Question

现在我想在jsp中获取这些值我的代码在这里

 <jsp:useBean id="loginBean" scope="session" class="vustudent.Login" />
        <input type="text" name="takei" value='<jsp:getProperty name="loginBean" property="loginid" />' />
        <%
            String dbId = request.getParameter("takei");
            Class.forName("org.apache.derby.jdbc.ClientDriver");
            String url= "jdbc:derby://localhost:1527/sample;create=true; user=app; password=app";
            Connection con = DriverManager.getConnection(url);  
            Statement st= con.createStatement();
            String query = "SELECT * FROM PARKTABLE WHERE ID =\'"+ dbId + "\' ";
            ResultSet rs = st.executeQuery(query);
            // iterate through the java resultset
      if (rs.next())
      {
        String placeOne = rs.getString("Place1");
        String placeTwo = rs.getString("Place2"); 
        System.out.println("place1" +placeOne);
        System.out.println("place1" +placeTwo);
      }
        %>
        </br>
        <input type="text" name="pl1value" value='placeOne' />

它在输入文本字段中打印placeOne而不是其值。我想从数据库中打印placeOne值红色或绿色。哪里错了？

Answer 1

需要进行三项更改

  String placeOne = null; // declare here
  String placeTwo = null; 
  if (rs.next())
  {
    placeOne = rs.getString("Place1");  // set value here
    placeTwo = rs.getString("Place2"); 
    System.out.println("place1" +placeOne);
    System.out.println("place1" +placeTwo);
  }
    %>
    </br>
    <input type="text" name="pl1value" value=''<%=placeOne%>' />  // print here

Answer 2

更改输入文字如下：

<input type="text" name="pl1value" value='<%=placeOne%>' />

然后，更改您的Java代码，如下所示：

String placeOne = "";
String placeTwo = "";

 if (rs.next())
      {
        placeOne = rs.getString("Place1");
        placeTwo = rs.getString("Place2"); 
        System.out.println("place1" +placeOne);
        System.out.println("place1" +placeTwo);
      }

因此，即使您的查询没有返回任何数据，您的输入类型也可以打印默认值。

Answer 3

作为Scary Wombat和Ye Win的帖子，它们在逻辑上是正确的。如果我是你，我实际上会使用PreparedStatement而不是Statement。我将使用while语句而不是if。请参阅下面的代码。

        String dbId = request.getParameter("takei");
        Class.forName("org.apache.derby.jdbc.ClientDriver");
        String url= "jdbc:derby://localhost:1527/sample;create=true; user=app; password=app";
        Connection con = DriverManager.getConnection(url);  
        String query = "SELECT * FROM PARKTABLE WHERE ID = ?";
        PreparedStatement st= con.prepareStatement(query);
        st.setString(0,dbId);
        ResultSet rs = st.executeQuery();

        String placeOne = null;
        String placeTwo = null;

        while (rs.next()) {
            String placeOne = rs.getString("Place1");
            String placeTwo = rs.getString("Place2"); 
            System.out.println("place1" +placeOne);
            System.out.println("place1" +placeTwo);
        }

我使用PreparedStatement来防止SQL注入，就像你在Statement上所做的那样，但是当其他程序员看到它时，它更具可读性和清晰性。我一直用ResultSet检索你的所有结果。

从数据库表中获取id =？的java

3 个答案: