1.JSON数据和Java对象的相互转换
JSON数据和Java对象的相互转换
* JSON解析器：
* 常见的解析器：Jsonlib，Gson，fastjson，jackson
1. Java对象转换JSON
1. 使用步骤：
1. 导入jackson的相关jar包
2. 创建Jackson核心对象 ObjectMapper
3. 调用ObjectMapper的相关方法进行转换
1. 转换方法：
* writeValue(参数1，obj):
参数1：
File：将obj对象转换为JSON字符串，并保存到指定的文件中
Writer：将obj对象转换为JSON字符串，并将json数据填充到字符输出流中
OutputStream：将obj对象转换为JSON字符串，并将json数据填充到字节输出流中
* writeValueAsString(obj):将对象转为json字符串2. 注解：
1. @JsonIgnore：排除某个属性不要转换成JSON,给类的属性上加上这个注解。
2. @JsonFormat：属性值得格式化日期字符串，取的是默认时区的时间
* @JsonFormat(pattern = "yyyy-MM-dd")
private Date birthday;
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")//给默认时区加上8个小时
3.指定转换json字符串是的别名 @JsonProperty("username")
@JsonProperty("username")
private String name;
4. 如果该字段的值是null,就不会转换成JSON
@JsonInclude(JsonInclude.Include.NON_NULL) //如果该字段的值是null,就不会转换成JSON
private Long num; //null
3. 复杂java对象转换
1. List：数组
2. Map：对象格式一致
2. JSON转为Java对象
1. 导入jackson的相关jar包
2. 创建Jackson核心对象 ObjectMapper
3. 调用ObjectMapper的相关方法进行转换
1. readValue(json字符串数据,Class)* Ajax的应用:校验用户名是否存在
1. 服务器响应的数据，在客户端使用时，要想当做json数据格式使用。有两种解决方案：
1. $.get(type):将最后一个参数type指定为"json"
2. 在服务器端设置MIME类型
response.setContentType("application/json;charset=utf-8");
//设置跨域请求
response.setHeader("Access-Control-Allow-Origin","*");
2.JSON字符串转换Java对象（使用截取字符串的方法）
测试类：
public class MyTest {
public static void main(String[] args) {
//前台给后台提交的数据，常见的有两种格式
// username=zhangsan&password=123456&age=23
//{"username":"张三","password":"123456"}
//把json字符串转换成java对象
String jsonStr = "{\"username\":\"张三\",\"password\":\"123456\"}";
String s = jsonStr.replaceAll("[{}\"]", "");
System.out.println(s);
String[] strings = s.split(",");
System.out.println(strings[0]);
System.out.println(strings[1]);
String[] a = strings[0].split(":");
System.out.println(a[0]);
System.out.println(a[1]);
String[] b = strings[1].split(":");
System.out.println(b[0]);
System.out.println(b[1]);
User user = new User();
user.setUsername(a[1]);
user.setPasswrod(b[1]);
System.out.println(user);
}
}
User对象：
public class User {
private String username;
private String passwrod;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPasswrod() {
return passwrod;
}
public void setPasswrod(String passwrod) {
this.passwrod = passwrod;
}
@Override
public String toString() {
return "User{" +
"username='" + username + '\'' +
", passwrod='" + passwrod + '\'' +
'}';
}
}
3.java对象转成json字符串（保存到文件）
普通转换（String jsonStr = “{“username”:“张三”,“password”:“123456”}”;）
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
public class MyTest {
public static void main(String[] args) throws IOException {
//Java对象转换成JSON字符串
//String jsonStr = "{\"username\":\"张三\",\"password\":\"123456\"}";
User user = new User("王五", "123456", 20, "18856259632");
Car car = new Car();
car.setCarName("宝马");
car.setCarPrice(888888.0);
//user.setCar(car);
ArrayList<String> list = new ArrayList<>();
list.add("张曼玉");
list.add("王祖贤");
user.setGirlfriend(list);
ObjectMapper mapper = new ObjectMapper();
String jsonStr = mapper.writeValueAsString(user);
System.out.println(jsonStr);
//{"username":"王五","password":"123456","age":20,"phoneNum":"18856259632",car:{carName:"宝马",carPrice:8888},girlfriend:["刘亦菲","张曼玉"]}
//把转好的数据保存到文件中
mapper.writeValue(new File("a.json"), user);
}
}
数组嵌套json（ [{}，{},{}] ）
