We can easily get active user's UserDetails in Spring Security. Spring Security provides "org.springframework.security.core.Authentication" which provides the required API for retrieving the logged in user details. The methods of this class are getAuthorities, getCredentials, getDetails, getPrincipal and getName. The last method getName gives user name.

From the below example you can see how we can retrieve logged in user's user-details:

spring-dispatcher-servlet.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd">
    <context:component-scan base-package="com.spring.controller" />
    <bean
      class="org.springframework.web.servlet.view.InternalResourceViewResolver">
      <property name="prefix">
        <value>/WEB-INF/pages/</value>
      </property>
      <property name="suffix">
        <value>.jsp</value>
      </property>
    </bean>

</beans>

Define the below configuration in your applicationContext-security.xml file

<beans:beans xmlns="http://www.springframework.org/schema/security"
    xmlns:beans="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/security
    http://www.springframework.org/schema/security/spring-security-3.1.xsd">

    <http auto-config="true">
        <intercept-url pattern="/welcome*" access="ROLE_USER" />

        <form-login login-page="/login" default-target-url="/welcome" authentication-failure-url="/loginfailed"/>
    </http>
    <authentication-manager>
      <authentication-provider>
        <user-service>
            <user name="Spring" password="123456" authorities="ROLE_USER" />
        </user-service>
      </authentication-provider>
    </authentication-manager>
</beans:beans>

Now define below code in your web.xml

<web-app id="WebApp_ID" version="2.4"
    xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
    http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

    <display-name>Spring MVC Application</display-name>

    <!-- Spring MVC -->
    <servlet>
        <servlet-name>spring-dispatcher</servlet-name>
        <servlet-class>
           org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>spring-dispatcher</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    <listener>
        <listener-class>
            org.springframework.web.context.ContextLoaderListener
        </listener-class>
    </listener>
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
            /WEB-INF/spring-dispatcher-servlet.xml,
            /WEB-INF/applicationContext-security.xml
        </param-value>
    </context-param>
    <!-- Spring Security -->
    <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>
</web-app>

Now write your controller as below:

LoginController.java

package com.evon.controller;

import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class LoginController {

    @RequestMapping(value="/welcome", method = RequestMethod.GET)
    public String getUserDetails(ModelMap model) {
        Authentication authentication = SecurityContextHolder.getContext().
                getAuthentication();
        String name = authentication.getName();
        model.addAttribute("username", name);
        model.addAttribute("message", "Welcome to Spring");
        return "success";

    }

    @RequestMapping(value="/login", method = RequestMethod.GET)
    public String login(ModelMap model) {

        return "login";

    }

}

success.jsp

<html>
<body>
    <h3>${message}</h3>    
    <br />
    <h3>Username : ${username}</h3>    
</body>
</html>

Hope this will help you :)