从数据库 table 中获取值，其中 id = ? java

Question

我有一个table Table name is PARKTABLE

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 而不是它的值。我想从数据库中打印 placeOne 值红色或绿色。我哪里错了？

Answer 1

需要进行三处更改

  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

如下更改您的输入文本：

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

然后，更改您的 Java 代码如下：

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);
      }

所以你的输入类型可以打印默认值，即使你的查询return没有数据。

Answer 3

Scary Wombat 和 Ye Win 的帖子在逻辑上是正确的。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，就像您在 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洁性。我用 while 在 ResultSet.

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从数据库 table 中获取值，其中 id = ? java

get value from database table where id = ? java

java

sql

jsp

derby