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 ResultSet
从 Java 类返回到 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 代码行,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.
一个
Product
类表示产品的真实世界实体,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.
}
DAO 类所有讨厌的 JDBC 工作并返回一个不错的 List
.
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;
}
}
servlet 类,用于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);
}
}
}
最后一个 JSP 文件位于 /WEB-INF/products.jsp
它使用 JSTL 迭代
List
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>
要使其工作,只需通过其 URL 调用 servlet.假设 servlet 被注解为 @WebServlet("/products")
或在 web.xml
中使用 <url-pattern>/products</url-pattern>
,然后就可以通过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
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