解决提交表单时Xss攻击的问题

红太狼 2022-06-09 10:39 172阅读 0赞

之前一直做内网系统，都是局域网，对安全问题一直考虑不周。

有一天对自己线上的表单做了一个测试，将<script>alert("xxx")</script>作为表单选项提交，在后台回显时，可想而知，后台弹出了一个alert("xxx")的巨大的bug。

\-------------------------------------

修改了Xss攻击时的问题，改成了一个过滤器

配置如下：

1.在web.xml中配置过滤器

<filter>
    	<filter-name>xssFilter</filter-name>
    	<filter-class>cn.xdf.wlyy.util.xss.XssFilter</filter-class>
    </filter>
    <filter-mapping>
    	<filter-name>xssFilter</filter-name>
    	<url-pattern>/*</url-pattern>
    </filter-mapping>

2.声明该过滤器

import javax.servlet.*;
    import javax.servlet.http.HttpServletRequest;
    import java.io.IOException;
    
    /**
     * XSS过滤
     * 
     */
    public class XssFilter implements Filter {
    
    	@Override
    	public void init(FilterConfig config) throws ServletException {
    	}
    
    	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
                throws IOException, ServletException {
    		XssHttpServletRequestWrapper xssRequest = new XssHttpServletRequestWrapper((HttpServletRequest) request);
    		chain.doFilter(xssRequest, response);
    	}
    
    	@Override
    	public void destroy() {
    	}
    
    }

3.该过滤器引入了一个包装类XssHttpServletRequestWrapper，该包装类对request请求中的参数进行取值和过滤

同时，有些富文本不需要过滤，可以把此字段取出，放到EXCLUSIVE\_FIELDS字段中，如我的不对matter,remark这两个字段进行标签的过滤

如下：

import java.io.ByteArrayInputStream;
    import java.io.IOException;
    import java.util.Arrays;
    import java.util.LinkedHashMap;
    import java.util.List;
    import java.util.Map;
    
    import javax.servlet.ReadListener;
    import javax.servlet.ServletInputStream;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletRequestWrapper;
    
    import org.apache.commons.io.IOUtils;
    import org.apache.commons.lang3.StringUtils;
    import org.springframework.http.MediaType;
    
    /**
     * XSS过滤处理
     * 
     */
    public class XssHttpServletRequestWrapper extends HttpServletRequestWrapper {
    	
    	private static final List<String> EXCLUSIVE_FIELDS = Arrays.asList("matter,remark".split(","));
    	
        //没被包装过的HttpServletRequest（特殊场景，需要自己过滤）
        HttpServletRequest orgRequest;
        //html过滤
        private final static HTMLFilter htmlFilter = new HTMLFilter();
    
        public XssHttpServletRequestWrapper(HttpServletRequest request) {
            super(request);
            orgRequest = request;
        }
    
        @Override
        public ServletInputStream getInputStream() throws IOException {
            //非json类型，直接返回
            if(!super.getHeader("Content-Type").equalsIgnoreCase(MediaType.APPLICATION_JSON_VALUE)){
                return super.getInputStream();
            }
    
            //为空，直接返回
            String json = IOUtils.toString(super.getInputStream(), "utf-8");
            if (StringUtils.isBlank(json)) {
                return super.getInputStream();
            }
    
            //xss过滤
            json = xssEncode(json);
            final ByteArrayInputStream bis = new ByteArrayInputStream(json.getBytes());
            return new ServletInputStream() {
                @Override
                public boolean isFinished() {
                    return true;
                }
    
                @Override
                public boolean isReady() {
                    return true;
                }
    
                @Override
                public void setReadListener(ReadListener readListener) {
    
                }
    
                @Override
                public int read() throws IOException {
                    return bis.read();
                }
            };
        }
    
        @Override
        public String getParameter(String name) {
            String value = super.getParameter(xssEncode(name));
            if (StringUtils.isNotBlank(value)) {
                value = xssEncode(value);
            }
            return value;
        }
    
        @Override
        public String[] getParameterValues(String name) {
            String[] parameters = super.getParameterValues(name);
            
            if (parameters == null || parameters.length == 0) {
                return null;
            }
            
            /**
             * 添加不过滤的字段值
             */
            if (EXCLUSIVE_FIELDS.contains(name)) {
            	return parameters;
            }
    
            for (int i = 0; i < parameters.length; i++) {
                parameters[i] = xssEncode(parameters[i]);
            }
            return parameters;
        }
    
