前言

本文代码实现一个中文的敏感词过滤器，预先将准备好的敏感词写入前缀树数据结构中实现快速检索，并且节省内存。一般用于检查注册用户名称、言论是否包含不文明的词汇。

可以判断内容是否包含敏感词；找出内容中的敏感词；将内容中的敏感词替换成设置的字符。

运行环境

代码使用了JDK8语法，以及测试框架Jupiter。以下是Maven配置：

<properties>
    <java.version>1.8</java.version>
    <maven.compiler.source>${java.version}</maven.compiler.source>
    <maven.compiler.target>${java.version}</maven.compiler.target>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

<dependencies>
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter</artifactId>
        <version>RELEASE</version>
        <scope>test</scope>
    </dependency>
</dependencies>

过滤器源码

import java.util.*;
import java.util.function.Predicate;

/**
 * 敏感词过滤器，限中文
 */
public class SensitiveWordFilters {

    /**
     * 如词典中有敏感词：[敏感, 敏感词]
     * true
     * ├── 匹配到[敏感]结束匹配
     * └── 比较省时，作简单判断用
     * false
     * ├── 匹配到[敏感词]才结束匹配
     * └── 相对费时，但是在替换敏感词的时候，能够替换掉更多匹配数据
     */
    private static final boolean SIMPLE_MATCH = false;

    /**
     * 忽略字符列表
     */
    private static final List<Character> IGNORE_CHAR_LIST = ignoreCharListInit();

    /**
     * 忽略部分字符
     * 如词典中有敏感词：[敏感词]，现验证文本[敏 感 词]，也会认定为敏感词，因为忽略了空格符
     * 同样在 重构字典、往字典中加敏感词时也会使用此断言
     */
    private static final Predicate<Character> CHAR_IGNORE =
            character -> Character.isSpaceChar(character) || IGNORE_CHAR_LIST.contains(character);

    /**
     * 重构字典
     */
    public static void refactoringBy(List<String> sensitiveWordList) {
        refactor(sensitiveWordList);
    }

    /**
     * 往字典中加敏感词
     */
    public static void add(List<String> sensitiveWordList) {
        sensitiveWordList.forEach(word -> recordToThe(SensitiveWordCache.dictionary, word));
    }

    /**
     * 往字典中加敏感词
     */
    public static void add(String sensitiveWord) {
        recordToThe(SensitiveWordCache.dictionary, sensitiveWord);
    }

    /**
     * true：text 中有敏感词
     */
    public static boolean foundIn(String text) {
        if (isEmpty(text)) {
            return false;
        }

        for (int i = 0; i < text.length(); i++) {
            if (checkSensitiveWord(text, i) > 0) {
                return true;
            }
        }

        return false;
    }

    /**
     * 从 text 中找出敏感词
     */
    public static Set<String> findOutFrom(String text) {
        if (isEmpty(text)) {
            return Collections.emptySet();
        }

        Set<String> resultSet = new TreeSet<>((o1, o2) -> o1.length() == o2.length() ? o1.compareTo(o2) : o2.length() - o1.length());
        for (int i = 0; i < text.length(); i++) {
            int endIndex = checkSensitiveWord(text, i);
            if (endIndex > 0) {
                resultSet.add(text.substring(i, ++endIndex));
            }
        }

        return resultSet;
    }

    /**
     * 替换 text 中的敏感词，每个字符换一个替换符
     *
     * @param text        文本
     * @param replaceChar 替换符
     * @return 替换后的文本
     */
    public static String replace(String text, String replaceChar) {
        Set<String> sensitiveWordSet = findOutFrom(text);
        if (sensitiveWordSet.isEmpty()) {
            return text;
        }

        for (String sensitiveWord : sensitiveWordSet) {
            text = text.replace(sensitiveWord, replacementOf(replaceChar, sensitiveWord.length()));
        }
        return text;
    }

    /**
     * 字典缓存
     */
    private static class SensitiveWordCache {

        /**
         * 字典/字典根节点
         */
        static Node dictionary;

        static {
            dictionary = new Node();
            dictionary.children = new HashMap<>(16);
        }

        private SensitiveWordCache() {
        }
    }

    /**
     * 重构字典
     *
     * @param sensitiveWordList 敏感字符列表
     */
    private static void refactor(List<String> sensitiveWordList) {
        Node newDictionary = new Node();
        newDictionary.children = new HashMap<>(16);
        synchronized (SensitiveWordCache.class) {
            for (String word : sensitiveWordList) {
                recordToThe(newDictionary, word);
            }
            SensitiveWordCache.dictionary = newDictionary;
        }
    }

