java实现cas单点登录

CAS是一个开源的企业级单点登录解决方案，支持多种身份验证方式，并提供了丰富的扩展接口。下面是一个简单的Java代码实现CAS单点登录的示例，假设已经在本地部署了CAS Server。

1. 添加CAS Client依赖

在应用系统的pom.xml文件中添加CAS Client的依赖：

<dependency>
    <groupId>org.jasig.cas.client</groupId>
    <artifactId>cas-client-core</artifactId>
    <version>3.6.0</version>
</dependency>

2. 配置CAS Client

在应用系统的配置文件中，需要配置CAS Server的URL、密钥等参数：

# CAS Server的URL
cas.server.url=https://cas.example.com:8443/cas
# CAS Server的登录URL
cas.server.login.url=${cas.server.url}/login
# CAS Server的登出URL
cas.server.logout.url=${cas.server.url}/logout
# CAS Server的验证URL
cas.server.validate.url=${cas.server.url}/validate
# CAS Server的服务名称
cas.server.service.name=https://app.example.com
# CAS Client的回调URL
cas.client.callback.url=https://app.example.com/callback
# CAS Client的密钥
cas.client.secret=secret

3. 配置过滤器

在应用系统的web.xml文件中配置CAS Client的过滤器：

<filter>
    <filter-name>CAS Authentication Filter</filter-name>
    <filter-class>org.jasig.cas.client.authentication.AuthenticationFilter</filter-class>
    <init-param>
        <param-name>casServerLoginUrl</param-name>
        <param-value>${cas.server.login.url}</param-value>
    </init-param>
    <init-param>
        <param-name>serverName</param-name>
        <param-value>${cas.server.service.name}</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>${cas.server.url}</param-value>
    </init-param>
    <init-param>
        <param-name>serverName</param-name>
        <param-value>${cas.server.service.name}</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>

<filter-mapping>
    <filter-name>CAS Authentication Filter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<filter-mapping>
    <filter-name>CAS Validation Filter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<filter-mapping>
    <filter-name>CAS HttpServletRequest Wrapper Filter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<filter-mapping>
    <filter-name>CAS Assertion Thread Local Filter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

4. 编写回调页面

当用户在CAS Server上登录成功后，CAS Server会将用户重定向到应用系统的回调页面。应用系统需要在回调页面中获取用户信息，并将用户信息存储在会话(session)中。

public class CallbackServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Assertion assertion = (Assertion) request.getSession().getAttribute(AbstractCasFilter.CONST_CAS_ASSERTION);
        if (assertion != null) {
            String username = assertion.getPrincipal().getName(); // 获取用户名
            // 将用户名存储在会话中
            // ...
        }
        response.sendRedirect(request.getContextPath() + "/index.jsp");
    }
}

以上就是一个简单的Java代码实现CAS单点登录的示例。需要注意的是，实际应用中还需要考虑安全性、可扩展性等方面的问题。