Java对象转 JSON 字符串

本案例所有代码均为原创，使用Java1.8类库编写，没有借鉴其他类似工具库和网上论坛博客，也许没有经过充分测试，可能出现未知bug，仅供参考学习使用。

Java对象就像一个文件夹一样，没有办法知道其深度，所以采用了递归。

性能方面没有测试，个人认为没有特别耗费性能的地方，除非你的对象包含很多层级。

它可以支持null，字符串，数字、日期、集合、数组以及自定义对象等多种数据类型，包括以上任意类型的多层嵌套。

另外对于存储基本类型元素的数组而言，实在没有更好的处理办法，因此占用了很多代码行数。

源码不多，如下：

package com.duyi.boot.utils;import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.*;/*** @author qiaoao* @description:* @date 2021/7/29 18:10*/
public class JsonUtil {private static JsonUtil util = new JsonUtil();public static String toJsonStr(Object obj) {return util.parseObj(obj, new StringBuilder());}private String parseObj(Object obj, StringBuilder builder) {if (builder == null) {throw new UnsupportedOperationException("builder can not be null");}if (obj == null) {return builder.append("\"null\"").toString();}Class clazz = obj.getClass();if (Collection.class.isAssignableFrom(clazz)) {Iterator iterator = ((Collection) obj).iterator();builder.append("[");while (iterator.hasNext()) {parseObj(iterator.next(), builder);if (iterator.hasNext())builder.append(",");}builder.append("]");} else if (Map.class.isAssignableFrom(clazz)) {//如果是map，key一定且必须是String类型，如果是对象，给他toString()Map map = ((Map) obj);Iterator iterator = map.keySet().iterator();builder.append("{");while (iterator.hasNext()) {Object key = iterator.next();builder.append("\"");builder.append(key);builder.append("\":");parseObj(map.get(key), builder);if (iterator.hasNext())builder.append(",");}builder.append("}");} else if (clazz.isArray()) {//数组/*** 虽然int[]类型的数组可以通过：Arrays.stream((int[]) obj).boxed().collect(Collectors.toList());* 转化为集合，但Arrays.stream()方法不支持char[] byte[] boolean[] float[]*/builder.append("[");if (obj instanceof int[]) {arrayHandle((int[]) obj, builder);} else if (obj instanceof byte[]) {arrayHandle((byte[]) obj, builder);} else if (obj instanceof char[]) {arrayHandle((char[]) obj, builder);} else if (obj instanceof long[]) {arrayHandle((long[]) obj, builder);} else if (obj instanceof float[]) {arrayHandle((float[]) obj, builder);} else if (obj instanceof short[]) {arrayHandle((short[]) obj, builder);} else if (obj instanceof double[]) {arrayHandle((double[]) obj, builder);} else if (obj instanceof boolean[]) {arrayHandle((boolean[]) obj, builder);} else if (obj instanceof Object[]) {List<Object> list = Arrays.asList((Object[]) obj);for (int i = 0; i < list.size(); i++) {parseObj(list.get(i), builder);if (i < list.size() - 1) {builder.append(",");}}} else {throw new UnsupportedOperationException(obj.getClass().toString());}builder.append("]");} else if (String.class.isAssignableFrom(clazz) || Date.class.isAssignableFrom(clazz)) {builder.append("\"");builder.append(obj);builder.append("\"");} else if (Number.class.isAssignableFrom(clazz) || Boolean.class.isAssignableFrom(clazz)) {builder.append(obj);} else {//自定义的实体类Field[] fields = clazz.getDeclaredFields();builder.append("{");for (int i = 0; i < fields.length; i++) {Field field = fields[i];if (Modifier.isPrivate(field.getModifiers())) {field.setAccessible(true);}builder.append("\"");builder.append(field.getName());builder.append("\":");Object value = null;try {value = field.get(obj);} catch (IllegalAccessException e) {e.printStackTrace();}parseObj(value, builder);if (i < fields.length - 1) {builder.append(",");}}builder.append("}");}return builder.toString();}private void arrayHandle(int[] arr, StringBuilder builder) {for (int i = 0; i < arr.length; i++) {parseObj(arr[i], builder);if (i < arr.length - 1) {builder.append(",");}}}private void arrayHandle(byte[] arr, StringBuilder builder) {for (int i = 0; i < arr.length; i++) {parseObj(arr[i], builder);if (i < arr.length - 1) {builder.append(",");}}}private void arrayHandle(char[] arr, StringBuilder builder) {for (int i = 0; i < arr.length; i++) {parseObj(arr[i], builder);if (i < arr.length - 1) {builder.append(",");}}}private void arrayHandle(long[] arr, StringBuilder builder) {for (int i = 0; i < arr.length; i++) {parseObj(arr[i], builder);if (i < arr.length - 1) {builder.append(",");}}}private void arrayHandle(float[] arr, StringBuilder builder) {for (int i = 0; i < arr.length; i++) {parseObj(arr[i], builder);if (i < arr.length - 1) {builder.append(",");}}}private void arrayHandle(short[] arr, StringBuilder builder) {for (int i = 0; i < arr.length; i++) {parseObj(arr[i], builder);if (i < arr.length - 1) {builder.append(",");}}}private void arrayHandle(double[] arr, StringBuilder builder) {for (int i = 0; i < arr.length; i++) {parseObj(arr[i], builder);if (i < arr.length - 1) {builder.append(",");}}}private void arrayHandle(boolean[] arr, StringBuilder builder) {for (int i = 0; i < arr.length; i++) {parseObj(arr[i], builder);if (i < arr.length - 1) {builder.append(",");}}}
}

