FilterConfig的对象由Web容器创建。这个对象可用于获取web.xml文件中的配置信息。
FilterConfig接口中有以下4个方法。
public void init(FilterConfig config): init()方法仅在初始化过滤器时被调用(只调用一次)public String getInitParameter(String parameterName): 返回指定参数名称的参数值。public java.util.Enumeration getInitParameterNames(): 返回包含所有参数名称的枚举。public ServletContext getServletContext(): 返回ServletContext对象。FilterConfig示例在此示例中，如果将web.xml的中的construction参数值为no，则请求将转发到servlet，如果将参数值设置为：yes，则过滤器将使用消息创建响应：”此页面正在处理中“。下面来看看FilterConfig的简单例子。
以下是这个项目中的几个主要的代码文件。在这里创建了4个文件：
MyFilterConfig.java
public class MyFilterConfig implements Filter {
FilterConfig config;
@Override
public void init(FilterConfig filterConfig) throws ServletException {
this.config = filterConfig;
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
// 设置服务器端的内容类型
servletResponse.setContentType("text/html;charset=utf-8");
// 设置服务器端的编码
servletResponse.setCharacterEncoding("utf-8");
// 设置客户端的编码
servletRequest.setCharacterEncoding("utf-8");
// 获取服务器端的输出对象
PrintWriter out = servletResponse.getWriter();
// 获取配置信息
String s = config.getInitParameter("construction");
if (s.equals("yes")){
out.println("此页面正在处理");
}else {
out.println("过滤之前");
filterChain.doFilter(servletRequest,servletResponse);
out.println("过滤之后");
}
}
@Override
public void destroy() {
}
}
HelloServlet.java
public class HelloServlet extends HttpServlet {
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
// 设置服务器端内容类型
response.setContentType("text/html;charset=utf-8");
// 设置服务器端编码
response.setCharacterEncoding("utf-8");
// 设置客户端编码
request.setCharacterEncoding("utf-8");
// 获取服务器端输出对象
PrintWriter out = response.getWriter();
out.println("Welcome to HelloServlet");
}
}
FilterConfig.html
DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>FilterConfig示例title>
head>
<body>
<div style="text-align: center">
<a href="helloServlet">查看Filter配置信息a>
div>
body>
html>
web.xml
<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>ServletRequestdisplay-name>
<welcome-file-list>
<welcome-file>FilterConfig.htmlwelcome-file>
welcome-file-list>
<servlet>
<servlet-name>HelloServletservlet-name>
<servlet-class>HeaderServletservlet-class>
servlet>
<servlet-mapping>
<servlet-name>HelloServletservlet-name>
<url-pattern>/helloServleturl-pattern>
servlet-mapping>
<filter>
<filter-name>MyFilterConfigfilter-name>
<filter-class>MyFilterConfigfilter-class>
<init-param>
<param-name>constructionparam-name>
<param-value>noparam-value>
init-param>
filter>
<filter-mapping>
<filter-name>MyFilterConfigfilter-name>
<url-pattern>/helloServleturl-pattern>
filter-mapping>
<web-app>