【JavaWeb】Filter
文章目录
- 1.Filter过滤器
- 2.Filter的初体验
- 3.Filter的生命周期
- 4.FilterConfig类
- 5.FilterChain过滤器链
- 6.Filter的拦截路径
1.Filter过滤器
(1).概念及作用
- Filter过滤器是JavaWeb的三大组件之一
- 三大组件分别是:Servlet程序,Listener监听器,
Filter过滤器 - Filter过滤器是JavaEE的规范,也就是
接口 - 作用:
拦截请求,过滤响应
拦截请求的常见应用场景有:权限检查,日记操做,事物管理等
2.Filter的初体验
- 根据我们之前学过的内容,我们知道,用户登录之后会把
用户登录的信息保存到Session域中,所以要检查用户是否登录,可以判断Session中是否包含用户登录的信息即可
Filter过滤器的使用步骤:
(1).编写一个类去实现Filter接口
(2).实现过滤方法doFilter()
(3).到web.xml中去配置Filter的拦截路径
我们部署工程的时候,在浏览器输入我们要访问的资源路径,之后的整个过程就如上图所示
有权限,就会访问到我们要访问的资源
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
HttpSession session = httpServletRequest.getSession();
Object user = session.getAttribute("user");
//如果为null,说明还没登录
if(user == null){
servletRequest.getRequestDispatcher("/login.jsp").forward(servletRequest,servletResponse);
return;
}else {
//让程序继续往下访问用户的目标资源
filterChain.doFilter(servletRequest,servletResponse);
}
}
<!--filter标签用于配置一个Filter过滤器-->
<filter>
<!--给filter起一个别名-->
<filter-name>AdminFilter</filter-name>
<!--配置filter的全类名-->
<filter-class>filter.AdminFilter</filter-class>
</filter>
<!--filter-mapping配置Filter过滤器的拦截路径-->
<filter-mapping>
<!--filter-name表示当前的拦截路径给哪个filter使用-->
<filter-name>AdminFilter</filter-name>
<!--url-pattern配置拦截路径
/ 表示请求地址为:http://ip:port/工程路径/ 映射到IDEA的web目录
/admin/* 表示请求地址为:http://ip:port/工程路径/admin/*
-->
/admin/*
没有权限就会返回到下图界面
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
这是登陆页面,login.jsp页面
</body>
</html>
注意:
利用jsp也可以起到拦截的作用,但是这种方法有一定的局限性,servlet程序只能写在jsp(只能拦截访问当前jsp资源),所以使用的是Filter用于拦截路径.
- 完整的用户登录和权限检查
public class LoginServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html; charset=UTF");
String username = req.getParameter("username");
String password = req.getParameter("password");
if("wyl168".equals(username) && "123456".equals(password)){
req.getSession().setAttribute("user",username);
resp.getWriter().write("登陆 成功! ! !");
}else{
req.getRequestDispatcher("/login.jsp").forward(req,resp);
}
}
}
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>filter.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/loginServlet</url-pattern>
</servlet-mapping>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
这是登陆页面,login.jsp页面</br>
<form action="http://localhost:8080/15_filter/loginServlet" method="get">
用户名: <input type="text" name="username"/></br>
密 码: <input type="password" name="password"/></br>
<input type="submit" />
</form>
</body>
</html>
说明:当用户提交完正确的用户名和密码,点击提交,就会执行Servlet程序,执行Servlet程序就会保存用户信息到Session域中,此时再次在浏览器输入要访问的资源路径,会执行Filter程序,执行Filter程序就会在Session中找到用户信息,所以就能访问到相应的资源了.
