JSP/Servlet基础——登录成功后返回之前的页面

笔记，只供自己参考，水平相当菜

配置过滤器，拦截用户请求，如果用户没有登录，就转到登录页面，登录成功后再返回到之前的页面

1 在web.xml中加入过滤器的配置

<?xml version="1.0" encoding="GBK"?>
<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"
	metadata-complete="true" version="3.0">
	<display-name>魔兽世界</display-name>
	<welcome-file-list>
		<welcome-file>index.html</welcome-file>
	</welcome-file-list>
	<servlet>
		<servlet-name>login</servlet-name>
		<servlet-class>servlet.LoginServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>login</servlet-name>
		<url-pattern>/login</url-pattern>
	</servlet-mapping>
	<!-- 定义Filter -->
	<filter>
		<filter-name>authority</filter-name>
		<filter-class>filter.AuthorityFilter</filter-class>
		<init-param>
			<param-name>encoding</param-name>
			<param-value>GBK</param-value>
		</init-param>
		<init-param>
			<param-name>loginPage</param-name>
			<param-value>/login</param-value>
		</init-param>
		<init-param>
            <param-name>ignoreTypes</param-name>
            <param-value>css</param-value>
        </init-param>
		<init-param>
			<param-name>proLogin</param-name>
			<param-value>/proLogin</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>authority</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
</web-app>

2 写过滤器AuthorityFilter.java

package filter;

import java.io.IOException;
import java.net.URLEncoder;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet Filter implementation class AuthorityFilter
 */
@WebFilter("/AuthorityFilter")
public class AuthorityFilter implements Filter
{

	private FilterConfig config;
	private String encoding;
	private String loginPage;
	private String ignoreType;

	/**
	 * Default constructor.
	 */
	public AuthorityFilter()
	{
		// TODO Auto-generated constructor stub
	}

	/**
	 * @see Filter#destroy()
	 */
	public void destroy()
	{
		config = null;
	}

	/**
	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
	 */
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException
	{
		long before = System.currentTimeMillis();
		System.out.println("/*******************/\nAuthorityFilter开始过滤...");
		HttpServletRequest hrequest = (HttpServletRequest) request;
		String requestPath = hrequest.getServletPath(); // 这里是不包含?以及?后面的字符串的
		System.out.println("AuthorityFilter截获到用户请求的地址："
				+ hrequest.getServletPath());
		
		// 设定编码
		request.setCharacterEncoding(encoding);

		// 是否是要忽略的类型
		if (requestPath.endsWith(ignoreType))
		{
			chain.doFilter(request, response);
		} else
		{
			HttpSession session = hrequest.getSession();
			if (session.getAttribute("user") == null
					&& !requestPath.endsWith(loginPage))
			{
				HttpServletResponse res = (HttpServletResponse) response;
				String ReturnUrl = URLEncoder.encode(config.getServletContext().getContextPath() + requestPath,"GBK"); 
				res.sendRedirect(config.getServletContext().getContextPath()
						+ loginPage + "?ReturnUrl=" + ReturnUrl);
				//res.sendRedirect("http://www.baidu.com");
				System.out.println("AuthorityFilter已经把页面重定向到登录页面");
			} else
			{
				chain.doFilter(request, response);
				System.out.println("AuthorityFilter过滤结束");
				System.out.println("请求被AuthorityFilter定位到"
						+ hrequest.getRequestURI());
			}
		}
		long after = System.currentTimeMillis();
		System.out.println("AuthorityFilter所花时间为：" + (after - before)
				+ "\n/*******************/");
	}

	/**
	 * @see Filter#init(FilterConfig)
	 */
	public void init(FilterConfig fConfig) throws ServletException
	{
		this.config = fConfig;
		encoding = config.getInitParameter("encoding");
		loginPage = config.getInitParameter("loginPage");
		ignoreType = config.getInitParameter("ignoreTypes");
	}

}

3 修改LoginServlet.java

package servlet;

import java.io.IOException;
import java.net.URLDecoder;
import java.sql.ResultSet;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import dao.DbDao;

/**
 * Servlet implementation class LoginServlet
 */
@WebServlet(description = "登录控制器", urlPatterns = { "/login" })
// 如果在web.xml中配置了，在Annotation中的配置就不会有效果
public class LoginServlet extends HttpServlet
{
	private static final long serialVersionUID = 1L;

	/**
	 * @see HttpServlet#HttpServlet()
	 */
	public LoginServlet()
	{
		super();
		// TODO Auto-generated constructor stub
	}

	/**
	 * @see HttpServlet#service(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void service(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException
	{
		System.out.println("LoginServlet开始处理用户登录请求：" + request.getRequestURI());
		String errMsg = "";
		HttpSession session = request.getSession(true);
		RequestDispatcher rd;
		String username = request.getParameter("username");
		String pass = request.getParameter("pass");
		String returnUrl = null;
		String rawQueryString = request.getQueryString();
		if (rawQueryString != null)
		{
			System.out.println("带有参数" + rawQueryString);
			try
			{
				String queryString = URLDecoder.decode(rawQueryString, "GBK");
				String[] paramPairs = queryString.split("&");
				String[] nameValue = paramPairs[0].split("=");
				if (nameValue[0].equalsIgnoreCase("ReturnUrl"))
				{
					returnUrl = nameValue[1];
				}
			} catch (Exception e)
			{
				e.printStackTrace();
				returnUrl = null;
			}
		}
		if (returnUrl != null)
		{
			session.setAttribute("returnUrl", returnUrl);
		}

		if (username != null)
		{
			try
			{
				DbDao dd = new DbDao("oracle.jdbc.driver.OracleDriver",
						"jdbc:oracle:thin:localhost:1521:orcl", "system",
						"abc123");
				ResultSet rs = dd.query("select pass from user_table "
						+ "where name=?", username);
				if (rs.next())
				{
					if (rs.getString("pass").equals(pass))
					{
						session.setAttribute("user", username);
						String reUrl = (String) session.getAttribute("returnUrl");
						if (session.getAttribute("returnUrl") == null) 
						{
							System.out.println("登录成功，跳到欢迎页面");
							((HttpServletResponse) response)
									.sendRedirect(getServletContext()
											.getContextPath() + "/welcome.jsp");
						} else
						{
							System.out.println("登录成功，返回之前的页面");
							((HttpServletResponse) response)
									.sendRedirect(reUrl);
						}
					} else
					{
						errMsg += "您的用户名密码不符合，请重新输入";
					}
				} else
				{
					errMsg += "您的用户名不存在，请先注册";
				}
			} catch (Exception e)
			{
				e.printStackTrace();
			}
		}
		if ((errMsg != null && !errMsg.equals("")) || username == null)
		{
			System.out.println("forward到login.jsp");
			rd = request.getRequestDispatcher("/login.jsp");
			request.setAttribute("err", errMsg);
			rd.forward(request, response);
			// （1）请求被redirect到/login?returnUrl...，让浏览器重新发送一个请求，这个请求为/login?returnUrl...
			// （2）浏览器发送这个请求，把地址刷新为/login?returnUrl...
			// （3）服务器记下returnUrl，把请求forword到login.jsp。login.jsp输出响应
			// (4)浏览器收到响应，渲染页面。地址栏还是login?returnUrl
			// (5)浏览器向服务器发送post请求，此时发的请求就是/login。
			// 浏览器的地址栏显示什么，是由浏览器根据它发送的请求决定的，此时它的请求是/login，所以它的地址栏就变成了/login
		}
	}

}