2019-08-22/XSS过滤器

做后端的同学都知道，XSS过滤器，防sql注入过滤器等是常用的 。关于什么是XSS攻击，网上的说法很多，自己百度一下吧。我们只需要加入一个xss过滤器就可以了。但大部分的文章都是针对普通的get/post请求进行的参数xss过滤，如果是post+appliccation/json等提交方式就显得无能为力了。很显然，对于普通的get/post,就按照之前的方式过滤参数就可以了（对于multipart等文件上传之类的参数做校验，这里暂时没有提供）。
为了方便起见，首先定义一些常量吧：

package cn.wjp.mydaily.common.filter;

public class HttpConst {
    /**
     * 几种常见的Content-Type
     */
    public static final String FORM_URLENCODED_CONTENT_TYPE ="application/x-www-form-urlencoded";

    public static final String JSON_CONTENT_TYPE = "application/json";

    public static final String MULTIPART_CONTENT_TYPE = "multipart/form-data";

    /**
     * 常见的post/get请求方式
     */
    public static final String POST_METHOD = "post";

    public static final String GET_METHOD = "get";

    public static final String OPTIONS_METHOD = "options";

}

接下来需要分别针对不同的表单提交类型写包装类，对于普通的get/post请求的包装类：

package cn.wjp.mydaily.common.filter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.IOException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Vector;

/**
 * 适用于普通get post请求  不包含multipart/form-data   application/json等请求
 * 缓存请求参数   重写获取参数的方法
 */
public class HttpServletRequestNormalWrapper extends HttpServletRequestWrapper {

    private Map<String, String[]> parameterMap = new HashMap<>(); // 所有参数的Map集合

    public HttpServletRequestNormalWrapper(HttpServletRequest request){
        super(request);
        Enumeration params = request.getParameterNames();//获得所有请求参数名
        StringBuffer paramsValue = new StringBuffer("");
        while (params.hasMoreElements()) {
            String name = params.nextElement().toString(); //得到参数名
            String[] value = request.getParameterValues(name);//得到参数对应值
            parameterMap.put(name,value);
        }
    }

    /**
     * 获取所有参数名
     *
     * @return 返回所有参数名
     */
    @Override
    public Enumeration<String> getParameterNames() {
        Vector<String> vector = new Vector<String>(parameterMap.keySet());
        return vector.elements();
    }

    /**
     * 获取指定参数名的值，如果有重复的参数名，则返回第一个的值 接收一般变量 ，如text类型
     *
     * @param name 指定参数名
     * @return 指定参数名的值
     */
    @Override
    public String getParameter(String name) {
        String[] values = parameterMap.get(name);
        if(values==null||values.length==0){
            return null;
        }
        return values[0];
        //如果有多个参数值的，请放开该注释  我这里没有做这么细致
        /*StringBuffer sb = new StringBuffer();
        for(int i=0;i<values.length;i++){
            if(i==values.length-1){
                sb.append(values[i]);
            }else{
                sb.append(values[i]).append(",");
            }
        }
        return sb.toString();*/
    }
    /**
     * 获取指定参数名的所有值的数组，如：checkbox的所有数据
     * 接收数组变量 ，如checkobx类型
     */
    @Override
    public String[] getParameterValues(String name) {
        return parameterMap.get(name);
    }

    @Override
    public Map<String, String[]> getParameterMap() {
        return parameterMap;
    }

    public void setParameterMap(Map<String, String[]> parameterMap) {
        this.parameterMap = parameterMap;
    }
}

对于post+application/json的请求，对应的包装类：

package cn.wjp.mydaily.common.filter;

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.*;

/**
 * 将body中的数据缓存起来  重写getInputStream  getReader 等方法  适用于application/json的post请求
 */
public class HttpServletRequestBodyReaderWrapper extends HttpServletRequestWrapper{

    private String body ="{}";//缓存请求体的内容

    public HttpServletRequestBodyReaderWrapper(HttpServletRequest request) throws IOException {
        super(request);
        StringBuilder stringBuilder = new StringBuilder("");
        BufferedReader bufferedReader = null;
        try {
            InputStream inputStream = request.getInputStream();
            if (inputStream != null) {
                bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
                char[] charBuffer = new char[1024];
                int bytesRead = -1;
                while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {
                    stringBuilder.append(charBuffer, 0, bytesRead);
                }
            }
        } catch (IOException ex) {
            throw ex;
        } finally {
            if (bufferedReader != null) {
                try {
                    bufferedReader.close();
                } catch (IOException ex) {
                    throw ex;
                }
            }
        }
        body = stringBuilder.toString();
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {
        final ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(body.getBytes("utf-8"));
        ServletInputStream servletInputStream = new ServletInputStream() {
            public boolean isFinished() {
                return false;
            }
            public boolean isReady() {
                return true;
            }
            public void setReadListener(ReadListener readListener) {}
            public int read() throws IOException {
                return byteArrayInputStream.read();
            }
        };
        return servletInputStream;

    }
    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(this.getInputStream()));
    }
    public String getBody() {
        return this.body;
    }

    public void setBody(String body) {
        this.body = body;
    }
}

接下来就是校验啦：

package cn.wjp.mydaily.common.filter;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.TypeReference;

import javax.servlet.*;
import javax.servlet.FilterConfig;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;

public class XssFilter implements Filter {

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest request =(HttpServletRequest)req;
        HttpServletResponse response =(HttpServletResponse)res;