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
public class MyTest2 {
public static void main(String[] args) throws IOException {
//[{}，{},{}]
User user1 = new User("王五", "12345685", 20, "18856259632");
User user2 = new User("赵六", "12345685", 28, "18856259632");
User user3 = new User("田七", "12345776", 24, "18856259632");
ArrayList<User> list = new ArrayList<>();
list.add(user1);
list.add(user2);
list.add(user3);
ObjectMapper mapper = new ObjectMapper();
String s = mapper.writeValueAsString(list);
System.out.println(s);
//把转好的数据保存到文件中
mapper.writeValue(new File("b.json"), list);
}
}
{“user1”:{},“user2”:{},“user3”:{}}
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
public class MyTest3 {
public static void main(String[] args) throws IOException {
//{"user1":{},"user2":{},"user3":{}}
User user1 = new User("王五", "12345685", 20, "18856259632");
User user2 = new User("赵六", "12345685", 28, "18856259632");
User user3 = new User("田七", "12345776", 24, "18856259632");
HashMap<String, User> hm = new HashMap<>();
hm.put("user1", user1);
hm.put("user2", user2);
hm.put("user3", user3);
ObjectMapper mapper = new ObjectMapper();
String s = mapper.writeValueAsString(hm);
System.out.println(s);
//把转好的数据保存到文件中
mapper.writeValue(new File("c.json"), hm);
}
}
User类和Car类
public class User {
private String username;
private String password;
private int age;
private String phoneNum;
private Car car;
private List<String> girlfriend;
public User() {
}
public User(String username, String password, int age, String phoneNum) {
this.username = username;
this.password = password;
this.age = age;
this.phoneNum = phoneNum;
}
public User(String username, String password, int age, String phoneNum, Car car, List<String> girlfriend) {
this.username = username;
this.password = password;
this.age = age;
this.phoneNum = phoneNum;
this.car = car;
this.girlfriend = girlfriend;
}
public List<String> getGirlfriend() {
return girlfriend;
}
public void setGirlfriend(List<String> girlfriend) {
this.girlfriend = girlfriend;
}
public Car getCar() {
return car;
}
public void setCar(Car car) {
this.car = car;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getPhoneNum() {
return phoneNum;
}
public void setPhoneNum(String phoneNum) {
this.phoneNum = phoneNum;
}
}
public class Car {
private String carName;
private Double carPrice;
public String getCarName() {
return carName;
}
public void setCarName(String carName) {
this.carName = carName;
}
public Double getCarPrice() {
return carPrice;
}
public void setCarPrice(Double carPrice) {
this.carPrice = carPrice;
}
@Override
public String toString() {
return "Car{" +
"carName='" + carName + '\'' +
", carPrice=" + carPrice +
'}';
}
}
4.注解的作用
测试类：
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.Date;
public class MyTest {
public static void main(String[] args) throws JsonProcessingException {
User user = new User();
user.setUsername("zhangsan");
user.setAge(12);
user.setPassword("999999");
user.setPhoneNum("110");
user.setBirthday(new Date());
user.setSal(2000.0);
ObjectMapper mapper = new ObjectMapper();
String s = mapper.writeValueAsString(user);
System.out.println(s);
}
}
User类：
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import java.util.Date;
public class User {
