Get logged-in user info in Jakarta EE – the simplest way

Ondrej MihalyiNovember 29th, 2021Last Updated: November 17th, 2021

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The security before Java EE 8 / Jakarta EE 8 used to be a bit complicated and confusing. Every specification provided its own way to retrieve information about the logged-in user. The situation greatly improved with the introduction of the Security API that provides a unified way to do that – simply inject the SecurityContext CDI bean.

There’s still a small catch – this only works in the servlet context and EJB context. Or, in other words, when processing an HTTP request or inside any type of EJB. The good thing is that this covers most of the cases in which you’ll ever need to retrieve user information. In the other rare cases, you need to use one of the APIs which I also describe in this post.

Unified access to user info using Security API

With the Security API, retrieving information about the current user is pretty easy straightforward:

Inject SecurityContext
Get the name of the user
- Call the method getCallerPrincipal()
- If the result is null, no user is logged in
- Otherwise, call the method getName() to get the name of the logged-in user
Verify that a user has a specific role (permission)
- Call the method isCallerInRole(roleName)

Full example of a servlet that prints user’s name and whether the user is in role “admin”:

@WebServlet(urlPatterns = "/servlet")
public class UserInfoServlet extends HttpServlet {

    @Inject
    SecurityContext userContext;
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        // retrieve the principal and later check whether it's null or not
        Principal callerPrincipal = userContext.getCallerPrincipal();

        resp.getOutputStream().println(String.format(
                "<html><body>"
                + "<p>User: %s</p>"
                + "<p>Is admin: %s</p>"
              + "</body></html>", 

        // print user's name only if the user is logger in and principal is not null
                callerPrincipal != null ? callerPrincipal.getName() : "not logged in",
        // true if user has admin role
                userContext.isCallerInRole("admin")));
    }
    
}

Alternative ways to access user info

In case you can’t use the Security API, you can still use one of the other APIs that provide similar access to user information. A lot of other specification APIs provide similar methods to retrieve the name of the logged-in user and to check whether the user is in a specific role. Below is a summary of all possible ways:

Specification API	Methods to call	How to retrieve the user context
Servlet	User name: `HttpServletRequest.getUserPrincipal`() Returns `null` if not logged in. In role: `HttpServletRequest.isUserInRole`()	`@Inject HttpServletRequest request;` `HttpServletRequest` is also passed to servlet’s methods
EJB	User name: `EJBContext.getCallerPrincipal()` If not logged in, returns a `Principal` with `getName() == "ANONYMOUS"` instead of `null` In role: EJBContext.isCallerInRole()	`EJBContext` or any of its subinterfaces can be injected in an EJB or retrieved via JNDI: `@Resource EJBContext ejbContext;` `(EJBContext)new InitialContext()` `.lookup("java:comp/EJBContext")`
REST	User name: `SecurityContext.getUserPrincipal()` Returns `null` if not logged in. In role: `SecurityContext.isUserInRole()`	`@Context SecurityContext security;`
JSF	User name: `ExternalContext.getUserPrincipal()` Returns `null` if not logged in. In role: `ExternalContext.isUserInRole()`	`@Inject ExternalContext externalContext;` `FacesContext.getCurrentInstance()` `.getExternalContext()`
CDI	User name: `@Inject Principal principal;` If not logged in, injects a `Principal` with `getName() == "ANONYMOUS"`, similar to EJB In role: Not available	`@Inject Principal principal;`
WebSocket	User name: `Session.getUserPrincipal()` Returns `null` if not logged in. In role: Not available	`Session` is passed as an argument to handlers of WebSocket events
XML Web Services	User name: `WebServiceContext.getUserPrincipal()` Returns `null` if not logged in. In role: `WebServiceContext.isUserInRole()`	`WebServiceContext` can be injected in a WS endpoint: `@Resource WebServiceContext wsContext;`

The Security specification also provides a summary of all the available methods to retrieve user’s name and role information in 4.5. Relationship to Other Specifications.

What’s the best way?

I’d certainly recommend using only the Security API’s SecurityContext whenever possible, for the following reasons:

It’s a unified API so you can learn and remember a single way to access user information
It’s easy to use, just inject it as a CDI bean
It provides all the information provided by any of the other APIs
It’s cleaner in case the user isn’t logged – returns null Principal instead of a Principal with a default name

The only drawback is that currently it only works in Servlet and EJB contexts. Even though these 2 contexts are the most widely used, it’s still possible that in some rare cases the Security API can’t be used. Hopefully, the future versions of the Security specification will also cover other contexts. And even if not, the contexts where it wouldn’t work are related to some legacy and old Jakarta APIs and are nowadays very rarely used. In fact so rarely that you will probably not use any of them ever.

Published on Java Code Geeks with permission by Ondrej Mihalyi, partner at our JCG program. See the original article here: Get logged-in user info in Jakarta EE – the simplest way

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