Java 如何从Jackson中的自定义反序列化程序调用默认反序列化程序
我在Jackson的自定义反序列化程序中遇到问题。我想访问默认序列化程序来填充我要反序列化的对象。在填充之后,我将执行一些自定义操作,但首先我想用默认的Jackson行为反序列化对象 这是我目前掌握的密码Java 如何从Jackson中的自定义反序列化程序调用默认反序列化程序,java,spring,hibernate,jackson,Java,Spring,Hibernate,Jackson,我在Jackson的自定义反序列化程序中遇到问题。我想访问默认序列化程序来填充我要反序列化的对象。在填充之后,我将执行一些自定义操作,但首先我想用默认的Jackson行为反序列化对象 这是我目前掌握的密码 public class UserEventDeserializer extends StdDeserializer<User> { private static final long serialVersionUID = 7923585097068641765L; p
public class UserEventDeserializer extends StdDeserializer<User> {
private static final long serialVersionUID = 7923585097068641765L;
public UserEventDeserializer() {
super(User.class);
}
@Override
@Transactional
public User deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
ObjectCodec oc = jp.getCodec();
JsonNode node = oc.readTree(jp);
User deserializedUser = null;
deserializedUser = super.deserialize(jp, ctxt, new User());
// The previous line generates an exception java.lang.UnsupportedOperationException
// Because there is no implementation of the deserializer.
// I want a way to access the default spring deserializer for my User class.
// How can I do that?
//Special logic
return deserializedUser;
}
}
public类UserEventDeserializer扩展StdDeserializer{
私有静态最终长serialVersionUID=7923585097068641765L;
公共UserEventDeserializer(){
super(User.class);
}
@凌驾
@交易的
公共用户反序列化(JsonParser jp,反序列化上下文ctxt)
抛出IOException、JsonProcessingException{
ObjectCodec oc=jp.getCodec();
JsonNode=oc.readTree(jp);
用户反序列化duser=null;
反序列化(jp,ctxt,new User());
//前一行生成一个异常java.lang.UnsupportedOperationException
//因为没有反序列化器的实现。
//我想要一种方法来访问我的用户类的默认spring反序列化程序。
//我该怎么做?
//特殊逻辑
返回反序列化数据采集器;
}
}
我需要的是一种初始化默认反序列化程序的方法,以便在启动特殊逻辑之前可以预先填充POJO
当从自定义反序列化器中调用反序列化时,无论我如何构造序列化器类,该方法似乎都是从当前上下文调用的。因为我的POJO中的注释。这会导致堆栈溢出异常,原因很明显
我尝试过初始化
BeanDeserializer
,但过程非常复杂,我没有找到正确的方法。我还尝试过重载AnnotationIntrospector
但没有效果,因为我认为这可能会帮助我忽略反序列化上下文中的注释。最后,我可能已经在使用JsonDeserializerBuilders
时取得了一些成功,尽管这需要我做一些神奇的事情来从Spring获得应用程序上下文。我将非常感谢任何能让我找到更干净的解决方案的事情,例如,我如何在不阅读JsonDeserializer
注释的情况下构建反序列化上下文。有两种方法可以做到这一点,但要正确地做到这一点需要做更多的工作。基本上,您不能使用子分类,因为默认反序列化程序需要的信息是从类定义构建的
因此,您最有可能使用的是构造一个BeanDeserializerModifier
,通过Module
接口注册它(使用SimpleModule
)。您需要定义/覆盖modifyDeserializer
,对于要添加自己的逻辑(类型匹配的地方)的特定情况,构建自己的反序列化程序,传递给定的默认反序列化程序。
然后在deserialize()
方法中,您可以委托调用,获取结果对象
或者,如果必须实际创建和填充对象,则可以这样做并调用重载版本的反序列化()
,该版本接受第三个参数;对象进行反序列化
另一种可能有效的方法(但不是100%确定)是指定Converter
对象(@JsonDeserialize(Converter=MyConverter.class)
)。这是Jackson 2.2的新功能。
在您的例子中,Converter实际上不会转换类型,而是简化修改对象:但我不知道这是否会让您完全按照您的要求执行,因为默认的反序列化程序将首先被调用,只有这样,您的转换器才能像StaxMan建议的那样,通过编写BeanDeserializerModifier
并通过SimpleModule
注册它来实现这一点。以下示例应该有效:
public class UserEventDeserializer extends StdDeserializer<User> implements ResolvableDeserializer
{
private static final long serialVersionUID = 7923585097068641765L;
private final JsonDeserializer<?> defaultDeserializer;
public UserEventDeserializer(JsonDeserializer<?> defaultDeserializer)
{
super(User.class);
this.defaultDeserializer = defaultDeserializer;
}
@Override public User deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException
{
User deserializedUser = (User) defaultDeserializer.deserialize(jp, ctxt);
// Special logic
return deserializedUser;
}
// for some reason you have to implement ResolvableDeserializer when modifying BeanDeserializer
// otherwise deserializing throws JsonMappingException??
