jackson（三）序列化反序列化依赖于getter setter方法

1.简介

在默认情况下，ObjectMapper在序列化属性时会依赖getter方法。反序列化是会依赖setter方法。

2.测试默认情况

/**
 * 测试用户
 * 将id 和 name属性的getter setter方法注释
 */
@ToString
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
//@JsonInclude(value = JsonInclude.Include.NON_NULL)
public class TestUser02 {
//    @Setter
//    @Getter
    private Integer id;
//    @Setter
//    @Getter
    private String name;
    @Setter
    @Getter
    private Integer age;
    @Setter
    @Getter
    private Date createTime;
}

/**
 * 测试入口
 */
public class TestJackson {
    public static void main(String[] args) {
        TestUser02 testUser022 = new TestUser02(1, "测试getter方法与序列化", 12, new Date());
        System.out.println("objectToJson >>>: " + JacksonUtil.object2Json(testUser022));
    }
}

// 测试结果 {"age":12,"createTime":1649213430746}
// 发现字段`id` `name`,并没有被序列化 

/**
 * 测试入口
 */
public class TestJackson {
    public static void main(String[] args) {
        String json = "{\"id\": 1,\"name\":\"测试setter方法与反序列化\",\"age\":12,\"createTime\":1649214442782}";
        System.out.println("json2Object >>>: " + JacksonUtil.json2Object(json, TestUser02.class));
    }
}

// 测试结果 直接报异常 找不到属性“id”
// com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "id" (class org.bj.core.jackson.TestUser02), not marked as ignorable (2 known properties: "createTime", "age"]) at [Source: (String)"{"id": 1,"name":"测试setter方法与序列化","age":12,"createTime":1649214442782}"; line: 1, column: 9]

由测试可知，在默认情况下，ObjectMapper在序列化属性时会依赖getter方法。反序列化是会依赖setter方法。

3.设置序列化反序列化不依赖getter setter

方式一 ObjectMapper设置

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE)
objectMapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY)

方式二 使用注解@JsonAutoDetect

@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
public class TestUser02 {...}

设置之后重新执行测试，会发现不管又没有getter setter方法都可以序列化 反序列化。

4.附录 jackson工具类

/**
 * jackson 的工具类
 */
public final class JacksonUtil {
    private static final ObjectMapper objectMapper;

    private JacksonUtil() {
    }

    static {
        objectMapper = new ObjectMapper()
            // 设置序列化反序列化采用直接处理字段的方式， 不依赖setter 和 getter
            // .setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE)
            // .setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY)
        ;
    }

    /**
     * json字符串 转成 java对象
     *
     * @param json json字符串
     * @param cls  java类型
     * @return {@link T}
     */
    public static <T> T json2Object(String json, Class<T> cls) {
        T t = null;
        try {
            t = objectMapper.readValue(json, cls);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return t;
    }

    /**
     * java对象 转成 json字符串
     *
     * @param obj java对象
     * @return {@link String}
     */
    public static String object2Json(Object obj) {
        String json = null;
        try {
            json = objectMapper.writeValueAsString(obj);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
        return json;
    }
}