        @Override
        public Map<String,String[]> getParameterMap() {
            Map<String,String[]> map = new LinkedHashMap<>();
            Map<String,String[]> parameters = super.getParameterMap();
            for (String key : parameters.keySet()) {
                String[] values = parameters.get(key);
                for (int i = 0; i < values.length; i++) {
                    values[i] = xssEncode(values[i]);
                }
                map.put(key, values);
            }
            return map;
        }
    
        @Override
        public String getHeader(String name) {
            String value = super.getHeader(xssEncode(name));
            if (StringUtils.isNotBlank(value)) {
                value = xssEncode(value);
            }
            return value;
        }
    
        private String xssEncode(String input) {
            return htmlFilter.filter(input);
        }
    
        /**
         * 获取最原始的request
         */
        public HttpServletRequest getOrgRequest() {
            return orgRequest;
        }
    
        /**
         * 获取最原始的request
         */
        public static HttpServletRequest getOrgRequest(HttpServletRequest request) {
            if (request instanceof XssHttpServletRequestWrapper) {
                return ((XssHttpServletRequestWrapper) request).getOrgRequest();
            }
    
            return request;
        }
    
    }

4.该包装类对取出的值进行html等标签的过滤，此方法是网上现有的方法，直接引用过来了

如下：

import java.util.*;
    import java.util.concurrent.ConcurrentHashMap;
    import java.util.concurrent.ConcurrentMap;
    import java.util.logging.Logger;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    
    /**
     *
     * HTML filtering utility for protecting against XSS (Cross Site Scripting).
     *
     * This code is licensed LGPLv3
     *
     * This code is a Java port of the original work in PHP by Cal Hendersen.
     * http://code.iamcal.com/php/lib_filter/
     *
     * The trickiest part of the translation was handling the differences in regex handling
     * between PHP and Java.  These resources were helpful in the process:
     *
     * http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html
     * http://us2.php.net/manual/en/reference.pcre.pattern.modifiers.php
     * http://www.regular-expressions.info/modifiers.html
     *
     * A note on naming conventions: instance variables are prefixed with a "v"; global
     * constants are in all caps.
     *
     * Sample use:
     * String input = ...
     * String clean = new HTMLFilter().filter( input );
     *
     * The class is not thread safe. Create a new instance if in doubt.
     *
     * If you find bugs or have suggestions on improvement (especially regarding
     * performance), please contact us.  The latest version of this
     * source, and our contact details, can be found at http://xss-html-filter.sf.net
     *
     * @author Joseph O'Connell
     * @author Cal Hendersen
     * @author Michael Semb Wever
     */
    public final class HTMLFilter {
    
        /** regex flag union representing /si modifiers in php **/
        private static final int REGEX_FLAGS_SI = Pattern.CASE_INSENSITIVE | Pattern.DOTALL;
        private static final Pattern P_COMMENTS = Pattern.compile("", Pattern.DOTALL);
        private static final Pattern P_COMMENT = Pattern.compile("^!--(.*)--$", REGEX_FLAGS_SI);
        private static final Pattern P_TAGS = Pattern.compile("<(.*?)>", Pattern.DOTALL);
        private static final Pattern P_END_TAG = Pattern.compile("^/([a-z0-9]+)", REGEX_FLAGS_SI);
        private static final Pattern P_START_TAG = Pattern.compile("^([a-z0-9]+)(.*?)(/?)$", REGEX_FLAGS_SI);
        private static final Pattern P_QUOTED_ATTRIBUTES = Pattern.compile("([a-z0-9]+)=([\"'])(.*?)\\2", REGEX_FLAGS_SI);
        private static final Pattern P_UNQUOTED_ATTRIBUTES = Pattern.compile("([a-z0-9]+)(=)([^\"\\s']+)", REGEX_FLAGS_SI);
        private static final Pattern P_PROTOCOL = Pattern.compile("^([^:]+):", REGEX_FLAGS_SI);
        private static final Pattern P_ENTITY = Pattern.compile("&#(\\d+);?");
        private static final Pattern P_ENTITY_UNICODE = Pattern.compile("&#x([0-9a-f]+);?");
        private static final Pattern P_ENCODE = Pattern.compile("%([0-9a-f]{2});?");
        private static final Pattern P_VALID_ENTITIES = Pattern.compile("&([^&;]*)(?=(;|&|$))");
        private static final Pattern P_VALID_QUOTES = Pattern.compile("(>|^)([^<]+?)(<|$)", Pattern.DOTALL);
        private static final Pattern P_END_ARROW = Pattern.compile("^>");
        private static final Pattern P_BODY_TO_END = Pattern.compile("<([^>]*?)(?=<|$)");
        private static final Pattern P_XML_CONTENT = Pattern.compile("(^|>)([^<]*?)(?=>)");
        private static final Pattern P_STRAY_LEFT_ARROW = Pattern.compile("<([^>]*?)(?=<|$)");
        private static final Pattern P_STRAY_RIGHT_ARROW = Pattern.compile("(^|>)([^<]*?)(?=>)");
        private static final Pattern P_AMP = Pattern.compile("&");
        private static final Pattern P_QUOTE = Pattern.compile("<");
        private static final Pattern P_LEFT_ARROW = Pattern.compile("<");
        private static final Pattern P_RIGHT_ARROW = Pattern.compile(">");
        private static final Pattern P_BOTH_ARROWS = Pattern.compile("<>");
    
        // @xxx could grow large... maybe use sesat's ReferenceMap
        private static final ConcurrentMap<String,Pattern> P_REMOVE_PAIR_BLANKS = new ConcurrentHashMap<String, Pattern>();
        private static final ConcurrentMap<String,Pattern> P_REMOVE_SELF_BLANKS = new ConcurrentHashMap<String, Pattern>();
    
        /** set of allowed html elements, along with allowed attributes for each element **/
        private final Map<String, List<String>> vAllowed;
        /** counts of open tags for each (allowable) html element **/
        private final Map<String, Integer> vTagCounts = new HashMap<String, Integer>();
    
        /** html elements which must always be self-closing (e.g. "<img />") **/
        private final String[] vSelfClosingTags;
        /** html elements which must always have separate opening and closing tags (e.g. "<b></b>") **/
        private final String[] vNeedClosingTags;
        /** set of disallowed html elements **/
        private final String[] vDisallowed;
        /** attributes which should be checked for valid protocols **/
        private final String[] vProtocolAtts;
        /** allowed protocols **/
        private final String[] vAllowedProtocols;
        /** tags which should be removed if they contain no content (e.g. "<b></b>" or "<b />") **/
        private final String[] vRemoveBlanks;
        /** entities allowed within html markup **/
        private final String[] vAllowedEntities;
        /** flag determining whether comments are allowed in input String. */
        private final boolean stripComment;
        private final boolean encodeQuotes;
        private boolean vDebug = false;
        /**
         * flag determining whether to try to make tags when presented with "unbalanced"
         * angle brackets (e.g. "<b text </b>" becomes "<b> text </b>").  If set to false,
         * unbalanced angle brackets will be html escaped.
         */
        private final boolean alwaysMakeTags;
    
        /** Default constructor.
         *
         */
        public HTMLFilter() {
            vAllowed = new HashMap<>();
    
            final ArrayList<String> a_atts = new ArrayList<String>();
            a_atts.add("href");
            a_atts.add("target");
            vAllowed.put("a", a_atts);
    
            final ArrayList<String> img_atts = new ArrayList<String>();
            img_atts.add("src");
            img_atts.add("width");
            img_atts.add("height");
            img_atts.add("alt");
            vAllowed.put("img", img_atts);
    
            final ArrayList<String> no_atts = new ArrayList<String>();
            vAllowed.put("b", no_atts);
            vAllowed.put("strong", no_atts);
            vAllowed.put("i", no_atts);
            vAllowed.put("em", no_atts);
    
            vSelfClosingTags = new String[]{"img"};
            vNeedClosingTags = new String[]{"a", "b", "strong", "i", "em"};
            vDisallowed = new String[]{};
            vAllowedProtocols = new String[]{"http", "mailto", "https"}; // no ftp.
            vProtocolAtts = new String[]{"src", "href"};
            vRemoveBlanks = new String[]{"a", "b", "strong", "i", "em"};
            vAllowedEntities = new String[]{"amp", "gt", "lt", "quot"};
            stripComment = true;
            encodeQuotes = true;
            alwaysMakeTags = true;
        }
    
        /** Set debug flag to true. Otherwise use default settings. See the default constructor.
         *
         * @param debug turn debug on with a true argument
         */
        public HTMLFilter(final boolean debug) {
            this();
            vDebug = debug;
    
        }
    
        /** Map-parameter configurable constructor.
         *
         * @param conf map containing configuration. keys match field names.
         */
        public HTMLFilter(final Map<String,Object> conf) {
    
            assert conf.containsKey("vAllowed") : "configuration requires vAllowed";
            assert conf.containsKey("vSelfClosingTags") : "configuration requires vSelfClosingTags";
            assert conf.containsKey("vNeedClosingTags") : "configuration requires vNeedClosingTags";
            assert conf.containsKey("vDisallowed") : "configuration requires vDisallowed";
            assert conf.containsKey("vAllowedProtocols") : "configuration requires vAllowedProtocols";
            assert conf.containsKey("vProtocolAtts") : "configuration requires vProtocolAtts";
            assert conf.containsKey("vRemoveBlanks") : "configuration requires vRemoveBlanks";
            assert conf.containsKey("vAllowedEntities") : "configuration requires vAllowedEntities";
    
            vAllowed = Collections.unmodifiableMap((HashMap<String, List<String>>) conf.get("vAllowed"));
            vSelfClosingTags = (String[]) conf.get("vSelfClosingTags");
            vNeedClosingTags = (String[]) conf.get("vNeedClosingTags");
            vDisallowed = (String[]) conf.get("vDisallowed");
            vAllowedProtocols = (String[]) conf.get("vAllowedProtocols");
            vProtocolAtts = (String[]) conf.get("vProtocolAtts");
            vRemoveBlanks = (String[]) conf.get("vRemoveBlanks");
            vAllowedEntities = (String[]) conf.get("vAllowedEntities");
            stripComment =  conf.containsKey("stripComment") ? (Boolean) conf.get("stripComment") : true;
            encodeQuotes = conf.containsKey("encodeQuotes") ? (Boolean) conf.get("encodeQuotes") : true;
            alwaysMakeTags = conf.containsKey("alwaysMakeTags") ? (Boolean) conf.get("alwaysMakeTags") : true;
        }
    
        private void reset() {
            vTagCounts.clear();
        }
    
        private void debug(final String msg) {
            if (vDebug) {
                Logger.getAnonymousLogger().info(msg);
            }
        }
    
        //---------------------------------------------------------------
        // my versions of some PHP library functions
        public static String chr(final int decimal) {
            return String.valueOf((char) decimal);
        }
    
        public static String htmlSpecialChars(final String s) {
            String result = s;
            result = regexReplace(P_AMP, "&", result);
            result = regexReplace(P_QUOTE, """, result);
            result = regexReplace(P_LEFT_ARROW, "<", result);
            result = regexReplace(P_RIGHT_ARROW, ">", result);
            return result;
        }
    
        //---------------------------------------------------------------
        /**
         * given a user submitted input String, filter out any invalid or restricted
         * html.
         *
         * @param input text (i.e. submitted by a user) than may contain html
         * @return "clean" version of input, with only valid, whitelisted html elements allowed
         */
        public String filter(final String input) {
            reset();
            String s = input;
    
            debug("************************************************");
            debug("              INPUT: " + input);
    
            s = escapeComments(s);
            debug("     escapeComments: " + s);
    
            s = balanceHTML(s);
            debug("        balanceHTML: " + s);
    
            s = checkTags(s);
            debug("          checkTags: " + s);
    
            s = processRemoveBlanks(s);
            debug("processRemoveBlanks: " + s);
    
            s = validateEntities(s);
            debug("    validateEntites: " + s);
    
            debug("************************************************\n\n");
            return s;
        }
    
        public boolean isAlwaysMakeTags(){
            return alwaysMakeTags;
        }
    
        public boolean isStripComments(){
            return stripComment;
        }
    
        private String escapeComments(final String s) {
            final Matcher m = P_COMMENTS.matcher(s);
            final StringBuffer buf = new StringBuffer();
            if (m.find()) {
                final String match = m.group(1); //(.*?)
                m.appendReplacement(buf, Matcher.quoteReplacement(""));
            }
            m.appendTail(buf);
    
            return buf.toString();
        }
    
        private String balanceHTML(String s) {
            if (alwaysMakeTags) {
                //
                // try and form html
                //
                s = regexReplace(P_END_ARROW, "", s);
                s = regexReplace(P_BODY_TO_END, "<$1>", s);
                s = regexReplace(P_XML_CONTENT, "$1<$2", s);
    
