如何使用MVC和DAO模式在JSP页面的HTML中显示JDBC ResultSet？

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。

假设要在网上商店中显示产品列表，则需要创建以下代码。

一个Product代表产品的真实世界的实体类，它应该只是一个Javabean的。

public class Product {    private Long id;    private String name;    private String description;    private BigDecimal price;    // Add/generate getters/setters/c'tors/equals/hashpre boilerplate.}

一个DAO类，它完成所有讨厌的JDBC工作并返回一个

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。

@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JSP文件中

/WEB-INF/products.jsp

JSTL <c:forEach>

List<Product>

${products}

<c:out>

<%@ 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>

要使其正常工作，只需通过其URL调用servlet。假设了一个Servlet注解

@WebServlet("/products")

web.xml

<url-pattern>/products</url-pattern>

http://example.com/contextname/products