Java实战之敏感词过滤器

<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-aop</artifactId>
</dependency>

<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-devtools</artifactId>
		<scope>runtime</scope>
</dependency>

<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-test</artifactId>
		<scope>test</scope>
</dependency>

<dependency>
		<groupId>org.apache.commons</groupId>
		<artifactId>commons-lang3</artifactId>
		<version>3.9</version>
</dependency>

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

        //子节点
        private Map<Character,TrieNode> subNodes = new HashMap<>();
		
		//isKeywordEnd的get、set方法
        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);
        }
    }

@Component
public class SensitiveFilter {
    // 替换符
    private static final String REPLACEMENT = "***";

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

    //bean的初始化方法，服务一启动，容器自动给bean执行此方法完成初始化
    //此方法的目的是读取敏感词文件，构建敏感词前缀树
    @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){
                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
    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;

            //设置结束标志
            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
            	情况一：符号在敏感词前面，将符号写入结果，如 ☆敏感词
            	情况二：符号在敏感词中间，则将符号与敏感词一起替换，如敏☆感☆词
            */
            if(isSymbol(c)){
                //若指针1处于根节点，对应情况一，将符号计入结果，让指针2向下走一步
                if(tempNode==rootNode){
                    sb.append(c);
                    begin++;
                }
                //无论符号在开头还是敏感词中间，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开头的的字符串不是敏感词
                sb.append(text.charAt(begin));
                //指针2和指针3共同指向指针2的下一个位置
                position = ++begin;
                //指针1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
                sb.append(REPLACEMENT);
                //进入下一个位置
                begin = ++position;
                //指针1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);
    }
}