如何修改Web的userAgent参数？

import web_webview from '@ohos.web.webview' 
import business_error from '@ohos.base' 
 
@Entry 
@Component 
struct WebComponent { 
  controller: web_webview.WebviewController = new web_webview.WebviewController(); 
  @State customUserAgent: string = 'test' 
 
  build() { 
    Column() { 
      Button('setCustomUserAgent') 
        .onClick(() => { 
          try { 
            let userAgent = this.controller.getUserAgent() + this.customUserAgent; 
            this.controller.setCustomUserAgent(userAgent); 
          } catch (error) { 
            let e:business_error.BusinessError = error as business_error.BusinessError; 
            console.error(`ErrorCode: ${e.code},  Message: ${e.message}`); 
          } 
        }) 
      Web({ src: 'http://www.huawei.com', controller: this.controller }) 
    } 
  } 
}