my problem has been solved. It is the timeout of webpack's proxy default setting. Just modify the default timeout.

the following key points:

timeout: 1920000,
detailed configuration:

proxyTable: {

    timeout: 1920000,
  }
},

searched for a long time and found this similar problem on stackoverflow,
https://stackoverflow.com/que...

I felt that this might be the reason, and then I created a new project on this machine that did not use proxy and found that there was no 2-minute limit, so it was very likely that the webpack agent set the timeout. I looked around the webpack official website and did not find the corresponding api
https://webpack.js.org/config...

I set a timeout of 5 minutes at the front end,

No timeout is set for the backend springboot;

however, two minutes after the request is made, the browser prompts for a timeout;

where are these two minutes set? Where is the default configuration of the browser or the back end

https://stackoverflow.com/que...

what web address? The web site was intercepted.
doesn't seem to work!

  dev: {
    // Paths
    assetsSubDirectory: 'static',
    assetsPublicPath: '/',
    proxyTable: {
      '/api': {
        timeout: 1920000,
        target: 'http://127.0.0.1:3006', // 
        changeOrigin: true, // 
        pathRewrite: {
          '^/api': '' // 
        },
        onProxyRes (proxyRes, req, res) {
          // console.log(req)
        }
      }
    },