HttpServletRequestWrapper模拟实现分布式Session

Posted 2020-06-14

HttpSession的内容都放在一个单独的Map中，模拟远程分布式Session。

1.使用HttpServletRequestWrapper创建自定义Request
2.使用动态代理包装自定义Request返回的HttpSession对象
3.创建过滤器，使用自定义Request替换原有的Request对象。
4.在Servlet中得到的HttpSession对象，写入和读取内容都假设通过远程Session服务器。

创建自定义的Request，返回动态代理的HttpSession

1. import java.lang.reflect.InvocationHandler;
2. import java.lang.reflect.Method;
3. import java.lang.reflect.Proxy;
4. import java.util.HashMap;
5. import java.util.Map;
6. import java.util.concurrent.ConcurrentHashMap;
8. import javax.servlet.http.HttpServletRequest;
9. import javax.servlet.http.HttpServletRequestWrapper;
10. import javax.servlet.http.HttpServletResponse;
11. import javax.servlet.http.HttpServletResponseWrapper;
12. import javax.servlet.http.HttpSession;
14. public class RemoteSessionRequest extends HttpServletRequestWrapper {
16.     public RemoteSessionRequest(HttpServletRequest request) {
17.         super(request);
18.     }
20.     @Override
21.     public HttpSession getSession() {
22.         return RemoteSessionHandler.getInstance(super.getSession());
23.     }
24. }
26. class RemoteSessionHandler implements InvocationHandler {
27.     //模拟远程Session服务器，Key表示SessionId,Value表示该Session的内容
28.     private static Map<String, Map<String, Object>> map = new ConcurrentHashMap<String, Map<String, Object>>();
30.     private HttpSession session = null;
32.     private RemoteSessionHandler(HttpSession httpSession) {
33.         this.session = httpSession;
34.     };
36.     public static HttpSession getInstance(HttpSession httpSession) {
37.         InvocationHandler handler = new RemoteSessionHandler(httpSession);
38.         return (HttpSession) Proxy.newProxyInstance(httpSession.getClass().getClassLoader(), httpSession.getClass().getInterfaces(), handler);
39.     }
41.     @Override
42.     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
43.         if ("setAttribute".equals(method.getName())) {
44.             String id = session.getId();
45.             Map<String, Object> m = map.get(id);
46.             if (m == null) {
47.                 m = new HashMap<String, Object>();
48.                 map.put(id, m);
49.             }
50.             m.put((String) args[0], args[1]);
51.             System.out.println("[存入]key:" + args[0] + ",value:" + args[1]);
52.             return null;
53.         } else if ("getAttribute".equals(method.getName())) {
54.             String id = session.getId();
55.             Map<String, Object> m = map.get(id);
56.             if (m == null) {
57.                 return null;
58.             }
59.             Object result = m.get(args[0]);
60.             System.out.println("[取出]key:" + args[0] + ",value:" + result);
61.             return result;
62.         }
63.         return method.invoke(session, args);
64.     }
66. }

使用过滤器替换原有的Request

1. import java.io.IOException;
2. import javax.servlet.Filter;
3. import javax.servlet.FilterChain;
4. import javax.servlet.FilterConfig;
5. import javax.servlet.ServletException;
6. import javax.servlet.ServletRequest;
7. import javax.servlet.ServletResponse;
8. import javax.servlet.annotation.WebFilter;
9. import javax.servlet.http.HttpServletRequest;
11. @WebFilter("/*")
12. public class SessionFilter implements Filter {
13.     @Override
14.     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
15.         chain.doFilter(new RemoteSessionRequest((HttpServletRequest) request), response);
16.     }
18.     @Override
19.     public void destroy() {
20.         // TODO Auto-generated method stub
22.     }
24.     @Override
25.     public void init(FilterConfig arg0) throws ServletException {
26.         // TODO Auto-generated method stub
28.     }
29. }

在Servlet中按照原有方式使用HttpSession。

1. protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
2.         HttpSession session = request.getSession();
3.         session.setAttribute("name", "Hello");
4.         session.getAttribute("name");
5.         session.getAttribute("other");
6.     }

结果可以看到，他已经模拟从远程服务器存取数据

[存入]key:name,value:Hello
[取出]key:name,value:Hello
[取出]key:other,value:null