我在servlet中创建一个名为“论坛”的项目。
但我坚持查询以从数据库中获取有关给定主题的结果...
我制作了一个名为index的servlet，当我单击该主题时，其中有一个主题。我收到某种错误，例如MessageDisplayed servlet的“ where子句”中的Unknown列“ pepsi” ...我认为查询中存在问题...
索引servlet的编码为：
@WebServlet("/Index")
public class Index extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String url = "jdbc:mysql://localhost:3306/df";
String driver = "com.mysql.jdbc.Driver";
String USER = "root";
String PASS = "root";
try {
Class.forName(driver);
Connection conn = (Connection) DriverManager.getConnection(url, USER, PASS);
out.print("<html><body>");
out.print("<a href='PostTopic'><input type='submit' value='Post New Topic'></a><br><br>");
String sql = "select topic_name from topic";
PreparedStatement ps = conn.prepareStatement(sql);
ResultSet rs = ps.executeQuery();
while(rs.next()){
String topic_name = rs.getString("topic_name");
HttpSession session = request.getSession();
session.setAttribute("topic_name", topic_name);
out.print("<a href='MessageDisplayed'>");
out.print(topic_name);out.print("</a>");
out.print("<br>");
}
out.print("</body></html>");
} catch (Exception e) {
out.print(e.getMessage());
}
out.close();
}
}
而MessageDisplayed servlet的编码为：
public class MessageDisplayed extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String url = "jdbc:mysql://localhost:3306/df";
String driver = "com.mysql.jdbc.Driver";
String USER = "root";
String PASS = "root";
try{
Class.forName(driver);
Connection conn = (Connection) DriverManager.getConnection(url, USER, PASS);
HttpSession session = request.getSession();
String topic = (String) session.getAttribute("topic_name");
String sql = "select user_name,comment from comments where topic_name="+topic;
PreparedStatement ps = conn.prepareStatement(sql);
// ps.setString(1, topic);
ResultSet rs = ps.executeQuery();
while(rs.next()){
String name = rs.getString("user_name");
String comment = rs.getString("comment");
out.print("<html><body>");
out.print("Name : "+name);out.print("<br>");out.print("Message : "+comment);out.print("<br>");
out.print("</body></html>");
}
}
catch(Exception e){
out.print(e.getMessage());
}
out.close();
}
}
该数据库有2个表主题表（topic_id，topic_name）和注释表（comment_id，comment，user_name，topic_id），插入工作正常。
但我无法获取结果
请尽快帮助我。
最佳答案
我认为这行是错误的
String sql = "select user_name,comment from comments where topic_name="+topic;
此外，您使用的方式也不是使用PreparedStatement的正确方式。
用这种方式
PreparedStatement ps = conn.prepareStatement("select user_name,comment from comments where topic_name=?");
ps.setString(1,topic);
关于java - 卡在创建查询以从数据库中获取结果吗？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/20312150/