FIlter应用

浏览器不缓存页面的过滤器

System.out.println("cacheFilterDO");
        response.setDateHeader("Expires", -1);
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        chain.doFilter(request, response);

解决中文乱码的过滤器Filter

<filter>
<filter-name>EncodingFilter</filter-name>
<filter-class>com.sdut.util.cn.EncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>utf-8</param-value>
</init-param>
</filter>

public void init(FilterConfig filterConfig) throws ServletException {
        encoding = filterConfig.getInitParameter("encoding");        
    }
    
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        request.setCharacterEncoding(encoding);//解决中文问题
        chain.doFilter(request, response);        
    }

 应用二（过滤论坛不雅字符例如shit，fuck等）

1，因为每次书写***Filter类都要继承Filter比较繁杂因此书写HttpFilter类

    每次都 extends HttpFilter代码简便

    HttpFilter.java

package com.wlc.DuoduiYi.servlet;

import java.io.IOException;

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;

/**
 * 自定义的httpfilter实现filter接口
 * 
 * @author wlc
 * 
 */
public abstract class HttpFilter implements Filter {

    public void destroy() {
    }

    /**
     * 原生的dofilter方法将方法内部的ServletRequest , ServletResponse转为 HttpServletRequest
     * ,HttpServletResponse 并调用了 doFilter(HttpServletRequest request,
     * HttpServletResponse response, FilterChain chain)方法
     * 若编写filter的过滤方法不建议继承该方法而应该继承doFilter(HttpServletRequest request,
     * HttpServletResponse response, FilterChain chain)方法
     */
    public void doFilter(ServletRequest req, ServletResponse resp,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;
        doFilter(request, response, chain);

    }

    /**
     * 抽象方法为http请求定制 必须实现的方法
     * 
     * @param request
     * @param response
     * @param chain
     * @throws IOException
     * @throws ServletException
     */
    // abstract定义抽象类或者抽象方法；抽象方法是指只定义了一个方法，但没有实现方法体；
    public abstract void doFilter(HttpServletRequest request,
            HttpServletResponse response, FilterChain chain)
            throws IOException, ServletException;

    /**
     * yon用于保存filterconfig对象
     */
    private FilterConfig filterConfig;

    /**
     * 不建议子类直接覆盖若直接覆盖将会导致filterConfig成员变量初始化失败
     */
    public void init(FilterConfig filterConfig) throws ServletException {
        this.filterConfig = filterConfig;
        init();
    }

    /**
     * 供子类继承的初始化方法可以通过getfilterConfig()获取FilterConfig对象
     */
    protected void init() {
    }

    /**
     * 直接返回init(servletConfig)的filterConfig对象
     * 
     * @return
     */
    public FilterConfig getFilterConfig() {
        return filterConfig;
    }
}

BBSFilter.java

package com.wlc.DuoduiYi.servlet;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class BBSFilter extends HttpFilter {

    @Override
    public void doFilter(HttpServletRequest request,
            HttpServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequest req = new MyHttpServletRequest(request);
        System.out.println("我是BBSFilter");
        chain.doFilter(req, response);
        System.out.println("我是BBSFilter");
    }

}

MyHttpServletResqust.java

package com.wlc.DuoduiYi.servlet;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class MyHttpServletRequest extends HttpServletRequestWrapper {

    public MyHttpServletRequest(HttpServletRequest request) {
        super(request);

    }

    @Override
    public String getParameter(String name) {
        String val = super.getParameter(name);
        if (val != null && val.contains(" fuck ")) {
            val = val.replace("fuck", "***");
            System.out.println("222");
        }

        return val;
    }
}

FontFilter.jsp

<body>
    <form action="helloNew.jsp" method="post">
        <table border="1">

            <tr>
                <td>BBS:</td>
                <td><input type="text" name="content"  /></td>
            </tr>


            <tr>
                <td><input type="submit" value="submit" />
                </td>

            </tr>


        </table>
    </form>
</body>

helloNew.jsp

<body>
    HELLO:${param.content}
    <br>
    <br>
</body>

输出结果