使用MVC和DAO模式在JSP页面中在HTML中显示JDBC结果集

兮子 2025-01-28 15:43:15

在设计良好的MVC方法中，JSP文件不应包含任何Java代码行，而Servlet类不应包含任何JDBC代码行。

假设您想在网络商店中显示产品列表，则需要创建以下代码。

a 产品代表产品真实实体的类，它应该只是 javabean 。

 公共类产品{

    私人长ID； 
    私有字符串名称；
    私人字符串描述；
    私人大型价格；

    //添加/生成getters/setters/c'tors/equals/equals/hashcode样板。
}

a dao JDBC工作并返回一个不错的 list＆lt; product＆gt; 。

 公共类productdao {

    私有数据源数据源；

    public Productdao（DataSource DataSource）{
        this.datasource = dataSource;
    }

    公共列表＆lt; product＆gt; list（）抛出sqlexception {
        列表＆lt; product＆gt; products = new arrayList＆lt; product＆gt;（）;

        尝试 （
            连接连接= dataSource.getConnection（）;
            准备陈述语句=连接。
            resultset resultset = statement.executequery（）;
        ）{
            while（resultset.next（））{
                产品产品=新产品（）;
                product.setId（resultset.getlong（“ id”））;
                product.setName（resultset.getString（“ name”））;
                product.setDescription（resultset.getString（“ description”））;
                product.setPrice（resultset.getBigDecimal（“ price”））;
                products.add（产品）;
            }
        }

        返回产品；
    }

}

a servlet class 获得列表并将其放在请求范围中。

  @webservlet（“/products”）
公共类Productserservlet扩展了httpservlet {

    @Resource（name =“ jdbc/yourdb”）//对于tomcat，定义AS＆lt; resource＆gt;在context.xml中，并声明为＆lt; resource-ref＆gt;在Web.xml中。
    私有数据源数据源；
    私人productdao productdao;

    @Override
    public void init（）{
        productDao = new ProductDao（DataSource）;
    }

    @Override
    受保护的void doget（httpservletrequest请求，httpservletresponse响应）抛出了servletexception，ioexception {
        尝试 {
            列表＆lt; product＆gt; products = productdao.list（）;
            request.setAttribute（“产品”，产品）; //将以JSP中的$ {products}提供
            request.getRequestDisPatcher（“/web-inf/products.jsp”）。forward（请求，响应）;
        } catch（sqlexception e）{
            投掷新的ServletException（“无法从DB中获取产品”，E）；
        }
    }

}

最后a jsp 在/web-inf/products.jsps.jsps.jsp 中使用/web-inf/products.jsp a href =“ https://stackoverflow.com/tags/jstl/info”> jstl ＆lt; c：foreach＆gt; 以迭代 list> list＆lt; product＆lt; product＆gt; 可在 el $ {products} ，并使用JSTL ＆lt; c：out＆gt; 逃脱字符串属性，以避免 XSS 当涉及用户 - 控制输入时，

 ＆lt;％@ taglib uri =“ http://java.sun.com/jsp/jstl/core/core” prefix =“ c”％＆gt;
＆lt;％@ taglib uri =“ http://java.sun.com/jsp/jstl/format” prefix =“ fmt”％＆gt;
...
＆lt; table＆gt;
    ＆lt; c：foreach项目=“ $ {products}” var =“ product”＆gt;
        ＆lt; tr＆gt;
            ＆lt; td＆gt; $ {product.id}＆lt;/td＆gt;
            ＆lt; td＆gt;＆lt; c：out value =“ $ {product.name}” /＆gt;＆lt; /td＆gt;
            ＆lt; td＆gt;＆lt; c：out value =“ $ {product.description}” /＆gt;＆lt; /td＆gt;
            ＆lt; td＆gt;＆lt; fmt：formatnumber value =“ $ {product.price}” type =“ crorner” crurnerncode =“ usd” /＆gt;＆lt;＆lt; /td＆gt;
        ＆lt;/tr＆gt;
    ＆lt;/c：foreach＆gt;
＆lt;/table＆gt;

为了使其工作，只需通过其URL致电servlet。前提是servlet被注释 @webservlet（“/products”）或用 web.xml 用＆lt; url-pattern＆gt;/products＆lt;/url-模式＆gt; ，然后您可以通过 http://example.com/contextname/products 来调用它

，请参见：

In a well designed MVC approach, the JSP file should not contain any line of Java code and the servlet class should not contain any line of JDBC code.

