使用StringSubstitutor时如何解决悬挂${导致的变量未替换问题？

// 构建映射表
Map<String, String> valuesMap = new HashMap<>();
valuesMap.put("animal", "quick brown fox");
valuesMap.put("target", "lazy dog");
String templateString = "The ${animal} jumped ${ over the ${target}.%";

// 初始化字符串替换器
StringSubstitutor sub = new StringSubstitutor(valuesMap);

// 执行替换
String resolvedString = sub.replace(templateString);

assertThat( resolvedString, is( "The quick brown fox jumped ${ over the lazy dog.%") );

• ${target}变量未被替换：

java.lang.AssertionError: 
Expected: is "The quick brown fox jumped ${ over the lazy dog.%"
     but: was "The quick brown fox jumped ${ over the ${target}.%"

问题出在模板字符串里的${ （带有空格的占位符起始），StringSubstitutor会将其判定为未闭合的变量占位符，后续的${target}会被视作这个未完成占位符的一部分，无法被独立识别替换。

修复方式：

• 要输出字面量${，需用反斜杠转义，调整模板字符串：

String templateString = "The ${animal} jumped \\${ over the ${target}.%";

• StringSubstitutor默认转义字符为\，无需额外配置，转义后${会被保留为普通文本，${target}就能正常替换为lazy dog，断言可通过。

内容的提问来源于stack exchange，提问作者Ian Lim