Question

我正在读这本书，Murach的Java Servlets和JSP第二版。他提供了一个通过.bat文件自动安装的数据库。

我尝试了他的例子并且工作正常。

现在我正在尝试使用他的数据库创建我的应用程序，但没有任何事情发生。以下是代码：

JSP：

<%-- 
    Document   : index
    Created on : 27/01/2012, 9:20:02 AM
    Author     : Camus
--%>

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Form</title>
    </head>
    <body>
        <h1>Type your information here!</h1>
        <form action="addToEmailList" method="get">
            <input type="text" name="firstName">First Name<br>
            <input type="text" name="lastName"> Last Name<br>
            <input type="text" name="emailAddress"> email
            <input type="submit" value="Submit">
        </form>
    </body>
</html>

的Servlet

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */


import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;


/**
 *
 * @author Camus
 */
public class addToEmailList extends HttpServlet {

    /** 
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

            String firstName = request.getParameter("firstName");
            String lastName = request.getParameter("lastName");
            String emailAddress = request.getParameter("emailAddress");

            User user = new User();
            user.setFirstName(firstName);
            user.setLastName(lastName);
            user.setEmailAddress(emailAddress);

            String query ="DELETE FROM user WHERE FirstName = 'Diogo'";

            try {
                String dbURL="jdbc:mysql://localhost:3306/murach";
            String username ="root";
            String password = "sesame";
                    Connection connection = DriverManager.getConnection(dbURL, username, password);

                    Statement statement = connection.createStatement();
                    statement.executeUpdate(query);
                connection.close();
            } 
            catch (Exception e) {
                e.printStackTrace();
        }


             String URL = "/result.jsp";
             RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(URL);
             dispatcher.forward(request, response);


    }

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** 
     * Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /** 
     * Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        processRequest(request, response);
    }

    /** 
     * Returns a short description of the servlet.
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>
}

我已经尝试了很多东西，当我检查数据库时，没有发生任何事情。我尝试了不同的查询，但没有更新任何内容。你们是否知道我做错了什么？

请帮帮我。我认为它应该是一个基本的错误，但是因为我正在学习并且真的不知道发生了什么。

提前致谢。

Answer 1

我想知道你提交表单时为什么要使用DELETE查询？我认为这应该是一个INSERT。

我认为你在一个问题上遇到了太多问题。您正在一次性学习JSP，servlet和数据库。发生了太多事情。

计算机科学就是分解：通过将复杂问题分解为更小，更易于管理的问题来解决复杂问题。

您不需要servlet或JSP来获取数据库。让它先工作。

以下是我推荐的内容：从Person类开始。

package model;

public class Person {
    private String firstName;
    private String lastName;
    private String email;

// Add constructors, getters, equals, hashcode, etc.
}

然后从持久性接口开始：

package persistence;

public interface PersonDao {
    List<Person> find(String lastName, String firstName);
    List<Person> find();
    void save(Person p);
    void update(Person p);
    void delete(Person p);
}

然后实现DAO接口：

package persistence;

public class PersonDaoImpl implements PersonDao {
    private Connection connection;

    public PersonDaoImpl(Connection connection) {
        this.connection = connection;
    }

    // Implement all the JDBC methods here.
}

像这样的实用程序类可能会对您有所帮助。使用它来查看您是否可以成功连接到数据库并执行某些操作：

package persistence;

import java.sql.*;
import java.util.*;

/**
 * util.DatabaseUtils
 * User: Michael
 * Date: Aug 17, 2010
 * Time: 7:58:02 PM
 */
public class DatabaseUtils
{
    private static final String DEFAULT_DRIVER = "oracle.jdbc.driver.OracleDriver";
    private static final String DEFAULT_URL = "jdbc:oracle:thin:@host:1521:database";
    private static final String DEFAULT_USERNAME = "username";
    private static final String DEFAULT_PASSWORD = "password";
/*
    private static final String DEFAULT_DRIVER = "org.postgresql.Driver";
    private static final String DEFAULT_URL = "jdbc:postgresql://localhost:5432/party";
    private static final String DEFAULT_USERNAME = "pgsuper";
    private static final String DEFAULT_PASSWORD = "pgsuper";
*/
/*
    private static final String DEFAULT_DRIVER = "com.mysql.jdbc.Driver";
    private static final String DEFAULT_URL = "jdbc:mysql://localhost:3306/party";
    private static final String DEFAULT_USERNAME = "party";
    private static final String DEFAULT_PASSWORD = "party";
*/

    public static void main(String[] args)
    {
        long begTime = System.currentTimeMillis();

