public void init(FilterConfig config): init()方法僅在初始化過濾器時(shí)被調(diào)用(只調(diào)用一次)。
public String getInitParameter(String parameterName): 返回指定參數(shù)名稱的參數(shù)值。
public java.util.Enumeration getInitParameterNames(): 返回包含所有參數(shù)名稱的枚舉。
public ServletContext getServletContext(): 返回ServletContext對(duì)象。

FilterConfig示例

在此示例中，如果將web.xml的中的construction參數(shù)值為no，則請(qǐng)求將轉(zhuǎn)發(fā)到servlet，如果將參數(shù)值設(shè)置為：yes，則過濾器將使用消息創(chuàng)建響應(yīng)：”此頁面正在處理中“。下面來看看FilterConfig的簡(jiǎn)單例子。

打開Eclipse，創(chuàng)建一個(gè)動(dòng)態(tài)Web項(xiàng)目：FilterConfig，其完整的目錄結(jié)構(gòu)如下所示 -

以下是這個(gè)項(xiàng)目中的幾個(gè)主要的代碼文件。在這里創(chuàng)建了4個(gè)文件：

index.html - 應(yīng)用程序入口
MyFilter.java - 過濾器實(shí)現(xiàn)
HelloServlet.java - 一個(gè)簡(jiǎn)單的Servlet
web.xml - 項(xiàng)目部署配置文件

下面是這幾個(gè)文件的具體代碼。

文件：index.html -

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>FilterConfig配置應(yīng)用示例</title>
</head>
<body>
    <div style="text-align: center;">
        <a href="servlet1">查看Filter配置信息</a>
    </div>
</body>
</html>

文件：MyFilter.java -

package com.yiibai;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.*;

public class MyFilter implements Filter {

    FilterConfig config;

    public void init(FilterConfig config) throws ServletException {
        this.config = config;
    }

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
            throws IOException, ServletException {
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/html;charset=UTF-8");
        req.setCharacterEncoding("UTF-8");
        PrintWriter out = resp.getWriter();

        String s = config.getInitParameter("construction");

        if (s.equals("yes")) {
            out.print("此頁面正在處理中");
        } else {
            chain.doFilter(req, resp);// sends request to next resource
        }
    }

    public void destroy() {
    }
}

文件：HelloServlet.java -

package com.yiibai;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.*;

public class HelloServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        request.setCharacterEncoding("UTF-8");
        PrintWriter out = response.getWriter();

        out.print("<br>welcome to servlet<br>");

    }

}

文件：web.xml -

<?xml version="1.0" encoding="UTF-8"?>
<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>FilterConfig</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>com.yiibai.HelloServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/servlet1</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>f1</filter-name>
        <filter-class>com.yiibai.MyFilter</filter-class>
        <init-param>
            <param-name>construction</param-name>
            <param-value>yes</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>f1</filter-name>
        <url-pattern>/servlet1</url-pattern>
    </filter-mapping>
</web-app>

在編寫上面代碼后，部署此Web應(yīng)用程序(在項(xiàng)目名稱上點(diǎn)擊右鍵->”Run On Server…”)，打開瀏覽器訪問URL： http://localhost:8080/FilterConfig/ ，如果沒有錯(cuò)誤，應(yīng)該會(huì)看到以下結(jié)果 -

點(diǎn)擊頁面中的鏈接，應(yīng)該會(huì)看到以下結(jié)果 -

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Servlet FilterConfig應(yīng)用示例

FilterConfig示例