3.Filter的生命周期
Filter的生命周期包含的方法:
(1).构造器方法
public AdminFilter(){
System.out.println("1.Filter构造器方法AdminFilter()");
}
(2).init初始化方法
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("2.Filter的init(FilterConfig filterConfig)初始化");
}
第(1)(2)步在web工程启动的时候执行(Filter已经创建)
(3).doFilter过滤方法
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("3.Filter的doFilter()过滤方法");
HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
HttpSession session = httpServletRequest.getSession();
Object user = session.getAttribute("user");
//如果为null,说明还没登录
if(user == null){
servletRequest.getRequestDispatcher("/login.jsp").forward(servletRequest,servletResponse);
return;
}else {
//让程序继续往下访问用户的目标资源
filterChain.doFilter(servletRequest,servletResponse);
}
}
第(3)步每次拦截到请求,就会执行
(4).destroy销毁
public void destroy() {
System.out.println("4.Filter的destroy()销毁方法");
}
第(4)步,停止web工程的时候,就会执行(停止web工程,也会销毁Filter过滤器)
4.FilterConfig类
基本介绍:
(1)见名知意,它是Filter过滤器的
配置文件类
(2)Tomcat每次创建Filter的时候,也会同时创建一个FilterConfig类,这里包含了Filter配置文件的配置信息
作用:获取Filter过滤器的配置内容(filter-name,init-param,ServletContext对象)
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("2.Filter的init(FilterConfig filterConfig)初始化");
//1.获取Filter的名称filter-name
System.out.println("filter-name的值是: " + filterConfig.getFilterName());
//2.获取Filter的初始化参数init-param
System.out.println("初始化参数username的值是: " + filterConfig.getInitParameter("username"));
System.out.println("初始化参数url的值是: " + filterConfig.getInitParameter("url"));
//3.获取ServletContext对象
System.out.println(filterConfig.getServletContext());
}
5.FilterChain过滤器链
FilterChain过滤器链(多个过滤器在一起工作)
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Filter1 前置代码");
filterChain.doFilter(servletRequest,servletResponse);
System.out.println("Filter1 后置代码");
}
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Filter2 前置代码");
filterChain.doFilter(servletRequest,servletResponse);
System.out.println("Filter2 后置代码");
}
<filter>
<filter-name>Filter1</filter-name>
<filter-class>filter.Filter1</filter-class>
</filter>
<filter-mapping>
<filter-name>Filter1</filter-name>
<url-pattern>/target.jsp</url-pattern>
</filter-mapping>
<filter>
<filter-name>Filter2</filter-name>
<filter-class>filter.Filter2</filter-class>
</filter>
<filter-mapping>
<filter-name>Filter2</filter-name>
<url-pattern>/target.jsp</url-pattern>
</filter-mapping>
如果是下面这种情况:
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Filter2 前置代码");
// filterChain.doFilter(servletRequest,servletResponse);
// System.out.println("Filter2 后置代码");
}
那么最后的结果是:
如果是这种情况:
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Filter1 前置代码");
// filterChain.doFilter(servletRequest,servletResponse);
// System.out.println("Filter1 后置代码");
}
那么结果就是:
注意:Filter1和Filter2的执行顺序,是根据web.xml里面的配置顺序有关
多个Filter过滤器执行的特点:
- 所有
filter和目标资源默认都执行在同一个线程中
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Filter1 前置代码");
System.out.println("Filter1 线程: " + Thread.currentThread().getName());
filterChain.doFilter(servletRequest,servletResponse);
System.out.println("Filter1 线程: " + Thread.currentThread().getName());
System.out.println("Filter1 后置代码");
}
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Filter2 前置代码");
System.out.println("Filter2 线程: " + Thread.currentThread().getName());
filterChain.doFilter(servletRequest,servletResponse);
System.out.println("Filter2 线程: " + Thread.currentThread().getName());
System.out.println("Filter2 后置代码");
}
<body>
<%
System.out.println("target.jsp页面执行了");
System.out.println("target.jsp 线程: " + Thread.currentThread().getName());
%>
</body>
- 多个Filter共同执行的时候,它们都使用
同一个Request对象
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Filter1 前置代码");
System.out.println("Filter1 线程: " + Thread.currentThread().getName());
servletRequest.setAttribute("key1","value1");
filterChain.doFilter(servletRequest,servletResponse);
System.out.println("Filter1 线程: " + Thread.currentThread().getName());
System.out.println("Filter1 后置代码");
}
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("Filter2 前置代码");
System.out.println("Filter2 线程: " + Thread.currentThread().getName());
System.out.println("Filter2取Filter1中保存的数据: " + servletRequest.getAttribute("key1"));
filterChain.doFilter(servletRequest,servletResponse);
System.out.println("Filter2 线程: " + Thread.currentThread().getName());
System.out.println("Filter2 后置代码");
}
6.Filter的拦截路径
- 精确匹配
<url-pattern>/target.jsp</url-pattern>
以上配置的路径,表示请求地址必须为:http://ip:port/工程路径/target.jsp
- 目录匹配
<url-pattern>/admin/</url-pattern>
以上配置的路径,表示请求地址必须为:http://ip:port/工程路径/admin/*
- 后缀名匹配
<url-pattern>*.html</url-pattern>
以上配置的路径,表示请求地址必须以.html结尾才会拦截到
这种匹配方式,后缀名可以自定义,Filter过滤器只关心请求的地址是否匹配,不关心请求的资源是否存在