Debugging LDAP with shiro in Tomcat - debugging

Question

I have a web service, and for that I want to authenticate users.
I'm trying to have a form based authentication with org.apache.shiro.realm.ldap.JndiLdapRealm as my realm.
But when I enter the credentials nothing happens but redirecting to login page again. And there's nothing get printed on the log.
My Question is how can I debug the shiro to figure out what is happening?
Edit:
Here is my shiro ini file
[main]
authc.loginUrl = /login.jsp
authc.successUrl = /index.jsp
ldapRealm = org.apache.shiro.realm.ldap.JndiLdapRealm
ldapRealm.userDnTemplate = sAMAccountName={0},DC=aaa,DC=bbb
ldapRealm.contextFactory.url = ldap://aaa.bbb.ccc:3268
ldapRealm.contextFactory.systemUsername = admin
ldapRealm.contextFactory.systemPassword= password
securityManager.realms = $ldapRealm
[urls]
/login.jsp = authc
/logout = logout
/** = authc
Edit 2: my login jsp
<form name="loginform" method="post">
plain
<label for="username">Username:</label>
<input type="text" id="username" name="username" />
<br/>
<label for="password">Password:</label>
<input type="password" id="password" name="password" />
<br/>
<label for="rememberMe">Remember me:</label>
<input type="checkbox" id="rememberMe" name="rememberMe" value="true" />
<br/>
<input type="submit" value="Login" />
</form>
my web.xml
<listener>
<listener-class>org.apache.shiro.web.env.EnvironmentLoaderListener</listener-class>
</listener>
<filter>
<filter-name>ShiroFilter</filter-name>
<filter-class>org.apache.shiro.web.servlet.ShiroFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>ShiroFilter</filter-name>
<url-pattern>/*</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>
<dispatcher>INCLUDE</dispatcher>
<dispatcher>ERROR</dispatcher>
</filter-mapping>