单点登录（因为原理一样，所以没有实现注销）

单点登录（Single Sign On），简称为 SSO，是目前比较流行的企业业务整合的解决方案之一。SSO的定义是在多个应用系统中，用户只需要登录一次就可以访问所有相互信任的应用系统。

实现原理：

1）客户访问系统，通过拦截访问地址，判断该用户是否登录了，如果已经在该登录过了，则可直接访问；否则，携带访问路径去验证中心。

2）然后验证中心，判断携带过来的路径是否合法，如果不合法，跳转到错误页面；反之，进行下一步令牌验证

3）如果持有令牌，则已经在其它相关系统登录过了，不需要再去登录页面了，然后携带已经（在其它相关系统）登录过的信息返回原来的系统，进行访问。如果没有令牌，该用户还没有登录过，跳转到登录页面

4）在登录页面进行登录，登录后，发放令牌，并且携带已登录信息返回原系统。

5）返回原系统后，保存令牌和已登录的信息

具体代码如下（本人在两台计算机上跑了两份代码，你可以在一台计算上支持多个Tomcat，让两份代码分别交个两个Tomcat运行，端口不冲突即可）

系统一的代码如下（其中验证系统嵌入在系统一中）：

package sysone.zr.com.controller;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

import javax.enterprise.inject.Default;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@Controller
public class VerifyController {
    
    private static List<String> urls = new ArrayList<String>();
    // 来源的连接地址
    private String from=null;
    
    static{
        urls.add("http://192.168.10.105:8080/lf/online/welcome.htm");
        urls.add("http://192.168.10.77:8080/zlf/online/welcome.htm");
    }
    
    @RequestMapping("/verifyInfo.htm")
    public String verifyInfo(HttpServletRequest request,HttpServletResponse response,
                           @RequestParam(value="url",required=false,defaultValue="") String url,
                           @RequestParam(value="token",required=false,defaultValue="") String token) throws IOException{
        System.out.println("==url:"+url);
        System.out.println("==token:"+token);
        if ("".equals(url)) {
            return "error";
        }
        
        // 判断是否属于相关系统的URL
        boolean isRight = false;
        for (String str : urls) {
            if (url.equals(str)) {
                isRight = true;
            }
        }
        // 不属于服务范畴，跳转到错误页面
        if (isRight==false) {
            return "error";
        }
        
        // 如果没有登录，就没有令牌，去登录页面
        if ("".equals(token)) {
            from = url;
            return "login";
        }else {
            String identifier = (String)request.getSession().getAttribute("token");
            // 验证通过（已经在其它系统登录过）
            if (token.equals(identifier)) {
                // 返回原来的系统
                response.sendRedirect(url+"?isLogin=true&token="+token);
            }
        }
        
        return "login";
    }
    
    
    @RequestMapping("login.htm")
    public void login(HttpServletResponse response,HttpServletRequest request,
                      @RequestParam(value="username",required=false,defaultValue="") String username,
                         @RequestParam(value="password",required=false,defaultValue="") String password) throws IOException{
        // 实际开发应该去数据库验证，再次忽略该步骤,错误返回相应提示也在此忽略
        if(username.equals("lf") && password.equals("lf")){
            String token = UUID.randomUUID().toString();
            // 保存令牌
            request.getSession().setAttribute("token", token);
            System.out.println("--from:"+from);
            // 重定向（携带参数返回原系统）
            response.sendRedirect(from+"?isLogin=true&token="+token);
            
        }
    }
}

package sysone.zr.com.controller;

import javax.servlet.http.HttpServletRequest;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
@RequestMapping("/lf/online")
public class WelcomeController {
    /**
     * 进入页面
     * @return
     */
    @RequestMapping("/welcome.htm")
    public String comeInPage(Model model,HttpServletRequest request){
        String token = (String)request.getSession().getAttribute("token");
        
        System.out.println("令牌："+token);
        model.addAttribute("token", token);
        return "welcome";
    }
    
}

package sysone.zr.com.interception;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

public class URLHandler implements HandlerInterceptor{

    @Override
    public void afterCompletion(HttpServletRequest arg0,
            HttpServletResponse arg1, Object arg2, Exception arg3)
            throws Exception {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response,
            Object arg2, ModelAndView arg3) throws Exception {
        
    
    }

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
            Object arg2) throws Exception {
        System.out.println("======进入拦截器======="+request.getRequestURI() );
        System.out.println(request.getRequestURL());
        // 获取session
        HttpSession session = request.getSession();
        
        String isLogin = (String)session.getAttribute("isLogin");
        System.out.println(isLogin);
        isLogin = isLogin==null ? "":isLogin;
        // 判断曾经是否登陆过该系统，如果登陆过往下执行，否则去验证系统
        if ("".equals("")) {
            // 获取相关参数
            isLogin = request.getParameter("isLogin");
            String token = request.getParameter("token");
            isLogin = isLogin==null ? "" : isLogin;
            token= token == null ? "" :token;
            /*
             * 如果是从验证系统跳转过来，便携带相关参数
             * 如果验证通过，保存数据
             */
            if ("true".equals(isLogin) && !"".equals(token)) {
                session.setAttribute("isLogin", isLogin);
                session.setAttribute("token", token);
            }else{
                // 获取路径
                StringBuffer url = request.getRequestURL();
                response.sendRedirect("http://192.168.10.105:8080/verifyInfo.htm?token="+token+"&url="+url);
            }
            
