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过滤器生命周期
- web应用程序启动时，web服务器创建Filter实例对象，以及对象初始化操作
- 当请求访问与过滤器关联的Web资源时，过滤器拦截请求，完成指定功能。
- Fliter对象创建后会驻留在内存，在web应用移除或者服务器停止时才销毁
- 过滤器的创建和销毁由web服务器负责
过滤器实现步骤
1、编写java类实现Fliter接口，并实现其doFilter方法
2、在web.xml文件中对Fliter类进行注册，并设置所拦截的资源。
过滤器链
- 在一个web应用中，多个过滤器组合起来称之为一个过滤器链
- 过滤器的调用顺序取决于过滤器在web.xml文件中的注册顺序
- 案例1 中文乱码过滤器实现
- web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
<display-name>FilterDemoWebProj</display-name>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<!-- 字符乱码过滤器配置 -->
<filter>
<filter-name>CharacterEncodingFilter</filter-name>
<filter-class>com.alan.filter.CharacterEncodingFilter</filter-class>
<init-param>
<param-name>systemName</param-name>
<param-value>filter Encoding</param-value>
</init-param>
<init-param>
<param-name>version</param-name>
<param-value>1.0</param-value>
</init-param>
<init-param>
<param-name>charSet</param-name>
<param-value>UTF-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<!-- 安全控制过滤器配置 -->
<filter>
<filter-name>SessionFilter</filter-name>
<filter-class>com.alan.filter.SessionFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>SessionFilter</filter-name>
<url-pattern>/message.jsp</url-pattern>
</filter-mapping>
</web-app>
- filter 中文乱码
package com.alan.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.HttpServletResponse;
public class CharacterEncodingFilter implements Filter {
//定义FilterConfig对象，将init传入的config对其赋值
private FilterConfig config;
public CharacterEncodingFilter() {
// TODO Auto-generated constructor stub
}
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
// String systemName = config.getInitParameter("systemName");
// String version = config.getInitParameter("version");
// System.out.println(systemName);
// System.out.println(version);
//中文编码过滤器实现
String charSet = config.getInitParameter("charSet");
request.setCharacterEncoding(charSet);
//此方法通知web服务器，连接请求已经执行完成
chain.doFilter(request, response);
}
public void init(FilterConfig fConfig) throws ServletException {
this.config = fConfig;
}
}
- filter 安全控制
package com.alan.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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class SessionFilter implements Filter {
public SessionFilter() {
}
public void destroy() {
}
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
// 用户登陆安全控制
// 1、向下转型
HttpServletRequest hresquest = (HttpServletRequest) request;
HttpServletResponse hresponse = (HttpServletResponse) response;
// 2、判断全局域中的username是否有值
String username = (String) hresquest.getServletContext().getAttribute("username");
if (username == null) {
hresponse.sendRedirect(hresquest.getContextPath() + "/index.jsp?flag=1");
return;
} else { // 此方法通知web服务器，连接请求已经执行完成
chain.doFilter(request, response);
return;
}
}
public void init(FilterConfig fConfig) throws ServletException {
}
}
dispatcher子元素
- <dispatcher></dispatcher>没有配置，默认为request
- 包括 request include forward error 四种配置方式
- 如果是重定向的话 需要配置为request？？？
- 可以对一个过滤器配置多个dispatcher子元素