Assuming that you want to show a list of products in a webshop, the following code needs to be created.

A Product class representing a real world entity of a product, it should be just a Javabean.

public class Product {

    private Long id; 
    private String name;
    private String description;
    private BigDecimal price;

    // Add/generate getters/setters/c'tors/equals/hashcode boilerplate.
}

A DAO class which does all the nasty JDBC work and returns a nice List<Product>.

public class ProductDAO {

    private DataSource dataSource;

    public ProductDAO(DataSource dataSource) {
        this.dataSource = dataSource;
    }

    public List<Product> list() throws SQLException {
        List<Product> products = new ArrayList<Product>();

        try (
            Connection connection = dataSource.getConnection();
            PreparedStatement statement = connection.prepareStatement("SELECT id, name, description, price FROM product");
            ResultSet resultSet = statement.executeQuery();
        ) {
            while (resultSet.next()) {
                Product product = new Product();
                product.setId(resultSet.getLong("id"));
                product.setName(resultSet.getString("name"));
                product.setDescription(resultSet.getString("description"));
                product.setPrice(resultSet.getBigDecimal("price"));
                products.add(product);
            }
        }

        return products;
    }

}

A servlet class which obtains the list and puts it in the request scope.

@WebServlet("/products")
public class ProductsServlet extends HttpServlet {

    @Resource(name="jdbc/YourDB") // For Tomcat, define as <Resource> in context.xml and declare as <resource-ref> in web.xml.
    private DataSource dataSource;
    private ProductDAO productDAO;

    @Override
    public void init() {
        productDAO = new ProductDAO(dataSource);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            List<Product> products = productDAO.list();
            request.setAttribute("products", products); // Will be available as ${products} in JSP
            request.getRequestDispatcher("/WEB-INF/products.jsp").forward(request, response);
        } catch (SQLException e) {
            throw new ServletException("Cannot obtain products from DB", e);
        }
    }

}

Finally a JSP file in /WEB-INF/products.jsp which uses JSTL <c:forEach> to iterate over List<Product> which is made available in EL by ${products}, and uses JSTL <c:out> to escape string properties in order to avoid XSS holes when it concerns user-controlled input.

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/format" prefix="fmt" %>
...
<table>
    <c:forEach items="${products}" var="product">
        <tr>
            <td>${product.id}</td>
            <td><c:out value="${product.name}" /></td>
            <td><c:out value="${product.description}" /></td>
            <td><fmt:formatNumber value="${product.price}" type="currency" currencyCode="USD" /></td>
        </tr>
    </c:forEach>
</table>

To get it to work, just call the servlet by its URL. Provided that the servlet is annotated @WebServlet("/products") or mapped in web.xml with <url-pattern>/products</url-pattern>, then you can call it by http://example.com/contextname/products

浏览器将请求发送到Web服务器，
将请求配置为通过Servlet或过滤器（控制器：Java代码，而不是JSP代码）
处理该请求的请求（称为操作，控制器的特定部分）
执行业务逻辑（即从示例中的数据库获取数据：模型）
基于配置/注释，操作到JSP。 JSP的作用仅是生成HTML代码（即显示您的数据：视图），

因为JSP通常使用JSP标签（例如JSTL）和JSP Expression语言，并且由于JSP标签和EL设计为从Javabeans获取信息，您最好以Javabeans或Javabeans集合的形式获得数据。