        }
        return true;
    }

}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd" >
    <!-- 包扫描 -->
    <context:component-scan base-package="sysone.zr.com" />
     <!-- 开启Springmvc注解驱动 -->
    <mvc:annotation-driven />

      <!-- SpringMVC视图解析器 --> 
    <bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
    
    <!-- 拦截器 -->
    <bean id="urlhandler" class="sysone.zr.com.interception.URLHandler"></bean>
    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/lf/online/**"/>
            <ref bean="urlhandler"/>
        </mvc:interceptor>
    </mvc:interceptors>
    
</beans> 

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>错误页面</title>
</head>
<body>
    <h1>抱歉找不到相关服务</h1>
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>登录页面</title>
</head>
<body>
    
    <form action="login.htm" method="post">
        用户名：<input name="username" /><br>
        密码：<input  name="password"  type="password" /><br>
        <input type="submit" value="login"/>
    </form>
    
    
</body>
</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>首页</title>
</head>
<body>
    <h1>欢迎进入系统1</h1>
    <a href="http://192.168.10.77:8080/zlf/online/welcome.htm?token=${token }">访问系统2</a>
</body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xmlns="http://java.sun.com/xml/ns/javaee" 
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
                              http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
         id="WebApp_ID" version="3.0">
  
   <!-- 配置springmvc核心 Servlet-->
    <servlet>
        <servlet-name>pringmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <!-- 配置文件加载的路径 -->
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc.xml</param-value>
        </init-param>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>pringmvc</servlet-name>
        <url-pattern>*.htm</url-pattern>
    </servlet-mapping>
    <!-- END 配置springmvc核心 Servlet-->
    

</web-app>

系统二的代码如下：

package sysone.zr.com.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
@RequestMapping("/zlf/online")
public class WelcomeController {
    /**
     * 进入页面
     * @return
     */
    @RequestMapping("/welcome.htm")
    public String comeInPage(){
        return "welcome";
    }
    
}

package sysone.zr.com.interception;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

public class URLHandler implements HandlerInterceptor{

    @Override
    public void afterCompletion(HttpServletRequest arg0,
            HttpServletResponse arg1, Object arg2, Exception arg3)
            throws Exception {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response,
            Object arg2, ModelAndView arg3) throws Exception {
        
    
    }

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
            Object arg2) throws Exception {
        System.out.println("======进入拦截器2======="+request.getRequestURI() );
        System.out.println(request.getRequestURL());
        // 获取session
        HttpSession session = request.getSession();
        
        String isLogin = (String)session.getAttribute("isLogin");
        System.out.println(isLogin);
        isLogin = isLogin==null ? "":isLogin;
        // 判断曾经是否登陆过该系统，如果登陆过往下执行，否则去验证系统
        if ("".equals("")) {
            // 获取相关参数
            isLogin = request.getParameter("isLogin");
            String token = request.getParameter("token");
            isLogin = isLogin==null ? "" : isLogin;
            token= token == null ? "" :token;
            /*
             * 如果是从验证系统跳转过来，便携带相关参数
             * 如果验证通过，保存数据
             */
            if ("true".equals(isLogin) && !"".equals(token)) {
                session.setAttribute("isLogin", isLogin);
                session.setAttribute("token", token);
            }else{
                // 获取路径
                StringBuffer url = request.getRequestURL();
                response.sendRedirect("http://192.168.10.105:8080/verifyInfo.htm?token="+token+"&url="+url);
            }
            
        }
        return true;
    }

}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd" >
    <!-- 包扫描 -->
    <context:component-scan base-package="sysone.zr.com" />
     <!-- 开启Springmvc注解驱动 -->
    <mvc:annotation-driven />

      <!-- SpringMVC视图解析器 --> 
    <bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
    
    <!-- 拦截器 -->
    <bean id="urlhandler" class="sysone.zr.com.interception.URLHandler"></bean>
    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/zlf/online/**"/>
            <ref bean="urlhandler"/>
        </mvc:interceptor>
    </mvc:interceptors>
    
</beans> 

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>系统2首页</title>
</head>
<body>
    <h1>欢迎进入系统2</h1>
    <a href="http://192.168.10.105:8080/lf/online/welcome.htm?token=${token }">访问系统1</a>
</body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xmlns="http://java.sun.com/xml/ns/javaee" 
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
                              http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
         id="WebApp_ID" version="3.0">
  
   <!-- 配置springmvc核心 Servlet-->
    <servlet>
        <servlet-name>pringmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <!-- 配置文件加载的路径 -->
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc.xml</param-value>
        </init-param>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>pringmvc</servlet-name>
        <url-pattern>*.htm</url-pattern>
    </servlet-mapping>
    <!-- END 配置springmvc核心 Servlet-->
    

</web-app>