如何在Google App Engine(Java)中启用会话支持？

<filter>
  <filter-name>SessionFilter</filter-name>
  <filter-class>com.example.SessionFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>SessionFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

package com.example;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;

public class SessionFilter implements Filter {
  public void init(FilterConfig config) throws ServletException {
    // 初始化操作
  }

  public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
      throws IOException, ServletException {
    HttpServletRequest request = (HttpServletRequest) req;
    HttpServletResponse response = (HttpServletResponse) res;

    // 检查会话是否存在
    HttpSession session = request.getSession(false);
    if (session == null) {
      // 如果会话不存在，创建一个新的会话
      session = request.getSession(true);
    }

    // 继续处理请求
    chain.doFilter(request, response);
  }

  public void destroy() {
    // 销毁操作
  }
}