@JsonProperty("name") //指定json字符中键的名称
private String username;
@JsonIgnore//排除某个属性不要转换成JSON,给类的属性上加上这个注解。
private String password;
private int age;
//@JsonIgnore
private String phoneNum;
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
private Date birthday;
@JsonInclude(JsonInclude.Include.NON_NULL)
private Double sal;
public Double getSal() {
return sal;
}
public void setSal(Double sal) {
this.sal = sal;
}
public User() {
}
public User(String username, String password, int age, String phoneNum) {
this.username = username;
this.password = password;
this.age = age;
this.phoneNum = phoneNum;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getPhoneNum() {
return phoneNum;
}
public void setPhoneNum(String phoneNum) {
this.phoneNum = phoneNum;
}
}
5.JSON字符串转换成Java对象
测试类：
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
public class MyTest {
public static void main(String[] args) throws IOException {
String jsonStr = "{\"username\":\"张三\",\"password\":\"123456\"}";
//保证你提供的Java类的属性名和类型以及层级结构和json字符串一一对应即可。
ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(jsonStr, User.class);
System.out.println(user);
}
}
User类：
public class User {
private String username;
private String password;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
@Override
public String toString() {
return "User{" +
"username='" + username + '\'' +
", password='" + password + '\'' +
'}';
}
}
6.复杂的JSON字符串转换成Java对象
Car类：
public class Car {
private String carName;
private Double carPrice;
public String getCarName() {
return carName;
}
public void setCarName(String carName) {
this.carName = carName;
}
public Double getCarPrice() {
return carPrice;
}
public void setCarPrice(Double carPrice) {
this.carPrice = carPrice;
}
@Override
public String toString() {
return "Car{" +
"carName='" + carName + '\'' +
", carPrice=" + carPrice +
'}';
}
}
House类：
public class House {
private String houseName;
private Double housePrice;
public String getHouseName() {
return houseName;
}
public void setHouseName(String houseName) {
this.houseName = houseName;
}
public Double getHousePrice() {
return housePrice;
}
public void setHousePrice(Double housePrice) {
this.housePrice = housePrice;
}
@Override
public String toString() {
return "House{" +
"houseName='" + houseName + '\'' +
", housePrice=" + housePrice +
'}';
}
}
Person类：
import java.util.List;
public class Person {
private String username;
private Integer age;
private Car car;
private List<String> girlfriend;
private List<House> house;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public Car getCar() {
return car;
}
public void setCar(Car car) {
this.car = car;
}
public List<String> getGirlfriend() {
return girlfriend;
}
public void setGirlfriend(List<String> girlfriend) {
this.girlfriend = girlfriend;
}
public List<House> getHouse() {
return house;
}
public void setHouse(List<House> house) {
this.house = house;
}
@Override
public String toString() {
return "Person{" +
"username='" + username + '\'' +
", age=" + age +
", car=" + car +
", girlfriend=" + girlfriend +
", house=" + house +
'}';
}
}
测试类：
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
public class MyTest {
public static void main(String[] args) throws IOException {
