过滤敏感词

package com.nowcoder.community.util;

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 final String REPLACEMENT = "***";

// 根节点
private TrieNode rootNode = 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());
    }
}

// 将一个敏感词添加到前缀树中
private void addKeyword(String keyword) {
    TrieNode tempNode = rootNode;
    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 待过滤的文本
 * @return 过滤后的文本
 */
public String filter(String text) {
    if (StringUtils.isBlank(text)) {
        return null;
    }

    // 指针1
    TrieNode tempNode = rootNode;
    // 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 == rootNode) {
                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开头的字符串不是敏感词
            sb.append(text.charAt(begin));
            // 进入下一个位置
            position = ++begin;
            // 重新指向根节点
            tempNode = rootNode;
        } else if (tempNode.isKeywordEnd()) {
            // 发现敏感词,将begin~position字符串替换掉
            sb.append(REPLACEMENT);
            // 进入下一个位置
            begin = ++position;
            // 重新指向根节点
            tempNode = rootNode;
        } 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
    public void addSubNode(Character c, TrieNode node) {
        subNodes.put(c, node);
    }

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

}

}