1. 什么是JSON？
JSON(JavaScript Object Notation) 是一种轻量级的数据交换格式。 易于人阅读和编写。同时也易于机器解析和生成。
JSON建构于两种结构：
“名称/值”对的集合（A collection of name/value pairs）。不同的语言中，它被理解为对象（object），纪录（record），结构（struct），字典（dictionary），哈希表（hash table），有键列表（keyed list），或者关联数组 （associative array）。
值的有序列表（An ordered list of values）。在大部分语言中，它被理解为数组（array）。
2. JAVA有哪些自动JSON转换的包
参考事例
- 2.1直接构建
import org.json.JSONObject;
public class JSONObjectSample {
public static void main(String[] args) {
createJson();
}
private static void createJson() {
JSONObject obj = new JSONObject();
obj.put("name", "zhangsan");
obj.put("age", 22);
obj.put("hobbies", new String[] {"dancing", "swimming"});
System.out.println(obj.toString());
}
}
- 2.2使用Map构建
public class JSONObjectSample {
public static void main(String[] args) {
createJsonByMap();
}
private static void createJsonByMap() {
Map<String, Object> data = new HashMap<String, Object>();
data.put("name", "zhangsan");
data.put("age", 22);
data.put("hobbies", new String[] {"dancing", "swimming"});
JSONObject obj = new JSONObject(data);
System.out.println(obj.toString());
}
}
- 2.3使用JAVA bean创建
import org.json.JSONObject;
class PersonInfo {
private String name;
private int age;
private String[] hobbies;
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
public void setHobbies(String[] hobbies) {
this.hobbies = hobbies;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public String[] getHobbies() {
return hobbies;
}
}
public class JSONObjectSample {
public static void main(String[] args) {
createJsonByJavaBean();
}
private static void createJsonByJavaBean() {
PersonInfo info = new PersonInfo();
info.setName("John");
info.setAge(22);
info.setHobbies(new String[] {"dancing", "swimming"});
JSONObject obj = new JSONObject(info);
System.out.println(obj);
}
}
3. 自己实现一个简易版的JSON解析器
- 代码仅供参考，功能不太完善，欢迎补充指正
public class JSONImpl implements JSON {
/**
* object -> String
*
* @param objects
* @return
*/
@Override
public String stringfy(Object[] objects) {
StringBuilder sb = new StringBuilder();
if(objects == null){
return "";
}
if(objects.length>1){
sb.append("{");
}
for(Object object: objects){
Map<String, Object> map = getKeyAndValue(object);
sb.append("{");
Iterator entries = map.entrySet().iterator();
while(entries.hasNext()){
Map.Entry entry = (Map.Entry) entries.next();
String key = (String)entry.getKey();
Object value = entry.getValue();
sb.append("\"");
sb.append(key);
sb.append("\"");
sb.append(":");
if(value!=null && value.getClass().isArray()){
//todo 改为其他类型
int[] arr = (int[]) value;
sb.append(Arrays.toString(arr));
}else if (value instanceof String){
sb.append("\"");
sb.append(value);
sb.append("\"");
}else{
String mapTemp = value.toString();
mapTemp = mapTemp.replace('=',':');
sb.append(mapTemp);
}
sb.append(",");
}
sb.deleteCharAt(sb.length()-1);
sb.append("}");
sb.append(",");
}
sb.deleteCharAt(sb.length()-1);
if(objects.length>1){
sb.append("}");
}
return sb.toString();
}
private Map<String, Object> getKeyAndValue(Object object){
Map<String, Object> map = new HashMap<>();
Class cla = object.getClass();
Field[] fs = cla.getDeclaredFields();
for(int i=0;i<fs.length;i++){
Field f = fs[i];
f.setAccessible(true);
Object val;
try{
val = f.get(object);
map.put(f.getName(), val);
}catch (IllegalArgumentException e){
e.printStackTrace();
}catch (IllegalAccessException e){
