HttpServletRequestWrapper simulates distributed sessions

HttpServletRequestWrapper simulates distributed sessions

The content of HttpSession is put in a separate Map to simulate a remote distributed Session.

1. Use HttpServletRequestWrapper to create a custom Request
2. Use Dynamic proxy to wrap the http session object returned by the custom Request
3. Create a filter and replace the original Request object with a custom Request.
4. the http Session object obtained in the Servlet is written and read through the remote Session server.

Creates a custom Request and returns the http session of the dynamic proxy.

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 {

// Simulate a remote Session server. The Key indicates the SessionId and the Value indicates the Session content.

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 ("[saved] 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 ("[retrieve] key:" + args [0] + ", value:" + result );

Return result;

}

Return method. invoke (session, args );

}

 

}
Use a filter to replace the original 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

 

}

}

Use HttpSession in Servlet in the original way.

Protected void doPost (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
HttpSession session = request. getSession ();

Session. setAttribute ("name", "Hello ");

Session. getAttribute ("name ");

Session. getAttribute ("other ");

}
The result shows that he has simulated data access from a remote server.

[Save] key: name, value: Hello
[Retrieve] key: name, value: Hello
[Retrieve] key: other, value: null

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