如何包装杰克逊序列化异常

Question

Jackson如果其中一个 getter 抛出异常，如何序列化对象？例子：public class Example {     public String getSomeField() {          //some logic which will throw in example NPE          throw new NullPointerException();     }}理想情况下我想得到JSON：{"someField":"null"}或者{"someField":"NPE"}

Answer 1

最通用的方法可能是实现 custom BeanPropertyWriter。您可以通过创建类来注册它BeanSerializerModifier。下面的示例展示了如何做到这一点。

import com.fasterxml.jackson.core.JsonGenerator;

import com.fasterxml.jackson.databind.BeanDescription;

import com.fasterxml.jackson.databind.ObjectMapper;

import com.fasterxml.jackson.databind.SerializationConfig;

import com.fasterxml.jackson.databind.SerializerProvider;

import com.fasterxml.jackson.databind.module.SimpleModule;

import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;

import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;

import java.util.List;

import java.util.stream.Collectors;

public class JsonApp {

    public static void main(String[] args) throws Exception {

        SimpleModule module = new SimpleModule();

        module.setSerializerModifier(new BeanSerializerModifier() {

            @Override

            public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {

                if (beanDesc.getBeanClass() == Response.class) {

                    return beanProperties.stream()

                            .map(SilentExceptionBeanPropertyWriter::new)

                            .collect(Collectors.toList());

                }

                return super.changeProperties(config, beanDesc, beanProperties);

            }

        });

        ObjectMapper mapper = new ObjectMapper();

        mapper.registerModule(module);

        System.out.println(mapper.writeValueAsString(new Response(1, "ONE")));

        System.out.println(mapper.writeValueAsString(new Response(-1, "MINUS")));

        System.out.println(mapper.writeValueAsString(new Response(-1, null)));

    }

}

class SilentExceptionBeanPropertyWriter extends BeanPropertyWriter {

    public SilentExceptionBeanPropertyWriter(BeanPropertyWriter base) {

        super(base);

    }

    @Override

    public void serializeAsField(Object bean, JsonGenerator gen, SerializerProvider prov) throws Exception {

        try {

            super.serializeAsField(bean, gen, prov);

        } catch (Exception e) {

            Throwable cause = e.getCause();

            gen.writeFieldName(_name);

            gen.writeString(cause.getClass().getName() + ":" + cause.getMessage());

        }

    }

}

class Response {

    private int count;

    private String message;

    public Response(int count, String message) {

        this.count = count;

        this.message = message;

    }

    public int getCount() {

        if (count < 0) {

            throw new IllegalStateException("Count is less than ZERO!");

        }

        return count;

    }

    public void setCount(int count) {

        this.count = count;

    }

    public String getMessage() {

        if (message == null) {

            throw new NullPointerException("message can not be null!");

        }

        return message;

    }

    public void setMessage(String message) {

        this.message = message;

    }

}

上面的例子打印：

{"count":1,"message":"ONE"}

{"count":"java.lang.IllegalStateException:Count is less than ZERO!","message":"MINUS"}

{"count":"java.lang.IllegalStateException:Count is less than ZERO!","message":"java.lang.NullPointerException:message can not be null!"}