HarmonyOS 超长JSON字符串解析

参考如下demo，日志过长需要进行分段打印：

import { BusinessError, request } from '@kit.BasicServicesKit';
import fs from '@ohos.file.fs';
import common from '@ohos.app.ability.common';
import buffer from '@ohos.buffer';
import util from '@ohos.util';
import { JSON } from '@kit.ArkTS';

// 获取应用文件路径
let context = getContext(this) as common.UIAbilityContext;
let filesDir = context.filesDir;

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';
  @State jsonStr: string = '';

  async download() {
    let config: request.agent.Config = {
      action: request.agent.Action.DOWNLOAD,
      url: 'https://app-demo.iandun.com/settings.json?v=1718157761736', // 需要手动将 url 替换为真实服务器的 HTTP 协议地址
      overwrite: true,
      saveas: filesDir + '/jsonStr.text' // 存储地址
    };
    try {
      request.agent.create(context, config).then((task: request.agent.Task) => {
        console.info(`Succeeded in creating a download task. result: ${task.config}`);
        console.info("存储地址：" + filesDir + '/jsonStr.text');
        task.start();
      }).catch((err: BusinessError) => {
        console.error(`Failed to create a download task, Code: ${err.code}, message: ${err.message}`);
      });
    } catch (e) {
      console.log(JSON.stringify(e))
    }
  }

  async readLocalFileWithStream(path: string) {
    try {
      // 存储每次读取的结果
      let buffers: buffer.Buffer[] = [];
      // 打开文件流
      let inputStream = fs.createStreamSync(path, 'r+');
      // 以流的形式读取源文件内容
      let bufSize = 4096;
      let readSize = 0;
      let buf = new ArrayBuffer(bufSize);

      class Option {
        public offset: number = 0;
        public length: number = bufSize;
      }

      let option = new Option();
      option.offset = readSize;
      let readLen = await inputStream.read(buf,
        option);
      // 存储当前读取结果
      buffers.push(buffer.from(buf.slice(0, readLen)))
      readSize += readLen;
      while (readLen > 0) {
        option.offset = readSize;
        readLen = await inputStream.read(buf,
          option);
        // 存储当前读取结果
        buffers.push(buffer.from(buf.slice(0, readLen)))
        readSize += readLen;
      }
      // 关闭文件流
      inputStream.closeSync();

      // 合并内容
      let finalBuf: ArrayBuffer = buffer.concat(buffers).buffer
      console.info(`final ArrayBuffer byteLength is ${finalBuf.byteLength}}`)
      // ArrayBuffer转string
      let textDecoder = util.TextDecoder.create('utf-8');
      let finalUnit = new Uint8Array(finalBuf)
      this.jsonStr = textDecoder.decodeWithStream(finalUnit)
      console.info(`final str Length is ${this.jsonStr.length}}`)
      // 修改打印日志输出大小, IDE控制台日志输出的设置：File->setting->Editor->general->Console下，有个override console cycle buffer size选项
      // 仍然超过需要分段打印
      console.info('final str is ' + this.jsonStr)
    } catch (error) {
      let err = error as BusinessError;
      console.error(`readLocalFileWithStream failed, code is ${err.code},message is ${err.message}`);
    }
  }

  build() {
    Column() {
      Text(this.message)
        .id('DownloadPageHelloWorld')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)
        .onClick(() => {
          this.download()
        })
      Text("获取json")
        .id('DownloadPageHelloWorld')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)
        .onClick(() => {
          this.readLocalFileWithStream(filesDir + '/jsonStr.text')
        })
    }
  }
}