我要评论tomcat共享多个web应用会话的实现方法
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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