因此，控制器（操作类）的作用是获取数据，创建包含数据的Javabean实例，以适合JSP的格式，将它们放在请求属性中，然后将其派往JSP。然后，JSP将通过Javabean实例迭代并显示其包含的内容。

您不应该自己实施MVC框架。使用现有的（条纹，支柱等）

回复收藏 0 原文

扭转时空 2025-01-28 15:43:15

我不知道应该如何将结果集从类文件返回到JSP页面

好吧，您不这样做。

mvc 的点是将模型（在这种情况下为 m db信息）与您的视图（ v a JSP）分开）以这种方式，您可以在不制动应用的情况下更改视图。

为此，您可能会使用中间对象表示您的数据（通常称为DTO - 在数据传输对象之后 - 不知道它们是如何称呼它的），而其他对象则获取它（通常是DAO）。

因此，基本上您有JSP文件，获取请求参数，然后从DAO中调用一种方法。 DAO在内部有连接到数据库并获取数据并构建DTO集合的方法，该集合将返回到JSP进行渲染。

像这样简化（和不安全）的代码类似的内容：

employee.java

class Employee {
   String name;
   int emplid;
}

opplyeedao.java

class EmployeeDAO { 
   ... method to connect 
   etc. 
   List<Employee> getAllNamed( String name ) { 
       String query = "SELECT name, emplid FROM employee where name like ?";
       ResultSet rs = preparedStatement.executeQuery etc etc.
       List<Employee> results = ....
       while( rs.hasNext() ) { 
          results.add( new Employee( rs.getString("name"), rs.getInt("emplid")));
       }
       // close resources etc 
       return results;
    }
}

employe.jsp

<%
   request.setAttribute("employees", dao.getAllNamed( request.getParameter("name") );
%>
<table>
<c:forEach items="${employees}" var="employee">
<tr><td>${employee.emplid}</td><td>${employee.name}</td></tr>
</c:forEach>
</table>

我希望这给您一个更好的主意。

I don't know how should I return the ResultSet from the class file to the JSP page

Well, you don't.

The point of MVC is to separate your model ( the M DB info in this case ) from your view ( V a jsp, in this case ) in such a way you can change the view without braking to application.

To do this you might use an intermediate object to represent your data ( usually called DTO - after Data Transfer Object -, don't know how they call it these days ), and other object to fetch it ( usually a DAO ).

So basically you have your JSP file, get the request parameters, and then invoke a method from the DAO. The dao, internally has the means to connect to the db and fetch the data and builds a collections of DTO's which are returned to the JSP for rendering.

Something like this extremely simplified ( and insecure ) code:

Employee.java

class Employee {
   String name;
   int emplid;
}

EmployeeDAO.java

class EmployeeDAO { 
   ... method to connect 
   etc. 
   List<Employee> getAllNamed( String name ) { 
       String query = "SELECT name, emplid FROM employee where name like ?";
       ResultSet rs = preparedStatement.executeQuery etc etc.
       List<Employee> results = ....
       while( rs.hasNext() ) { 
          results.add( new Employee( rs.getString("name"), rs.getInt("emplid")));
       }
       // close resources etc 
       return results;
    }
}

employee.jsp

<%
   request.setAttribute("employees", dao.getAllNamed( request.getParameter("name") );
%>
<table>
<c:forEach items="${employees}" var="employee">
<tr><td>${employee.emplid}</td><td>${employee.name}</td></tr>
</c:forEach>
</table>

I hope this give you a better idea.

回复收藏 0 原文

夏日浅笑〃 2025-01-28 15:43:15

我有问题。我不明确理解代码。我的代码也有类似的问题。

我创建了数据库SQL并填写。然后，我想实现来自数据库和其他JSP页面中富裕数据的MainServlet（下面的代码），我想在H1，H2 ECC等部分中插入该数据...我必须使用$ {} Sintax，但我不喜欢知道这是怎么回事。

简而言之，在JSP文件（下面的代码，我必须使用$ {} sintax）我想“呼叫” Mainservlet，在那里我想从数据库中富裕数据并在JSP文件中查看。

希望我能正确解释，非常感谢！

mainservlet.java

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


/**
 * Servlet implementation class MainServlet
 */
@WebServlet({ "/MainServlet" })
public class MainServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final String PATH_JSP = "/WEB-INF/";
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public MainServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Servlet#init(ServletConfig)
     */
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub
    }

    /**
     * @see Servlet#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String doveAndare = request.getParameter("azione");
        if(doveAndare==null)
            doveAndare = "index";
        try {
            String driverString = "com.mysql.cj.jdbc.Driver";
            Class.forName(driverString);
            String connString = "jdbc:mysql://localhost:3306/ldd_jewels?user=root&password=";
            Connection conn = DriverManager.getConnection(connString);
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM JEWEL");
            while (rs.next() == true) {
                System.out.println(rs.getString("Category") + "\t" + rs.getString("Name"));
                
                /* I try that but does not work
                request.setAttribute("name", rs.getString("Name"));
                javax.servlet.RequestDispatcher dispatcher = request.getRequestDispatcher("/WEB-INF/widering_male.jsp");
                dispatcher.forward(request, response); */
            }
            stmt.close();
            conn.close();
        } catch(Exception e) {
            e.printStackTrace();
        }
        request.getRequestDispatcher(PATH_JSP+doveAndare+".jsp").forward(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

dublerow.jsp

   <section id="portfolio-details" class="portfolio-details">
        <div class="container">
          <div class="row gy-4">
            <div class="col-lg-8">
              <div class="portfolio-details-slider swiper">
                <div class="swiper-wrapper align-items-center">
                  <div class="swiper-slide">
                    <img src="assets/img/jewels/doublerow_1.jpg" alt="" />
                  </div>

                  <div class="swiper-slide">
                    <img src="assets/img/jewels/doublerow_2.jpg" alt="" />
                  </div>

                  <div class="swiper-slide">
                    <img src="assets/img/jewels/doublerow_3.jpg" alt="" />
                  </div>
                </div>
                <div class="swiper-pagination"></div>
              </div>
            </div>

            <div class="col-lg-4">
              <div class="portfolio-info">
                <h3>Product details</h3>
                <ul>
                  <li><strong>Code</strong>: 1S3D5</li>
                  <li><strong>Category</strong>: Bracelets</li>
                  <li><strong>Name</strong>: Double Row Hinged Bangle</li>
                  <li><strong>Gender</strong>: Female</li>
                  <li><strong>Material</strong>: Yellow gold</li>
                  <li><strong>Size</strong>: 121mm</li>
                  <li><strong>Price</strong>: €5500</li>
                </ul>
              </div>
              <div class="portfolio-description">
                <h2>Description of product</h2>
                <p>
                  The entwined ends of Tiffany Knot’s signature motif symbolize
                  the power of connections between people. Balancing strength
                  and elegance, each Tiffany Knot design is a complex feat of
                  craftsmanship. This bangle is crafted with yellow gold and
                  polished by hand for high shine. Wear on its own or partnered
                  with classic silhouettes for an unexpected pairing.
                </p>
              </div>
            </div>
          </div>
        </div>
      </section>

这是我的数据库：

我想将每个珠宝插入不同页面（每个珠宝都有一个JSP文件）

I have a problem. I don't understand clearly the code. I have a similar problem with my code.

I have created database SQL and filled up. Then I want to implement a MainServlet (code below) that richieve data from database and in a different jsp page, I want to insert that data in section like h1, h2 ecc... I must use the ${} sintax but I don't know how do that.

Briefly, In jsp file (code below, I MUST USE ${} SINTAX) I want to "call" MainServlet and there I want to richieve data from database and view in jsp file.

I hope I have explained correctly, thank you very much!

MainServlet.java

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


/**
 * Servlet implementation class MainServlet
 */
@WebServlet({ "/MainServlet" })
public class MainServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private static final String PATH_JSP = "/WEB-INF/";
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public MainServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Servlet#init(ServletConfig)
     */
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub
    }

    /**
     * @see Servlet#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String doveAndare = request.getParameter("azione");
        if(doveAndare==null)
            doveAndare = "index";
        try {
            String driverString = "com.mysql.cj.jdbc.Driver";
            Class.forName(driverString);
            String connString = "jdbc:mysql://localhost:3306/ldd_jewels?user=root&password=";
            Connection conn = DriverManager.getConnection(connString);
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM JEWEL");
            while (rs.next() == true) {
                System.out.println(rs.getString("Category") + "\t" + rs.getString("Name"));
                
                /* I try that but does not work
                request.setAttribute("name", rs.getString("Name"));
                javax.servlet.RequestDispatcher dispatcher = request.getRequestDispatcher("/WEB-INF/widering_male.jsp");
                dispatcher.forward(request, response); */
            }
            stmt.close();
            conn.close();
        } catch(Exception e) {
            e.printStackTrace();
        }
        request.getRequestDispatcher(PATH_JSP+doveAndare+".jsp").forward(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

doublerow.jsp

   <section id="portfolio-details" class="portfolio-details">
        <div class="container">
          <div class="row gy-4">
            <div class="col-lg-8">
              <div class="portfolio-details-slider swiper">
                <div class="swiper-wrapper align-items-center">
                  <div class="swiper-slide">
                    <img src="assets/img/jewels/doublerow_1.jpg" alt="" />
                  </div>

                  <div class="swiper-slide">
                    <img src="assets/img/jewels/doublerow_2.jpg" alt="" />
                  </div>

                  <div class="swiper-slide">
                    <img src="assets/img/jewels/doublerow_3.jpg" alt="" />
                  </div>
                </div>
                <div class="swiper-pagination"></div>
              </div>
            </div>

            <div class="col-lg-4">
              <div class="portfolio-info">
                <h3>Product details</h3>
                <ul>
                  <li><strong>Code</strong>: 1S3D5</li>
                  <li><strong>Category</strong>: Bracelets</li>
                  <li><strong>Name</strong>: Double Row Hinged Bangle</li>
                  <li><strong>Gender</strong>: Female</li>
                  <li><strong>Material</strong>: Yellow gold</li>
                  <li><strong>Size</strong>: 121mm</li>
                  <li><strong>Price</strong>: €5500</li>
                </ul>
              </div>
              <div class="portfolio-description">
                <h2>Description of product</h2>
                <p>
                  The entwined ends of Tiffany Knot’s signature motif symbolize
                  the power of connections between people. Balancing strength
                  and elegance, each Tiffany Knot design is a complex feat of
                  craftsmanship. This bangle is crafted with yellow gold and
                  polished by hand for high shine. Wear on its own or partnered
                  with classic silhouettes for an unexpected pairing.
                </p>
              </div>
            </div>
          </div>
        </div>
      </section>

This is my database:

I want to insert each jewel in different pages (each jewel have a jsp file)

回复收藏 0 原文

可爱咩 2025-01-28 15:43:15

您可以使用 ＆lt; c：foreach＆gt; tag

您可以在以下链接中找到详细的示例 示例使用

回复收藏 0 原文

我爱人 2025-01-28 15:43:15

我认为，将表数据包含在列表之类的集合中，并从Java类返回列表，然后在JSP中重复使用此集合，这将更好。

回复收藏 0 原文

使用MVC和DAO模式在JSP页面中在HTML中显示JDBC结果集

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

评论（6）

，请参见：

See also:

关于作者

相关话题

热门标签

推荐作者

檐前雨

鹿港巷口少年归

qq_32QL4xcD

sum_

DLL

唐婉

友情链接

使用MVC和DAO模式在JSP页面中在HTML中显示JDBC结果集

如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

评论（6）

，请参见：

See also:

关于作者

相关话题

热门标签

推荐作者

檐前雨

鹿港巷口少年归

qq_32QL4xcD

sum_

DLL

唐婉

友情链接

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。