如果getters抛出异常,如何让Jackson忽略属性

Question

我有很多类来自供应商,他们喜欢在属性访问上随机抛出RuntimeExceptions.

public Object getSomeProperty() {
    if (!someObscureStateCheck()) {
        throw new IllegalStateExcepion();
    }
    return calculateTheValueOfProperty(someRandomState);
}

我无法更改类,无法添加注释,为每个类定义mixins是不现实的,因为堆栈的这一部分经常变化.

如果杰克逊的getter抛出异常,我如何让杰克逊忽略一个属性？

Answer 1

要在Jackson中执行自定义序列化,您可以注册一个模块,BeanSerializerModifier其中指定了所需的任何修改.在你的情况,BeanPropertyWriter.serializeAsField负责序列化的各个字段的方法,所以你应该让自己BeanPropertyWriter忽略的领域系列化异常,并注册了一个模块BeanSerializerModifier使用changeProperties,以取代所有默认BeanPropertyWriter用自己实现的实例.以下示例演示:

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.databind.ser.*;

import java.io.IOException;
import java.util.List;
import java.util.stream.Collectors;

public class JacksonIgnorePropertySerializationExceptions {

    public static void main(String[] args) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(new SimpleModule().setSerializerModifier(new BeanSerializerModifier() {
            @Override
            public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
                return beanProperties.stream().map(bpw -> new BeanPropertyWriter(bpw) {
                    @Override
                    public void serializeAsField(Object bean, JsonGenerator gen, SerializerProvider prov) throws Exception {
                        try {
                            super.serializeAsField(bean, gen, prov);
                        } catch (Exception e) {
                            System.out.println(String.format("ignoring %s for field '%s' of %s instance", e.getClass().getName(), this.getName(), bean.getClass().getName()));
                        }
                    }
                }).collect(Collectors.toList());
            }
        }));

        mapper.writeValue(System.out, new VendorClass());
    }

    public static class VendorClass {
        public String getNormalProperty() {
            return "this is a normal getter";
        }

        public Object getProblematicProperty() {
            throw new IllegalStateException("this getter throws an exception");
        }

        public String getAnotherNormalProperty() {
            return "this is a another normal getter";
        }
    }
}

上面的代码使用Jackson 2.7.1和Java 1.8输出以下代码:

ignoring java.lang.reflect.InvocationTargetException for field 'problematicProperty' of JacksonIgnorePropertySerializationExceptions$VendorClass instance
{"normalProperty":"this is a normal getter","anotherNormalProperty":"this is a another normal getter"}

显示getProblematicProperty,抛出一个IllegalStateException,将从序列化值中省略.