Filter简介：
Filter也称之为过滤器，它是Servlet技术中最激动人心的技术，WEB开发人员通过Filter技术，对web服务器管理的所有web资源：例如Jsp, Servlet, 静态图片文件或静态 html 文件等进行拦截，从而实现一些特殊的功能。
例如实现URL级别的权限访问控制、过滤敏感词汇、压缩响应信息等一些高级功能。
Servlet API中提供了一个Filter接口，开发web应用时，如果编写的Java类实现了这个接口，则把这个java类称之为过滤器Filter。通过Filter技术，开发人员可以实现用户在访问某个目标资源之前，对访问的请求和响应进行拦截。
Code:
web.xml:
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1"> <display-name>SpringMVCDemo Web Application</display-name> <servlet> <servlet-name>mvc-dispatcher</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>mvc-dispatcher</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> <servlet> <servlet-name>HelloServlet</servlet-name> <servlet-class>com.gaussic.servlet.HelloWorldServlet</servlet-class> <load-on-startup>0</load-on-startup> </servlet> <servlet-mapping> <servlet-name>HelloServlet</servlet-name> <url-pattern>/servlet/HelloWorld</url-pattern> </servlet-mapping> <!-- 编码过滤器 --> <filter> <filter-name>setCharacterEncoding</filter-name> <filter-class>com.gaussic.filter.EncodingFilter</filter-class> <init-param> <param-name>charset</param-name> <param-value>utf-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>setCharacterEncoding</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <!-- 请求url日志记录过滤器 --> <filter> <filter-name>logfilter</filter-name> <filter-class>com.gaussic.filter.LogFilter</filter-class> <!--配置logfilter过滤器的初始化参数--> <init-param> <description>配置logfilter过滤器的初始化参数</description> <param-name>name</param-name> <param-value>gacl</param-value> </init-param> <init-param> <description>配置logfilter过滤器的初始化参数</description> <param-name>like</param-name> <param-value>java</param-value> </init-param> </filter> <filter-mapping> <filter-name>logfilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> </web-app>
特别注意servlet,filter
过滤器Filter:
package com.gaussic.filter; 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; import java.io.IOException; import java.util.Enumeration; import java.util.HashMap; import java.util.Map; /** * Created by Administrator on 2017/3/31 0031. */ public class EncodingFilter implements Filter { private FilterConfig filterConfig = null; private String defaultCharset = "UTF-8"; // 项目结束时就已经进行销毁 public void destroy() { System.out.println("end do the encoding filter!"); } public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) resp; //得到在web.xml中配置的字符编码 String charset = filterConfig.getInitParameter("charset"); System.out.println("before encoding filter！"); if(charset==null){ charset = defaultCharset; } request.setCharacterEncoding(charset); response.setCharacterEncoding(charset); response.setContentType("text/html;charset="+charset); MyCharacterEncodingRequest requestWrapper = new MyCharacterEncodingRequest(request); chain.doFilter(requestWrapper, response); //chain.doFilter(req, resp); System.out.println("after encoding filter！"); System.err.println("------------------8888----------------------"); } // 项目启动时就已经进行读取 public void init(FilterConfig config) throws ServletException { this.filterConfig = config; System.out.println("begin do the encoding filter!"); } }
对get的请求返回内容进行转码：
package com.gaussic.filter; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletRequestWrapper; /** * Created by Administrator on 2017/3/31 0031. */ public class MyCharacterEncodingRequest extends HttpServletRequestWrapper { //定义一个变量记住被增强对象(request对象是需要被增强的对象) private HttpServletRequest request; //定义一个构造函数，接收被增强对象 public MyCharacterEncodingRequest(HttpServletRequest request) { super(request); this.request = request; } /* 覆盖需要增强的getParameter方法 * @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String) */ @Override public String getParameter(String name) { try{ //获取参数的值 String value= this.request.getParameter(name); if(value==null){ return null; } //如果不是以get方式提交数据的，就直接返回获取到的值 if(!this.request.getMethod().equalsIgnoreCase("get")) { return value; }else{ //如果是以get方式提交数据的，就对获取到的值进行转码处理 value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding()); return value; } }catch (Exception e) { throw new RuntimeException(e); } } }
日志过滤器：
