Java多表查询

最新推荐文章于 2025-06-15 11:37:15 发布

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本文介绍了如何在Java中进行多表查询，通过示例展示了在Servlet中使用jsp和Web.xml配置来实现用户数据的分页查询，包括获取user表的总数和分页查询的方法。

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.jsp:

<body>
    <table width="90%" border="1" cellspacing="0">
    	<tr>
    		<td width="5%" class="td_title">用户id</td>
    		<td width="5%" class="td_title">用户名</td>
    		<td width="5%" class="td_title">密码</td>
    		<td width="7%" class="td_title">用户权限</td>
    		<td width="7%" class="td_title">用户状态</td>	
    	</tr>    
    <c:forEach items="${users}" var="user">
    	<tr>
    		<td width="5%" class="td_title">${user.user_id}</td>
    		<td width="5%" class="td_title">${user.user_name}</td>
    		<td width="5%" class="td_title">${user.password}</td>
    	<td width="5%" class="td_title">${user.user_power}</td>
    	<td width="5%" class="td_title">${user.user_state}</td>
    	</tr>
    </c:forEach>
    </table>
  </body>

Servlet:
·.usersum()：查询user表的总数
·.findAll(PageUtil.pageSize,PageUtil.curPage)：查询user表的总页数和当前页数

public class UserServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	private UserService userService = new UserServiceImpl();
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doPost(request, response);
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		request.setCharacterEncoding("utf-8");
		String type = request.getParameter("type");
		if ("finduserAll".equals(type)) {
			finduserAll(request, response);
		} 
	}
	public void finduserAll(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// 判断当前页是否等于null，等则赋值为1
		String curPage = request.getParameter("curPage") == null ? "1": request.getParameter("curPage");
		// 给封装的当前页赋值
		PageUtil.curPage = Integer.parseInt(curPage);
		// 赋值总条数
		PageUtil.totalCount = (int) userService.usersum();
		// 赋值总页数= 总条数 + 每页页数
		PageUtil.totalPage = PageUtil.pageTotal(PageUtil.totalCount,PageUtil.pageSize);
		List<User> users = userService.findAll(PageUtil.pageSize,PageUtil.curPage);
		// 返回jsp
		request.setAttribute("users", users);
		// 给公共分页赋值
Page page = new Page(PageUtil.totalPage, PageUtil.totalCount,
				PageUtil.curPage, PageUtil.pageSize);
				request.setAttribute("page", page);
		// 转发到list页面
	request.getRequestDispatcher("/jsp/usermanage/usermanage.jsp").forward(
				request, response);
	}

Web.xml:

<servlet>
  	<servlet-name>UserServlet</servlet-name>
  	<servlet-class>com.fjm.web.UserServlet</servlet-class>
</servlet>
<servlet-mapping>
   <servlet-name>UserServlet</servlet-name>
   <url-pattern>/servlet/UserServlet</url-pattern>
</servlet-mapping>