嵌套异常是什么意思java.lang.NumberFormatException？

Question

无法将类型“ java.lang.String”的值转换为所需的类型“ int”；嵌套的异常为java.lang.NumberFormatException：对于输入字符串：“ {” joinDate“：null，” name“：” Hamza“，” hospital_Clinic“：null，” doctor_name“：” Dr.Iqra“，” p_id“：4 }” ，在客户端，它获取ID但无法将其删除，每次发生相同的错误时，我都无法理解这里发生的事情，谁能解释一下为什么这个错误再次出现，谢谢，这是代码：

#provider.ts

@Injectable()
export class DatabasedataProvider {
  public allpatient:Patient[]=[];
  public url:string = "http://localhost:8080";


  constructor(private http: HttpClient) {

  }
  getAllPatient(): Observable<any> {

    return this.http.get(this.url+'/patients')

  }



  addPatient(Patient_add:Patient): Observable<any> {

    let body = JSON.stringify(Patient_add);
    return this.http.post(this.url+'/patients', body)
 }


  deletePatient(patient:Patient): Observable<any>{
    let body=JSON.stringify(patient);
    return this.http.delete(this.url+'/patients/'+body);

  }


  editPatient(item:Patient) : Observable<any> {

    let body = JSON.stringify(item);
    return this.http.post('http://localhost:8080/patients/'+item, body)


  }


  }

#view/delete.ts

deletePatient(id:Patient){

    this.databasedata.deletePatient(id).subscribe(

      (data:any)=>{

        if(data.affectedRows==1){
           let mes=this._toast.create({
            message:'Task Deleted Successfully',
            duration:2000,
            position:'bottom'
          });

          this.AllPatient.splice(this.AllPatient.indexOf(id),1);
          mes.present();
        }

        else{
          let mes=this._toast.create({
            message:'Error in deleting task',
            duration:2000,
            position:'bottom'
          });
          mes.present();
        }
      }
  ,)}