void无法解除引用

Question

我有一个编辑成员的方法,我想将错误打印到文件中,但如果我尝试将堆栈跟踪打印到Error_Report.txt文件中,我一直无法取消引用错误.无论如何我可以把它打印出来吗？这是我的代码.

public void edit() {
  FileWriter fw = new FileWriter(new File("Error_Report.txt"));
  Connection con;
  Statement stmt;
  ResultSet rs;

  int id = (int)_id.getSelectedItem();
  String name = _name.getText();
  String user = _username.getText();
  String pass = _password.getText();
  String pos = _position.getSelectedItem().toString();

  try {
    Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
    con = DriverManager.getConnection("jdbc:odbc:collegesys", 
                                      "root", "0blivi0n");

    stmt = con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
                               ResultSet.CONCUR_READ_ONLY);

    PreparedStatement prep = con.prepareStatement("UPDATE `main` WHERE ID = ?");
    prep.setInt(1, id);
    prep.setString(2, name);
    prep.setString(3, user);
    prep.setString(4, pass);
    prep.setString(5, pos);

    prep.execute();
  } catch(SQLException sqle) {
    String sql = sqle.printStackTrace().toString();
    fw.write("" + sql);
  } catch(ClassNotFoundException cnfe) {
    fw.write("" + cnfe);
  }
}

Answer 1

你的问题是printStackTrace没有返回任何东西,所以没有什么可以转换为字符串.像这样写.

PrintWriter writer = new PrintWriter(fw);
sqle.printStackTrace(writer);
writer.close();