e.printStackTrace();
}
}
return map;
}
/**
* String -> Object
* 使用栈实现
*
* @param str
* @return
*/
@Override
public Map<String, Object> parse(String str) {
str = removeSpace(str);
char[] cArr = str.toCharArray();
int length = cArr.length;
Stack<Character> stack1 = new Stack<>();
Stack<String> stack2 = new Stack<>();
Map<String, Object> map = new HashMap<>(length);
int i = 0;
while (i < length) {
if (cArr[i] == ':') {
StringBuilder sb = new StringBuilder();
while (!(stack1.peek() == '{' || stack1.peek() == ',')) {
sb.append(stack1.pop());
}
if(stack1.peek() == ','){
stack1.pop();
}
stack1.push(':');
stack2.push(sb.reverse().toString());
//map
if(i+1<length&&cArr[i+1]=='{'){
sb = new StringBuilder();
while (cArr[i] != '}') {
i++;
sb.append(cArr[i]);
}
String key = stack2.pop();
key = key.substring(1, key.length() - 1);
Map<String, Object> subMap = parse(sb.toString());
map.put(key, subMap);
if(cArr[i+1] == ','){
i++;
}
stack1.pop();
}
} else if (cArr[i] == ',' || cArr[i] == '}') {
StringBuilder sb = new StringBuilder();
if(stack2.isEmpty()){
break;
}
while (stack1.peek() != ':') {
sb.append(stack1.pop());
}
stack1.pop();
stack1.push(cArr[i]);
String key = stack2.pop();
if (key.contains("\"")) {
key = key.substring(1, key.length() - 1);
}
String top = sb.reverse().toString();
if ("true".equals(top)) {
map.put(key, true);
} else if ("false".equals(top)) {
map.put(key, false);
} else if ("null".equals(top)) {
map.put(key, null);
} else {
char[] chars = top.toCharArray();
if (chars[0] == '[') {
//数组
Object[] objs = parseArray(top);
map.put(key, Arrays.toString(objs));
} else if ('0' <= chars[0] && '9' >= chars[0]) {
//数字
top = top.replaceAll(",", "");
try {
if (top.contains("e")) {
map.put(key, parseBigDecimal(top));
} else if (top.contains(".")) {
map.put(key, parseDouble(top));
} else {
map.put(key, parseInteger(top));
}
} catch (NumberFormatException e) {
map.put(key, top);
}
} else if ('\"' == chars[0]) {
//字符串
map.put(key, top.substring(1, top.length() - 1));
} else {
//对象
map.put(key, top);
}
}
} else if (cArr[i] == '[') {
stack1.push('[');
while (cArr[i] != ']') {
i++;
stack1.push(cArr[i]);
}
} else {
stack1.push(cArr[i]);
}
i++;
}
return map;
}
/**
* 解析数组
* @param str
* @return
*/
private Object[] parseArray(String str) {
str = str.substring(1, str.length() - 1);
String[] strArray = str.split(",");
Object[] objs = new Object[strArray.length];
for (int i = 0; i < strArray.length; i++) {
//转换成不同的类型
//todo 需要继续完善
//objs[i] = parse(strArray[i]);
objs[i] = i;
}
return objs;
}
/**
* String -> double
* @param str
* @return
*/
private double parseDouble(String str) {
return Double.parseDouble(str);
}
/**
* String -> int
* @param str
* @return
*/
private int parseInteger(String str) {
return Integer.parseInt(str);
}
/**
* String -> Double
* @param str
* @return
*/
private Double parseBigDecimal(String str) {
BigDecimal bd = new BigDecimal(str);
return bd.doubleValue();
}
/**
* remove the space
* @param str
* @return
*/
private String removeSpace(String str) {
StringBuffer sb = new StringBuffer();
int index = 0;
char currentChar;
while (index < str.length()) {
currentChar = str.charAt(index);
if (currentChar == ' ' || currentChar == '\t' || currentChar == '\n') {
} else {
sb = sb.append(currentChar);
}
index++;
}
return sb.toString();
}
}
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