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","*");
1.普通截取字符串方法将JSON字符串转换成Java对象
主方法MyTest
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);
}
}
对象User
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 + ''' +
'}';
}
}
2.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 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 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 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);
}
}
所用到的car类和user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 +
'}';
}
}
import java.util.List;
public class User {
private String username;
private String password;
private int age;
private String phoneNum;
private Car car;
private List 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 girlfriend) {
this.username = username;
this.password = password;
this.age = age;
this.phoneNum = phoneNum;
this.car = car;
this.girlfriend = girlfriend;
}
public List getGirlfriend() {
return girlfriend;
}
public void setGirlfriend(List 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;
}
}
3.Java对象转换成json字符串
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);
}
}
4.JSON字符串转换成Java对象
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);
}
}
5.复杂的JSON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 girlfriend;
private List 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 getGirlfriend() {
return girlfriend;
}
public void setGirlfriend(List girlfriend) {
this.girlfriend = girlfriend;
}
public List getHouse() {
return house;
}
public void setHouse(List house) {
this.house = house;
}
@Override
public String toString() {
return "Person{" +
"username='" + username + ''' +
", age=" + age +
", car=" + car +
", girlfriend=" + girlfriend +
", house=" + house +
'}';
}
}
最终测试类MyTest
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);
}
}
天气JSON转换Java对象
public class MyTest {
public static void main(String[] args) {
String jsonStr = "{"data":{"yesterday":{"date":"20日星期四","high":"高温 2℃","fx":"东南风","low":"低温 0℃"," +
""fl":"","type":"霾"},"city":"商洛","forecast":[{"date":"21日星期五","high":"高温 0℃"," +
""fengli":"","low":"低温 -1℃","fengxiang":"东南风","type":"小雪"},{"date":"22日星期六","high":"高温 2℃"," +
""fengli":"","low":"低温 -1℃","fengxiang":"东南风","type":"小雪"},{"date":"23日星期天","high":"高温 1℃"," +
""fengli":"","low":"低温 -2℃","fengxiang":"东南风","type":"小雪"},{"date":"24日星期一","high":"高温 1℃"," +
""fengli":"","low":"低温 -4℃","fengxiang":"西北风","type":"阴"},{"date":"25日星期二","high":"高温 1℃"," +
""fengli":"","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"}";
}
}
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
这样子就会将JSON字符串自动转换成一个Java对象了。
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