package com.gaussic.filter; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; import java.io.IOException; import java.util.Enumeration; /** * Created by Administrator on 2017/3/31 0031. */ public class LogFilter implements Filter { FilterConfig config; public void destroy() { this.config = null; } public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { // 获取ServletContext 对象，用于记录日志 ServletContext context = this.config.getServletContext(); //long before = System.currentTimeMillis(); System.out.println("before the log filter!"); //context.log("开始过滤"); // 将请求转换成HttpServletRequest 请求 HttpServletRequest hreq = (HttpServletRequest) req; // 记录日志 System.out.println("Log Filter已经截获到用户的请求的地址:"+hreq.getServletPath() ); //context.log("Filter已经截获到用户的请求的地址: " + hreq.getServletPath()); try { // Filter 只是链式处理，请求依然转发到目的地址。 chain.doFilter(req, res); } catch (Exception e) { e.printStackTrace(); } System.out.println("after the log filter!"); } public void init(FilterConfig config) throws ServletException { System.out.println("begin do the log filter!"); this.config = config; //得到过滤器的名字 String filterName = config.getFilterName(); //得到在web.xml文件中配置的初始化参数 String initParam1 = config.getInitParameter("name"); String initParam2 = config.getInitParameter("like"); //返回过滤器的所有初始化参数的名字的枚举集合。 Enumeration<String> initParameterNames = config.getInitParameterNames(); System.out.println(filterName); System.out.println(initParam1); System.out.println(initParam2); while (initParameterNames.hasMoreElements()) { String paramName = (String) initParameterNames.nextElement(); System.out.println(paramName); } System.out.println("begin do the log filter end!"); } }
Servlet:
package com.gaussic.servlet; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.PrintWriter; /** * Created by Administrator on 2017/3/31 0031. */ public class HelloWorldServlet extends HttpServlet { /** * 查看httpservlet实现的service一看便知，起到了一个controll控制器的作用(转向的) * 之后便是跳转至我们熟悉的doget,dopost等方法中 */ @Override protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println("doservice..."+this.getInitParameter("encoding")); super.service(req, resp); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println("doget..."); String username = req.getParameter("username"); //获取请求方式 String method = req.getMethod(); //获取输出流 PrintWriter out = resp.getWriter(); out.write("Method："+method); out.write("<br/>"); out.write("接收到的参数："+username); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { System.out.println("dopost..."); doGet(req, resp); } }
运行以后日志：
begin do the encoding filter! begin do the log filter! logfilter gacl java like name begin do the log filter end! //...... before encoding filter！ before the log filter! Log Filter已经截获到用户的请求的地址:/ after the log filter! after encoding filter！ ------------------8888---------------------- before encoding filter！ before the log filter! Log Filter已经截获到用户的请求的地址:/ after the log filter! after encoding filter！ ------------------8888---------------------- before encoding filter！ before the log filter! Log Filter已经截获到用户的请求的地址:/ after the log filter! after encoding filter！ ------------------8888---------------------- 31-Mar-2017 16:33:57.245 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory D:Program FilesTomcat9webappsmanager 31-Mar-2017 16:33:57.322 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory D:Program FilesTomcat9webappsmanager has finished in 75 ms ------------------8888---------------------- before encoding filter！ before the log filter! Log Filter已经截获到用户的请求的地址:/servlet/HelloWorld doservice...null doget... after the log filter! after encoding filter！ before encoding filter！ before the log filter! Log Filter已经截获到用户的请求的地址:/servlet/HelloWorld doservice...null doget... after the log filter! after encoding filter！ ------------------8888---------------------- "D:Program FilesTomcat9incatalina.bat" stop Using CATALINA_BASE: "C:UsersAdministrator.IntelliJIdea2016.3system omcatUnnamed_SpringMVCDemo" Using CATALINA_HOME: "D:Program FilesTomcat9" Using CATALINA_TMPDIR: "D:Program FilesTomcat9 emp" Using JRE_HOME: "D:Program FilesJavajdk1.8.0_102" Using CLASSPATH: "D:Program FilesTomcat9inootstrap.jar;D:Program FilesTomcat9in omcat-juli.jar" 31-Mar-2017 16:37:14.434 INFO [main] org.apache.catalina.core.StandardServer.await A valid shutdown command was received via the shutdown port. Stopping the Server instance. 31-Mar-2017 16:37:14.435 INFO [main] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["http-nio-8085"] 31-Mar-2017 16:37:14.487 INFO [main] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["ajp-nio-55366"] 31-Mar-2017 16:37:14.537 INFO [main] org.apache.catalina.core.StandardService.stopInternal Stopping service Catalina end do the encoding filter!
http://www.cnblogs.com/xdp-gacl/p/3948353.html