json  序列化和反序列化

https://github.com/FasterXML/jackson
jackson 2.13.5 

jackson-core  jackson-annotations   jackson-databind

jackson-core 
核心包，提供基于"流模式"解析的相关 API，它包括 JsonPaser 和 JsonGenerator 

jackson-annotations   注解包，提供标准注解功能
jackson-databind      数据绑定包
提供基于  对象绑定  解析的相关 API （ObjectMapper） 和  树模型 解析的相关 API （JsonNode）



Jackson JSON  对象绑定

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

String str = objectMapper.writeValueAsString(pet);
Pet pet2 = objectMapper.readValue(str,Pet.class);

List< Pet> pets = new ArrayList< >();
pets.add(pet);
pets.add(pet2);
str = objectMapper.writeValueAsString(pets);
Pet[] petArr = objectMapper.readValue(str, Pet[].class);
pets = objectMapper.readValue(str,new TypeReference< List< Pet>>(){});


str = objectMapper.writeValueAsString(pet);
Map< String, Object> jsonMap = objectMapper.readValue(str,new TypeReference< Map< String,Object>>(){});

java.util.Date对象序列化 默认转为 long型的值
	
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
objectMapper.setDateFormat(dateFormat);



Jackson JSON 树模型

JsonNode jsonNode = objectMapper.readValue(str, JsonNode.class);
jsonNode = objectMapper.readTree(str);
JsonNode idNode = jsonNode.get("id");

long id = jsonNode.get("id").asLong();
String name = jsonNode.get("name").asText();
int age =  jsonNode.get("age").asInt();

// JsonNode 不可变 ,子类 ObjectNode
ObjectNode petNode = objectMapper.createObjectNode();
petNode.put("id",id);
petNode.put("name",name);
petNode.put("age",age);
petNode.remove("age");

Iterator< String> fieldNames = jsonNode.fieldNames();

JsonNode 可表示 对象 或  数组
get 方法 传入 string 访问字段，传入int ,根据索引访问数组

str = objectMapper.writeValueAsString(pets);
// 数组
jsonNode = objectMapper.readTree(str);
for(int i=0;i< jsonNode.size();i++){
    System.out.println(jsonNode.get(i));
}

Map< String,Pet> petMap = new HashMap< >();
petMap.put("pet1",pet);
str = objectMapper.writeValueAsString(petMap);
jsonNode = objectMapper.readTree(str);

// JSON路径表达式 必须 / 开头
JsonNode nameNode = jsonNode.at("/pet1/name");



Jackson注解

Read + Write注解

@JsonIgnore
不读取或写入属性

public class PersonIgnore {
    @JsonIgnore
    public long  personId = 0;
    public String name = null;
}

@JsonIgnoreProperties({"firstName", "lastName"})
public class PersonIgnoreProperties {
    public long   personId = 0;
    public String  firstName = null;
    public String  lastName  = null;

}

@JsonIgnoreType

@JsonAutoDetect   读写对象时包括非public修饰的属性


@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY )
public class PersonAutoDetect {

    private long  personId = 123;
    public String name     = null;

}



Read注解

@JsonSetter
@JsonAnySetter
@JsonCreator
@JacksonInject
@JsonDeserialize  指定自定义反序列化器类



public class PersonImmutable {

    private long   id   = 0;
    private String name = null;

    @JsonCreator
    public PersonImmutable(
            @JsonProperty("id")  long id,
            @JsonProperty("name") String name  ) {

        this.id = id;
        this.name = name;
    }

    public long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

}




Write注解

@JsonInclude
@JsonGetter
@JsonAnyGetter
@JsonPropertyOrder
@JsonRawValue
@JsonValue
@JsonSerialize  指定自定义序列化类 

@JsonInclude(JsonInclude.Include.NON_EMPTY)
public class PersonInclude {

    public long  personId = 0;
    public String name     = null;

}


public class PersonGetter {

    private long  personId = 0;

    @JsonGetter("id")
    public long personId() { return this.personId; }

    @JsonSetter("id")
    public void personId(long personId) { this.personId = personId; }

}

@JsonPropertyOrder({"name", "personId"})
public class PersonPropertyOrder {

    public long  personId  = 0;
    public String name     = null;

}



import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.text.SimpleDateFormat;

public class JacksonUtil {

    static final ObjectMapper objectMapper = new ObjectMapper();
    private static final String DATETIME_FORMAT = "yyyy-MM-dd HH:mm:ss";

    static{
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        // null 字段不输出
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);

        objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        objectMapper.setDateFormat(new SimpleDateFormat(DATETIME_FORMAT));


    }

    public static  T readValue(String content, Class valueType)throws Exception{
        return objectMapper.readValue(content,valueType);
    }

    public static String toJsonString(Object obj,boolean pretty)throws Exception{
        if(obj==null){
            return null;
        }
        if(pretty){
            return objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj);
        }
        return objectMapper.writeValueAsString(obj);
    }

}




https://gitee.com/dyyx/work2024/blob/master/demo/appdemo/src/main/java/demo/jackson/JacksonDemo.java

https://gitee.com/dyyx/work2024/blob/master/demo/appdemo/src/main/java/demo/util/JacksonUtil.java