一、在java开发中常用的json解析方式有jackson、fastjson、gson、net.sf.json。
1、jackson
jackson为用来序列化和反序列化json的java的开源框架，spring mvc默认的json解析器就是jackson。
com.fasterxml.jackson.core jackson-databind2.13.1
public static void main(String[] args) throws JsonProcessingException {
String json1 = "{"id":1,"name":"first","stus":[{"id":101,"name":"刘一","age":16}]}";
String json2 = "["北京","天津","杭州"]";
ObjectMapper objectMapper = new ObjectMapper();
Grade grade = objectMapper.readValue(json1, Grade.class);
System.out.println(grade);
List list = objectMapper.readValue(json2, new TypeReference>() {});
System.out.println(list);
ArrayList students = new ArrayList<>();
for (int i = 0; i < 3; i++) {
students.add(new Student(100 + i, "大哥" + i, 1000 + i));
}
Grade grade2 = new Grade(22, "first", students);
ObjectMapper objectMapper2 = new ObjectMapper();
String json = objectMapper2.writevalueAsString(grade2);
System.out.println(json);
}
2、fastjson
fastjson是阿里系产品，效率最高。
com.alibaba fastjson1.2.47
public static void main(String[] args) {
String json1 = "{'id':1,'name':'first','stus':[{'id':101,'name':'刘铭','age':16}]}";
String json2 = "['北京','天津','杭州']";
Grade grade = JSON.parseObject(json1, Grade.class);
System.out.println(grade);
List list = JSON.parseArray(json2, String.class);
System.out.println(list);
ArrayList list2 = new ArrayList<>();
for (int i = 1; i < 3; i++) {
list2.add(new Student(101 + i, "大哥", 20 + i));
}
Grade grade2 = new Grade(100001, "first", list2);
String json = JSON.toJSonString(grade);
System.out.println(json);
}
3、gson
gson是谷歌产品，也很好用
com.google.code.gson gson2.8.9
public static void main(String[] args) {
String json1 = "{'id':1,'name':'first','stus':[{'id':101,'name':'刘一','age':16}]}";
String json2 = "['北京','天津','杭州']";
Gson gson = new Gson();
Grade grade = gson.fromJson(json1, Grade.class);
System.out.println(grade);
ArrayList list = gson.fromJson(json2, new TypeToken>() {}.getType());
System.out.println(list);
ArrayList list2 = new ArrayList<>();
for (int i = 1; i < 3; i++) {
list2.add(new Student(101 + i, "大哥", 20 + i));
}
Grade grade2 = new Grade(100001, "first", list2);
Gson gson2 = new Gson();
String json = gson2.toJson(grade2);
System.out.println(json);
}
4、net.sf.json
json官方解析工具，最具有通用性。
net.sf.json-lib json-lib2.4 jdk15
public static void main(String[] args) {
String json = "{'id':1,'name':'first','stus':[{'id':101,'name':'刘一','age':16},{'id':102,'name':'刘二','age':23}]}";
JSonObject jsonObject = JSONObject.fromObject(json);
System.out.println(jsonObject);
Map map = jsonObject;
for (Map.Entry entry : map.entrySet()) {
System.out.println(entry.getKey() + ": " + entry.getValue());
}
Grade grade = new Grade();
grade.setId(jsonObject.getInt("id"));
grade.setName(jsonObject.getString("name"));
ArrayList students = new ArrayList<>();
grade.setStus(students);
JSonArray stus = jsonObject.getJSonArray("stus");
for (Object o : stus) {
JSonObject jsonObject1 = JSONObject.fromObject(o);
Student student = new Student(jsonObject1.getInt("id"), jsonObject1.getString("name"), jsonObject1.getInt("age"));
grade.getStus().add(student);
}
System.out.println("grade: " + grade);
JSonObject jsonObject2 = new JSonObject();
jsonObject2.put("id", 100);
jsonObject2.put("name", "大哥");
jsonObject2.put("age", 30);
JSonObject jsonObject3 = new JSonObject();
jsonObject3.put("id", 102);
jsonObject3.put("name", "二哥");
jsonObject3.put("age", 10);
JSonArray jsonArray = new JSonArray();
jsonArray.add(jsonObject2);
jsonArray.add(jsonObject3);
System.out.println("jsonArray: " + jsonArray);
}
二、在springboot开发中返回json的方式有jackson、gson、fastjson。
json是目前主流的前后端数据传输方式，轻量级的数据交换格式。
1、jackson
springboot工程添加web依赖时默认提供了jackson组件，不需添加额外的依赖。
实例
public class UserVO extends baseVO {
private static final long serialVersionUID = 1L;
private long id;
private String userName;
private String name;
...
