java – Jackson ObjectMapper DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT

我在Jersey应用程序中使用Jackson进行JSON序列化/反序列化.我想在我的java POJO属性中将JSON中的空字符串读取为null值.我试图在Object Mapper上设置DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT但它不起作用.这是下面的代码

import java.io.IOException;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

public class TestMapper {

    /**
     * @param args
     */
    public static void main(String[] args) {
        TestMapper.testJson();

    }

    public static void testJson(){
        String jsonString = "{\"name\":\"First Name\",\"phone\":\"\",\"unknown\":\"test\"}";
        ObjectMapper result = new ObjectMapper();
        //result.setDeserializationConfig(result.getDeserializationConfig().with(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT));
        //result.enable(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
        /*DeserializationConfig deserializeConfig = result.getDeserializationConfig();
        deserializeConfig.with(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);*/
        result.configure(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);
        result.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    try {
            TestBean testBean = result.readValue(jsonString, TestBean.class);
            if(testBean.getPhone()!=null&& testBean.getPhone().equals("")){
                System.out.print("Phone Number is empty string");
            }else{
                System.out.print("Phone Number is null");
            }
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

豆子如下

public class TestBean {

    private String name;
    private String phone;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPhone() {
        return phone;
    }
    public void setPhone(String phone) {
        this.phone = phone;
    }
    public TestBean(String name, String phone) {
        super();
        this.name = name;
        this.phone = phone;
    }
    public TestBean() {
        super();
    }


}

输出始终是

Phone Number is empty string

我不知道为什么这不起作用.我正在使用Jackson 1.9.2.

解决方法:

注意ACCEPT_EMPTY_STRING_AS_NULL_OBJECT的javadoc

Feature that can be enabled to allow JSON empty String value (“”) to be bound to POJOs as null.

因此,可以使用空String将null映射到POJO. String不是POJO,它被视为JSON原始值.

你不能在这里使用它.

ACCEPT_EMPTY_STRING_AS_NULL_OBJECT可以用于类似的东西

{"name":"First Name","phone":"","unknown":"test"}

你可以在哪里制作某些POJO类型的TestBean.phone字段

class Phone {
    private String number;
}

然后反序列化将使电话字段为空.

标签：json,java,jackson,json-deserialization
来源： https://codeday.me/bug/20190528/1174422.html