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.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

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import javax.servlet.http.HttpSession;

public class RemoteSessionRequest extends HttpServletRequestWrapper {

    public RemoteSessionRequest(HttpServletRequest request) {
        super(request);
    }

    @Override
    public HttpSession getSession() {
        return RemoteSessionHandler.getInstance(super.getSession());
    }
}

class RemoteSessionHandler implements InvocationHandler {
    //模拟远程Session服务器，Key表示SessionId,Value表示该Session的内容
    private static Map<String, Map<String, Object>> map = new ConcurrentHashMap<String, Map<String, Object>>();

    private HttpSession session = null;

    private RemoteSessionHandler(HttpSession httpSession) {
        this.session = httpSession;
    };

    public static HttpSession getInstance(HttpSession httpSession) {
        InvocationHandler handler = new RemoteSessionHandler(httpSession);
        return (HttpSession) Proxy.newProxyInstance(httpSession.getClass().getClassLoader(), httpSession.getClass().getInterfaces(), handler);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if ("setAttribute".equals(method.getName())) {
            String id = session.getId();
            Map<String, Object> m = map.get(id);
            if (m == null) {
                m = new HashMap<String, Object>();
                map.put(id, m);
            }
            m.put((String) args[0], args[1]);
            System.out.println("[存入]key:" + args[0] + ",value:" + args[1]);
            return null;
        } else if ("getAttribute".equals(method.getName())) {
            String id = session.getId();
            Map<String, Object> m = map.get(id);
            if (m == null) {
                return null;
            }
            Object result = m.get(args[0]);
            System.out.println("[取出]key:" + args[0] + ",value:" + result);
            return result;
        }
        return method.invoke(session, args);
    }

}

使用过滤器替换原有的Request

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;

@WebFilter("/*")
public class SessionFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        chain.doFilter(new RemoteSessionRequest((HttpServletRequest) request), response);
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub

    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        // TODO Auto-generated method stub

    }
}

在Servlet中按照原有方式使用HttpSession。

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

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