Sending date input via json

I have a ionic project which has a formulary that i send via HTTP as JSON to my java REST API and then to my database. Everything works fine when using only strings and numbers. But now i need to send one of the inputs as date type. How can i convert the date type so i can pass it as json? And how do i need to recieve it in my java API?

Date input

 <input formControlName="startDate"  type="date" useValueAsDate/>

Http method

postData(params){
    let headers = new Headers();
    headers.append('Content-type','application/json');
    return this.http.post(this.api,params,{
      headers: headers
  }).map(
    (res:Response) => {return res.json();}
  );