Jackson介绍及使用-CFANZ编程社区

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

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

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;
    }
}