//{"username":"王五","age":20,"car":{"carName":"宝马","carPrice":8888},"girlfriend":["刘亦菲","张曼玉"],"house":[{"houseName":"江滨花园",
// "housePrice":50000},
// {"houseName":"巴黎世家","housePrice":150000}]}
String jsonStr = "{\"username\":\"王五\",\"age\":20,\"car\":{\"carName\":\"宝马\",\"carPrice\":8888},\"girlfriend\":[\"刘亦菲\",\"张曼玉\"]," +
"\"house\":[{\"houseName\":\"江滨花园\",\"housePrice\":50000},{\"houseName\":\"巴黎世家\",\"housePrice\":150000}]}";
ObjectMapper mapper = new ObjectMapper();
Person person = mapper.readValue(jsonStr, Person.class);
System.out.println(person);
}
}7.天气JSON字符串转换Java对象
测试类：
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
public class MyTest {
public static void main(String[] args) throws IOException {
String jsonStr = "{\"data\":{\"yesterday\":{\"date\":\"20日星期四\",\"high\":\"高温 2℃\",\"fx\":\"东南风\",\"low\":\"低温 0℃\"," +
"\"fl\":\"<![CDATA[2级]]>\",\"type\":\"霾\"},\"city\":\"商洛\",\"forecast\":[{\"date\":\"21日星期五\",\"high\":\"高温 0℃\"," +
"\"fengli\":\"<![CDATA[2级]]>\",\"low\":\"低温 -1℃\",\"fengxiang\":\"东南风\",\"type\":\"小雪\"},{\"date\":\"22日星期六\",\"high\":\"高温 2℃\"," +
"\"fengli\":\"<![CDATA[1级]]>\",\"low\":\"低温 -1℃\",\"fengxiang\":\"东南风\",\"type\":\"小雪\"},{\"date\":\"23日星期天\",\"high\":\"高温 1℃\"," +
"\"fengli\":\"<![CDATA[1级]]>\",\"low\":\"低温 -2℃\",\"fengxiang\":\"东南风\",\"type\":\"小雪\"},{\"date\":\"24日星期一\",\"high\":\"高温 1℃\"," +
"\"fengli\":\"<![CDATA[1级]]>\",\"low\":\"低温 -4℃\",\"fengxiang\":\"西北风\",\"type\":\"阴\"},{\"date\":\"25日星期二\",\"high\":\"高温 1℃\"," +
"\"fengli\":\"<![CDATA[1级]]>\",\"low\":\"低温 -4℃\",\"fengxiang\":\"北风\",\"type\":\"阴\"}]," +
"\"ganmao\":\"感冒多发期，适当减少外出频率，适量补充水分，适当增减衣物。\",\"wendu\":\"-1\"},\"status\":1000,\"desc\":\"OK\"}";
ObjectMapper mapper = new ObjectMapper();
TianQi tianQi = mapper.readValue(jsonStr, TianQi.class);
String date = tianQi.getData().getYesterday().getDate();
System.out.println(date);
}
}
TianQi类：
@JsonIgnoreProperties(ignoreUnknown = true)
public class TianQi {
/**
* data : {"yesterday":{"date":"20日星期四","high":"高温 2℃","fx":"东南风","low":"低温 0℃","fl":"<![CDATA[2级]]>","type":"霾"},"city":"商洛","forecast":[{
* "date":"21日星期五","high":"高温 0℃","fengli":"<![CDATA[2级]]>","low":"低温 -1℃","fengxiang":"东南风","type":"小雪"},{"date":"22日星期六","high":"高温 2℃",
* "fengli":"<![CDATA[1级]]>","low":"低温 -1℃","fengxiang":"东南风","type":"小雪"},{"date":"23日星期天","high":"高温 1℃","fengli":"<![CDATA[1级]]>","low":"低温
* -2℃","fengxiang":"东南风","type":"小雪"},{"date":"24日星期一","high":"高温 1℃","fengli":"<![CDATA[1级]]>","low":"低温 -4℃","fengxiang":"西北风","type":"阴"},{
* "date":"25日星期二","high":"高温 1℃","fengli":"<![CDATA[1级]]>","low":"低温 -4℃","fengxiang":"北风","type":"阴"}],"ganmao
* ":"感冒多发期，适当减少外出频率，适量补充水分，适当增减衣物。","wendu":"-1"}
* status : 1000
* desc : OK
*/
private DataBean data;
private int status;
private String desc;
public DataBean getData() {
return data;
}
public void setData(DataBean data) {
this.data = data;
}
public int getStatus() {
return status;
}
public void setStatus(int status) {
this.status = status;
}
public String getDesc() {
return desc;
}
public void setDesc(String desc) {
this.desc = desc;
}
@JsonIgnoreProperties(ignoreUnknown = true)
public static class DataBean {
/**
* yesterday : {"date":"20日星期四","high":"高温 2℃","fx":"东南风","low":"低温 0℃","fl":"<![CDATA[2级]]>","type":"霾"}
