如果getters抛出异常，如何让Jackson忽略属性

Question

我有很多来自供应商的类，它们喜欢在属性访问上随机抛出RuntimeException。

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

我不能更改类，不能添加注释，而且为每个类定义混合是不现实的，因为堆栈的这部分经常更改。

如果属性的getter抛出异常，如何使Jackson忽略该属性？

Answer 1

要在Jackson中执行自定义序列化，可以使用指定所需修改的BeanSerializerModifier注册模块。在您的情况下，BeanPropertyWriter。serializeAsField是负责序列化单个字段的方法，因此您应该创建自己的BeanPropertyWriter，它忽略字段序列化的异常，并向BeanSerializerModifier注册一个模块，该模块使用changeProperties将所有默认BeanPropertyWriter实例替换为您自己的实现。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";
        }
    }
}

以上代码使用Jackson 2.7.1和Java 1.8输出以下内容：

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"}

显示将从序列化的值中忽略引发非法状态异常的getProblematicProperty。