鱼在海上飞 2018-05-10 08:49 采纳率: 100%
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谁能帮忙填写完整，判断用户名是否存在的功能

![图片说明](https://img-ask.csdn.net/upload/201805/10/1525942080_633430.png)图片说明琢磨一天了，想看看你们怎么配置的。

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  • lianjie_c 2018-05-10 10:03
    关注

    Servlet.java

     public class Servlet extends HttpServlet {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        request.setCharacterEncoding("UTF-8");

        String name = request.getParameter("username");

        String url = "jdbc:mysql://localhost:3306/test";
        String user = "root";
        String password = "root";

        Connection conn = null;
        PreparedStatement pst = null;
        ResultSet rs = null;

        response.setContentType("text/html");
        response.setCharacterEncoding("UTF-8");

        OutputStream os = response.getOutputStream();
        try {
            Class.forName("com.mysql.jdbc.Driver");

            conn = DriverManager.getConnection(url, user, password);
            String sql = "select username from test where username=? ";
            pst = conn.prepareStatement(sql);
            pst.setString(1, name);
            rs = pst.executeQuery();

            if(rs.next()) {
                System.out.println("用户名"+name+"已存在");
                String message = "用户名"+name+"已存在";
                os.write(message.getBytes("UTF-8"));
                os.close();
                return;
            }

            System.out.println(name+"用户名不存在");
            String message = "success";
            os.write(message.getBytes("UTF-8"));
            os.close();

        } catch (Exception e) {
            e.printStackTrace();

            String message = "系统异常";
            os.write(message.getBytes("UTF-8"));
            os.close();
        } finally {
            if(rs!=null) {
                try {
                    rs.close();
                    rs = null;
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(pst!=null) {
                try {
                    pst.close();
                    pst = null;
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(conn!=null) {
                try {
                    conn.close();
                    conn = null;
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }

}

    jsp

     <body>
    <form id="form">
        用户名：<input type="text" name="username" id="username" onblur="checkUsername(this.value)"/><br>
        密码：<input type="password" name="password" id="password" /><br>
        验证码：<input type="text" name="code" id="code" /><br>
    </form>
    <script type="text/javascript" src="http://apps.bdimg.com/libs/jquery/2.1.4/jquery.min.js"></script>
    <script type="text/javascript">
    function checkUsername(username) {
        if($.trim(username)=="") {
            alert("用户名为空");
            return;
        }
        $.ajax({
            url:"Servlet",
            type:"post",
            dataType:"text",
            data:{
                username:username
            },
            success:function(data){
                if(data!="success") {
                    alert(data);
                }
            }
        });
    }
    </script>
  </body>

    web.xml

     <servlet-mapping>
    <servlet-name>Servlet</servlet-name>
    <url-pattern>/Servlet</url-pattern>
  </servlet-mapping>
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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