            } else {
                //
                // escape stray brackets
                //
                s = regexReplace(P_STRAY_LEFT_ARROW, "<$1", s);
                s = regexReplace(P_STRAY_RIGHT_ARROW, "$1$2><", s);
    
                //
                // the last regexp causes '<>' entities to appear
                // (we need to do a lookahead assertion so that the last bracket can
                // be used in the next pass of the regexp)
                //
                s = regexReplace(P_BOTH_ARROWS, "", s);
            }
    
            return s;
        }
    
        private String checkTags(String s) {
            Matcher m = P_TAGS.matcher(s);
    
            final StringBuffer buf = new StringBuffer();
            while (m.find()) {
                String replaceStr = m.group(1);
                replaceStr = processTag(replaceStr);
                m.appendReplacement(buf, Matcher.quoteReplacement(replaceStr));
            }
            m.appendTail(buf);
    
            s = buf.toString();
    
            // these get tallied in processTag
            // (remember to reset before subsequent calls to filter method)
            for (String key : vTagCounts.keySet()) {
                for (int ii = 0; ii < vTagCounts.get(key); ii++) {
                    s += "</" + key + ">";
                }
            }
    
            return s;
        }
    
        private String processRemoveBlanks(final String s) {
            String result = s;
            for (String tag : vRemoveBlanks) {
                if(!P_REMOVE_PAIR_BLANKS.containsKey(tag)){
                    P_REMOVE_PAIR_BLANKS.putIfAbsent(tag, Pattern.compile("<" + tag + "(\\s[^>]*)?></" + tag + ">"));
                }
                result = regexReplace(P_REMOVE_PAIR_BLANKS.get(tag), "", result);
                if(!P_REMOVE_SELF_BLANKS.containsKey(tag)){
                    P_REMOVE_SELF_BLANKS.putIfAbsent(tag, Pattern.compile("<" + tag + "(\\s[^>]*)?/>"));
                }
                result = regexReplace(P_REMOVE_SELF_BLANKS.get(tag), "", result);
            }
    
            return result;
        }
    
        private static String regexReplace(final Pattern regex_pattern, final String replacement, final String s) {
            Matcher m = regex_pattern.matcher(s);
            return m.replaceAll(replacement);
        }
    
        private String processTag(final String s) {
            // ending tags
            Matcher m = P_END_TAG.matcher(s);
            if (m.find()) {
                final String name = m.group(1).toLowerCase();
                if (allowed(name)) {
                    if (!inArray(name, vSelfClosingTags)) {
                        if (vTagCounts.containsKey(name)) {
                            vTagCounts.put(name, vTagCounts.get(name) - 1);
                            return "</" + name + ">";
                        }
                    }
                }
            }
    
            // starting tags
            m = P_START_TAG.matcher(s);
            if (m.find()) {
                final String name = m.group(1).toLowerCase();
                final String body = m.group(2);
                String ending = m.group(3);
    
                //debug( "in a starting tag, name='" + name + "'; body='" + body + "'; ending='" + ending + "'" );
                if (allowed(name)) {
                    String params = "";
    
                    final Matcher m2 = P_QUOTED_ATTRIBUTES.matcher(body);
                    final Matcher m3 = P_UNQUOTED_ATTRIBUTES.matcher(body);
                    final List<String> paramNames = new ArrayList<String>();
                    final List<String> paramValues = new ArrayList<String>();
                    while (m2.find()) {
                        paramNames.add(m2.group(1)); //([a-z0-9]+)
                        paramValues.add(m2.group(3)); //(.*?)
                    }
                    while (m3.find()) {
                        paramNames.add(m3.group(1)); //([a-z0-9]+)
                        paramValues.add(m3.group(3)); //([^\"\\s']+)
                    }
    
                    String paramName, paramValue;
                    for (int ii = 0; ii < paramNames.size(); ii++) {
                        paramName = paramNames.get(ii).toLowerCase();
                        paramValue = paramValues.get(ii);
    
    //          debug( "paramName='" + paramName + "'" );
    //          debug( "paramValue='" + paramValue + "'" );
    //          debug( "allowed? " + vAllowed.get( name ).contains( paramName ) );
    
