Question

我有这堂课：

public class Interets {
    static Statement St ;
    public ResultSet rs;

    public Interets(Integer IdUser) throws SQLException, ServletException, IOException{
        String res=" ";


    try{

        ResultSet result = St.executeQuery("SELECT description FROM interets, avoir, consomateur WHERE avoir.id_interet=interets.id_interets AND avoir.id_user=consomateur.code_bar AND consomateur.code_bar="+IdUser+"");

            ResultSetMetaData resultMeta = (ResultSetMetaData) result.getMetaData();


            while(result.next()){         
                String Newligne=System.getProperty("line.separator"); 
            for(int i = 1; i <= resultMeta.getColumnCount(); i++)

           res=res+Newligne+result.getObject(i).toString();

              System.out.println(res);

            }
        }
        catch (Exception e) {
            System.out.println("Erreur dans la requete d'affichage ");
        }

    }
}

我想在这样的JSP中调用它的构造函数：

<div id="corps"><h1>
<%Interets inte=new Interets(${IdUser})%>
    </h1>
</div>

但是我遇到了像

这样的语法错误

“令牌上的语法错误”）“，; expected”

和

“令牌上的语法错误，错误的构造”

所以我该怎么办呢。谢谢

Answer 1

由于您使用的是<% ... %>，因此您应该编写有效的 Java代码，因此您在语句的末尾会遗漏分号;：

<%Interets inte=new Interets(${IdUser})%>
                                       ^here you're missing a semicolon...

此外，您不能将EL与scriptlet混合使用，因此代码应为：

<%
    Integer idUser = (Integer)request.getAttribute("IdUser");
    //if the attribute is stored in HttpSession (probably)
    //or ServletContext (oddly), use the right method to get it
    Interets inte =new Interets(idUser);
%>

请注意，这可能会解决您当前的编译问题，但您当前的设计存在一些问题，例如：您没有在Statement类中的任何位置初始化Interets，但仍在构造函数中使用它...

在尝试打开与数据库的连接并在Web环境中打印结果之前，您应该首先学习基本的Java和基本JDBC。我不会深入研究这些主题，而是为您当前的代码编写一个可能的解决方案，我会评论错误的代码，以便您注意到错误或不应该做的事情：

public class Interets {
    //static Statement St ;
    //public ResultSet rs;

    public List<String> getDescriptionOfInterets(Integer idUser) {
        String res=" ";
        //these three: Connection, Statement, ResultSet MUST ALWAYS be local
        //variables of a method, NEVER assigned to class field AND NEVER to
        //static variables to avoid synchronization problems in a
        //multithreaded environment such as a web application
        Connection con = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        List<String> descriptionList = new ArrayList<String>();
        try{
            //this is one way to open a database connection
            //you should change it to a database connection pool
            //which is a different topic you should search about
            //since you didn't say which database you're working with
            //I'll assume it's mysql
            Class.forName("com.mysql.jdbc.Driver");
            //similar with the database credentials
            String user = "root";
            String password = "root";
            con = DriverManager.getConnection(
                "jdbc:mysql://localhost:3306/dbname", user, password);
            /*
            ResultSet result = St.executeQuery("SELECT description FROM interets, avoir, consomateur WHERE avoir.id_interet=interets.id_interets AND avoir.id_user=consomateur.code_bar AND consomateur.code_bar="+IdUser+"");

            ResultSetMetaData resultMeta = (ResultSetMetaData) result.getMetaData();
            */
            ps = con.prepareStatement("SELECT description "
                + "FROM interets, avoir, consomateur "
                + "WHERE avoir.id = interets.id AND "
                + "avoir.id?user = consomateur.code_bar AND "
                + "contomateur.code_bar = ?");
            ps.setInt(1, idUser);

            rs = ps.executeQuery();
            //while(result.next()){
            while (rs.next) {
                //String Newligne=System.getProperty("line.separator"); 
                //for(int i = 1; i <= resultMeta.getColumnCount(); i++)
                //res=res+Newligne+result.getObject(i).toString();
                //System.out.println(res);
                descriptionList.add(rs.getString(1));
            }
        } catch (Exception e) {
            //Handle your error! This is very important to check the causes of the problem
            //you should at least print the stacktrace
            //printing a single line saying "oh no! I got an error" doesn't help
            System.out.println("Erreur dans la requete d'affichage.");
            e.printStacktrace();
        } finally {
            //remember to ALWAYS close the opened resources
            close(rs);
            close(ps);
            close(con);
        }
    }

    public void close(ResultSet rs) {
        if (rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                //silent...
            }
        }
    }

    public void close(Statement st) {
        if (st != null) {
            try {
                st.close();
            } catch (SQLException e) {
                //silent...
            }
        }
    }

    public void close(Connection con) {
        if (con != null) {
            try {
                con.close();
            } catch (SQLException e) {
                //silent...
            }
        }
    }
}

然后在你的JSP中：

Description of Interets
<table>
<%
    Integer idUser = (Integer)request.getAttribute("IdUser");
    //if the attribute is stored in HttpSession (probably)
    //or ServletContext (oddly), use the right method to get it
    Interets interets = new Interets();
    List<String> descriptionList = interets.getDescriptionOfInterets(idUser);
    for (String description : descriptionList) {
    %>
        <tr>
            <td><%= description %></td>
        </tr>
    <%
    }
%>
</table>

甚至更好，使用Servlet，Expression Language和JSTL（假设您的JSP名为“interets.jsp”并位于根程序包中）：

@WebServlet("/interets")
public class InteretsServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
        HttpSession session = request.getSession();
        Integer idUser = (Integer)session.getAttribute("IdUser");
        Interets interets = new Interets();
        List<String> descriptionList = interets.getDescriptionOfInterets(idUser);
        request.setAttribute("descriptionList", descriptionList);
        request.getRequestDispatcher("/interets.jsp").forward(request, response);
    }
}

JSP可能看起来像

Description of Interets
<table>
    <c:forEach items="${descriptionList}" value="description">
        <tr>
            <td>${description}</td>
        </tr>
    </c:forEach>
</table>

在JSP中使用参数调用构造函数

1 个答案: