将java对象转换为json对象，市面上有很多第三方jar包，如下：
jackson(最常用)
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.11.2</version>
</dependency>
gson
<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.8.5</version>
</dependency>fastjson
<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.62</version>
</dependency>一、构建测试项目
开发工具为：IDEA
后端技术：Spring boot ，Maven
引入依赖
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.4.3</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>json</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>json</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
</project>
可以从上面看出，并未引入Jackson相关依赖，这是因为Spring boot的起步依赖spring-boot-starter-web 已经为我们传递依赖了Jackson JSON库。
当我们不用它，而采用其他第三方jar包时，我们可以排除掉它的依赖，可以为我们的项目瘦身。
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<artifactId>jackson-core</artifactId>
<groupId>com.fasterxml.jackson.core</groupId>
</exclusion>
</exclusions>
</dependency>二、jackson转换
1.构建User实体类
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@NoArgsConstructor
@AllArgsConstructor
public class UserEntity {
private String userName;
private int age;
private String sex;
}
代码如下（示例）：
import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns
import warnings
warnings.filterwarnings('ignore')
import ssl
ssl._create_default_https_context = ssl._create_unverified_context2.controller类
Java对象转换为json对象
@Controller
public class JsonController {
@GetMapping("/json1")
//思考问题，正常返回它会走视图解析器，而json需要返回的是一个字符串
//市面上有很多的第三方jar包可以实现这个功能，jackson，只需要一个简单的注解就可以实现了
//@ResponseBody，将服务器端返回的对象转换为json对象响应回去
@ResponseBody
public String json1() throws JsonProcessingException {
//需要一个jackson的对象映射器，就是一个类，使用它可以将对象直接转换成json字符串
ObjectMapper mapper = new ObjectMapper();
//创建对象
UserEntity userEntity = new UserEntity("笨笨熊", 18, "男");
System.out.println(userEntity);
//将java对象转换为json字符串
String str = mapper.writeValueAsString(userEntity);
System.out.println(str);
//由于使用了@ResponseBody注解，这里会将str以json格式的字符串返回。
return str;
}
@GetMapping("/json2")
@ResponseBody
public String json2() throws JsonProcessingException {
ArrayList<UserEntity> userEntities = new ArrayList<>();
UserEntity user1 = new UserEntity("笨笨熊", 18, "男");
UserEntity user2 = new UserEntity("笨笨熊", 18, "男");
UserEntity user3 = new UserEntity("笨笨熊", 18, "男");
userEntities.add(user1);
userEntities.add(user2);
userEntities.add(user3);
return new ObjectMapper().writeValueAsString(userEntities);
}
}Date对象转换为json对象
@GetMapping("/json3")
@ResponseBody
public String json3() throws JsonProcessingException {
ObjectMapper mapper = new ObjectMapper();
//Date默认返回时间戳，所以需要关闭它的时间戳功能
mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
//时间格式化问题 自定义时间格式对象
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
//让mapper指定时间日期格式为simpleDateFormat
mapper.setDateFormat(simpleDateFormat);
//写一个时间对象
Date date = new Date();
return mapper.writeValueAsString(date);
}提取工具类JsonUtils
public class JsonUtils {
public static String getJson(Object object){
return getJson(object,"yyyy-MM-dd HH:mm:ss");
}
public static String getJson(Object object,String dateFormat) {
ObjectMapper mapper = new ObjectMapper();
//Date默认返回时间戳，所以需要关闭它的时间戳功能
mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
//时间格式化问题 自定义时间格式对象
SimpleDateFormat simpleDateFormat = new SimpleDateFormat(dateFormat);
//让mapper指定时间日期格式为simpleDateFormat
mapper.setDateFormat(simpleDateFormat);
try{
return mapper.writeValueAsString(object);
}catch (JsonProcessingException e){
e.printStackTrace();
}
return null;
}
}优化后：
@GetMapping("/json4")
@ResponseBody
public String json4() throws JsonProcessingException {
Date date = new Date();
return JsonUtils.getJson(date);
}三、gson转换
- 引入上述gson依赖
- Controller类
@RestController
public class gsonController {
@GetMapping("/gson1")
public String json1() throws JsonProcessingException {
ArrayList<UserEntity> userEntities = new ArrayList<>();
UserEntity user1 = new UserEntity("笨笨熊", 18, "男");
UserEntity user2 = new UserEntity("笨笨熊", 18, "男");
UserEntity user3 = new UserEntity("笨笨熊", 18, "男");
userEntities.add(user1);
userEntities.add(user2);
userEntities.add(user3);
Gson gson = new Gson();
String str = gson.toJson(userEntities);
return str;
}
}四、fastjson转换
- 引入相关依赖
- Controller类
@RestController
public class FastJsonController {
@GetMapping("/fastjson1")
public String json1() throws JsonProcessingException {
ArrayList<UserEntity> userEntities = new ArrayList<>();
UserEntity user1 = new UserEntity("笨笨熊", 18, "男");
UserEntity user2 = new UserEntity("笨笨熊", 18, "男");
UserEntity user3 = new UserEntity("笨笨熊", 18, "男");
userEntities.add(user1);
userEntities.add(user2);
userEntities.add(user3);
String str = JSON.toJSONString(userEntities);
return str;
}
}
