来源：tomcat如何共享多个web应用会话
作者：seaboat 汪洋之舟
问题
今天有位朋友问了个问题，大致是：tomcat下两个Java web，一个是商城，一个是直播，从商城登录后，再跳转到直播，发现处于非登录状态。
解决思路
- 将session抽出来成一个session服务，统一通过该服务操作session。
- tomcat内部用会话管理器获取会话时遍历所有context内的会话。
方案1
重写获取session方法即可。
方案2
找了源码发现已经支持类似遍历所有context内的会话的形式，首先获取session时，如果cressContext属性为true，则会在获取不到时尝试遍历所有context是否存在该sessionid，如果存在则在本context根据sessionid创建自己的session对象。
public HttpSession getSession(boolean create) {
if (crossContext) {
// There cannot be a session if no context has been assigned yet
if (context == null)
return (null);
// Return the current session if it exists and is valid
if (session != null && session.isValid()) {
return (session.getSession());
}
HttpSession other = super.getSession(false);
if (create && (other == null)) {
// First create a session in the first context: the problem is
// that the top level request is the only one which can
// create the cookie safely
other = super.getSession(true);
}
if (other != null) {
Session localSession = null;
try {
localSession =
context.getManager().findSession(other.getId());
if (localSession != null && !localSession.isValid()) {
localSession = null;
}
} catch (IOException e) {
// Ignore
}
if (localSession == null && create) {
localSession =
context.getManager().createSession(other.getId());
}
if (localSession != null) {
localSession.access();
session = localSession;
return session.getSession();
}
}
return null;
} else {
return super.getSession(create);
}
}
context（web应用）获取跨应用session时通过类似下面操作获取：
request.getSession().getServletContext().getContext("/app2").getAttribute("att2");
这是因为request会根据cookies的sessionid获取到session对象，这时不会报找不到，因为前面已经根据其他sessionid创建了一个session对象，然后getContext操作会获取对应url的context，接着进行会话操作。
public ServletContext getContext(String uri) {
// Validate the format of the specified argument
if (uri == null || !uri.startsWith("/")) {
return null;
}
Context child = null;
try {
// Look for an exact match
Container host = context.getParent();
child = (Context) host.findChild(uri);
// Non-running contexts should be ignored.
if (child != null && !child.getState().isAvailable()) {
child = null;
}
// Remove any version information and use the mapper
if (child == null) {
int i = uri.indexOf("##");
if (i > -1) {
uri = uri.substring(0, i);
}
// Note: This could be more efficient with a dedicated Mapper
// method but such an implementation would require some
// refactoring of the Mapper to avoid copy/paste of
// existing code.
MessageBytes hostMB = MessageBytes.newInstance();
hostMB.setString(host.getName());
MessageBytes pathMB = MessageBytes.newInstance();
pathMB.setString(uri);
MappingData mappingData = new MappingData();
((Engine) host.getParent()).getService().findConnectors()[0].getMapper().map(
hostMB, pathMB, null, mappingData);
child = (Context) mappingData.context;
}
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
return null;
}
if (child == null) {
return null;
}
if (context.getCrossContext()) {
// If crossContext is enabled, can always return the context
return child.getServletContext();
} else if (child == context) {
// Can still return the current context
return context.getServletContext();
} else {
// Nothing to return
return null;
}
}
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