以下为测试代码：

import java.util.*;/*** @author qiaoao* @description:* @date 2021/7/30 14:06*/
public class Demo {private long aLong;private int aInt;public short aShort;private static boolean isAlive;private String name;private byte[] bytes;private Date[] dates;private int[][][] superIntArr;private String[][] strings;private List<Map<Integer,String>> list;private Set<int[]> set;private Map<String,List<int[]>> map;public static void main(String[] args) throws IllegalAccessException {Demo demo = Demo.getObj();String json = JsonUtil.toJsonStr(demo);System.out.println(json);}public static Demo getObj(){Demo demo = new Demo();demo.setaLong(1000012L);demo.setaInt(120);Demo.setIsAlive(true);demo.setaShort((short)78);demo.setName("Demo Test");byte[] bytes = new byte[2];bytes[0] = 1;bytes[1] = 127;demo.setBytes(bytes);Date[] dates = new Date[3];dates[1] = new Date();demo.setDates(dates);int[][][] superIntArr = new int[2][2][2];for (int i = 0;i<superIntArr.length;i++){for (int j = 0;j<superIntArr[i].length;j++){for (int k = 0;k<superIntArr[j].length;k++){superIntArr[i][j][k] = (int)(Math.random()*100);}}}demo.setSuperIntArr(superIntArr);String[][] strings = new String[5][2];for (int i = 0; i < strings.length; i++) {for (int j = 0; j < strings[i].length; j++) {strings[i][j] = String.valueOf(Math.random());}}demo.setStrings(strings);List<Map<Integer,String>> list = new LinkedList<>();Map<Integer,String> map = new Hashtable<>();map.put(1,"demo1");map.put(2,"demo2");map.put(3,"demo3");Map<Integer,String> map2 = new Hashtable<>();map2.put(12,"demo12");map2.put(22,"demo22");map2.put(32,"demo32");list.add(map);list.add(map2);demo.setList(list);Set<int[]> set = new HashSet<>();for (int i = 0;i<5;i++){int len = (int)(Math.random()*10)+2;int[] tempArr = new int[len];for (int j = 0; j < tempArr.length; j++) {tempArr[j] = 100 - j;}set.add(tempArr);}demo.setSet(set);Map<String,List<int[]>> maps = new LinkedHashMap<>();for (int i = 0;i<=3;i++){List<int[]> tempList = new Stack<>();for (int j = 20;j>=0;j--){int[] hh = new int[5];for (int k = 0; k < hh.length; k++) {hh[k] = k+j;}tempList.add(hh);}maps.put("list"+i,tempList);}demo.setMap(maps);return demo;}public static void setIsAlive(boolean isAlive) {Demo.isAlive = isAlive;}public void setaLong(long aLong) {this.aLong = aLong;}public void setaInt(int aInt) {this.aInt = aInt;}public void setaShort(short aShort) {this.aShort = aShort;}public void setName(String name) {this.name = name;}public void setBytes(byte[] bytes) {this.bytes = bytes;}public void setDates(Date[] dates) {this.dates = dates;}public void setSuperIntArr(int[][][] superIntArr) {this.superIntArr = superIntArr;}public void setStrings(String[][] strings) {this.strings = strings;}public void setList(List<Map<Integer, String>> list) {this.list = list;}public void setSet(Set<int[]> set) {this.set = set;}public void setMap(Map<String, List<int[]>> map) {this.map = map;}
}

