Node.js nestjs中的Observables-异步读取文件
我正在尝试一个异步读取json文件并将其作为响应(作为rxjs可观察数据)发送出去的用例。这是我使用的服务Node.js nestjs中的Observables-异步读取文件,node.js,rxjs,observable,nestjs,behaviorsubject,Node.js,Rxjs,Observable,Nestjs,Behaviorsubject,我正在尝试一个异步读取json文件并将其作为响应(作为rxjs可观察数据)发送出去的用例。这是我使用的服务 import { logger } from './../../shared/utils/logger'; import { Injectable } from '@nestjs/common'; import * as fs from 'fs'; import * as path from 'path'; import { BehaviorSubject, Observable, pi
import { logger } from './../../shared/utils/logger';
import { Injectable } from '@nestjs/common';
import * as fs from 'fs';
import * as path from 'path';
import { BehaviorSubject, Observable, pipe, of, from, throwError, merge} from 'rxjs';
import { map, filter, scan, take, debounce, switchMap, retry, catchError, mergeMap, delay, zip, tap, mapTo } from 'rxjs/operators';
import { HttpResponseModel } from '../model/config.model';
import { isNullOrUndefined } from 'util';
@Injectable()
export class NewProviderService {
serviceSubject: BehaviorSubject<HttpResponseModel[]>;
filePath: string;
httpResponseObjectArray: HttpResponseModel[];
constructor() {
this.serviceSubject = new BehaviorSubject<HttpResponseModel[]>([]);
this.filePath = path.resolve(__dirname, './../../shared/assets/httpTest.json');
this.setSubject();
}
readFileFromJSON() {
this.readFileFromJsonSync();
fs.exists(this.filePath.toString(), exists => {
if (exists) {
fs.readFile(this.filePath.toString(), 'utf-8', (err, data) => {
logger.info('file read without parsin', data);
this.httpResponseObjectArray = JSON.parse(data).HttpTestResponse;
logger.info('array obj is:', this.httpResponseObjectArray);
logger.info('file read after parsing', JSON.parse(data));
return this.httpResponseObjectArray;
});
} else {
return null;
}
});
}
getObservable(): Observable<HttpResponseModel[]> {
// create an observable
// return Observable.create(observer => {
// observer.next(this.readFileFromJSON());
// });
return of(this.readFileFromJsonSync()).pipe(map(data => {
logger.info('inside obs methid', data);
return data;
}));
}
setSubject() {
this.getObservable().subscribe(data => {
logger.info('data before setting in sub', data);
this.serviceSubject.next(data);
});
}
}
如果我同步读取文件,效果会很好
用以下方法替换readFileFromJSON()
,效果良好
readFileFromJsonSync(): HttpResponseModel[] {
const objRead = JSON.parse(fs.readFileSync(this.filePath.toString(), {encoding: 'utf-8'}));
logger.info('object read is', objRead.HttpTestResponse);
return objRead.HttpTestResponse;
}
因此,我在异步读取文件时遗漏了一些内容。我不确定我做错了什么。有人能帮忙吗?问题是您实际上没有在
readFileFromJSON
中返回任何内容。它将异步运行fs.exists
和fs.readFile
以及相应的回调,但回调的结果将被忽略
您应该使用承诺
。您可以自己创建一个Promise
,也可以使用像bluebird这样的库,将fs
从基于回调的API转换为基于Promise
的API。有关更多信息,请参阅
非常感谢。我像上面一样创建了一个promise API,并使用“from”操作符将observable方法转换为从promise读取。成功了!!!。
readFileFromJsonSync(): HttpResponseModel[] {
const objRead = JSON.parse(fs.readFileSync(this.filePath.toString(), {encoding: 'utf-8'}));
logger.info('object read is', objRead.HttpTestResponse);
return objRead.HttpTestResponse;
}
return new Promise(function(resolve, reject) {
fs.readFile(this.filePath.toString(), 'utf-8', (err, data) => {
if (err) {
reject(err);
} else {
const httpResponseObjectArray = JSON.parse(data).HttpTestResponse;
resolve(httpResponseObjectArray);
}
});
});