Question

我创建了一个处理数据库并从中选择数据的代码，它可以正常工作并获取数据这个代码：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


        Connection conn = null;
        Statement statement = null;


        String SelectQuiry = "SELECT `name`, `email`, `birtdate` FROM `table1` WHERE id = 1";
        try{
        conn = DriverManager.getConnection(Con_String, Username, Passsword);



        statement = conn.createStatement();    // create statement

        //statement.executeQuery(SelectQuiry);   // execute statement




        ResultSet RS = statement.executeQuery(SelectQuiry);   // execute statement 



        while(RS.next())
        {
            String name = RS.getString("name");
            String email = RS.getString("email");
            String birthday = RS.getString("birtdate");

        );

        }
        RS.close();


        }catch(Exception e)
        {


        }
        finally
        {
            if(statement != null)
            {conn.close();}

        }
        PrintWriter out = response.getWriter();


        out.println(HTML_START + "<h2>Hi There!</h2><br/>"
                    + "<h3>Name "+ name +"</h3> <br/>"
                    + "<h3>email "+ email +"</h3> <br/>"
                    + "<h3>Ubd "+ birthday +"</h3> <br/>"
                    +HTML_END);
          try {
            Class.forName("com.mysql.jdbc.Driver");
        } catch (ClassNotFoundException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

但是当我将这些代码执行到方法中并在doget中调用此方法时，它总是返回null 这是返回null的代码：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


    DbMangement dbmangement = new DbMangement();

    try {
        String[] person = dbmangement.SelectData();
        Username = person[0];
        email = person[1];
        birthday = person[2];
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    PrintWriter out = response.getWriter();


    out.println(HTML_START + "<h2>Hi There!</h2><br/>"
                + "<h3>Name "+ Username +"</h3> <br/>"
                + "<h3>email "+ email +"</h3> <br/>"
                + "<h3>Ubd "+ birthday +"</h3> <br/>"
                +HTML_END);
      try {
        Class.forName("com.mysql.jdbc.Driver");
    } catch (ClassNotFoundException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }



}

这是另一个班级

public class DbMangement {
    private static final String Username = "root";
    private static final String Passsword = "";
    private static final String Con_String ="jdbc:mysql://localhost/testdb";



    public  String[] SelectData() throws SQLException
    {

        Connection conn = null;
        Statement statement = null;
        String[] Person = null;

        //String SqlQuiry = "INSERT INTO table1 VALUES (1 , 'ahmed' , 'mohamed' , '12/2/2014') ";

        String SelectQuiry = "SELECT `name`, `email`, `birtdate` FROM `table1` WHERE id = 1";
        try{
        conn = DriverManager.getConnection(Con_String, Username, Passsword);
        //System.out.println("connected");


        statement = conn.createStatement();    // create statement

        //statement.executeQuery(SelectQuiry);   // execute statement




        ResultSet RS = statement.executeQuery(SelectQuiry);   // execute statement 
        //System.out.println("Executed !!");


        while(RS.next())
        {
            Person[0] = RS.getString("name");
            Person[1] = RS.getString("email");
            Person[2] = RS.getString("birtdate");

            //System.out.print("Name is "+UUsername +" Email Is : " +Uemail+ "bd is :" + Ubirthday);



        }
        RS.close();


        }catch(Exception e)
        {
            System.err.println(e);
            return null;

        }
        finally
        {
            if(statement != null)
            {conn.close();

            return Person;
            }

        }
        return Person;
        }

有任何建议请解决这个问题吗？

由于

Answer 1

看起来Person对象永远不会被初始化（例如：Person = new String[3]）。您只需将Person赋值为null，然后将其返回：

String[] Person = null;

...

while(RS.next()) {
    Person[0] = RS.getString("name");
    Person[1] = RS.getString("email");
    Person[2] = RS.getString("birtdate");

    //System.out.print("Name is "+UUsername +" Email Is : " +Uemail+ "bd is :" + Ubirthday);
}

...

return Person;

mysql数据库的servlet返回null

1 个答案: