验证登录页面时，Struts2拦截器会话获取空值

Question

I am a beginner in Struts2 and I'm trying to do this scenario on my own web project :

• When user access login page, server will authenticate whether that he/she has login as "admin" / "user" by accessing the session using interceptor, If the user has no privilege data (it's null) inside the session, they will be passed to login page.
• If the user has login as "admin", user will be redirected to "admin" page.
• If the user has login as "user", user will be redirected to "user" page.

I was trying these codes, If i don't use interceptor, I can access the session, but if i use the interceptor what I get is, the session is still null and giving error 500 instead with NPE. I don't know what is wrong with it.

Thanks for any of you who help me.

struts.xml

<struts>
    <constant name="struts.action.extension" value=","/>
    <constant name="struts.custom.i18n.resources" value="global" />
    <constant name="struts.devMode" value="true" />
    <!-- Configuration for the default package. -->
    <include file="strutsconf/struts-user.xml"/>

</struts>

struts-pageauth.xml

<struts>
    <package name="struts-pageauth" namespace="/" extends="struts-default">
        <interceptors>

            <interceptor name="loginpageauth" class="control.intercept.UserAuthenticationLogin"/>

            <interceptor-stack name="loginauth">
                <interceptor-ref name="createSession"/>
                <interceptor-ref name="loginpageauth"/>
                <interceptor-ref name="defaultStack"/>
            </interceptor-stack>

        </interceptors>
    </package>
</struts>

strusts-user.xml

<struts>
    <constant name="struts.custom.i18n.resources" value="prop-user" />

    <include file="strutsconf/struts-pageauth.xml"/>

    <package name="struts-user" namespace="/" extends="struts-default, struts-pageauth">

        <action name="login" method="login" class="control.action.Login">

            <interceptor-ref name="loginauth"/>
            <result name="admin">/main/admin/Admin.jsp</result>
            <result name="user">/main/user/User.jsp</result>
            <result name="error">/Login.jsp</result>
        </action>

        <action name="logout" method="logout" class="control.action.Login">
            <result name="success">/Login.jsp</result>
            <result name="error">/Login.jsp</result>
        </action>

    </package>
</struts>

UserAuthenticationLogin.java

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package control.intercept;

import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.interceptor.Interceptor;
import java.util.Map;
import org.apache.struts2.interceptor.SessionAware;

public class UserAuthenticationLogin extends ActionSupport implements SessionAware, Interceptor {

    public void setSession(Map<String, Object> map) {
        this.sessionMap = map;
    }

    public void destroy() {
        System.out.println("UserAuthentication Interceptor destroy() called");
    }

    public void init() {
        System.out.println("UserAuthentication Interceptor init() called");
    }

    public String intercept(ActionInvocation ai) throws Exception {
        System.out.println("=========================DEBUG========================");
        System.out.println("UserAuthentication Interceptor intercept() called");
        System.out.println(getText("auth.privilage")); // I can access this properties
        System.out.println(this.sessionMap); // It gets NULL ??
//        System.out.println(this.sessionMap.get(getText("auth.privilage")));
        if(this.sessionMap.get(getText("auth.privilage"))==null) {
            return ai.invoke();
        }
        else if(this.sessionMap.get(getText("auth.privilage")).equals("admin")) {
            return "admin";
        }
        else if(this.sessionMap.get(getText("auth.privilage")).equals("user")) {
            return "user";
        }
        else {
            return "login";
        }
    }

    private String id;
    private String password;
    private String admin;
    private Map<String, Object> sessionMap;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getAdmin() {
        return admin;
    }

    public void setAdmin(String admin) {
        this.admin = admin;
    }

    public Map<String, Object> getSessionMap() {
        return sessionMap;
    }

    public void setSessionMap(Map<String, Object> sessionMap) {
        this.sessionMap = sessionMap;
    }
}

Login.java

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package control.action;

import com.opensymphony.xwork2.ActionSupport;
import java.util.Map;
import org.apache.struts2.interceptor.SessionAware;

public class Login extends ActionSupport implements SessionAware {

    public void setSession(Map<String, Object> map) {
        this.sessionMap = map;
    }

    public String login() throws Exception {
        if(id.equals("admin") && password.equals("admin")) {
            this.sessionMap.put("id", "admin");
            this.sessionMap.put("priv", "admin");
            return "admin";
        }
        if(id.equals("user") && password.equals("user")) {
            this.sessionMap.put("id", "user");
            this.sessionMap.put("priv", "user");
            return "user";
        }
        else {
            setErr_msg(super.getText("error.login"));
            return super.ERROR;
        }
    }

    public String logout() throws Exception {
        this.sessionMap.remove("id");
        this.sessionMap.remove("priv");
        return super.SUCCESS;
    }

    private String id;
    private String password;
    private String err_msg;
    private String admin;
    private Map<String, Object> sessionMap;

    public Map<String, Object> getSessionMap() {
        return sessionMap;
    }

    public void setSessionMap(Map<String, Object> sessionMap) {
        this.sessionMap = sessionMap;
    }

    public String getAdmin() {
        return admin;
    }

    public void setAdmin(String admin) {
        this.admin = admin;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getErr_msg() {
        return err_msg;
    }

    public void setErr_msg(String err_msg) {
        this.err_msg = err_msg;
    }

}

Answer 1

The sessionMap is injected by ServletConfigInterceptor in Actions implementing the SessionAware interface, not Interceptors.

The right way to get the Session Map in an Interceptor is:

Map<String, Object> session = ActionContext.getContext().getSession();

_{Note: be careful in messing with Actions and Interceptors together: it's strange to see an Interceptor implementing ActionSupport... It's not a problem with your code because you are using declarative xml configuration, but Convention Plugin would scan the packages (luckily you have a package with an unmatching name) for classes extending ActionSupport and would detect it as an Action, making it ThreadLocal, that is not what an Interceptor has meant to be. Then you have to remember to be careful upgrading your code in the future to avoid unexpected result.}