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