Spring singleton #autowired service and shared state - spring

Question

I have a controller and a filter in which I inject a particular service.
In that service I have a Hashmap where I try to store certain information. The issue that I am running into is that although it appears that that a single instance of that service is created and injected into my controller and my filter it seems that there an two instances of the Map. I'm at a loss as to why. No matter how I tried to instantiate the map (or inject it) the behavior is still the same.
It turns out the issue is that two instances of the service are created and injected one in the controller and one in the filter. It's not clear to me why this is happening and how to resolve it.
Following is an extract of the code:
#Controller
public MyController {
#Autowired
private MyService myService;
someEndpoint() {
....
myService.putData(key, value);
.....
}
}
public class MyFilter extends GenericFilterBean {
#Autowired
private MyService myService;
public void doFilter(...) {
//this is where I have a problem.
// the reference myService.myMap seems to be pointing to a different instance
// than the service.myMap in the controller which doesn't make any sense to me
// the filter obviously intercepts all requests so I would expect that after that particular
// endpoint is accessed the data will be there for subsequent requests
myService.getData(..);
}
.....
}
#Service
public class MyService {
private Map <String,String> myMap = new HashMap <String,String> ();
public String getData(String key) {
return myMap.get(key);
}
public void putData(String key, String value){
myMap.put(key,value);
}
}
Here is an extract of the app-config.xml
<?xml version="1.0" encoding="utf-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:tx="http://www.springframework.org/schema/tx"
xmlns:security="http://www.springframework.org/schema/security"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-3.2.xsd">
<context:component-scan base-package="com.mycompany.myPackage"/>
<context:annotation-config />
.......
<security:http
........
........
<security:custom-filter ref="myFilter" position="FORM_LOGIN_FILTER" />
....
...........
<bean class="com.mycompany.filters.MyFilter" id="myFilter"/>
and the web.xml
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/app-config.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<servlet>
<servlet-name>Dispatcher Servlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/app-config.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>Dispatcher Servlet</servlet-name>
<url-pattern>/webservice/*</url-pattern>
</servlet-mapping>
<filter>
<filter-name>springSecurityFilterChain</filter-name>
<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
<filter-name>springSecurityFilterChain</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
Any help is greatly appreciated.

Answer 1

In your web.xml you set:
<servlet>
<servlet-name>Dispatcher Servlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/app-config.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
which creates one web application context initiated by your servlet.
Then you also have:
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/app-config.xml</param-value>
</context-param>
which also creates a parent root web application context, in your case a duplicate one.
This scheme, properly used, favors the cases where you may have more servlets, each one defining its own isolated context but inherit bean definitions from a common root context (services, datasources etc). It also gives a good practice roadmap for creating layered contexts, i.e. prevent your service beans to have dependencies on your mvc layer.
Unless you have more than one configuration files, you should assign an empty value to the contextConfigLocation of your servlet configuration as :
<servlet>
<servlet-name>Dispatcher Servlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value></param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
Be careful. Do not omit the parameter. Spring will infer some default configuration file name based on your servlet and will complain if it does not exist.

Answer 2

GenericFilterBean is not in an application context. I would expect java.lang.InstantiationException in the code above. You can get your bean via the filter's ServletContext. Any other instantiation trick will cause map duplication.

Answer 3

Are you sure that there is only one instance of MyService class created? The simplest way to check this is to provide default constructor implementation and print some text in it. Please check this and let me know, because I have some suspicions.
If this is true, and there are two instances of MyService class, there is possibility that when you put some data to map, you use instance A of MyService and when you get data from the map you use instance B of MyService... I will wait for your response to continue/stop this thinking.