@JsonFormat(pattern = "yyyy-MM-dd hh:mm:ss", timezone = "GMT+8")
private Date createTime;
...
}
在实体类的属性上添加 @JsonFormat 注解可以实现时间类型的自定义格式。
@RequestMapping(value = "/getUserPage", method = RequestMethod.POST)
public Object getUserPage(@RequestBody UserDTO params) throws ParamException {
...
PageData> result = ***;
return ResponseData.ok(result, "查询成功！");
}
JSON的解析离不开 HttpMessageConvert接口，HttpMessageConvert是一个消息转换工具，主要有两方面的功能：将服务端返回的对象序列化成JSON字符串；将前端传来的JSON字符串反序列化成Java对象。
自定义MappingJackson2HttpMessageConverter类，删除 @JsonFormat注解，新建一个配置类
@Configuration
public class WebMVCConfig {
@Bean
MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter(){
MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd"));
converter.setObjectMapper(objectMapper);
return converter;
}
}
或自定义ObjectMapper类
@Configuration
public class WebMVCConfig {
@Bean
ObjectMapper objectMapper(){
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd"));
return objectMapper;
}
}
两种自定义的作用的是一样的。
2、gson
gson也在springboot工程中提供了自动化配置的，需要去掉spring-boot-starter-json依赖，然后引入gson依赖。
org.springframework.boot spring-boot-starter-weborg.springframework.boot spring-boot-starter-jsoncom.google.code.gson gson
自定义GsonHttpMessageConverter类
@Configuration
public class WebMVCConfig {
@Bean
GsonHttpMessageConverter gsonHttpMessageConverter(){
GsonHttpMessageConverter converter=new GsonHttpMessageConverter();
converter.setGson(new GsonBuilder().setDateFormat("yyyy-MM-dd").create());
return converter;
}
}
或自定义Gson类
@Configuration
public class WebMVCConfig {
@Bean
Gson gson() {
return new GsonBuilder().setDateFormat("yyyy-MM-dd").create();
}
}
3、fastjson
fastjson是阿里系的开源框架，需要引入第三方的依赖。
org.springframework.boot spring-boot-starter-weborg.springframework.boot spring-boot-starter-jsoncom.alibaba fastjson1.2.74
因为 SpringBoot没有提供相关的自动化配置类，所以我们需要手动创建 FastJson的消息转换工具类。
@Configuration
public class WebMVCConfig {
@Bean
FastJsonHttpMessageConverter fastJsonHttpMessageConverter() {
FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
FastJsonConfig config = new FastJsonConfig();
config.setDateFormat("yyyy-MM-dd HH:mm:ss");
config.setCharset(Charset.forName("UTF-8"));
config.setSerializerFeatures(
SerializerFeature.WriteClassName,
SerializerFeature.WriteMapNullValue,
SerializerFeature.PrettyFormat,
SerializerFeature.WriteNullListAsEmpty,
SerializerFeature.WriteNullStringAsEmpty
);
converter.setFastJsonConfig(config);
return converter;
}
}
注意，不同的json解析组件对数据的处理是不一样的，如null或空值或时间的显示处理。
