过滤器-Filter
- 是J2EE SERVLET下模块下的组件
- Filter的作用是对URL做统一的拦截
- Filter通常用于应用程序层面进行全局处理
过滤链:
E ---->tomcat{过滤器1->过滤器2->servlet/jsp}
jsp/servlet->过滤器2->过滤器1->响应
开发过滤器的三要素:
- 任何接口都要实现javax.servlet.Filter接口
- 在Filter的接口中doFilter()方法中写过滤器的功能代码
- 在WEB.xml中对过滤器进行配置,说明URL的范围
开发我的第一个过滤器:
package com.imooc.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 MyFirstFilter implements Filter{
@Override
public void destroy() {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
// TODO Auto-generated method stub
System.out.println("过滤器已经生效");
chain.doFilter(request, response);
}
@Override
public void init(FilterConfig arg0) throws ServletException {
// TODO Auto-generated method stub
}
}
web.xml配置
<?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>first-filter</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.jsp</welcome-file>
<welcome-file>default.htm</welcome-file>
</welcome-file-list>
<filter>
<filter-name>myFirstFilter</filter-name>
<filter-class>com.imooc.filter.MyFirstFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>myFirstFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>
效果:
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过滤器的生命周期:
初始化【tomcat启动时Web应用被加载时过滤器对象被创建,并且立即加载init方法进行初始化,此时对象长期存在】
提供服务,每次资源加载都会被执行过滤器
销毁【应用重启、关闭时执行destory方法】
验证
package com.imooc.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 MyFirstFilter implements Filter{ @Override public void destroy() { // TODO Auto-generated method stub System.out.println("过滤器已被销毁"); } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // TODO Auto-generated method stub System.out.println("过滤器已经生效"); chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { // TODO Auto-generated method stub System.out.println("过滤器初始化成功"); } }
过滤器的特性:
- 过滤器对象在WEB应用启动时被创建且唯一
- 唯一的过滤器对象在并发环境下采用"多线程"方法控制
过滤器的两种开发模式:(先执行配置的,在执行注解的)
在WEB.XML种配置
采用注解形式开发
@WebFilter(filterName =“MyAnnoationFilter”,urlPatterns=“/*”)
配置与注解如何选择?
- 配置形式维护性好,适合应用全局过滤
- 注解形式开发体验更好,使用小项目敏捷开发
开发字符集过滤器
WEB中文乱码的解决:
[
- GET请求-server.xml中增加URIEncoding=”UTF-8";
- POST请求-使用request.setCharacterEncoding(“UTF-8”);
- 响应-response.setContentType("text/html;charset=“UTF-8”);
]
package com.imooc.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.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebFilter(filterName ="CharacterEncodingFilter",urlPatterns="/*")
public class CharacterEncodingFilter implements Filter{
@Override
public void destroy() {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
System.out.println("执行字符过滤");
// TODO Auto-generated method stub
HttpServletRequest req =(HttpServletRequest)request;
req.setCharacterEncoding("UTF-8");
HttpServletResponse resp =(HttpServletResponse)response;
resp.setContentType("text/html;charset=UTF-8");
chain.doFilter(req,resp);
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub
}
}
过滤器参数化配置
过滤器为了增强灵活性,允许配置信息放在web.xml中
在web.xml中配置设置过滤器参数
<?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>first-filter</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.jsp</welcome-file>
<welcome-file>default.htm</welcome-file>
</welcome-file-list>
<filter>
<filter-name>myFirstFilter</filter-name>
<filter-class>com.imooc.filter.MyFirstFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>myFirstFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<!-- @WebFilter(filterName ="CharacterEncodingFilter",urlPatterns="/*") -->
<filter>
<filter-name>CharacterEncodingFilter</filter-name>
<filter-class>com.imooc.filter.CharacterEncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>GBK</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CharacterEncodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>
JAVA
package com.imooc.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.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CharacterEncodingFilter implements Filter{
private String encoding;
@Override
public void destroy() {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
System.out.println("执行字符过滤");
// TODO Auto-generated method stub
HttpServletRequest req =(HttpServletRequest)request;
req.setCharacterEncoding(encoding);
HttpServletResponse resp =(HttpServletResponse)response;
resp.setContentType("text/html;charset="+encoding);
chain.doFilter(req,resp);
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub
encoding = filterConfig.getInitParameter("encoding");
System.out.println("编码为"+encoding);
}
}
url-pattern设置过滤范围
url-pattern常用写法:
- /index.jsp 执行资源精准匹配
- /servlet/* 以前缀进行模糊匹配
- *.jsp 以后缀进行模糊匹配
过滤链:
过滤器开发注意事项:
- 每一个过滤器都具有单独职能
- 执行顺序由filter-mapping顺序决定
- 调用chain.doFilter()将请求向后传递
利用注解实现过滤链时,是根据类名的字典序执行的,所以一般这种都用配置文件配置
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