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);
    
 
//替換符
    private static String REPLACEMENT = "***";

    //根節點
    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){
                //新增到字首樹
                this.addKeyword(keyword);
            }
        } catch (IOException e) {
            logger.error("載入敏感詞檔案失敗："+e.getMessage());
        }

    }


    //將敏感詞新增到字首樹當中
    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){
                //初始化子節點
                subNode=new TrieNode();
                tempNode.addSubNode(c,subNode);
            }

            //指向子節點，進入下一輪迴圈
            tempNode=subNode;

            //設定結束標識
            if (i==keyword.length()-1){
                tempNode.setKeywordEnd(true);
            }
        }
    }


    /**
     * 過濾敏感詞
     * @param text 待過濾文字
     * @return 過濾後的文字
     */
    public String filter(String text){
        if (StringUtils.isBlank(text)){
            return null;
        }

        //指標1
        TrieNode tempNode=root;

        //指標2
        int begin=0;
        //指標3
        int position=0;
        //結果
        StringBuilder sb=new StringBuilder();

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

            //跳過符號
            if (isSymbol(c)){
                //若指標1處於根節點，將此符號計入結果，讓指標2向下走一步
                if (tempNode==root){
                    sb.append(c);
                    begin++;
                }
                //無論符號在開頭或中間，指標3都向下走一步
                position++;
                continue;

            }

            //檢查下級節點
            tempNode=tempNode.getSubNode(c);
            if (tempNode==null){
                //以begin開頭的字元不是敏感詞
                sb.append(text.charAt(begin));
                //進入下一個位置
                position=++begin;
                //重新指向根節點
                tempNode=root;
            }else if (tempNode.isKeywordEnd()){
                //發現敏感詞，將begin-position字串替換掉
                sb.append(REPLACEMENT);
                begin=++position;
                //重新指向根節點
                tempNode=root;
            }else {
                //檢查下一個字元
                position++;
            }
        }
        //將最後一批字元計入結果
        sb.append(text.substring(begin));
        return sb.toString();
    }


    //判斷是否為符號
    private boolean isSymbol(Character c){
        // 0x2E80-0x9FFF是東亞文字範圍
        return !CharUtils.isAsciiAlphanumeric(c) && (c<0x2E80||c>0x9FFF);
    }

    //字首樹
    private class TrieNode {
        //關鍵詞結束標識
        private boolean isKeywordEnd = false;

        //子節點(key是下級字元，value是下級節點）
        private Map<Character, TrieNode> subNodes = new HashMap<>();

        public boolean isKeywordEnd() {
            return isKeywordEnd;
        }

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

        //新增子節點方法
        public void addSubNode(Character key, TrieNode value) {
            subNodes.put(key, value);
        }

        //獲取子節點方法
        public TrieNode getSubNode(Character key) {
            return subNodes.get(key);
        }
    }

}