npm install @codingame/monaco-languageclient-react You need to create an infrastructure object and render the LanguageClient component:
import React from "react";
import LanguageClient, { Infrastructure } from "@codingame/monaco-languageclient-react";
class MyInfrastructure implements Infrastructure {
  automaticTextDocumentUpdate = false
  rootUri = 'file://...'
  useMutualizedProxy() { return false }
  getFileContent(resource, languageClient) { return ... }
  openConnection(id) {
    // create connection
  }
}
const infrastructure = new MyInfrastructure()
function LanguageClientContainer() {
  return (
   <LanguageClient
     id='java'
     infrastructure={infrastructure}
   />
  );
}