javascript - Angular 5 不显示服务器的响应值

Question

看来我的客户端没有捕获来自服务器的响应值并显示它。

这是我的组件代码:

export class MyComponent implements OnInit {

  data: string;

  constructor(private myService: MyService) {}

  ngOnInit() {}

  testCall() {
    this.myService.getData().subscribe(data => this.data = data);
    console.log("Data: " + this.data);
  }
}

服务代码:

@Injectable()
export class MyService {

  private url = 'http://localhost:5000/myproj/api/test';

  constructor(private http: HttpClient) { }

  // Get data from the server
  getData(): Observable<string> {
    console.log("in getData() method");
    return this.http.get<string>(this.url)
      .pipe(
        catchError(this.handleError) // then handle the error
      );
  }

  private handleError(error: HttpErrorResponse) {
    if (error.error instanceof ErrorEvent) {
      // A client-side or network error occurred. Handle it accordingly.
      console.error('An error occurred:', error.error.message);
    } else {
      // The backend returned an unsuccessful response code.
      // The response body may contain clues as to what went wrong,
      console.error(
        `Backend returned code ${error.status}, ` +
        `body was: ${error.error}`);
    }
    // return an observable with a user-facing error message
    return new ErrorObservable('Something went wrong; please try again later.');
  };
}

请求发送到服务器，服务器以响应正文中的数据和状态代码 200 进行响应，您可以在 Internet Explorer 的开发人员工具中看到该状态代码:

但由于某种原因，当我调用服务方法getData()时，Angular客户端代码调用我定义的catchError()方法，并打印:

Backend returned code 200, body was: [object Object]
ERROR Something went wrong; please try again later.

为什么服务器返回状态 200(正常)，但 Angular 客户端却调用 catchError() 方法？

编辑:

这是我的服务器端 API 代码:

@RequestMapping(value = "/test", method = RequestMethod.GET, produces = "text/plain")
    public String testApi(HttpServletRequest request) {

        System.out.println("in /test");

        String response = "my response";

        return response;
    }

Answer 1

响应正文不是正确的 JSON 格式，因此反序列化时会产生“无效字符”错误。该服务需要正确格式的 JSON。

使用“application/json”更新您的 API 以返回有效的 JSON 对象并返回一个对象，如以下帖子所示:Spring MVC - How to return simple String as JSON in Rest Controller