在我们拿到一团未经格式化的json字符串时，非常不方便查看，比如这样

{"APP_HEAD": {"TOTAL_NUM": "-1","PGUP_OR_PGDN": "0"},"SYS_HEAD": {"RET": [{"RET_CODE": "000000","RET_MSG": "000000 SUCCESS"},{"RET_CODE": "000001","RET_MSG": "000001 SUCCESS"}],"AUTH_USER_ID": null,"RUN_DATE": "20211222","MESSAGE_CODE": "369285","SOURCE_BRANCH_NO": "142857"},"BODY": [{"createDate":"20220630","fileName":"RB_TRAN_HIST_20220630_2_1.txt","filePath":"/acc/abcd/20220630","fileScence":"abcd","fileType":"txt","systemId":"ACC"},{"createDate":"20220630","fileName":"RB_TRAN_HIST_20220630_2_2.txt","filePath":"/acc/abcd/20220630","fileScence":"abcd","fileType":"txt","systemId":"ACC"}]}

因此随手写了个工具类用来格式化json。注意，原json字符串必须语法无误，并且不包含换行、空格、缩进等，否则会保留下来。
ok废话不多说上代码

package com.xxx.util;
 
/**
 * json字符串格式化
 * @AuThor wangbyn
 */
public class JsonUtil {
 
        public static String format(String jsonStr) {
                int level = 0;
                StringBuffer jsonForMatStr = new StringBuffer();
                for (int i = 0; i < jsonStr.length(); i++) {
                        char c = jsonStr.charAt(i);
                        if (level > 0 && '\n' == jsonForMatStr.charAt(jsonForMatStr.length() - 1)) {
                                jsonForMatStr.append(getLevelStr(level));
                        }
                        switch (c) {
                                case '{':
                                case '[':
                                        jsonForMatStr.append(c).append("\n");
                                        level++;
                                        break;
                                case ',':
                                        jsonForMatStr.append(c).append("\n");
                                        break;
                                case '}':
                                case ']':
                                        jsonForMatStr.append("\n");
                                        level--;
                                        jsonForMatStr.append(getLevelStr(level));
                                        jsonForMatStr.append(c);
                                        break;
                                default:
                                        jsonForMatStr.append(c);
                                        break;
                        }
                }
 
                return jsonForMatStr.toString();
 
        }
 
        private static String getLevelStr(int level) {
                StringBuffer levelStr = new StringBuffer();
                for (int levelI = 0; levelI < level; levelI++) {
                        levelStr.append("\t");
                }
                return levelStr.toString();
        }
 
        public static void main(String[] args) {
                String json = "{\"APP_HEAD\": {\"TOTAL_NUM\": \"-1\",\"PGUP_OR_PGDN\": \"0\"},\"SYS_HEAD\": {\"RET\": [{\"RET_CODE\": \"000000\",\"RET_MSG\": \"000000 SUCCESS\"},{\"RET_CODE\": \"000001\",\"RET_MSG\": \"000001 SUCCESS\"}],\"AUTH_USER_ID\": null,\"RUN_DATE\": \"20211222\",\"MESSAGE_CODE\": \"369285\",\"SOURCE_BRANCH_NO\": \"142857\"},\"BODY\": [{\"createDate\":\"20220630\",\"fileName\":\"RB_TRAN_HIST_20220630_2_1.txt\",\"filePath\":\"/acc/abcd/20220630\",\"fileScence\":\"abcd\",\"fileType\":\"txt\",\"systemId\":\"ACC\"},{\"createDate\":\"20220630\",\"fileName\":\"RB_TRAN_HIST_20220630_2_2.txt\",\"filePath\":\"/acc/abcd/20220630\",\"fileScence\":\"abcd\",\"fileType\":\"txt\",\"systemId\":\"ACC\"}]}";
                System.out.println(format(json));
        }
}

运行后效果