    /**
     * 将敏感字符记录在节点上
     *
     * @param node 节点
     * @param word 敏感字符
     */
    private static void recordToThe(Node node, String word) {
        Objects.requireNonNull(node);
        synchronized (SensitiveWordCache.class) {
            for (int i = 0, lastIndex = word.length() - 1; i < word.length(); i++) {
                Character key = word.charAt(i);

                if (!CHAR_IGNORE.test(key)) {
                    // 放置子节点
                    Node next = node.get(key);
                    if (Objects.isNull(next)) {
                        next = new Node();
                        node.putChild(key, next);
                    }
                    node = next;
                }

                if (i == lastIndex) {
                    node.isEnd = true;
                }
            }
        }
    }

    /**
     * 从 startIndex 开始匹配敏感字符
     *
     * @param text       文本
     * @param startIndex 文本起始位置
     * @return 0-没有敏感字符，>0 敏感字符终止位置
     */
    private static int checkSensitiveWord(String text, int startIndex) {
        int endIndex = 0;
        Node node = SensitiveWordCache.dictionary;
        for (int i = startIndex; i < text.length(); i++) {
            Character key = text.charAt(i);

            if (CHAR_IGNORE.test(key)) {
                continue;
            }

            node = node.get(key);
            if (Objects.isNull(node)) {
                break;
            }

            if (node.isEnd) {
                endIndex = i;
                if (SIMPLE_MATCH) {
                    break;
                }
            }
        }

        return endIndex;
    }

    private static boolean isEmpty(String str) {
        return str == null || "".equals(str);
    }

    /**
     * 生成完整的替换符
     *
     * @param replaceChar 单字符替换符
     * @param num         替换数量
     * @return 完整替换符
     */
    private static String replacementOf(String replaceChar, int num) {
        int minJointLength = 2;
        if (num < minJointLength) {
            return replaceChar;
        }

        StringBuilder replacement = new StringBuilder();
        for (int i = 0; i < num; i++) {
            replacement.append(replaceChar);
        }
        return replacement.toString();
    }

    /**
     * 字典数据节点
     */
    private static class Node {
        /**
         * true：敏感词结尾
         */
        boolean isEnd;

        /**
         * 子节点列表
         */
        Map<Character, Node> children;

        Node get(Character key) {
            return Objects.nonNull(children) ? children.get(key) : null;
        }

        void putChild(Character key, Node node) {
            if (Objects.isNull(children)) {
                children = new HashMap<>(16);
            }
            children.put(key, node);
        }
    }

    /**
     * 初始化忽略字符列表
     */
    private static List<Character> ignoreCharListInit() {
        List<Character> ignoreCharList = new ArrayList<>(10);
        ignoreCharList.add('|');
        ignoreCharList.add('-');
        return Collections.unmodifiableList(ignoreCharList);
    }

    private SensitiveWordFilters() {
    }
}

过滤器测试类

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import java.util.Arrays;

class SensitiveWordFiltersTest {

    /**
     * 重构字典
     */
    @Test
    void refactoringBy() {
        SensitiveWordFilters.refactoringBy(Arrays.asList(getSensitiveWords()));
    }

    /**
     * 往字典中加敏感词
     */
    @Test
    void add() {
        SensitiveWordFilters.add(Arrays.asList("敏感词"));
    }

    /**
     * 判断内容是否包含敏感词
     */
    @Test
    void foundIn() {
        SensitiveWordFilters.refactoringBy(Arrays.asList(getSensitiveWords()));
        Assertions.assertTrue(SensitiveWordFilters.foundIn("白银混蛋"));
    }

    /**
     * 从内容中找出敏感词
     */
    @Test
    void findOutFrom() {
        SensitiveWordFilters.refactoringBy(Arrays.asList(getSensitiveWords()));
        System.out.println(SensitiveWordFilters.findOutFrom("白银混蛋"));
    }

    /**
     * 替换内容中的敏感词
     */
    @Test
    void replace() {
        SensitiveWordFilters.refactoringBy(Arrays.asList(getSensitiveWords()));
        String string = "就算是一个 顶-级 高 手，也会被那个白银 混蛋坑得很惨";
        System.out.println(SensitiveWordFilters.replace(string, "*"));
    }

    private static String[] getSensitiveWords() {
        return sensitiveWords.split("\\|");
    }

    static final String sensitiveWords = "顶级|白银|混蛋";
}