杰克逊:字段类型限制

Question

如果传递的 pojo 包含意外类型的字段，是否可以让杰克逊在写入 json 时抛出异常？ 我想与自定义序列化程序一起提供的预期类型。

Answer 1

Jackson 将所有属性包装在com.fasterxml.jackson.databind.ser.BeanPropertyWriter对象中，它们负责序列化值。我们可以使用自定义实现来修饰这些对象：

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.json.JsonMapper;
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 JsonTypeApp {
public static void main(String[] args) throws Exception {
SimpleModule fieldRestrictionModule = new SimpleModule("FieldRestriction");
fieldRestrictionModule.setSerializerModifier(new BeanSerializerModifier() {
@Override
public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
return beanProperties.stream().map(p -> new PrimitivesOnlyBeanPropertyWriter(p)).collect(Collectors.toList());
}
});
ObjectMapper mapper = JsonMapper.builder()
.addModule(fieldRestrictionModule)
.build();
System.out.println(mapper.writeValueAsString(new Test()));
}
}
class PrimitivesOnlyBeanPropertyWriter extends BeanPropertyWriter {
public PrimitivesOnlyBeanPropertyWriter(BeanPropertyWriter writer) {
super(writer);
}
@Override
public void serializeAsField(Object bean, JsonGenerator gen, SerializerProvider prov) throws Exception {
if (getType().isPrimitive()) {
super.serializeAsField(bean, gen, prov);
} else {
throw new IllegalStateException(getType().getTypeName() + " is not allowed!");
}
}
}

如果类Test只包含基元字段，则对象将被正确序列化。在其他情况下 -java.lang.IllegalStateException将被抛出。