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)

<!-- 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@AllArgsConstructorpublic class UserEntity { private String userName; private int age; private String sex; }

代码如下（示例）：

import numpy as npimport pandas as pdimport matplotlib.pyplot as pltimport seaborn as snsimport warningswarnings.filterwarnings(’ignore’)import sslssl._create_default_https_context = ssl._create_unverified_context2.controller类

Java对象转换为json对象

@Controllerpublic 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

@RestControllerpublic 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

@RestControllerpublic 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; }}

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