步骤 2 : 编写 FirstFilter 步骤 3 : 配置web.xml 步骤 4 : 访问页面 步骤 5 : init() 方法 步骤 6 : Filter启动失败
Filter就像一个一个哨卡,用户的请求需要经过Filter
并且可以有多个过滤器
开发一个简单的FirstFilter,用来打印用户访问ip地址和访问的页面
HttpServletRequest request = (HttpServletRequest) req; doFilter()方法中的req参数的类型是ServletRequest,需要转换为HttpServletRequest类型方便调用某些方法 (参考 request常见方法) String ip = request.getRemoteAddr(); 获取来路用户的ip地址 String url = request.getRequestURL().toString(); 获取用户访问的页面地址 System.out.printf("%s %s 访问了 %s%n", date, ip, url); 在控制台打印出来 chain.doFilter(request, response); 过滤器 放行,表示继续运行下一个过滤器,或者最终访问的某个servlet,jsp,html等等
package filter; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; 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 FirstFilter implements Filter { @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; String ip = request.getRemoteAddr(); String url = request.getRequestURL().toString(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date d = new Date(); String date = sdf.format(d); System.out.printf("%s %s 访问了 %s%n", date, ip, url); chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { } }
在web.xml中进行filter的配置,和servlet的配置很类似
<url-pattern>/*</url-pattern>
表示所有的访问都会过滤 如果配置成
<url-pattern>*.jsp</url-pattern>
就表示只过滤jsp
<filter> <filter-name>FirstFilter</filter-name> <filter-class>filter.FirstFilter</filter-class> </filter> <filter-mapping> <filter-name>FirstFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
<filter> <filter-name>FirstFilter</filter-name> <filter-class>filter.FirstFilter</filter-class> </filter> <filter-mapping> <filter-name>FirstFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
重启tomcat,所有用户的访问信息,都可以打印出来
package filter; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; 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 FirstFilter implements Filter { @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; String ip = request.getRemoteAddr(); String url = request.getRequestURL().toString(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date d = new Date(); String date = sdf.format(d); System.out.printf("%s %s 访问了 %s%n", date, ip, url); chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { System.out.println("First Filter init()"); } }
Filter是web应用非常重要的一个环节,如果Filter启动失败,或者本身有编译错误,
不仅这个Filter不能使用,
整个web应用会启动失败,导致用户无法访问页面
在启动tomcat过程中,也会看到这样的字样:
严重: Context [] startup failed due to previous errors
这常常用于提示Filter启动失败了
package filter; import java.io.IOException; import java.text.SimpleDateFormat; import java.util.Date; 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 FirstFilter implements Filter { @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) res; String ip = request.getRemoteAddr(); String url = request.getRequestURL().toString(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date d = new Date(); String date = sdf.format(d); System.out.printf("%s %s 访问了 %s%n", date, ip, url); chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { System.out.println("故意造成一个异常"); Object o = null; o.toString(); } }
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问答区域
2021-01-03
加上Filter后无法客户端跳转
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2020-07-18
关于ip地址
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2020-07-01
文件都正常,但tomcat启动后无法自动显示FirstFilter.java文件中的doFilter()方法内容
2020-06-26
为什么会打印两次init?
2020-06-19
加了Filter之后,启动tomcat总是报错
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