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测试数据/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测试数据/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测试数据/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://HdhCmsTestw3.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_context

2.controller类

Java对象转换为json对象

@Controller public class Json Controller {   @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 ; } }

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

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