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(L); 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":,"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.","0."],["0.06673","0.74005"],["0.07729","0.33631"],["0.1504","0.26739"],["0.","0."]],"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]]}}