我想从用户那里获取数据，并将其与我的java数据库进行比较

如标题所示，我已尽力将用户输入与我的数据库进行比较，它与真实输入一起工作，但当我的数据库中不存在输入时，我不知道我下面的代码有什么问题，请帮助

 private class da implements ActionListener{
     public void actionPerformed(ActionEvent e){
               Connection con = null;
          Statement state = null;
          Statement state2 = null;
          ResultSet rs = null;
          ResultSet rs2 = null;
          String url = "jdbc:mysql://localhost:3306/المكتبة";
          String unicode = "?useUnicode=yes&characterEncoding=UTF-8";
      try{
    con = DriverManager.getConnection(url+unicode,"root","");
    state = con.createStatement();
    state2 = con.createStatement();
    rs = state.executeQuery("SELECT * FROM library WHERE author ='"+name.getText()+"'")
            ;
   rs2=state2.executeQuery("SELECT * FROM library WHERE bookname ='"+title.getText()+"'");




    while(rs.next()){
        String authorname = rs.getString("author");
        String bookname = rs.getString("bookname");
        String categort = rs.getString("category");
        int isbn = Integer.parseInt(rs.getString("ISBN"));
        String data = "اسم المؤلف: "+authorname+"\n"+"اسم الكتاب: "+bookname+"\n"+"التصنيف: "+categort+"\n"+"ISBN: "+isbn;



            if(name.getText().trim().equals(authorname))
                txt.setText(data);
            else
                txt.setText("dosen't exist");










    }

    while(rs2.next()){
        String authorname = rs.getString("author");
        String bookname = rs.getString("bookname");
        String categort = rs.getString("category");
        int isbn = Integer.parseInt(rs2.getString("ISBN"));
        String data2 = "اسم المؤلف: "+authorname+"\n"+"اسم الكتاب: "+bookname+"\n"+"التصنيف: "+categort+"\n"+"ISBN: "+isbn;
       txt.setText(data2);

    }
      }
      catch(Exception t){

      }

} }

}

---

首先，不要在sql查询中使用字符串组合，请使用PreparedStatement

试着这样做：

PreparedStatement upd = connect.prepareStatement("select * from library where author=?");
upd.setString(1,VariableToholdAuthor);

ResultSet rs = upd.executeQuery();
while(rs.next())
{
  CompareVariable = rs.getString("name");
}

这对你有帮助