使用 MVC 和 DAO 模式在 JSP 页面的 HTML 中显示 JDBC ResultSet-Java问题

Show JDBC ResultSet in HTML in JSP page using MVC and DAO pattern(使用 MVC 和 DAO 模式在 JSP 页面的 HTML 中显示 JDBC ResultSet)

本文介绍了使用 MVC 和 DAO 模式在 JSP 页面的 HTML 中显示 JDBC ResultSet的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我正在使用 JSP 和 JDBC 实现 MVC.我已经将一个数据库类文件导入到我的 JSP 文件中，我想显示一个 DB 表的数据.我不知道我应该如何将 Java 类中的 ResultSet 返回到 JSP 页面并将其嵌入到 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.

我怎样才能做到这一点?

How can I achieve this?

推荐答案

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

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，则需要创建以下代码.

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

代表产品真实世界实体的 Product 类，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.
}

一个 DAO 类所有讨厌的 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;
    }

}

一个 servlet 类，它获取列表并将其放入请求范围内.

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);
        }
    }

}

最后是 /WEB-INF/products.jsp 中的 JSP 文件它使用 JSTL <c:forEach> 来迭代 List<Product> 由 ${products} 在 EL 中提供，并使用 JSTL<c:out> 转义字符串属性，以避免在涉及用户时出现 XSS 漏洞-受控输入.

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>

要让它工作，只需通过它的 URL 调用 servlet.前提是 servlet 被注释为 @WebServlet("/products") 或在 web.xml 中使用 <url-pattern>/products</url-pattern>，那么就可以通过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