HttpServletRequestWrapper模拟实现分布式Session

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

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;
7. import javax.servlet.http.HttpServletRequest;
8. import javax.servlet.http.HttpServletRequestWrapper;
9. import javax.servlet.http.HttpServletResponse;
10. import javax.servlet.http.HttpServletResponseWrapper;
11. import javax.servlet.http.HttpSession;
12. public class RemoteSessionRequest extends HttpServletRequestWrapper {
13. public RemoteSessionRequest(HttpServletRequest request) {
14. super(request);
15. }
16. @Override
17. public HttpSession getSession() {
18. return RemoteSessionHandler.getInstance(super.getSession());
19. }
20. }
21. class RemoteSessionHandler implements InvocationHandler {
22. //模拟远程Session服务器，Key表示SessionId,Value表示该Session的内容
23. private static Map<String, Map<String, Object>> map = new ConcurrentHashMap<String, Map<String, Object>>();
24. private HttpSession session = null;
25. private RemoteSessionHandler(HttpSession httpSession) {
26. this.session = httpSession;
27. };
28. public static HttpSession getInstance(HttpSession httpSession) {
29. InvocationHandler handler = new RemoteSessionHandler(httpSession);
30. return (HttpSession) Proxy.newProxyInstance(httpSession.getClass().getClassLoader(), httpSession.getClass().getInterfaces(), handler);
31. }
32. @Override
33. public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
34. if ("setAttribute".equals(method.getName())) {
35. String id = session.getId();
36. Map<String, Object> m = map.get(id);
37. if (m == null) {
38. m = new HashMap<String, Object>();
39. map.put(id, m);
40. }
41. m.put((String) args[0], args[1]);
42. System.out.println("[存入]key:" + args[0] + ",value:" + args[1]);
43. return null;
44. } else if ("getAttribute".equals(method.getName())) {
45. String id = session.getId();
46. Map<String, Object> m = map.get(id);
47. if (m == null) {
48. return null;
49. }
50. Object result = m.get(args[0]);
51. System.out.println("[取出]key:" + args[0] + ",value:" + result);
52. return result;
53. }
54. return method.invoke(session, args);
55. }
56. }

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;
10. @WebFilter("/*")
11. public class SessionFilter implements Filter {
12. @Override
13. public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
14. chain.doFilter(new RemoteSessionRequest((HttpServletRequest) request), response);
15. }
16. @Override
17. public void destroy() {
18. // TODO Auto-generated method stub
19. }
20. @Override
21. public void init(FilterConfig arg0) throws ServletException {
22. // TODO Auto-generated method stub
23. }
24. }

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