cas认证后跳转，出错，求助了

版本：
server-3.4.12
client-3.2.1服务端已配好，访问也正常web.xml:
<filter>  
<filter-name>CAS Single Sign Out Filter</filter-name>  
<filter-class>org.jasig.cas.client.session.SingleSignOutFilter</filter-class>  
</filter>
 
<filter>  
<filter-name>CASFilter</filter-name>  
<filter-class>org.jasig.cas.client.authentication.AuthenticationFilter</filter-class>  
<init-param>  
<param-name>casServerLoginUrl</param-name>  
<param-value>https://localhost:8443/cas/login</param-value>  
</init-param>  
<init-param>  
<param-name>serverName</param-name>  
<param-value>http://localhost:8080</param-value>  
</init-param>  
</filter> <filter>  
<filter-name>CAS Validation Filter</filter-name>  
<filter-class>org.jasig.cas.client.validation.Cas20ProxyReceivingTicketValidationFilter</filter-class>  
        <init-param>  
            <param-name>casServerUrlPrefix</param-name>  
            <param-value>https://localhost:8443/cas</param-value>  
        </init-param>  
        <init-param>  
            <param-name>serverName</param-name>  
            <param-value>http://localhost:8080</param-value>  
        </init-param>  
    </filter>      <filter>  
     <filter-name>CAS HttpServletRequest Wrapper Filter</filter-name>  
     <filter-class>org.jasig.cas.client.util.HttpServletRequestWrapperFilter</filter-class>  
    </filter>    <filter>  
     <filter-name>CAS Assertion Thread Local Filter</filter-name>  
     <filter-class>org.jasig.cas.client.util.AssertionThreadLocalFilter</filter-class>  
    </filter>server和client都在我本地电脑上证书cn=localhost
也导入到jdk里了现在通过client端认证，能跳转到server认证页面，输入用户名密码后，跳转回来，页面报错了：
java.lang.RuntimeException: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
org.jasig.cas.client.util.CommonUtils.getResponseFromServer(CommonUtils.java:341)
org.jasig.cas.client.util.CommonUtils.getResponseFromServer(CommonUtils.java:305)
org.jasig.cas.client.validation.AbstractCasProtocolUrlBasedTicketValidator.retrieveResponseFromServer(AbstractCasProtocolUrlBasedTicketValidator.java:50)
org.jasig.cas.client.validation.AbstractUrlBasedTicketValidator.validate(AbstractUrlBasedTicketValidator.java:207)
org.jasig.cas.client.validation.AbstractTicketValidationFilter.doFilter(AbstractTicketValidationFilter.java:169)
org.jasig.cas.client.authentication.AuthenticationFilter.doFilter(AuthenticationFilter.java:116)
org.jasig.cas.client.session.SingleSignOutFilter.doFilter(SingleSignOutFilter.java:76)请问怎么回事