Servlet過濾器
由Servlet容器管理的對象，過濾器的功能是在原數據和目的數據之間起過濾作用的中間組件。
簡單實例實現：
過濾器功能：在訪問指定資源之前，打印一條日誌，訪問指定資源之後，打印一條日誌
package com.jike.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.annotation.WebFilter;
/**
* Servlet Filter implementation class FilterOne
*/
public class FilterOne implements Filter {
/**
* Default constructor.
*/
public FilterOne() {
System.out.println("=======構造函數==========");
}
/**
* @see Filter#init(FilterConfig)
*/
public void init(FilterConfig fConfig) throws ServletException {
//Servlet啓動時執行init方法，
// 這點和Servlet是有區別的
// servlet在第一次被訪問是執行init方法，過濾器在容器啓動時執行init方法
System.out.println("=======初始化=========");
String initParam = fConfig.getInitParameter("param");
System.out.println("param=" + initParam);
}
/**
* @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
*/
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("=======開始doFilter=========");
chain.doFilter(request, response);
System.out.println("=======結束doFilter=========");
}
/**
* @see Filter#destroy()
*/
public void destroy() {
System.out.println("======銷燬=========");
}
}在web.xml中添加：
<filter> <filter-name>FilterOne</filter-name> <filter-class>com.jike.filter.FilterOne</filter-class> <init-param> <param-name>param</param-name> <param-value>thystar</param-value> </init-param> </filter> <filter-mapping> <filter-name>FilterOne</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
訪問：http://localhost:8080/JSPStudy/Hello
過濾器的應用範圍：
權限控制
日誌記錄
圖像轉換
數據壓縮
過濾器鏈：
過濾器鏈的執行順序根據部署描述符中的順序。
在上個程序的基礎上再添加一個FilterTwo，代碼相同。配置web.xml ,在控制欄查看運行結果。
使用過濾器進行權限校驗：
處理流程：
首先，建立jsp文件：
index爲首頁，在index.jsp中：
<%@ 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>Insert title here</title>
</head>
<body>
<a href="<%= request.getContextPath() %>/11/Hello.jsp" >Hello.jsp</a>
<% //用於根據當前用戶不同的登陸狀態顯示連接
String flag = "";
Object obj = session.getAttribute("flag");// 獲取登陸狀態
if(obj != null){
flag = obj.toString();
}
if(flag.equals("login_success")){// 如果登陸
%>
<a href="<%= request.getContextPath()%>/LogoutServlet">退出</a>
<%}else{ // 如果未登錄
%>
<a href="<%= request.getContextPath()%>/11/login.jsp">登陸</a>
<%
}
%>
</body>
</html>在login.jsp中
<%@ 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">
<!-- 使用css美化當前頁面 -->
<style type="text/css">
body{
color: #000;
font-size: 14px;
margin: 20px auto;
}
</style>
<script type="text/javascript">
function check(form){
if(document.forms.loginForm.uname.value==""){
alert("請輸入用戶名");
document.forms.loginForm.uname.focus();
return false;
}
if(document.forms.loginForm.upwd.value==""){
alert("請輸入密碼");
document.forms.loginForm.upwd.focus();
return false;
}
}
</script>
<title>Insert title here</title>
</head>
<body>
<form action="<%= request.getContextPath() %>/LoginServlet11" name="loginForm">
<%if(request.getAttribute("return_uri") != null){ %>
<input type="hidden" name="return_uri" value="<%= request.getAttribute("return_uri") %>">
<%} %>
<table border="1" cellspacing="0" cellpadding="5" bordercolor="silver" align="center">
<tr>
<!-- 提示信息 -->
<td colspan="2" align="center" bgcolor="#E8E8E8">用戶登陸</td>
</tr>
<tr>
<td>用戶名：</td>
<td><input type="text" name="uname" /></td>
</tr>
<tr>
<td>密碼：</td>
<td><input type="password" name="upwd" /></td>
</tr>
<tr>
<td colspan="2" align="center">
<input type="submit" name="submit" onclick="return check(this);"/>
<input type="reset" name="reset"/>
</td>
</tr>
</table>
</form>
</body>
</html>在Hello.jsp中：
<%@ 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>Insert title here</title> </head> <body> <%! String str = "Hello world"; %> <% out.println(str); %> <br/> <a href="<%= request.getContextPath() %>/11/index.jsp">index.jsp</a> </body> </html>
此時，jsp頁面設計完成。
接下來，完成登陸和退出Servlet的編寫
新建Servlet：
在LoginServlet11中，
package com.jike.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginServlet11 extends HttpServlet {
public LoginServlet11() {
super();
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 獲取用戶提交的表單數據
String uname = request.getParameter("uname");
String passwd = request.getParameter("upwd");
// returnUri用戶訪問登陸頁之前訪問的頁面，通過這個值，登陸成功後的用戶和以重新返回登陸前的頁面
String returnUri = request.getParameter("return_uri");
// 輸出這三個值
System.out.println("username:" + uname);
System.out.println("password:" + passwd);
