js ajax jsp页面

// AJAX请求示例
function loadData() {
    var xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function() {
        if (xhr.readyState == 4 && xhr.status == 200) {
            document.getElementById("result").innerHTML = xhr.responseText;
        }
    };
    xhr.open("GET", "data.jsp", true);
    xhr.send();
}

<%@ page import="java.sql.*" %>
<%
    String username = request.getParameter("username");
    // 防止SQL注入
    String safeUsername = username.replaceAll("[^a-zA-Z0-9]", "");
    Connection conn = null;
    PreparedStatement pstmt = null;
    ResultSet rs = null;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "user", "password");
        pstmt = conn.prepareStatement("SELECT * FROM users WHERE username = ?");
        pstmt.setString(1, safeUsername);
        rs = pstmt.executeQuery();
        while (rs.next()) {
            out.println(rs.getString("username"));
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        // 关闭资源
        if (rs != null) rs.close();
        if (pstmt != null) pstmt.close();
        if (conn != null) conn.close();
    }
%>