使用spring boot开发时java对象和Json对象转换的问题

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)

1. <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
2. <dependency>
3. <groupId>com.fasterxml.jackson.core</groupId>
4. <artifactId>jackson-databind</artifactId>
5. <version>2.11.2</version>
6. </dependency>

gson

1. <!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
2. <dependency>
3. <groupId>com.google.code.gson</groupId>
4. <artifactId>gson</artifactId>
5. <version>2.8.5</version>
6. </dependency>

fastjson

1. <!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
2. <dependency>
3. <groupId>com.alibaba</groupId>
4. <artifactId>fastjson</artifactId>
5. <version>1.2.62</version>
6. </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

1. <?xml version="1.0" encoding="UTF-8"?>
2. <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
3. xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
4. <modelVersion>4.0.0</modelVersion>
5. <parent>
6. <groupId>org.springframework.boot</groupId>
7. <artifactId>spring-boot-starter-parent</artifactId>
8. <version>2.4.3</version>
9. <relativePath/> <!-- lookup parent from repository -->
10. </parent>
11. <groupId>com.example</groupId>
12. <artifactId>json</artifactId>
13. <version>0.0.1-SNAPSHOT</version>
14. <name>json</name>
15. <description>Demo project for Spring Boot</description>
16. <properties>
17. <java.version>1.8</java.version>
18. </properties>
19. <dependencies>
20. <dependency>
21. <groupId>org.springframework.boot</groupId>
22. <artifactId>spring-boot-starter-thymeleaf</artifactId>
23. </dependency>
24. <dependency>
25. <groupId>org.springframework.boot</groupId>
26. <artifactId>spring-boot-starter-web</artifactId>
27. </dependency>
28.  
29. <dependency>
30. <groupId>org.projectlombok</groupId>
31. <artifactId>lombok</artifactId>
32. <optional>true</optional>
33. </dependency>
34. <dependency>
35. <groupId>org.springframework.boot</groupId>
36. <artifactId>spring-boot-starter-test</artifactId>
37. <scope>test</scope>
38. </dependency>
39. </dependencies>
40.  
41. <build>
42. <plugins>
43. <plugin>
44. <groupId>org.springframework.boot</groupId>
45. <artifactId>spring-boot-maven-plugin</artifactId>
46. <configuration>
47. <excludes>
48. <exclude>
49. <groupId>org.projectlombok</groupId>
50. <artifactId>lombok</artifactId>
51. </exclude>
52. </excludes>
53. </configuration>
54. </plugin>
55. </plugins>
56. </build>
57.  
58. </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。

1. <dependency>
2. <groupId>org.springframework.boot</groupId>
3. <artifactId>spring-boot-starter-web</artifactId>
4. <exclusions>
5. <exclusion>
6. <artifactId>jackson-core</artifactId>
7. <groupId>com.fasterxml.jackson.core</groupId>
8. </exclusion>
9. </exclusions>
10. </dependency>

二、jackson转换

1.构建User实体类

1. import lombok.AllArgsConstructor;
2. import lombok.Data;
3. import lombok.NoArgsConstructor;
4.  
5. @Data
6. @NoArgsConstructor
7. @AllArgsConstructor
8. public class UserEntity {
9.  
10. private String userName;
11.  
12. private int age;
13.  
14. private String sex;
15.  
16. }

代码如下（示例）：

1. import numpy as np
2. import pandas as pd
3. import matplotlib.pyplot as plt
4. import seaborn as sns
5. import warnings
6. warnings.filterwarnings('ignore')
7. import ssl
8. ssl._create_default_https_context = ssl._create_unverified_context

