java - 覆盖全局 jackson 配置

Question

我的应用程序 null 值不会被序列化为 json，这没问题。但在一种特定情况下，我希望将空值发送给客户端。我怎样才能做到这一点？

class User  {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

对于这个类，我尝试使用 JsonInclude.Always，但其默认值稍后会在配置中被覆盖。

Answer 1

使用JsonIninclude注释。示例:

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Test {

    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setSerializationInclusion(Include.NON_NULL);

        System.out.println(mapper.writeValueAsString(new User()));
    }
}

@JsonInclude
class User  {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

上面的代码打印:

{"name":null}

JsonInclude 中的默认值为 ALWAYS:

/**
 * Inclusion rule to use for instances (values) of types (Classes) or
 * properties annotated.
 */
public Include value() default Include.ALWAYS;

其他选项是使用 JsonSerialize 注释:

@JsonSerialize(include = Inclusion.ALWAYS)
class User  {

    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

结果与 JsonInclude 相同。