Springboot中解析JSON字符串(jackson库ObjectMapper解析JSON字符串)

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#spring boot #jackson #解析json字符串

于 2023-11-07 21:04:35 首次发布

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1、ObjectMapper与JSONObject比较

1、ObjectMapper属于jackson库的一部分,JSONObject属于alibaba的fastjson，两者各有优劣，可根据自己的系统环境选择使用哪种技术。

2、目前来看，Jackson社区相对活跃，Spring MVC和Spring Boot都默认使用Jackson。

核心主要有三个部分：

jackson-core(核心包)、jackson-databind(数据绑定包)、jackson-annotations(注解包)

3、依赖包不同

//JSONObject依赖包

<dependency>

    <groupId>com.alibaba.fastjson2</groupId>

    <artifactId>fastjson2</artifactId>

    <version>2.0.42</version>

</dependency>

//ObjectMapper依赖包

<dependency>

    <groupId>com.fasterxml.jackson.core</groupId>

    <artifactId>jackson-databind</artifactId>

    <version>2.14.2</version>

</dependency>

2、ObjectMapper使用概述

ObjectMapper通过writeValue()实现序列化，通过readValue()实现反序列化。

ObjectMapper通过Feature枚举类，初始化了很多的默认配置。

2.1、工程的pom.xml导包信息

spring-boot-starter-web包中包含了jackson包，不需要单独导入

<?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>2.7.17</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.txc</groupId>
    <artifactId>objectmapper</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>objectmapper</name>
    <description>objectmapper</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <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>

2.2、创建案例中的测试对象

案例中使用lombok注解生成get和set方法，也可以直接写get和set方法

@Setter
@Getter
@AllArgsConstructor
@NoArgsConstructor
@ToString
public class Student {
    private String stu_id;
    private String stu_name;
}

2.3、对象和JSON相互转化

2.3.1、测试代码

/**
 * 实现对象和JSON之间互转
 */
@RequestMapping("/jsonObjectChange")
@ResponseBody
public  void  jsonObjectChange() throws Exception{
    ObjectMapper mapper = new ObjectMapper();
    String param = "{\"stu_id\":\"1001\",\"stu_name\":\"晓春\",\"stu_sex\":\"男\",\"stu_age\":\"34\",\"stu_addr\":\"安徽合肥\",\"stu_pwd\":\"123456\"}";
    //将字符串转换为对象—反序列化过程
    Student student = mapper.readValue(param, Student.class);
    System.out.println("===json转对象==="+student.toString());
    //将对象转化成JSON—序列化过程
    String  json = mapper.writeValueAsString(student);
    System.out.println("===对象转json==="+json);
}

2.3.2、测试结果展示

2.4、集合和JSON像话转化

2.4.1、测试代码

/**
 * 集合和JSON相互转化
 */
@RequestMapping("/listAndJSONChange")
@ResponseBody
public void  arrayToObject() throws Exception{
    Student student1=new Student("1001","晓春1","男","34","安徽合肥","123456");
    Student student2=new Student("1002","晓春2","男","34","安徽合肥","123456");
    ObjectMapper mapper = new ObjectMapper();
    //集合转json
    String param = mapper.writeValueAsString(Arrays.asList(student1,student2));
    System.out.println("==集合转json=="+param);
    //数组json转化成集合
    List<Student> list= mapper.readValue(param, List.class);
    System.out.println("==数组json转集合=="+list);
}

2.4.2、测试结果展示

2.5、Map和JSON相互转化

2.5.1、测试代码

/**
 * map和json相互转化
 */
@RequestMapping("/mapAndJsonChange")
@ResponseBody
public void  mapAndJsonChange() throws Exception{
    ObjectMapper mapper = new ObjectMapper();
    Map<String, Object> map = new HashMap<>();
    map.put("id", "1001");
    map.put("name","晓春");
    map.put("student", new Student("6","6","6","6","6","6"));
    String param = mapper.writeValueAsString(map);
    System.out.println("===map转json==="+param);
    Map<String, Object> resultMap = mapper.readValue(param, Map.class);
    System.out.println("===json转map==="+resultMap);
}

2.5.2、测试结果展示

3、如果不需要JSON与其他转化，而是直接获取

使用readTree，通过节点树的方式直接获取JSON属性对应的值

使用链接：https://blog.youkuaiyun.com/tangshiyilang/article/details/134326627

4、在Springboot工程中，通过配置的方式，配置ObjectMapper配置

方便使用，一次性配置，会在springboot工程启动的时候自动获取配置

@Configuration
public class ObjectMapperConfig {

    @Bean("objectMapper")
    public ObjectMapper getObjectMapper(){
        ObjectMapper  mapper = new ObjectMapper();
        //属性为NULL 不序列化
        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        //属性为默认值不序列化
        mapper.setSerializationInclusion(JsonInclude.Include.NON_DEFAULT);

        //反序列化时,遇到未知属性不报错
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

        //如果是空对象的时候,不抛异常
        mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);

        //修改序列化后日期格式
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));

        return mapper;
    }


}