        String contentType = request.getContentType();//获取contentType请求头
        String method = request.getMethod();//获取请求方法  post/get
        //1 处理get请求  get请求的Content-Type一般为application/x-www-form-urlencoded  或者  text/html
        if(method.trim().equalsIgnoreCase(HttpConst.GET_METHOD)){
            HttpServletRequestNormalWrapper wrapperRequest = new HttpServletRequestNormalWrapper(request);
            Map<String, String[]> parameterMap = wrapperRequest.getParameterMap();
            parameterMap =cleanXSSForNormalRequest(parameterMap);
            wrapperRequest.setParameterMap(parameterMap);
            chain.doFilter(wrapperRequest, response);
            return;
        }
        //2 处理post请求  只处理application/x-www-form-urlencoded  application/json,对于multipart/form-data，直接放行
        if(method.trim().equalsIgnoreCase(HttpConst.POST_METHOD)){
            if(contentType.trim().toLowerCase().contains(HttpConst.MULTIPART_CONTENT_TYPE)){
                chain.doFilter(request, response);
                return;
            }
            //处理application/x-www-form-urlencoded
            if(contentType.trim().toLowerCase().contains(HttpConst.FORM_URLENCODED_CONTENT_TYPE)){
                HttpServletRequestNormalWrapper wrapperRequest = new HttpServletRequestNormalWrapper(request);
                Map<String, String[]> parameterMap = wrapperRequest.getParameterMap();
                parameterMap =cleanXSSForNormalRequest(parameterMap);
                wrapperRequest.setParameterMap(parameterMap);
                chain.doFilter(wrapperRequest, response);
                return;
            }
            //处理application/json
            if(contentType.trim().toLowerCase().contains(HttpConst.JSON_CONTENT_TYPE)){
                HttpServletRequestBodyReaderWrapper requestWrapper = new HttpServletRequestBodyReaderWrapper(request);
                String body = requestWrapper.getBody();
                body =cleanXSSForPostJsonRequest(body);
                requestWrapper.setBody(body);
                chain.doFilter(requestWrapper, response);
                return;
            }
        }
        chain.doFilter(request, response);
        return;

    }

    public String cleanXSS(String value) {
        if(value==null||value.trim().isEmpty()){
            return null;
        }
        value = value.replaceAll("<", "& lt;").replaceAll(">", "& gt;");
        value = value.replaceAll("\\(", "& #40;").replaceAll("\\)", "& #41;");
        value = value.replaceAll("'", "& #39;");
        value = value.replaceAll("\"", "& #34;");
        value = value.replaceAll("`", "");
        value = value.replaceAll("eval\\((.*)\\)", "");
        value = value.replaceAll("[\\\"\\\'][\\s]*javascript:(.*)[\\\"\\\']", "\"\"");
        value = value.replaceAll("script", "");
        return value;
    }

    /**
     * 普通的post/get请求
     * @param parameterMap
     */
    public Map<String,String[]> cleanXSSForNormalRequest(Map<String,String[]> parameterMap){
        Map<String,String[]> cleanMap = new HashMap<>();
        if(parameterMap==null||parameterMap.size()==0){
            return cleanMap;
        }
        for (Map.Entry<String,String[]> entry : parameterMap.entrySet()) {
            String key = entry.getKey();
            String[] value = entry.getValue();
            String cleanKey = cleanXSS(key);
            String[] cleanValue = null;
            if(value!=null&&value.length>0){
                cleanValue = new String[value.length];
                for(int i=0;i<value.length;i++){
                    cleanValue[i]=cleanXSS(value[i]);
                }
            }
            cleanMap.put(cleanKey,cleanValue);
        }
        //打印用
        StringBuffer printStr = new StringBuffer();
        for (Map.Entry<String,String[]> entry1 : cleanMap.entrySet()) {
            printStr.append(entry1.getKey()).append("=").append(Arrays.asList(entry1.getValue())).append("&");
        }
        System.out.println("XssFilter:发送的请求参数:"+JSON.toJSONString(printStr));
        return cleanMap;
    }

    /**
     * post的application/json请求
     * @param body
     */
    public String cleanXSSForPostJsonRequest(String body){
        String cleanBody = "{}";
        if(body==null||body.trim().isEmpty()||body.trim().equalsIgnoreCase("{}")||!body.trim().contains(":")){
            return cleanBody;
        }
        Map<String,Object> map = JSON.parseObject(body,new TypeReference<Map<String,Object>>(){});
        if(map==null||map.size()==0){
            return cleanBody;
        }
        Map<String,Object> cleanMap = new HashMap<>();
        for (Map.Entry<String,Object> entry : map.entrySet()) {
            String key = entry.getKey();
            Object value = entry.getValue();
            String valueStr = String.valueOf(value);
            if(valueStr==null||valueStr.trim().isEmpty()||valueStr.trim().equalsIgnoreCase("null")){
                valueStr = null;
            }
            cleanMap.put(cleanXSS(key),cleanXSS(valueStr));
        }
        cleanBody = JSON.toJSONString(cleanMap);
        System.out.println("XssFilter:发送的请求参数:"+cleanBody);
        return cleanBody;
    }


    @Override
    public void destroy() {
    }

    @Override
    public void init(FilterConfig arg0) {
    }
}