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

java jdbc mvc dao

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


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2020-01-10

共1个答案

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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/hashcode 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,使用JSTL <c:forEach>进行迭代,List<Product>在EL中使它可用${products},并使用JSTL <c:out>来转义字符串属性,以便避免在涉及用户控制的输入时出现XSS漏洞。

<%@ 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")或映射在web.xml<url-pattern>/products</url-pattern>,那么你可以把它叫做http://example.com/contextname/products

2020-01-10

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