分页和异步验证注册

1.分页

分页条:【首页】【上一页】[1][2][3][4]【下一页】【尾页】
分页功能的实现:
物理分页:一次只查10条记录,点击下一页,再去查询后10条,使用sql语句进行控制的分页
缺点:经常需要和数据库交互
优点:数据量特别大,不会导致内存溢出
逻辑分页:一次性将所有数据全都查询出来,根据需要进行截取.List集合进行控制. subList();
缺点:数据量如果特别大,容易导致内存溢出.
优点:与数据库交互次数少.
不同的数据库对分页的语句也是不一样的
MYSQL进行分页: 使用limit关键字.
* select * from xxx limit a,b;


根据页数计算 limit后面的两个参数：
* currPage begin pageSize
　　　　1 　　 0 　　   10
　　　　2 　　 10 　　 10
　　　　3 　　 20 　　 10
* begin = (currPage - 1) * pageSize;
参数的传递:
* 前台--->后台:currPage
* 后台--->前台:currPage,totalPage(总页数),totalCount(总记录数),pageSize,List
使用JavaBean封装参数：
* 后台--->前台:传递一个JavaBean就可以.

实现:

在index.jsp中添加一个分页访问数据的链接

<a href="${ pageContext.request.contextPath }/ProductFindByPageServlet?currentPage=1">分页查询商品</a>

在web.servlet层创建ProductFindByPageServlet

public class ProductFindByPageServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * 分页的servlet
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            //获取表单数据
            int currentPage = Integer.parseInt(request.getParameter("currentPage"));
            //调用业务逻辑
            ProductService ps = new ProductService();
            PageBean pageBean = ps.findByPage(currentPage);
            //分发转向
            request.setAttribute("pageBean", pageBean);
            request.getRequestDispatcher("/jsp/product_page.jsp").forward(request, response);
        } catch (Exception e) {
            e.printStackTrace();
        } 
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

把当前页传递到service层,在service层处理业务逻辑
因为在业务层需要把当前页,总页,总记录数等数据封装到一个pageBean中,所以首先先创建pageBean类

public class PageBean {
    //当前页
    private int currentPage;
    //总记录数
    private int totalCount;
    //每页显示数
    private int pageSize;
    //总页数
    private int totalPage;
    //每页显示的数据信息
    private List<Product> list;
    public PageBean(int currentPage, int totalCount, int pageSize, int totalPage, List<Product> list) {
        super();
        this.currentPage = currentPage;
        this.totalCount = totalCount;
        this.pageSize = pageSize;
        this.totalPage = totalPage;
        this.list = list;
    }
    public PageBean() {
        super();
    }
    public int getCurrentPage() {
        return currentPage;
    }
    public void setCurrentPage(int currentPage) {
        this.currentPage = currentPage;
    }
    public int getTotalCount() {
        return totalCount;
    }
    public void setTotalCount(int totalCount) {
        this.totalCount = totalCount;
    }
    public int getPageSize() {
        return pageSize;
    }
    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }
    public int getTotalPage() {
        return totalPage;
    }
    public void setTotalPage(int totalPage) {
        this.totalPage = totalPage;
    }
    public List<Product> getList() {
        return list;
    }
    public void setList(List<Product> list) {
        this.list = list;
    }
    
}

编写业务层

    /**
     * 把当前页,总记录数,每页显示数,总页数,封装到pagebean,返回给servlet
     * @throws SQLException 
     * */
    public PageBean findByPage(int currentPage) throws SQLException {
        //创建pagebean对象
        PageBean pb = new PageBean();
        //设置当前页,封装到pagebean
        pb.setCurrentPage(currentPage);
        //设置每页显示数,并封装到pagebean
        int pageSize = 10;
        pb.setPageSize(pageSize);
        /**
         * 调用dao层获取到总记录数,封装到pagebean中
         * */
        int totalCount = pd.findCount();
        pb.setTotalCount(totalCount);
        //得到总页数,封装到pagebean
        /*Double numCount = (double) (totalCount/pageSize);
        int totalPage = numCount.intValue();*/
        double tc = totalCount;
        //向上取整
        Double num  = Math.ceil(tc/pageSize);
        int totalPage = num.intValue();
        pb.setTotalPage(totalPage);
        //获取limit的第一个参数(从第几条开始)
        int begin = (currentPage - 1) * pageSize;
        /**
         * 调用dao层,获取每页显示的product数据,封装到list中在封装到pagebean中
         * */
        //传入limit需要的开始页和每页显示的记录数
        List<Product> list = pd.findByPage(begin,pageSize);
        pb.setList(list);
        return pb;
    }