2.controller类

Java对象转换为json对象

1. @Controller
2. public class JsonController {
3.  
4. @GetMapping("/json1")
5. //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
6. //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
7. //@ResponseBody，将服务器端返回的对象转换为json对象响应回去
8. @ResponseBody
9. public String json1() throws JsonProcessingException {
10. //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
11. ObjectMapper mapper = new ObjectMapper();
12. //创建对象
13. UserEntity userEntity = new UserEntity("笨笨熊", 18, "男");
14. System.out.println(userEntity);
15. //将java对象转换为json字符串
16. String str = mapper.writeValueAsString(userEntity);
17. System.out.println(str);
18. //由于使用了@ResponseBody注解，这里会将str以json格式的字符串返回。
19. return str;
20. }
21.  
22. @GetMapping("/json2")
23. @ResponseBody
24. public String json2() throws JsonProcessingException {
25.  
26. ArrayList<UserEntity> userEntities = new ArrayList<>();
27.  
28. UserEntity user1 = new UserEntity("笨笨熊", 18, "男");
29. UserEntity user2 = new UserEntity("笨笨熊", 18, "男");
30. UserEntity user3 = new UserEntity("笨笨熊", 18, "男");
31.  
32. userEntities.add(user1);
33. userEntities.add(user2);
34. userEntities.add(user3);
35.  
36. return new ObjectMapper().writeValueAsString(userEntities);
37. }
38. }

Date对象转换为json对象

1. @GetMapping("/json3")
2. @ResponseBody
3. public String json3() throws JsonProcessingException {
4. ObjectMapper mapper = new ObjectMapper();
5. //Date默认返回时间戳，所以需要关闭它的时间戳功能
6. mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
7. //时间格式化问题 自定义时间格式对象
8. SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
9. //让mapper指定时间日期格式为simpleDateFormat
10. mapper.setDateFormat(simpleDateFormat);
11. //写一个时间对象
12. Date date = new Date();
13. return mapper.writeValueAsString(date);
14.  
15. }

提取工具类JsonUtils

1. public class JsonUtils {
2.  
3. public static String getJson(Object object){
4. return getJson(object,"yyyy-MM-dd HH:mm:ss");
5. }
6. public static String getJson(Object object,String dateFormat) {
7. ObjectMapper mapper = new ObjectMapper();
8. //Date默认返回时间戳，所以需要关闭它的时间戳功能
9. mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
10. //时间格式化问题 自定义时间格式对象
11. SimpleDateFormat simpleDateFormat = new SimpleDateFormat(dateFormat);
12. //让mapper指定时间日期格式为simpleDateFormat
13. mapper.setDateFormat(simpleDateFormat);
14. try{
15. return mapper.writeValueAsString(object);
16. }catch (JsonProcessingException e){
17. e.printStackTrace();
18. }
19. return null;
20. }
21. }

优化后：

1. @GetMapping("/json4")
2. @ResponseBody
3. public String json4() throws JsonProcessingException {
4. Date date = new Date();
5. return JsonUtils.getJson(date);
6.  
7. }

三、gson转换

引入上述gson依赖

Controller类

1. @RestController
2. public class gsonController {
3. @GetMapping("/gson1")
4. public String json1() throws JsonProcessingException {
5.  
6. ArrayList<UserEntity> userEntities = new ArrayList<>();
7.  
8. UserEntity user1 = new UserEntity("笨笨熊", 18, "男");
9. UserEntity user2 = new UserEntity("笨笨熊", 18, "男");
10. UserEntity user3 = new UserEntity("笨笨熊", 18, "男");
11.  
12. userEntities.add(user1);
13. userEntities.add(user2);
14. userEntities.add(user3);
15.  
16. Gson gson = new Gson();
17. String str = gson.toJson(userEntities);
18.  
19. return str;
20. }
21. }

四、fastjson转换

引入相关依赖

Controller类

1. @RestController
2. public class FastJsonController {
3. @GetMapping("/fastjson1")
4. public String json1() throws JsonProcessingException {
5.  
6. ArrayList<UserEntity> userEntities = new ArrayList<>();
7.  
8. UserEntity user1 = new UserEntity("笨笨熊", 18, "男");
9. UserEntity user2 = new UserEntity("笨笨熊", 18, "男");
10. UserEntity user3 = new UserEntity("笨笨熊", 18, "男");
11.  
12. userEntities.add(user1);
13. userEntities.add(user2);
14. userEntities.add(user3);
15.  
16. String str = JSON.toJSONString(userEntities);
17.  
18. return str;
19. }
20. }

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原文链接：https://blog.csdn.net/BBQ__ZXB/article/details/114264184