【九月打卡】第十三天 过滤器-Filter过滤器应用实践

课程信息

● 学习课程：Java工程师2022版
● 章节名称：过滤器-Fileter过滤器应用实践
● 讲师：八戒猪

课程内容

WebFilter注解的使用
配置形式维护性更好，适合应用全局过滤
注解形式开发体验更好，适合小型项目敏捷开发
过滤器更推荐使用配置方式，servlet推荐使用注解方式。
1、过滤器的配置形式：

<filter>
   <filter-name>firstfilter</filter-name>
   <filter-class>indi.xxmas.filter.FirstFilter</filter-class>
</filter>
<filter-mapping>
   <filter-name>firstfilter</filter-name>
   <!--    /*对所有的请求进行拦截    -->
   <url-pattern>/*</url-pattern>
</filter-mapping>

2、过滤器的注解形式：

@WebFilter(filterName="annotationFileter",urlPatterns="/*")
public class AnnotationFileter implements Filter{}

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”)

public void doFilter(ServletRequest request,ServletResponse response, FilterChain chain){
	HttpServletRequest req = (HttpServletRequest)request;
	HttpServeltResponse resp = (HttpSerbletResponse) response;
	req.setCharaterEncoding("UTF-8");
	resp.setContentType("text/html;charset="UTF-8");
	chain.doFilter(request, response);
}

3.过滤器参数化
允许配置信息放在web.xml中设置过滤参数

 <filter>
        <filter-name>characterEncodingFilter</filter-name>
        <filter-class>com.imooc.filter.CharacterEncodingFilter</filter-class>
<!--        初始化参数设置-->
        <init-param>
            <param-name>encoding</param-name>
            <param-value>utf-8</param-value>
        </init-param>
        <init-param>
            <param-name>encoding1</param-name>
            <param-value>GBK</param-value>
        </init-param>
    </filter>

public class CharacterEncodingFilter implements Filter {
//1、设置全局变量
private String encoding;

@Override
public void init(FilterConfig filterConfig) throws ServletException {
// 2、从配置文件中获取初始化参数
    encoding = filterConfig.getInitParameter("encoding");
}

@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
    HttpServletRequest request = (HttpServletRequest) servletRequest;
    HttpServletResponse response = (HttpServletResponse) servletResponse;
// 针对post的请求进行字符集设置
    request.setCharacterEncoding(encoding);//3、引入参数
    response.setContentType("text/html;charset=" + encoding);
    filterChain.doFilter(servletRequest, servletResponse);
}

@Override
public void destroy() {

}

《注解形式的初始化参数设置》

过滤器不推荐使用注解方式进行配置。注解中，配置注解需要使用{}

@WebFilter(filterName = "characterEncoding", urlPatterns = "/*",
        initParams = {
                @WebInitParam(name = "encoding", value = "utf-8"),
                @WebInitParam(name = "edcoding2", value = "GBK")
        })//注解中的数组，需要使用{}

4.url-pattern常用写法
/index.html -执行资源精准配皮
/servlet/*以前缀进行模糊匹配
*.html以后缀进行模糊匹配
不支持前缀和后缀一起模糊匹配
5.过滤链的开发注意事项
每一个过滤器应具有单独的职能
过滤器的执行顺序以为准
调用chain.doFilter()请求向后传递
6.多端设备自动匹配

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws Exception {
  HttpServletRequest request = (HttpServletRequest) servletRequest;
  HttpServletResponse response = (HttpServletResponse) servletResponse;
  String url = req.getRequestURI();
  String userAgent = request.getHeader("user-agent");
  String targetUri = null;
	if(uri.startsWith("/desktop") || uri.startsWith("/mobile"){
  	    chain.doFilter(servletRequest, servletResponse);
	}else {
    if(userAgent.toLowerCase().indexOf("android") != -1 || userAgent.toLowerCase().indexOf("iphone")){
    	targetUri = "/mobile" + uri;
    }else {
    	targetUri = "/desktop" + uri;
    }
    resp.sendRedirect(targetUri);
  }
}

监听器-Listener
过滤器Filter是主动对URL过滤拦截
监听器Listener是被动触发的对Web对象进行监听
三种监听对象
ServletContext–对全局ServletContext及其属性进行监听
HttpSession–对用户会话及其属性操作进行监听
ServletRequest–对请求及其属性操作进行监听

学习收获

学习了过滤器的配置形式，web.xml配置和注解配置形式，字符过滤器使用，
过滤器参数化，参数放在web.xml中,url-pattern设置过滤范围（精准，前缀，后缀），过滤链的开发注意事项，过滤器和监听器的区别

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