//返回总记录数

public int findCount() throws SQLException {
        String sql = "select count(*) from product";
        Long l = (Long) qr.query(sql, new ScalarHandler());
        return l.intValue();
    }
    //拿到分页的当前分页的数据
    public List<Product> findByPage(int begin, int pageSize) throws SQLException {
        String sql = "select * from product limit ?,?";
        Object [] params = {begin,pageSize};
        List<Product> list = qr.query(sql, new BeanListHandler<Product>(Product.class), params);
        return list;
    }

2.AJAX异步验证注册

首先是不使用jq的方式用 异步完成验证注册

这是一个输入用户名界面的div

　　　　　　　　　　<div>
                    请输入用户名:<input type="text" name="username" id="username" class="clickevent" />
                    <span id="show"></span>        
                </div>

为这个标签绑定一个失去焦点的事件

document.getElementById("username").onblur = function() {
    
    //获取异步对象
    var xhr = createXMLHttp;
    //设置监听
    xhr.onreadystatechange = function() {
        var username = document.getElementById("username").value;
        if(xhr.readyState == 4 && xhr.status == 200) {
            var data = xhr.responseText;
            if(data == 1) {
                document.getElementById("show").innerHTML = "<font color='green'>用户名可以使用</font>";
            }else {
                document.getElementById("show").innerHTML = "<font color='red'>用户名已经被占用</font>";
            }
            document.getElementById("show").innerHTML = "bbb";
        }
    }
    xhr.open("POST","/AJAX/CheckServlet",true);
    xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
    xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
    xhr.send("username="+username);
    xhr.send("username="+username);
}
//提供一个异步对象创建的方法
function createXMLHttp() {
    var xmlHttp;
    try { // Firefox, Opera 8.0+, Safari
        xmlHttp = new XMLHttpRequest();
    } catch (e) {
        try {// Internet Explorer
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e) {
            }
        }
    }
    return xmlHttp;
}

编写CheckServlet

public class CheckServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * 异步校验用户名
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        String username = request.getParameter("username");
        System.out.println("username="+username);
        try {
            UserService us = new UserService();
            User user = us.checkUser(username);
            System.out.println(user);
            if(user == null) {
                //response.getWriter().println(1);
                response.getWriter().println("<font color='green'>用户名可以使用</font>");
            }else {
                //response.getWriter().println(2);
                response.getWriter().println("<font color='red'>用户名已经被占用</font>");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

业务层

public class UserService {
    
    UserDao ud = new UserDao();
    public User checkUser(String username) throws SQLException {
        User user = ud.check(username);
        return user;
    }
    
}

dao层

public class UserDao {
QueryRunner qr = new QueryRunner(JDBCUtils.getDataSource());
public User check(String username) throws SQLException {
String sql = "select * from users where username = ?";

Object [] params = {username};

User user = qr.query(sql, new BeanHandler<User>(User.class), params);


return user;
}

}

但是jq框架让异步验证更简便,所以更推荐使用异步
JQuery的AJAX
JQuery的AJAX部分方法:
* Jq的对象.load(路径,参数,回调函数);
* $.get(路径,参数,回调函数,数据类型);
* $.post(路径,参数,回调函数,数据类型);
* $.ajax();
* serialize(); -- JQ的AJAX传递参数的时候需要使用的方法.


首先引入两个jq的文件

<script type="text/javascript" src="${pageContext.request.contextPath }/js/jquery-1.8.3.js"></script>
<script type="text/javascript" src="${ pageContext.request.contextPath }/js/jquery.js"></script>

编写jquery.js

$(function () {
    //给用户名文本框添加事件
    $("#username").blur(function() {
        //获取文本框中的值
        var username = $(this).val();
        //调用方法
        $("#show").load("/AJAX/CheckServlet",{"username":username});
    });
});
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原文地址：https://www.cnblogs.com/learnjfm/p/6936976.html