执行结果如下：

{"aLong":1000012,"aInt":120,"aShort":78,"isAlive":true,"name":"Demo Test","bytes":[1,127],"dates":["null","Fri Jul 30 15:25:35 CST 2021","null"],"superIntArr":[[[11,99],[47,20]],[[20,72],[59,49]]],"strings":[["0.11307908409828815","0.22341871804534985"],["0.5005992982006673","0.5893604912974005"],["0.6892806476807729","0.4169059518233631"],["0.650889741691504","0.8702143841026739"],["0.26192826894369403","0.31877430959379016"]],"list":[{"3":"demo3","2":"demo2","1":"demo1"},{"32":"demo32","12":"demo12","22":"demo22"}],"set":[[100,99,98],[100,99,98,97,96,95],[100,99,98,97,96,95,94,93,92,91],[100,99,98,97,96,95,94,93],[100,99,98,97,96,95,94,93]],"map":{"list0":[[20,21,22,23,24],[19,20,21,22,23],[18,19,20,21,22],[17,18,19,20,21],[16,17,18,19,20],[15,16,17,18,19],[14,15,16,17,18],[13,14,15,16,17],[12,13,14,15,16],[11,12,13,14,15],[10,11,12,13,14],[9,10,11,12,13],[8,9,10,11,12],[7,8,9,10,11],[6,7,8,9,10],[5,6,7,8,9],[4,5,6,7,8],[3,4,5,6,7],[2,3,4,5,6],[1,2,3,4,5],[0,1,2,3,4]],"list1":[[20,21,22,23,24],[19,20,21,22,23],[18,19,20,21,22],[17,18,19,20,21],[16,17,18,19,20],[15,16,17,18,19],[14,15,16,17,18],[13,14,15,16,17],[12,13,14,15,16],[11,12,13,14,15],[10,11,12,13,14],[9,10,11,12,13],[8,9,10,11,12],[7,8,9,10,11],[6,7,8,9,10],[5,6,7,8,9],[4,5,6,7,8],[3,4,5,6,7],[2,3,4,5,6],[1,2,3,4,5],[0,1,2,3,4]],"list2":[[20,21,22,23,24],[19,20,21,22,23],[18,19,20,21,22],[17,18,19,20,21],[16,17,18,19,20],[15,16,17,18,19],[14,15,16,17,18],[13,14,15,16,17],[12,13,14,15,16],[11,12,13,14,15],[10,11,12,13,14],[9,10,11,12,13],[8,9,10,11,12],[7,8,9,10,11],[6,7,8,9,10],[5,6,7,8,9],[4,5,6,7,8],[3,4,5,6,7],[2,3,4,5,6],[1,2,3,4,5],[0,1,2,3,4]],"list3":[[20,21,22,23,24],[19,20,21,22,23],[18,19,20,21,22],[17,18,19,20,21],[16,17,18,19,20],[15,16,17,18,19],[14,15,16,17,18],[13,14,15,16,17],[12,13,14,15,16],[11,12,13,14,15],[10,11,12,13,14],[9,10,11,12,13],[8,9,10,11,12],[7,8,9,10,11],[6,7,8,9,10],[5,6,7,8,9],[4,5,6,7,8],[3,4,5,6,7],[2,3,4,5,6],[1,2,3,4,5],[0,1,2,3,4]]}}

可以放到 json 在线格式化页面里检验：

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