Jackson介绍及使用

墨蓝 2024-03-30 17:54 72阅读 0赞

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**目录**

一、介绍

1. 简介

2. Jackson的三个核心模块

二、实际应用

1. 案例一

三、总结

--------------------

## 一、介绍 ##

### 1. 简介 ###

Jackson是一个简单的、功能强大的、基于Java的应用库。它可以很方便完成Java对象和Json对象(xml文档or其它格式）进行互转。也是Spring家族的默认JSON/XML解析器。

### 2. Jackson的三个核心模块 ###

(1) jackson-core:定义了低级的流式API，包括了JSON处理细节。  
(2) jackson-annotations:包含了Jackson的注解。  
(3) jackson-databind:实现了对象和JSON之间的转换，这个包依赖上面两个包。

> 不怎么了解JSON的同学：[JSON介绍][JSON]

## 二、实际应用 ##

### 1. 案例一 ###

> 在我们编写的接口中，经常会有一些冗余字段没有赋值，如果有非常多的冗余字段都为null，不仅给调试接口带来的不必要的麻烦，也占用了资源。

(1) 场景：

接口调用方要求我们提供的createAccount接口，如果接口调用异常响应：错误编码和信息。成功响应新增的账号信息。

(2) 代码：[git地址][git]

a. pom.xml

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
        <version>2.7.5</version>
    </dependency>

b. Controller代码

import com.wxy.common.exception.BusinessException;
    import org.springframework.web.bind.annotation.PostMapping;
    import org.springframework.web.bind.annotation.RequestBody;
    import org.springframework.web.bind.annotation.RestController;
    
    import java.time.LocalDateTime;
    
    /**
     * JacksonAccountController
     *
     * @author wxy
     * @since 2023-01-23
     */
    @RestController
    public class JacksonAccountController {
        /**
         * 创建账号
         *
         * @param accountVo accountVo
         * @return JacksonRsp<AccountVo>
         */
        @PostMapping("/accounts")
        public JacksonRsp<AccountVO> create(@RequestBody AccountVO accountVo) {
            JacksonRsp<AccountVO> jacksonRsp = new JacksonRsp<>();
            try {
                jacksonRsp.setResult(createAccount(accountVo, true));
            } catch (Exception e) {
                jacksonRsp.setCode("CreateAccountError");
                jacksonRsp.setMessage(e.getMessage());
            }
    
            return jacksonRsp;
        }
    
        /**
         * 创建账号
         *
         * @param accountVo 账号实体
         * @param flag      是否正常执行
         * @return AccountVo
         */
        private AccountVO createAccount(AccountVO accountVo, boolean flag) {
            if (flag) {
                // 创建账号成功
                accountVo.setCreateTime(LocalDateTime.now());
                return accountVo;
            } else {
                // 创建失败 抛出异常
                throw new BusinessException("create account error");
            }
        }
    }

c. VO代码

import java.time.LocalDateTime;
    
    /**
     * AccountVo
     *
     * @author wxy
     * @since 2023-01-23
     */
    public class AccountVO {
        private String id;
    
        private String name;
    
        private String desc;
    
        private LocalDateTime createTime;
    
        public String getId() {
            return id;
        }
    
        public void setId(String id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getDesc() {
            return desc;
        }
    
        public void setDesc(String desc) {
            this.desc = desc;
        }
    
        public LocalDateTime getCreateTime() {
            return createTime;
        }
    
        public void setCreateTime(LocalDateTime createTime) {
            this.createTime = createTime;
        }
    }

d. JacksonRsp代码

/**
     * JacksonRsp
     *
     * @param <T> 结果类型
     * @author wxy
     * @since 2023-01-23
     */
    public class JacksonRsp<T> {
        /**
         * 编码
         */
        private String code;
    
        /**
         * 错误信息
         */
        private String message;
    
        /**
         * 响应结果
         */
        private T result;
    
        public String getCode() {
            return code;
        }
    
        public void setCode(String code) {
            this.code = code;
        }
    
        public String getMessage() {
            return message;
        }
    
        public void setMessage(String message) {
            this.message = message;
        }
    
        public T getResult() {
            return result;
        }
    
        public void setResult(T result) {
            this.result = result;
        }
    }

> 正常响应结果(响应有null值)：
> 
> \{
> 
> "code": null,
> 
> "message": null,
> 
> "result": \{
> 
> "id": "account\_01",
> 
> "name": "账号01",
> 
> "desc": "this is account",
> 
> "createTime": "2023-01-23T16:12:24.6055759"
> 
> \}
> 
> \}
> 
> 异常响应结果：
> 
> \{
> 
> "code": "CreateAccountError",
> 
> "message": "create account error",
> 
> "result": null
> 
> \}

d. JacksonConfig

import com.fasterxml.jackson.annotation.JsonInclude;
    import com.fasterxml.jackson.core.JsonGenerator;
    import com.fasterxml.jackson.databind.JsonSerializer;
    import com.fasterxml.jackson.databind.ObjectMapper;
    import com.fasterxml.jackson.databind.SerializerProvider;
    import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.context.annotation.Primary;
    import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
    
    import java.io.IOException;
    
    /**
     * JacksonConfig
     *
     * @author wxy
     * @since 2022-01-23
     */
    @Configuration
    public class JacksonConfig {
        @Bean
        @Primary
        @ConditionalOnMissingBean(ObjectMapper.class)
        public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
            ObjectMapper objectMapper = builder.createXmlMapper(false).build();
            // 屏蔽掉值为null的参数
            objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
    
            /// 修改值为null的参数值(需要处理打开方法并修改逻辑)
            /*objectMapper.getSerializerProvider()
                    .setNullValueSerializer(new JsonSerializer<>() {
                @Override
                public void serialize(Object o, JsonGenerator jsonGenerator,
                                      SerializerProvider serializerProvider) throws IOException {
                    jsonGenerator.writeString("");
                }
            });*/
            return objectMapper;
        }
    }

> 正常响应结果(增加JacksonConfig，响应无null值)：
> 
> \{
> 
> "result": \{
> 
> "id": "account\_01",
> 
> "name": "账号01",
> 
> "desc": "this is account",
> 
> "createTime": "2023-01-23T17:52:55.7194902"
> 
> \}
> 
> \}
> 
> 异常响应结果：
> 
> \{
> 
> "code": "CreateAccountError",
> 
> "message": "create account error"
> 
> \}

## 三、总结 ##

Jackson的使用方式还有很多，感兴趣可以网上搜索。去除响应JSON中为null的参数也有很多做法，例如：[面向对象根据不同场景返回不同响应体(关注案例三)][Link 1]

**参考文章：**

1. [Jackson介绍][Jackson]

[Mr.]: https://blog.csdn.net/qq_45871274/article/details/129162237?spm=1001.2014.3001.5502
[JSON]: https://baike.baidu.com/item/JSON/2462549
[git]: https://gitee.com/xy_wang/this-project/tree/develop/learn/src/main/java/com/wxy/learn/jackson
[Link 1]: https://blog.csdn.net/qq_45871274/article/details/128507171?spm=1001.2014.3001.5501
[Jackson]: http://www.dubby.cn/detail.html?id=9068