目录
1.过滤器Filter
filter是对客户端访问资源的过滤，符合条件放行，不符合条件不放行，并且可以对目 标资源访问前后进行逻辑处理
步骤：
- 编写一个过滤器的类实现Filter接口
- 实现接口中尚未实现的方法(着重实现doFilter方法)
- 在web.xml中进行配置(主要是配置要对哪些资源进行过滤)
package web.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;
public class QuickFilter1 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
System.out.println("quick running...");
//放行请求
chain.doFilter(request, response);
}
@Override
public void destroy() {
}
}
<filter>
<filter-name>QuickFilter1</filter-name>
<filter-class>web.filter.QuickFilter1</filter-class>
</filter>
<filter-mapping>
<filter-name>QuickFilter1</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping><url-pattern>/*</url-pattern>
filter对所有servlet资源进行过滤 。
package web.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Servlet1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.getWriter().write("Servlet1 running...");
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}2.filter的访问过程
package web.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;
public class QuickFilter2 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
System.out.println("quick2 running...");
}
@Override
public void destroy() {
}
}
<filter>
<filter-name>QuickFilter2</filter-name>
<filter-class>web.filter.QuickFilter2</filter-class>
</filter>
<filter-mapping>
<filter-name>QuickFilter2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>当访问servlet1时，quickFilter1放行请求chain.doFilter(request, response);，quickFilter1将资源放行给quickFilter2，quickFilter2不放行请求，最终在页面打印不出Servlet1 running...
3.Filter的API
1）Filter生命周期
init(FilterConfig filterConfig)：代表filter对象初始化方法filter创建时执行init方法
doFilter(ServletRequest request, ServletResponse response, FilterChain chain)：
代表filter执行过滤的核心方法，如果某资源已经被配置到filter进行过滤，那么每次访问这个资源都会执行doFilter方法
destory()：代表是filter销毁方法当filter对象销毁时执行该方法
Filter对象的生命周期：
Filter何时创建：服务器启动时就创建该filter对象
Filter何时销毁：服务器关闭时filter销毁
2）Filter的API详解
<filter>
<filter-name>QuickFilter1</filter-name>
<filter-class>web.filter.QuickFilter1</filter-class>
<init-param>
<param-name>aaa</param-name>
<param-value>AAA</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>QuickFilter1</filter-name>
<url-pattern>/*</url-pattern>package web.filter;
import java.io.IOException;
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;
public class QuickFilter1 implements Filter {
@Override
//filter创建时执行init方法
public void init(FilterConfig filterConfig) throws ServletException {
//1.获得web.xml中的filter的名字<filter-name>QuickFilter1</filter-name>
System.out.println(filterConfig.getFilterName());//QuickFilter1
//2.获得当前filter的初始化参数
System.out.println(filterConfig.getInitParameter("aaa"));//AAA
filterConfig.getServletContext();
System.out.println("init...");
}
@Override
//doFilter是Filter的核心过滤方法
/*
* request:内部封装的客户端http请求的内容
* response:代表响应
* FilterChain:过滤器对象
*/
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
System.out.println("quick running...");
//放行请求
chain.doFilter(request, response);
}
@Override
//filter对象销毁时执行destroy方法
public void destroy() {
System.out.println("destroy...");
}
}
init(FilterConfig filterConfig)
其中参数config代表该Filter对象的配置信息的对象，内部封装是该filter的配置信息。
doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
ServletRequest/ServletResponse：每次在执行doFilter方法时web容器负责创建一个request和一个response对象作为doFilter的参数传递进来。该request和该response就是在访问目标资源的service方法时的request和response。
FilterChain：过滤器链对象，通过该对象的doFilter方法可以放行该请求
4.Filter的配置
url-pattern配置
1.完全匹配 /sertvle1
2.目录匹配 /aaa/bbb/* ----最多的
/user/*：访问前台的资源进入此过滤器
/admin/*：访问后台的资源时执行此过滤器
3.扩展名匹配 *.abc *.jsp
注意：url-pattern可以使用servlet-name替代，也可以混用
dispatcher：访问的方式
REQUEST：默认值，代表直接访问某个资源时执行filter,转发时不再执行filter
FORWARD：转发时才执行filter
INCLUDE: 包含资源时执行filter
ERROR：发生错误时 进行跳转是执行filter
<dispatcher>REQUEST</dispatcher>package web.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Servlet1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//response.getWriter().write("Servlet1 running...");
//转发直接访问一次
//request.getRequestDispatcher("/servlet2").forward(request, response);
//重定向直接访问两次
//response.sendRedirect(request.getContextPath()+"/servlet2");
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}package web.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Servlet2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.getWriter().write("hello haohao...");
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}