java根据sessionid获取session

import java.util.HashMap;
import java.util.Map;

import javax.servlet.http.HttpSession;

/**
 * 
 * ClassName: SessionContext
 * 
 * @Description: 获取sessionID
 * @author liangbo
 * @date 2016-3-18
 */
public class SessionContext {

	private static SessionContext instance;
	private Map<String, HttpSession> sessionMap;

	private SessionContext() {
		sessionMap = new HashMap<String, HttpSession>();
	}

	public static SessionContext getInstance() {
		if (instance == null) {
			instance = new SessionContext();
		}
		return instance;
	}

	public synchronized void addSession(HttpSession session) {
		if (session != null) {
			sessionMap.put(session.getId(), session);
		}
	}

	public synchronized void delSession(HttpSession session) {
		if (session != null) {
			sessionMap.remove(session.getId());
		}
	}

	public synchronized HttpSession getSession(String sessionId) {
		if (sessionId == null)
			return null;
		return sessionMap.get(sessionId);
	}
}

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * 
 * ClassName: SessionListener
 * 
 * @Description: sessionid web.xml监听器
 * @author liangbo
 * @date 2016-3-18
 */
public class SessionListener implements HttpSessionListener {

	private SessionContext context = SessionContext.getInstance();

	@Override
	public void sessionCreated(HttpSessionEvent sessionEvent) {
		context.addSession(sessionEvent.getSession());
	}

	@Override
	public void sessionDestroyed(HttpSessionEvent sessionEvent) {
		HttpSession session = sessionEvent.getSession();
		context.delSession(session);
	}

}