                        if (allowedAttribute(name, paramName)) {
                            if (inArray(paramName, vProtocolAtts)) {
                                paramValue = processParamProtocol(paramValue);
                            }
                            params += " " + paramName + "=\"" + paramValue + "\"";
                        }
                    }
    
                    if (inArray(name, vSelfClosingTags)) {
                        ending = " /";
                    }
    
                    if (inArray(name, vNeedClosingTags)) {
                        ending = "";
                    }
    
                    if (ending == null || ending.length() < 1) {
                        if (vTagCounts.containsKey(name)) {
                            vTagCounts.put(name, vTagCounts.get(name) + 1);
                        } else {
                            vTagCounts.put(name, 1);
                        }
                    } else {
                        ending = " /";
                    }
                    return "<" + name + params + ending + ">";
                } else {
                    return "";
                }
            }
    
            // comments
            m = P_COMMENT.matcher(s);
            if (!stripComment && m.find()) {
                return  "<" + m.group() + ">";
            }
    
            return "";
        }
    
        private String processParamProtocol(String s) {
            s = decodeEntities(s);
            final Matcher m = P_PROTOCOL.matcher(s);
            if (m.find()) {
                final String protocol = m.group(1);
                if (!inArray(protocol, vAllowedProtocols)) {
                    // bad protocol, turn into local anchor link instead
                    s = "#" + s.substring(protocol.length() + 1, s.length());
                    if (s.startsWith("#//")) {
                        s = "#" + s.substring(3, s.length());
                    }
                }
            }
    
            return s;
        }
    
        private String decodeEntities(String s) {
            StringBuffer buf = new StringBuffer();
    
            Matcher m = P_ENTITY.matcher(s);
            while (m.find()) {
                final String match = m.group(1);
                final int decimal = Integer.decode(match).intValue();
                m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
            }
            m.appendTail(buf);
            s = buf.toString();
    
            buf = new StringBuffer();
            m = P_ENTITY_UNICODE.matcher(s);
            while (m.find()) {
                final String match = m.group(1);
                final int decimal = Integer.valueOf(match, 16).intValue();
                m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
            }
            m.appendTail(buf);
            s = buf.toString();
    
            buf = new StringBuffer();
            m = P_ENCODE.matcher(s);
            while (m.find()) {
                final String match = m.group(1);
                final int decimal = Integer.valueOf(match, 16).intValue();
                m.appendReplacement(buf, Matcher.quoteReplacement(chr(decimal)));
            }
            m.appendTail(buf);
            s = buf.toString();
    
            s = validateEntities(s);
            return s;
        }
    
        private String validateEntities(final String s) {
            StringBuffer buf = new StringBuffer();
    
            // validate entities throughout the string
            Matcher m = P_VALID_ENTITIES.matcher(s);
            while (m.find()) {
                final String one = m.group(1); //([^&;]*)
                final String two = m.group(2); //(?=(;|&|$))
                m.appendReplacement(buf, Matcher.quoteReplacement(checkEntity(one, two)));
            }
            m.appendTail(buf);
    
            return encodeQuotes(buf.toString());
        }
    
        private String encodeQuotes(final String s){
            if(encodeQuotes){
                StringBuffer buf = new StringBuffer();
                Matcher m = P_VALID_QUOTES.matcher(s);
                while (m.find()) {
                    final String one = m.group(1); //(>|^)
                    final String two = m.group(2); //([^<]+?)
                    final String three = m.group(3); //(<|$)
                    m.appendReplacement(buf, Matcher.quoteReplacement(one + regexReplace(P_QUOTE, """, two) + three));
                }
                m.appendTail(buf);
                return buf.toString();
            }else{
                return s;
            }
        }
    
        private String checkEntity(final String preamble, final String term) {
    
            return ";".equals(term) && isValidEntity(preamble)
                    ? '&' + preamble
                    : "&" + preamble;
        }
    
        private boolean isValidEntity(final String entity) {
            return inArray(entity, vAllowedEntities);
        }
    
        private static boolean inArray(final String s, final String[] array) {
            for (String item : array) {
                if (item != null && item.equals(s)) {
                    return true;
                }
            }
            return false;
        }
    
        private boolean allowed(final String name) {
            return (vAllowed.isEmpty() || vAllowed.containsKey(name)) && !inArray(name, vDisallowed);
        }
    
        private boolean allowedAttribute(final String name, final String paramName) {
            return allowed(name) && (vAllowed.isEmpty() || vAllowed.get(name).contains(paramName));
        }
    }

完毕！