目录
Filter系列教材 (一)- 过滤器 Filter 教程
Filter系列教材 (二)- 使用Filter进行中文问题处理
Filter系列教材 (三)- 使用Filter进行登陆验证功能的开发
Filter系列教材 (一)- 过滤器 Filter 教程
步骤1:Filter概念
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
步骤 1 : Filter概念
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
![Filter概念](https://imgconvert.csdnimg.cn/aHR0cHM6Ly9zdGVwaW1hZ2V3bS5ob3cyai5jbi8xNzE5LnBuZw?x-oss-process=image/format,png)
步骤 2 : 编写 FirstFilter
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
![编写 FirstFilter](https://imgconvert.csdnimg.cn/aHR0cHM6Ly9zdGVwaW1hZ2V3bS5ob3cyai5jbi8xNzE3LnBuZw?x-oss-process=image/format,png)
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 { } } |
步骤 3 : 配置web.xml
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 > |
步骤 4 : 访问页面
重启tomcat,所有用户的访问信息,都可以打印出来
![访问页面](https://imgconvert.csdnimg.cn/aHR0cHM6Ly9zdGVwaW1hZ2V3bS5ob3cyai5jbi8xNzIwLnBuZw?x-oss-process=image/format,png)
步骤 5 : init() 方法
与Servlet需要配置自启动才会随着tomcat的启动而执行init()方法不一样。
Filter一定会随着tomcat的启动自启动。
![init() 方法](https://imgconvert.csdnimg.cn/aHR0cHM6Ly9zdGVwaW1hZ2V3bS5ob3cyai5jbi8xNzIxLnBuZw?x-oss-process=image/format,png)
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()" ); } } |
步骤 6 : Filter启动失败
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
![Filter启动失败](https://imgconvert.csdnimg.cn/aHR0cHM6Ly9zdGVwaW1hZ2V3bS5ob3cyai5jbi8xNzIyLnBuZw?x-oss-process=image/format,png)
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(); } } |
Filter系列教材 (二)- 使用Filter进行中文问题处理
步骤1:使用Servlet处理的局限性
步骤2:使用Filter处理
步骤3:配置web.xml
步骤4:测试
步骤 1 : 使用Servlet处理的局限性
在通过Servlet获取中文参数 的章节中知道,可以通过
request.setCharacterEncoding( "UTF-8" ); |
正确获取UTF-8编码的中文,但是如果有很多servlet都需要获取中文,那么就必须在每个Servlet中增加这段代码。
有一个简便的办法,那就是通过Filter过滤器进行中文处理 ,那么所有的Servlet都不需要单独处理了。
步骤 2 : 使用Filter处理
创建一个 EncodingFilter ,设置如下代码
HttpServletRequest request = (HttpServletRequest) req; request.setCharacterEncoding( "UTF-8" ); |
doFilter方法的第一个参数req,是ServletRequest 类型的,不支持setCharacterEncoding,所以要先强制转换为HttpServletRequest
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 EncodingFilter 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; request.setCharacterEncoding( "UTF-8" ); chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { } } |
步骤 3 : 配置web.xml
配置EncodingFilter
<url-pattern>/*</url-pattern> |
表示为所有的访问都使用该Filter
< filter > < filter-name >EncodingFilter</ filter-name > < filter-class >filter.EncodingFilter</ filter-class > </ filter > < filter-mapping > < filter-name >EncodingFilter</ filter-name > < url-pattern >/*</ url-pattern > </ filter-mapping > |
步骤 4 : 测试
测试前,记得把HeroAddServlet中的
request.setCharacterEncoding( "UTF-8" ); |
注释掉
![测试](https://imgconvert.csdnimg.cn/aHR0cHM6Ly9zdGVwaW1hZ2V3bS5ob3cyai5jbi8xNzI2LnBuZw?x-oss-process=image/format,png)
package servlet; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import bean.Hero; import dao.HeroDAO; public class HeroAddServlet extends HttpServlet { protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // request.setCharacterEncoding("UTF-8"); Hero hero = new Hero(); hero.setName(request.getParameter( "name" )); hero.setHp(Float.parseFloat(request.getParameter( "hp" ))); hero.setDamage(Integer.parseInt(request.getParameter( "damage" ))); new HeroDAO().add(hero); response.sendRedirect( "/listHero" ); } } |
Filter系列教材 (三)- 使用Filter进行登陆验证功能的开发
步骤1:在Servlet中进行登陆验证的局限性
步骤2:使用Filter处理
步骤3:配置web.xml
步骤4:练习-在login.jsp页面的js,css和图片文件
步骤5:答案-在login.jsp页面的js,css和图片文件
步骤 1 : 在Servlet中进行登陆验证的局限性
在用户是否登陆的验证中,我们可以通过在HeroListServlet中增加对session的判断代码来做到登陆验证。
但是按照这样的做法,所有的Servlet都要加上一样的代码,就会显得比较累赘。
与通过Filter处理中文问题一样,也可以通过Filter一次性解决所有的登陆验证问题
步骤 2 : 使用Filter处理
创建一个AuthFilter 类
String uri = request.getRequestURI(); if (uri.endsWith( "login.html" ) || uri.endsWith( "login" )) { chain.doFilter(request, response); return ; } |
首先判断是否是访问的login.html和loginHero,因为这两个页面就是在还没有登陆之前就需要访问的
String userName = (String) request.getSession().getAttribute( "userName" ); if ( null == userName) { response.sendRedirect( "login.html" ); return ; } |
从Session中获取userName,如果没有,就表示不曾登陆过,跳转到登陆页面。
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 AuthFilter 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 uri = request.getRequestURI(); if (uri.endsWith( "login.html" ) || uri.endsWith( "login" )) { chain.doFilter(request, response); return ; } String userName = (String) request.getSession().getAttribute( "userName" ); if ( null == userName) { response.sendRedirect( "login.html" ); return ; } chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { } } |
步骤 3 : 配置web.xml
配置AuthFilter
< filter > < filter-name >AuthFilter</ filter-name > < filter-class >filter.AuthFilter</ filter-class > </ filter > < filter-mapping > < filter-name >AuthFilter</ filter-name > < url-pattern >/*</ url-pattern > </ filter-mapping > |
更多内容,点击了解: https://how2j.cn/k/filter/filter-tutorial/588.html?p=81777