前缀树实现过滤敏感词

原文：

https://blog.csdn.net/weixin_42700635/article/details/105637764

import org.apache.commons.lang3.CharUtils;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

@Component
public class SensitiveFilter {

    private static final Logger logger = LoggerFactory.getLogger(SensitiveFilter.class);
    //替换符
    private static String REPLACEMENT = "***";

    //根节点
    private TrieNode root = new TrieNode();

    @PostConstruct
    public void init() {

        try (InputStream is = this.getClass().getClassLoader().getResourceAsStream("sensitive-words.txt");
             BufferedReader reader=new BufferedReader(new InputStreamReader(is));
        ) {
            String keyword;
            while ((keyword=reader.readLine())!=null){
                //添加到前缀树
                this.addKeyword(keyword);
            }
        } catch (IOException e) {
            logger.error("加载敏感词文件失败："+e.getMessage());
        }

    }


    //将敏感词添加到前缀树当中
    private void addKeyword(String keyword){
        TrieNode tempNode=root;
        for (int i=0;i<keyword.length();i++){
            char c=keyword.charAt(i);
            TrieNode subNode=tempNode.getSubNode(c);
            if (subNode==null){
                //初始化子节点
                subNode=new TrieNode();
                tempNode.addSubNode(c,subNode);
            }

            //指向子节点，进入下一轮循环
            tempNode=subNode;

            //设置结束标识
            if (i==keyword.length()-1){
                tempNode.setKeywordEnd(true);
            }
        }
    }


    /**
     * 过滤敏感词
     * @param text 待过滤文本
     * @return 过滤后的文本
     */
    public String filter(String text){
        if (StringUtils.isBlank(text)){
            return null;
        }

        //指针1
        TrieNode tempNode=root;

        //指针2
        int begin=0;
        //指针3
        int position=0;
        //结果
        StringBuilder sb=new StringBuilder();

        while (position<text.length()){
            char c=text.charAt(position);

            //跳过符号
            if (isSymbol(c)){
                //若指针1处于根节点，将此符号计入结果，让指针2向下走一步
                if (tempNode==root){
                    sb.append(c);
                    begin++;
                }
                //无论符号在开头或中间，指针3都向下走一步
                position++;
                continue;

            }

            //检查下级节点
            tempNode=tempNode.getSubNode(c);
            if (tempNode==null){
                //以begin开头的字符不是敏感词
                sb.append(text.charAt(begin));
                //进入下一个位置
                position=++begin;
                //重新指向根节点
                tempNode=root;
            }else if (tempNode.isKeywordEnd()){
                //发现敏感词，将begin-position字符串替换掉
                sb.append(REPLACEMENT);
                begin=++position;
                //重新指向根节点
                tempNode=root;
            }else {
                //检查下一个字符
                position++;
            }
        }
        //将最后一批字符计入结果
        sb.append(text.substring(begin));
        return sb.toString();
    }


    //判断是否为符号
    private boolean isSymbol(Character c){
        // 0x2E80-0x9FFF是东亚文字范围
        return !CharUtils.isAsciiAlphanumeric(c) && (c<0x2E80||c>0x9FFF);
    }

    //前缀树
    private class TrieNode {
        //关键词结束标识
        private boolean isKeywordEnd = false;

        //子节点(key是下级字符，value是下级节点）
        private Map<Character, TrieNode> subNodes = new HashMap<>();

        public boolean isKeywordEnd() {
            return isKeywordEnd;
        }

        public void setKeywordEnd(boolean keywordEnd) {
            isKeywordEnd = keywordEnd;
        }

        //添加子节点方法
        public void addSubNode(Character key, TrieNode value) {
            subNodes.put(key, value);
        }

        //获取子节点方法
        public TrieNode getSubNode(Character key) {
            return subNodes.get(key);
        }
    }

}