuilder
            .path(this.tablePath)
            .queryParam("active", "true")
            .queryParam("state", "1")
            .build())
        .accept(MediaType.APPLICATION_JSON)
        .retrieve()
        .bodyToMono(new ParameterizedTypeReference<Result<ProjectTask>>() {
        });
  }

如果你想让get这个方法成为一个通用方法，它适用于所有类型的Result，那么你应该看看this stackoverflow question。