javaweb增删改查

JavaWeb 中的增删改查通常是指对数据库中的数据进行操作。下面是一个简单的示例：

1. 增加数据

public class AddDataServlet extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获取表单数据
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        String gender = request.getParameter("gender");
        
        // 将数据插入数据库
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
            String sql = "insert into student(name, age, gender) values(?, ?, ?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, name);
            pstmt.setInt(2, age);
            pstmt.setString(3, gender);
            pstmt.executeUpdate();
            
            // 返回成功信息
            response.getWriter().write("添加成功！");
        } catch (Exception e) {
            e.printStackTrace();
            response.getWriter().write("添加失败！");
        } finally {
            try {
                if (pstmt != null) pstmt.close();
                if (conn != null) conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

2. 查询数据

public class QueryDataServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 查询数据库中的数据
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
            String sql = "select * from student";
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            
            // 将查询结果转换成 JSON 格式并返回
            JSONArray jsonArray = new JSONArray();
            while (rs.next()) {
                JSONObject obj = new JSONObject();
                obj.put("id", rs.getInt("id"));
                obj.put("name", rs.getString("name"));
                obj.put("age", rs.getInt("age"));
                obj.put("gender", rs.getString("gender"));
                jsonArray.add(obj);
            }
            response.getWriter().write(jsonArray.toJSONString());
        } catch (Exception e) {
            e.printStackTrace();
            response.getWriter().write("查询失败！");
        } finally {
            try {
                if (rs != null) rs.close();
                if (pstmt != null) pstmt.close();
                if (conn != null) conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

3. 修改数据

public class UpdateDataServlet extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获取表单数据
        int id = Integer.parseInt(request.getParameter("id"));
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        String gender = request.getParameter("gender");
        
        // 更新数据库中的数据
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
            String sql = "update student set name=?, age=?, gender=? where id=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, name);
            pstmt.setInt(2, age);
            pstmt.setString(3, gender);
            pstmt.setInt(4, id);
            pstmt.executeUpdate();
            
            // 返回成功信息
            response.getWriter().write("更新成功！");
        } catch (Exception e) {
            e.printStackTrace();
            response.getWriter().write("更新失败！");
        } finally {
            try {
                if (pstmt != null) pstmt.close();
                if (conn != null) conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

4. 删除数据

public class DeleteDataServlet extends HttpServlet {
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 获取表单数据
        int id = Integer.parseInt(request.getParameter("id"));
        
        // 删除数据库中的数据
        Connection conn = null;
        PreparedStatement pstmt = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "password");
            String sql = "delete from student where id=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, id);
            pstmt.executeUpdate();
            
            // 返回成功信息
            response.getWriter().write("删除成功！");
        } catch (Exception e) {
            e.printStackTrace();
            response.getWriter().write("删除失败！");
        } finally {
            try {
                if (pstmt != null) pstmt.close();
                if (conn != null) conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

这些 Servlet 可以通过前端页面的表单进行操作，例如：

<form action="AddDataServlet" method="post">
    <input type="text" name="name" placeholder="姓名">
    <input type="number" name="age" placeholder="年龄">
    <input type="radio" name="gender" value="男">男
    <input type="radio" name="gender" value="女">女
    <input type="submit" value="添加">
</form>

<table>
    <thead>
        <tr>
            <th>ID</th>
            <th>姓名</th>
            <th>年龄</th>
            <th>性别</th>
            <th>操作</th>
        </tr>
    </thead>
    <tbody id="data">
    </tbody>
</table>

<script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
<script>
    $(document).ready(function() {
        // 查询数据
        $.get("QueryDataServlet", function(data) {
            var jsonArray = JSON.parse(data);
            for (var i = 0; i < jsonArray.length; i++) {
                var obj = jsonArray[i];
                $("#data").append("<tr><td>" + obj.id + "</td><td>" + obj.name + "</td><td>" + obj.age + "</td><td>" + obj.gender + "</td><td><button onclick='updateData(" + obj.id + ")'>修改</button><button onclick='deleteData(" + obj.id + ")'>删除</button></td></tr>");
            }
        });
        
        // 添加数据
        $("form").submit(function(event) {
            event.preventDefault();
            var form = $(this);
            $.post(form.attr("action"), form.serialize(), function(response) {
                alert(response);
                location.reload();
            });
        });
    });
    
    // 修改数据
    function updateData(id) {
        var name = prompt("请输入姓名：");
        var age = prompt("请输入年龄：");
        var gender = prompt("请输入性别（男/女）：");
        $.post("UpdateDataServlet", {id: id, name: name, age: age, gender: gender}, function(response) {
            alert(response);
            location.reload();
        });
    }
    
    // 删除数据
    function deleteData(id) {
        if (confirm("确定要删除吗？")) {
            $.post("DeleteDataServlet", {id: id}, function(response) {
                alert(response);
                location.reload();
            });
        }
    }
</script>