        String driver = ((args.length > 0) ? args[0] : DEFAULT_DRIVER);
        String url = ((args.length > 1) ? args[1] : DEFAULT_URL);
        String username = ((args.length > 2) ? args[2] : DEFAULT_USERNAME);
        String password = ((args.length > 3) ? args[3] : DEFAULT_PASSWORD);

        Connection connection = null;

        try
        {
            connection = createConnection(driver, url, username, password);
            DatabaseMetaData meta = connection.getMetaData();
            System.out.println(meta.getDatabaseProductName());
            System.out.println(meta.getDatabaseProductVersion());

            String sqlQuery = "SELECT PERSON_ID, FIRST_NAME, LAST_NAME FROM PERSON ORDER BY LAST_NAME";
            System.out.println("before insert: " + query(connection, sqlQuery, Collections.EMPTY_LIST));

            connection.setAutoCommit(false);
            String sqlUpdate = "INSERT INTO PERSON(FIRST_NAME, LAST_NAME) VALUES(?,?)";
            List parameters = Arrays.asList( "Foo", "Bar" );
            int numRowsUpdated = update(connection, sqlUpdate, parameters);
            connection.commit();

            System.out.println("# rows inserted: " + numRowsUpdated);
            System.out.println("after insert: " + query(connection, sqlQuery, Collections.EMPTY_LIST));
        }
        catch (Exception e)
        {
            rollback(connection);
            e.printStackTrace();
        }
        finally
        {
            close(connection);
            long endTime = System.currentTimeMillis();
            System.out.println("wall time: " + (endTime - begTime) + " ms");
        }
    }

    public static Connection createConnection(String driver, String url, String username, String password) throws ClassNotFoundException, SQLException
    {
        Class.forName(driver);

        if ((username == null) || (password == null) || (username.trim().length() == 0) || (password.trim().length() == 0))
        {
            return DriverManager.getConnection(url);
        }
        else
        {
            return DriverManager.getConnection(url, username, password);
        }
    }

    public static void close(Connection connection)
    {
        try
        {
            if (connection != null)
            {
                connection.close();
            }
        }
        catch (SQLException e)
        {
            e.printStackTrace();
        }
    }


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

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

    public static void rollback(Connection connection)
    {
        try
        {
            if (connection != null)
            {
                connection.rollback();
            }
        }
        catch (SQLException e)
        {
            e.printStackTrace();
        }
    }

    public static List<Map<String, Object>> map(ResultSet rs) throws SQLException
    {
        List<Map<String, Object>> results = new ArrayList<Map<String, Object>>();

        try
        {
            if (rs != null)
            {
                ResultSetMetaData meta = rs.getMetaData();
                int numColumns = meta.getColumnCount();
                while (rs.next())
                {
                    Map<String, Object> row = new HashMap<String, Object>();
                    for (int i = 1; i <= numColumns; ++i)
                    {
                        String name = meta.getColumnName(i);
                        Object value = rs.getObject(i);
                        row.put(name, value);
                    }
                    results.add(row);
                }
            }
        }
        finally
        {
            close(rs);
        }

        return results;
    }

    public static List<Map<String, Object>> query(Connection connection, String sql, List<Object> parameters) throws SQLException
    {
        List<Map<String, Object>> results = null;

        PreparedStatement ps = null;
        ResultSet rs = null;

        try
        {
            ps = connection.prepareStatement(sql);

            int i = 0;
            for (Object parameter : parameters)
            {
                ps.setObject(++i, parameter);
            }

            rs = ps.executeQuery();
            results = map(rs);
        }
        finally
        {
            close(rs);
            close(ps);
        }

        return results;
    }

    public static int update(Connection connection, String sql, List<Object> parameters) throws SQLException
    {
        int numRowsUpdated = 0;

        PreparedStatement ps = null;

        try
        {
            ps = connection.prepareStatement(sql);

            int i = 0;
            for (Object parameter : parameters)
            {
                ps.setObject(++i, parameter);
            }

            numRowsUpdated = ps.executeUpdate();
        }
        finally
        {
            close(ps);
        }

        return numRowsUpdated;
    }
}

我不知道sql / java还能做什么

1 个答案: