使用MVC和DAO模式在JSP页面中以HTML格式显示JDBC ResultSet [英] Show JDBC ResultSet in HTML in JSP page using MVC and DAO pattern

问题描述

我正在使用JSP和JDBC实现MVC。我已将数据库类文件导入到我的JSP文件中，并且我想显示数据库表的数据。我不知道如何将 ResultSet 从Java类返回到JSP页面并将其嵌入HTML中。

I'm implementing MVC using JSP and JDBC. I have imported a database class file to my JSP file and I would like to show the data of a DB table. I don't know how I should return the ResultSet from the Java class to the JSP page and embed it in HTML.

如何实现这一目标？

推荐答案

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

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.

假设您要在网上商店中显示产品列表，则需要使用以下代码：已创建。

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

• 一个产品类，代表一个真实世界的实体产品，它应该只是一个 Javabean 。

• 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 类，它可以完成所有讨厌的JDBC工作并返回一个不错的 List< Product> 。

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 类获取列表并将其放入请求范围。

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);
        }
    }

}

最后在 /WEB-INF/products.jsp JSP 文件>使用 JSTL < c：forEach> 进行迭代列表<产品> EL 提供 $ {products} ，并使用JSTL < c：out> 来转义字符串属性以避免XSS 漏洞。

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>

要让它发挥作用，只需致电servlet的URL。前提是servlet注释为 @WebServlet（/ products），或者使用<$ c映射到 web.xml $ c>< url-pattern> / products< / url-pattern> ，然后您可以通过 http://example.com/contextname/products

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

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• 在Servlet中执行doGet和doPost


• 我应该如何连接到JDBC数据库基于servlet的应用程序中的/ datasource？


• 设计模式基于Web的应用程序


• RequestDispatcher.forward（）vs HttpServletResponse .sendRedirect（）


• 如何将具有未知列数的ResultSet映射到List并将其显示在HTML表格中？


• 我如何通过通过单击JSP页面中的超链接或按钮将当前项目转换为Java方法？

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• How should I connect to JDBC database / datasource in a servlet based application?
• Design Patterns web based applications
• RequestDispatcher.forward() vs HttpServletResponse.sendRedirect()
• How to map a ResultSet with unknown amount of columns to a List and display it in a HTML table?
• How do I pass current item to Java method by clicking a hyperlink or button in JSP page?

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