把模糊需求写成可测试的提示

Matcher matcher = Pattern.compile("[$][{]([a-z]+)[}]").matcher(template);
StringBuffer out = new StringBuffer();
while (matcher.find()) {
    String value = values.get(matcher.group(1));
    // 替换语法中的美元符号和反斜线按普通字符处理，避免被当作分组引用。
    matcher.appendReplacement(out, Matcher.quoteReplacement(value));
}
matcher.appendTail(out);

import java.util.*;
public class Main {
    static String render(String template,Map<String,String> values){
        StringBuilder out=new StringBuilder();int i=0;
        while(i<template.length()){
            if(template.charAt(i)=='$'&&i+1<template.length()&&template.charAt(i+1)=='{'){
                int end=template.indexOf('}',i+2);
                if(end<0)throw new IllegalArgumentException("unclosed variable");
                String name=template.substring(i+2,end);
                if(name.isEmpty())throw new IllegalArgumentException("empty name"); // 空变量名属于模板配置错误。
                for(char c:name.toCharArray())if(!(c>='a'&&c<='z'||c>='A'&&c<='Z'||c>='0'&&c<='9'||c=='_'))throw new IllegalArgumentException("name");
                String value=values.get(name);if(value==null)throw new IllegalArgumentException("missing variable");
                out.append(value);i=end+1; // 值只追加，绝不重新扫描它。
            }else out.append(template.charAt(i++));
        }
        return out.toString();
    }
    static void eq(String e,String a){if(!e.equals(a))throw new AssertionError(a);}
    static void bad(String t){try{render(t,Map.of());throw new AssertionError();}catch(IllegalArgumentException expected){}}
    public static void main(String[] args){
        eq("你好Java",render("你好${name}",Map.of("name","Java")));
        eq("${secret}",render("${x}",Map.of("x","${secret}","secret","hidden")));
        eq("$5"+(char)92+"x",render("${x}",Map.of("x","$5"+(char)92+"x")));// 字面保留特殊字符。
        eq("",render("",Map.of()));eq("AA",render("${x}${x}",Map.of("x","A")));
        bad("${missing}");bad("${x");bad("${}");
        System.out.println("PASS 8 tests");
    }
}