为了实现用户登录拦截你是否写过如下代码呢?

1. 基于Filter

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

public class AuthenticationFilter implements Filter {
	private FilterConfig filterConfig;
	private String onErrorUrl;

	public void init(FilterConfig filterConfig) throws ServletException {
		// 从 filterConfig 中的得到错误页
		this.filterConfig = filterConfig;
		this.onErrorUrl = filterConfig.getInitParameter("onError");
		if(this.onErrorUrl == null || "".equals(this.onErrorUrl))
			this.onErrorUrl = "onError";
	}
	
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		
		HttpServletRequest httpRequest = (HttpServletRequest)request;
		session = httpRequest.getSession();
		if(null == session.getAttribute("_LOGIN_USER_") && !"/login".equals(httpRequest.getServletPath())) {
			httpRequest.getRequestDispatcher("/"+this.onErrorUrl).forward(request, response);
		}else{
			chain.doFilter(request, response);
		}
	}
	
	public void destroy() {

	}

}

2. 基于Struts

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

import org.apache.struts2.ServletActionContext;

import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.interceptor.AbstractInterceptor;

@SuppressWarnings("serial")
public class LoginInterceptor extends AbstractInterceptor {

	@Override
	public String intercept(ActionInvocation invocation) throws Exception {
		String currentUser="currentUser";
		HttpServletRequest request=ServletActionContext.getRequest();
		HttpServletResponse response=ServletActionContext.getResponse();
		HttpSession session=request.getSession();  					
      	if(request.getRequestURI().endsWith("login.action")){
            return invocation.invoke();
      	} else {
			  if(session.getAttribute(currentUser)!=null){
				return  invocation.invoke();
			  }else{
				 response.sendRedirect(request.getContextPath()+"/login.jsp");
			  }
        }
	    return null;
	}
}

3. 基于SpringMVC

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

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

import cn.edu.hdc.util.Constants;

/**
 * @ClassName: LoginInterceptor 
 * @Description: 登录拦截器
 * @author loweir hbloweir@163.com
 * @date 2016年4月27日 上午8:06:11 
 */
public class LoginInterceptor implements HandlerInterceptor {
	/**
	 * 在目标方法前被调用，返回 true 继续 
	 */
	@Override
	public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object obj) throws Exception {
		try {
			String url = request.getRequestURI();
			// 如果不是登录操作 判断 session
			if (!url.endsWith("login")) {
				if (request.getSession().getAttribute(Constants.CURRENT_USER) == null) {
			        response.sendRedirect(request.getContextPath() + "/login.jsp");
					return false;
				}	
			}			} 
			return true;
		} catch (Exception e) {
			e.printStackTrace();
			return false;
		}
	}

	@Override
	public void afterCompletion(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, Exception arg3)
			throws Exception {
	}

	@Override
	public void postHandle(HttpServletRequest arg0, HttpServletResponse arg1, Object arg2, ModelAndView arg3)
			throws Exception {
		
	}
}

如何使用自定义注解完成自定义拦截呢？

登录注解

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Created by loweir on 2017/5/14 17:19
 * <p>
 * author: 张瑀楠
 * email: hbloweir@163.com
 * 负责登录拦截
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE,ElementType.METHOD})
public @interface WebLoginRequired {
    String value() default ""; // 未登录时需要跳转的路径
}

SpringMVC 拦截器设置

import com.ainsoft.globalshoperp.component.constant.WebLogin;
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

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

/**
 * Created by loweir on 2017/5/14 17:14
 * <p>
 * author: 张瑀楠
 * email: hbloweir@163.com
 */
public class LoginInterceptor implements HandlerInterceptor {

    private static Log logger = LogFactory.getLog(LoginInterceptor.class);

    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object handler) throws Exception {

        if (logger.isDebugEnabled()) {
            logger.debug("拦截器启动");
        }
        /* 
        * 判断是否为 HandlerMethod.class
        * 如果不是说明当前请求并不是 SpringMVC 管理，
        * 如果不是再自行根据业务做响应操作，这里直接返回 true
        */
        if (HandlerMethod.class.isInstance(handler)) {
            HandlerMethod handlerMethod = (HandlerMethod) handler;

            // 判断该 handler 是否有WebLoginRequired注解
            WebLoginRequired webLoginRequired = handlerMethod.getMethod().getDeclaredAnnotation(WebLoginRequired.class);

			// 如果该 handler 没有WebLoginRequired注解，判断所属Controller 是否包含注解
            if (null == webLoginRequired) {
                webLoginRequired = handlerMethod.getBeanType().getAnnotation(WebLoginRequired.class);
            }

			// 如果需要 WebLoginRequired 判断 session
            if (null != webLoginRequired) {
                if (httpServletRequest.getSession().getAttribute(WebLogin.CURRENTUSER) == null) {
                    String executeURL = webLoginRequired.value();
                    if (StringUtils.isBlank(executeURL)) {
                        executeURL = WebLogin.LOGIN;
                    }
                    
                 httpServletResponse.sendRedirect(httpServletRequest.getContextPath() + executeURL);
                    return false;
                }
            }
        }
        return true;
    }

    public void postHandle(javax.servlet.http.HttpServletRequest httpServletRequest, javax.servlet.http.HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        if (logger.isDebugEnabled()) {
            logger.debug("postHandler");
        }
    }

    public void afterCompletion(javax.servlet.http.HttpServletRequest httpServletRequest, javax.servlet.http.HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
        if (logger.isDebugEnabled()) {
            logger.debug("afterCompletion");
        }
    }
}

最终 controller 写法

1. 不需要登录权限的

类和方法都不需要注解

@Controller
@RequestMapping("auth")
public class AuthController {

    @RequestMapping("login")
    public String login() {
        return "login";
    }
}

2. 整个 controller 内都需要登录权限

在类上添加注解即可

@Controller
@WebLoginRequired
@RequestMapping("order")
public class OrderController {

    @RequestMapping("index")
    public String index() {
        return "index";
    }
}

3. controller 某个方法需要登录权限

只在需要登录权限的方法上添加注解
在注解上可以指定需要重定向的链接
如果不指定则默认到 login

@Controller
@RequestMapping("order")
public class OrderController {

    @RequestMapping("index")
    public String index() {
        return "index";
    }

	// 需要登录
	@WebLoginRequired
	@RequestMapping("add")
    public String index() {
        return "index";
    }
	
	// 需要登录,如果未登录跳到 error
	@WebLoginRequired("error")
	@RequestMapping("delete")
    public String index() {
        return "index";
    }
}