Servlet案例5：用戶登錄失敗信息回顯

登錄失敗信息回顯不會的新的一個頁面，而是顯示在登錄頁面

一種方法是：

登錄頁面表單中每個欄位後添加<span>標簽寫入失敗信息，利用ajax技術

通過改變<span>標簽的display:none屬性添加失敗信息

這裡用的類似的方法：

資料庫準備略，

註意寫好對應的user類供BeanHandler使用

sevlet：

package login;

import java.io.IOException;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;

public class LoginServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        // 獲得用戶名密碼
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        // 在資料庫中查詢
        User login = null;
        try {
            login = login(username, password);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        if (login != null) {
            // 成功,跳轉首頁
            response.sendRedirect(request.getContextPath());
        } else {
            // 錯誤
            // 在request域中存入錯誤信息
            request.setAttribute("loginInfo", "用戶名或密碼錯誤");
            request.getRequestDispatcher("/login.jsp").forward(request, response);
        }

    }

    public User login(String username, String password) throws SQLException {
        QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());
        String sql = "select * from user where username=? and password=?";
        User user = runner.query(sql, new BeanHandler<User>(User.class), username, password);
        return user;

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

抽取連接池類：

package login;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class DataSourceUtils {

    private static DataSource dataSource = new ComboPooledDataSource();

    private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();

    // 直接可以獲取一個連接池
    public static DataSource getDataSource() {
        return dataSource;
    }

    // 獲取連接對象
    public static Connection getConnection() throws SQLException {

        Connection con = tl.get();
        if (con == null) {
            con = dataSource.getConnection();
            tl.set(con);
        }
        return con;
    }

    // 開啟事務
    public static void startTransaction() throws SQLException {
        Connection con = getConnection();
        if (con != null) {
            con.setAutoCommit(false);
        }
    }

    // 事務回滾
    public static void rollback() throws SQLException {
        Connection con = getConnection();
        if (con != null) {
            con.rollback();
        }
    }

    // 提交並且 關閉資源及從ThreadLocall中釋放
    public static void commitAndRelease() throws SQLException {
        Connection con = getConnection();
        if (con != null) {
            con.commit(); // 事務提交
            con.close();// 關閉資源
            tl.remove();// 從線程綁定中移除
        }
    }

    // 關閉資源方法
    public static void closeConnection() throws SQLException {
        Connection con = getConnection();
        if (con != null) {
            con.close();
        }
    }

    public static void closeStatement(Statement st) throws SQLException {
        if (st != null) {
            st.close();
        }
    }

    public static void closeResultSet(ResultSet rs) throws SQLException {
        if (rs != null) {
            rs.close();
        }
    }

}

註意寫好c3p0-config.xml、web.xml配置文件

在登錄頁面加上這一句代碼

<div><%=request.getAttribute("loginInfo")==null?"":request.getAttribute("loginInfo")%></div>

即可實現簡單的信息回顯