import com.alibaba.fastjson.JSONObject;
import org.springframework.util.StringUtils;

import java.util.ArrayList;
import java.util.List;

public class Test {

public static final String expressionPrefix = "${";
public static final String expressionSuffix = "}";

public static void main(String[] args) {
    String context = "${a}我在${b}中${c}${d}${e}";
    List<String> list = parse(context);
    // ["a","b","c","d","e"]
    System.out.println(JSONObject.toJSON(list));

    context = replace(context, "a", "1");
    context = replace(context, "b", "2");

    // 1我在2中${c}${d}${e}
    System.out.println(context);
}

/**
 * 将内容中表达式替换为值
 * @param context
 * @param expressionValue 表达式中的值，不包含前缀和后缀
 * @param value
 * @return
 */
public static String replace(String context, String expressionValue, String value){
    String oldValue = expressionPrefix + expressionValue + expressionSuffix;
    // 转义正则表达式中的特殊字符
    String escapedOldValue = oldValue.replaceAll("([\\[\\]{}()*+?.\\\\^$|])", "\\\\$1");
    return context.replaceAll(escapedOldValue, value);
}

/**
 * 解析所有表达式
 * @param context
 * @return
 */
public static List<String> parse(String context){
    List<String> list = new ArrayList<>();
    if(StringUtils.hasText(context)){
        int root = 0;
        while (true){
            int start = context.indexOf(expressionPrefix, root);
            if(start == -1){
                break;
            }

            int end = context.indexOf(expressionSuffix, start + expressionPrefix.length());
            if(end == -1){
                break;
            }else{
                String tmp = context.substring(start + expressionPrefix.length(), end);
                end = end + expressionSuffix.length();
                list.add(tmp);
            }

            root = end;
        }
    }

    return list;
}

}