* city : 商洛
* forecast : [{"date":"21日星期五","high":"高温 0℃","fengli":"<![CDATA[2级]]>","low":"低温 -1℃","fengxiang":"东南风","type":"小雪"},{"date":"22日星期六",
* "high":"高温 2℃","fengli":"<![CDATA[1级]]>","low":"低温 -1℃","fengxiang":"东南风","type":"小雪"},{"date":"23日星期天","high":"高温 1℃",
* "fengli":"<![CDATA[1级]]>","low":"低温 -2℃","fengxiang":"东南风","type":"小雪"},{"date":"24日星期一","high":"高温 1℃","fengli":"<![CDATA[1级]]>",
* "low":"低温 -4℃","fengxiang":"西北风","type":"阴"},{"date":"25日星期二","high":"高温 1℃","fengli":"<![CDATA[1级]]>","low":"低温 -4℃","fengxiang":"北风",
* "type":"阴"}]
* ganmao : 感冒多发期，适当减少外出频率，适量补充水分，适当增减衣物。
* wendu : -1
*/
private YesterdayBean yesterday;
private String city;
private String ganmao;
private String wendu;
private List<ForecastBean> forecast;
public YesterdayBean getYesterday() {
return yesterday;
}
public void setYesterday(YesterdayBean yesterday) {
this.yesterday = yesterday;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getGanmao() {
return ganmao;
}
public void setGanmao(String ganmao) {
this.ganmao = ganmao;
}
public String getWendu() {
return wendu;
}
public void setWendu(String wendu) {
this.wendu = wendu;
}
public List<ForecastBean> getForecast() {
return forecast;
}
public void setForecast(List<ForecastBean> forecast) {
this.forecast = forecast;
}
@JsonIgnoreProperties(ignoreUnknown = true)
public static class YesterdayBean {
/**
* date : 20日星期四
* high : 高温 2℃
* fx : 东南风
* low : 低温 0℃
* fl : <![CDATA[2级]]>
* type : 霾
*/
private String date;
private String high;
private String fx;
private String low;
private String fl;
private String type;
public String getDate() {
return date;
}
public void setDate(String date) {
this.date = date;
}
public String getHigh() {
return high;
}
public void setHigh(String high) {
this.high = high;
}
public String getFx() {
return fx;
}
public void setFx(String fx) {
this.fx = fx;
}
public String getLow() {
return low;
}
public void setLow(String low) {
this.low = low;
}
public String getFl() {
return fl;
}
public void setFl(String fl) {
this.fl = fl;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
}
@JsonIgnoreProperties(ignoreUnknown = true)
public static class ForecastBean {
/**
* date : 21日星期五
* high : 高温 0℃
* fengli : <![CDATA[2级]]>
* low : 低温 -1℃
* fengxiang : 东南风
* type : 小雪
*/
private String date;
private String high;
private String fengli;
private String low;
private String fengxiang;
private String type;
public String getDate() {
return date;
}
public void setDate(String date) {
this.date = date;
}
public String getHigh() {
return high;
}
public void setHigh(String high) {
this.high = high;
}
public String getFengli() {
return fengli;
}
public void setFengli(String fengli) {
this.fengli = fengli;
}
public String getLow() {
return low;
}
public void setLow(String low) {
this.low = low;
}
public String getFengxiang() {
return fengxiang;
}
public void setFengxiang(String fengxiang) {
this.fengxiang = fengxiang;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
}
}
}
总结：创建一个天气类，给IDEA中安装一个GsonFormat插件，就可以将复杂的JSON字符串转换成Java对象
之后在新建类的页面，鼠标右键单击打开Generate，进去之后找到GsonFormat选项，进去之后把需要转换的JSON字符串粘贴进去，会自动生成我们想要的Java对象
进去之后点击左下角setting按键，设置好所用的jar包
最后就会将JSON字符串自动转换成一个Java对象了。
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