意外的Servlet缓存

Question

I have a Tomcat7 web App consisting of an HTML file with form, as well as a Servlet and a Java bean. The HTML form calls the Servlet, which takes the request parameters, does some preparations, creates an instance of the bean and calls it's String doSearch(String arg1, int arg2) method. Each time the Servlet is called, it sets the bean to null and creates a new Instance.

The problem is that in each session the former results (created by the bean) stay visible (which should not appear). I don't use any static variables or classes.

When I run the code as Java Program it works as expected. The only way to get rid of the old results for now is restarting Tomcat

Any help is greatly appreciated.

Thanks.

The war File can be downloaded from https://drive.google.com/open?id=0B5P_61PgIb6gc0VfRC1sbzdhUjQ

Answer 1

Odds are you are storing the information, but the wrong location.

Java servlets support four storage areas (Application, Session, Request, and Page).

The application will hold information until you explicitly remove it or restart the application.

The Session will hold information until you explicitly remove it, you restart the application, or a session timeout cleans the information from the application. Sessions are not really persistent things (http is connectionless), but are simulated by associating a series of similar requests (same web browser, originating IP address, originating operating system, etc.). Future connections with a full set of matching criteria will be able to access the information stored in the Session created with the matching criteria. This permits Tomcat to pretend to have a persistent conversation despite http not permitting a real continuous connection.

The Request will hold information for the duration of a single request. This is useful if you partition your web site's logic into page-less operations (sometimes called commands or actions) and then attach the information to the Request to be pulled out by formatting logic (like a jsp presentation layer).

The Page will hold information for the duration of a single page. For example, if one were in a specific web page (as noted by a specific URL) and due to some logic the request was redirected to a different page, the information would be lost before the other page could access it.

I imagine that you've either stored your information in the Application or the Session, and have been testing with a single web browser. If you connect with a different web browser and you don't see the information created with a prior connection on a different web browser, you are likely storing the information in the Session. Odds are you wish to store this information in the Request.

To store something in a request, get the ServletRequest object (or a subclass of it) and use the .setAttribute(String name, Object o) method. To access it at a later time, use the .getAttribute(String name) method which will return the stored object.