java过滤器学习总结

/*** @ author StormMaybin* @ date 2016-12-03*/

生命不息，奋斗不止！

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What’s the Filter

Filter也称之为过滤器，它是Servlet技术中比较激动人心的技术，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。

如何使用Filter

1. 创建一个Filter类，实现javax.servlet.Filter接口
2. 实现doFilter()方法，进行拦截
3. 在web.xml中进行配置

package com.yiyexiaoyuan.filter;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;/** * Servlet Filter implementation class TestFilter */ //实现Filter接口public class TestFilter implements Filter{    /**     * Default constructor.     */    public TestFilter()    {        // TODO Auto-generated constructor stub    }    /**     * @see Filter#destroy()     */     //Filter结束时候调用    public void destroy()    {        // TODO Auto-generated method stub    }    /**     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)     */     //拦截主体代码    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException    {        //去下一个Filter        chain.doFilter(request, response);    }    /**     * @see Filter#init(FilterConfig)     */     //初始化时候调用    public void init(FilterConfig fConfig) throws ServletException    {        // TODO Auto-generated method stub    }}

在web.xml中配置

<filter>    <display-name>TestFilter</display-name>    <filter-name>TestFilter</filter-name>    <filter-class>com.yiyexiaoyuan.filter.TestFilter</filter-class>  </filter>  <filter-mapping>    <filter-name>TestFilter</filter-name>    <url-pattern>/TestFilter</url-pattern>  </filter-mapping>

应用场景

解决中文乱码的Filter

package com.yiyexiaoyuan.filter;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;/** * Servlet Filter implementation class PageEncodingFilter */public class PageEncodingFilter implements Filter{    private String encoding = "UTF-8";    protected FilterConfig filterConfig;    public void init(FilterConfig filterConfig) throws ServletException    {        this.filterConfig = filterConfig;        // 本过滤器默认编码是UTF-8，但也可以在web.xml配置文件里设置自己需要的编码        if (filterConfig.getInitParameter("encoding") != null)            encoding = filterConfig.getInitParameter("encoding");    }    public void doFilter(ServletRequest srequset, ServletResponse sresponse,            FilterChain filterChain) throws IOException, ServletException    {        HttpServletRequest request = (HttpServletRequest) srequset;        request.setCharacterEncoding(encoding);        filterChain.doFilter(srequset, sresponse);    }    public void destroy()    {        this.encoding = null;    }}

web.xml配置

<filter>    <display-name>PageEncodingFilter</display-name>    <filter-name>PageEncodingFilter</filter-name>    <filter-class>com.yiyexiaoyuan.filter.PageEncodingFilter</filter-class>    <init-param>      <param-name>encoding</param-name>      <param-value>UTF-8</param-value>    </init-param>  </filter>  <filter-mapping>    <filter-name>PageEncodingFilter</filter-name>    <url-pattern>/servlet/*</url-pattern>  </filter-mapping>

防止SQL注入Filter实现

package com.yiyexiaoyuan.filter;import java.io.IOException;import java.util.Enumeration;import javax.security.auth.message.callback.PrivateKeyCallback.Request;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 net.sf.json.JSONObject;//过滤sql关键字的Filter public class SQLFilter implements Filter{    public void doFilter(ServletRequest request, ServletResponse response,            FilterChain chain) throws IOException, ServletException    {        HttpServletRequest req = (HttpServletRequest) request;        HttpServletResponse res = (HttpServletResponse) response;        // 获得所有请求参数名        Enumeration params = req.getParameterNames();        String sql = "";        while (params.hasMoreElements())        {            // 得到参数名            String name = params.nextElement().toString();            // System.out.println("name===========================" + name +            // "--");            // 得到参数对应值            String[] value = req.getParameterValues(name);            for (int i = 0; i < value.length; i++)            {                sql = sql + value[i];            }           }        System.out.println("提交方式:"+req.getMethod());        System.out.println("被匹配字符串：" + sql);        if (sqlValidate(sql))        {            req.getSession().setAttribute("error_message", "别整这个啊，老实点不好吗？");            throw new RuntimeException("恶意代码注入异常");        }        else        {            String   request_uri   =   req.getRequestURI();              System.out.println(request_uri);            chain.doFilter(request, response);        }    }    // 校验    protected static boolean sqlValidate(String str)    {        str = str.toLowerCase();// 统一转为小写        // String badStr = "and|exec";        String badStr = "'|and|exec|execute|insert|select|delete|update|count|drop|chr|mid|master|truncate|char|declare|sitename|net user|xp_cmdshell|or|like|;|--|+|,|*|/";        /*         * String badStr =         * "'|and|exec|execute|insert|create|drop|table|from|grant|use|group_concat|column_name|"         * +         * "information_schema.columns|table_schema|union|where|select|delete|update|order|by|count|*|"         * + "chr|mid|master|truncate|char|declare|or|;|-|--|+|,|like|//|/|%|#";         */// 过滤掉的sql关键字，可以手动添加        String[] badStrs = badStr.split("\\|");        for (int i = 0; i < badStrs.length; i++)        {            if (str.indexOf(badStrs[i]) != -1)            {                System.out.println("匹配到：" + badStrs[i]);                return true;            }        }        return false;    }    public void init(FilterConfig filterConfig) throws ServletException    {        // throw new UnsupportedOperationException("Not supported yet.");    }    public void destroy()    {        // throw new UnsupportedOperationException("Not supported yet.");    }}

web.xml配置

  <filter>    <display-name>SQLFilter</display-name>    <filter-name>SQLFilter</filter-name>    <filter-class>com.yiyexiaoyuan.filter.SQLFilter</filter-class>  </filter>  <filter-mapping>    <filter-name>SQLFilter</filter-name>    <url-pattern>/servlet/*</url-pattern>  </filter-mapping>  <filter>

生命不息，奋斗不止！