package org.web3j.protocol;import com.fasterxml.jackson.core.JsonParser;import com.fasterxml.jackson.databind.BeanDescription;import com.fasterxml.jackson.databind.DeserializationConfig;import com.fasterxml.jackson.databind.DeserializationFeature;import com.fasterxml.jackson.databind.JsonDeserializer;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.ObjectReader;import com.fasterxml.jackson.databind.deser.BeanDeserializerModifier;import com.fasterxml.jackson.databind.module.SimpleModule;import org.web3j.protocol.core.Response;import org.web3j.protocol.deserializer.RawResponseDeserializer;/** * Factory for managing our ObjectMapper instances. */public class ObjectMapperFactory {    private static final ObjectMapper DEFAULT_OBJECT_MAPPER = new ObjectMapper();    static {        configureObjectMapper(DEFAULT_OBJECT_MAPPER, false);    }    public static ObjectMapper getObjectMapper() {        return getObjectMapper(false);    }    public static ObjectMapper getObjectMapper(boolean shouldIncludeRawResponses) {        if (!shouldIncludeRawResponses) {            return DEFAULT_OBJECT_MAPPER;        }        return configureObjectMapper(new ObjectMapper(), true);    }    public static ObjectReader getObjectReader() {        return DEFAULT_OBJECT_MAPPER.reader();    }    private static ObjectMapper configureObjectMapper(            ObjectMapper objectMapper, boolean shouldIncludeRawResponses) {        if (shouldIncludeRawResponses) {            SimpleModule module = new SimpleModule();            module.setDeserializerModifier(new BeanDeserializerModifier() {                @Override                public JsonDeserializer
      modifyDeserializer(DeserializationConfig config,                                                              BeanDescription beanDesc,                                                              JsonDeserializer
      deserializer) {                    if (Response.class.isAssignableFrom(beanDesc.getBeanClass())) {                        return new RawResponseDeserializer(deserializer);                    }                    return deserializer;                }            });            objectMapper.registerModule(module);        }        objectMapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);        return objectMapper;    }}

这个类改变了我对工厂模式的看法，之前我认为工厂模式是生产一个类的多个不同子类的对象的，工厂类里存在if-else或switch语句判断生产的子类。对于工厂模式，现在看来只产生一个类的对象也可以，不存在不同子类的情况，不存在if-else或switch语句。ObjectMapperFactory只生产ObjectMapper这一个类的对象，只是根据需要提供一个默认生产好的ObjectMapper对象，或根据条件生产定制的ObjectMapper。