System.out.println("return_uri:" + returnUri);
RequestDispatcher rd = null;
// 非空校驗
if (uname == null || passwd == null) {
request.setAttribute("msg", "用戶名或密碼爲空");
rd = request.getRequestDispatcher("/11/login.jsp");
rd.forward(request, response);
} else {// 否則執行登陸邏輯
if (uname.equals("star") && passwd.equals("123")) {// 如果登陸成功
// 則在當前用戶的session對象中保存一個key爲flag，值爲login_success的字符串
// 用於表面當前用戶處於登陸狀態
request.getSession().setAttribute("flag", "login_success");
// 接下來根據returnUri的值進行跳轉
if (returnUri != null) {
rd = request.getRequestDispatcher(returnUri);
rd.forward(request, response);
} else {
rd = request.getRequestDispatcher("/11/index.jsp");// 跳轉回首頁
rd.forward(request, response);
}
} else {// 用戶登陸失敗
// 在當前用戶session對象中保存一個key爲flag，值爲login_error的字符串
// 用於表面當前用戶登陸失敗
request.getSession().setAttribute("flag", "login_error");
request.setAttribute("msg", "用戶名或密碼錯誤");
rd = request.getRequestDispatcher("/11/login.jsp");
rd.forward(request, response);
}
}
}
}用於退出的LogoutServlet
package com.jike.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
// 用於 退出的邏輯
public class LogoutServlet extends HttpServlet {
public LogoutServlet() {
super();
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 直接刪除session對象，跳轉回首頁
request.getSession().invalidate();
response.sendRedirect(request.getContextPath() + "/11/index.jsp");
}
}在web.xml中添加配置：
<servlet> <description>This is the description of my J2EE component</description> <display-name>This is the display name of my J2EE component</display-name> <servlet-name>LoginServlet11</servlet-name> <servlet-class>com.jike.servlet.LoginServlet11</servlet-class> </servlet> <servlet> <description>This is the description of my J2EE component</description> <display-name>This is the display name of my J2EE component</display-name> <servlet-name>LogoutServlet</servlet-name> <servlet-class>com.jike.servlet.LogoutServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>LoginServlet11</servlet-name> <url-pattern>/LoginServlet11</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>LogoutServlet</servlet-name> <url-pattern>/LogoutServlet</url-pattern> </servlet-mapping>
myeclipse會自動生成這個配置
接下來，添加權限過濾器，只有登陸的客戶才能訪問Hello.jsp
新建過濾器：
package com.jike.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.RequestDispatcher;
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;
public class PermissionFilter implements Filter {
public PermissionFilter() {
// TODO Auto-generated constructor stub
}
public void init(FilterConfig fConfig) throws ServletException {
// TODO Auto-generated method stub
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
// 強制類型轉換
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse resp = (HttpServletResponse) response;
// 獲取請求中的ServletPath
String servletPath = req.getServletPath();
// 獲取session對象
HttpSession session = req.getSession();
// 獲取session對象的flag的值，強制轉換爲String類型
String flag = (String) session.getAttribute("flag");
// 如果用戶訪問的是首頁，或login.jsp或者執行登陸操作
if (servletPath != null
&& (servletPath.equals("/11/login.jsp")
|| (servletPath.equals("/11/index.jsp")) || (servletPath
.equals("/LoginServlet11")))) {
chain.doFilter(request, response);// 將請求轉發給下一個組件處理
} else {// 對於請求的其他的url都會進行權限校驗
// 如果用戶處於登陸狀態，可以直接訪問
if (flag != null && flag.equals("login_success")) {
chain.doFilter(request, response);
} else if (flag != null && flag.equals("login_error")) {// 如果登陸失敗
req.setAttribute("msg", "登陸失敗， 請重新登陸");
// 把用戶訪問的url保存到request對象中
req.setAttribute("return_uri", servletPath);
RequestDispatcher rd = req
.getRequestDispatcher("/11/login.jsp");
rd.forward(req, resp);
} else {// 如果沒有登陸
req.setAttribute("msg", "尚未登錄");
req.setAttribute("return_uri", servletPath);// 保存url
RequestDispatcher rd = req
.getRequestDispatcher("/11/login.jsp");
rd.forward(req, resp);
}
}
}
public void destroy() {
// TODO Auto-generated method stub
}
}在web.xml中添加配置：
<filter> <filter-name>PermissionFilter</filter-name> <filter-class>com.jike.filter.PermissionFilter</filter-class> </filter> <filter-mapping> <filter-name>PermissionFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
訪問 ：http://localhost:8080/JSPStudy/index.jsp
測試
極客學院：http://www.jikexueyuan.com/course/644.html