@Override public void resolve(DeserializationContext ctxt) throws JsonMappingException
{
((ResolvableDeserializer) defaultDeserializer).resolve(ctxt);
}
public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException
{
SimpleModule module = new SimpleModule();
module.setDeserializerModifier(new BeanDeserializerModifier()
{
@Override public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config, BeanDescription beanDesc, JsonDeserializer<?> deserializer)
{
if (beanDesc.getBeanClass() == User.class)
return new UserEventDeserializer(deserializer);
return deserializer;
}
});
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(module);
User user = mapper.readValue(new File("test.json"), User.class);
}
}
公共类UserEventDeserializer扩展STDESerializer实现ResolvableDeserializer
{
私有静态最终长serialVersionUID=7923585097068641765L;
私有最终JsonDeserializer defaultDeserializer;
公共UserEventDeserializer(JsonDeserializer defaultDeserializer)
{
super(User.class);
this.defaultDeserializer=defaultDeserializer;
}
@重写公共用户反序列化(JsonParser jp,反序列化上下文ctxt)
抛出IOException、JsonProcessingException
{
User deserializedUser=(用户)defaultDeserializer.deserialize(jp,ctxt);
//特殊逻辑
返回反序列化数据采集器;
}
//由于某些原因,在修改BeanDeserializer时必须实现ResolvableDeserializer
//否则反序列化会引发JsonMappingException??
@重写公共void resolve(反序列化上下文ctxt)引发JsonMappingException
{
((ResolvableDeserializer)defaultDeserializer).resolve(ctxt);
}
公共静态void main(字符串[]args)抛出JsonParseException、JsonMappingException、IOException
{
SimpleModule=新的SimpleModule();
module.setDeserializerModifier(新的BeanDeserializerModifier()
{
@重写公共JsonDeserializer modifyDeserializer(反序列化配置、BeanDescription BeanDeserializer、JsonDeserializer反序列化器)
{
if(beanDesc.getBeanClass()==User.class)
返回新的UserEventDeserializer(反序列化器);
返回反序列化器;
}
});
ObjectMapper mapper=新的ObjectMapper();
映射器注册表模块(模块);
User=mapper.readValue(新文件(“test.json”)、User.class);
}
}
我不同意使用BeanSerializerModifier
,因为它强制在中央ObjectMapper
中声明一些行为更改,而不是在自定义反序列化程序本身中,事实上,它是用JsonSerialize
注释实体类的并行解决方案。如果您也有类似的感受,您可能会感激我在这里的回答:对我来说,一个更简单的解决方案就是添加另一个Ob bean
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import org.springframework.context.annotation.Bean;
import java.io.IOException;
public class IdWrapperDeserializer<T> extends StdDeserializer<T> {
private Class<T> clazz;
public IdWrapperDeserializer(Class<T> clazz) {
super(clazz);
this.clazz = clazz;
}
@Bean
public ObjectMapper objectMapper() {
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, true);
mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
mapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE);
mapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
return mapper;
}
@Override
public T deserialize(JsonParser jp, DeserializationContext dc) throws IOException, JsonProcessingException {
String json = jp.readValueAsTree().toString();
// do your custom deserialization here using json
// and decide when to use default deserialization using local objectMapper:
T obj = objectMapper().readValue(json, clazz);
return obj;
}
}
@Bean
public ObjectMapper objectMapper() {
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, true);
mapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
mapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.NONE);
mapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
SimpleModule testModule = new SimpleModule("MyModule")
.addDeserializer(Category.class, new IdWrapperDeserializer(Category.class))
mapper.registerModule(testModule);
return mapper;
}
public User deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
ObjectCodec oc = jp.getCodec();
JsonNode node = oc.readTree(jp);
User deserializedUser = null;
DeserializationConfig config = ctxt.getConfig();
JavaType type = TypeFactory.defaultInstance().constructType(User.class);
JsonDeserializer<Object> defaultDeserializer = BeanDeserializerFactory.instance.buildBeanDeserializer(ctxt, type, config.introspect(type));
if (defaultDeserializer instanceof ResolvableDeserializer) {
((ResolvableDeserializer) defaultDeserializer).resolve(ctxt);
}
JsonParser treeParser = oc.treeAsTokens(node);
config.initialize(treeParser);
if (treeParser.getCurrentToken() == null) {
treeParser.nextToken();
}
deserializedUser = (User) defaultDeserializer.deserialize(treeParser, context);
return deserializedUser;
}
// your class
@JsonDeserialize(using = UserEventDeserializer.class)
public class User {
...
}
// extra user class
// reset deserializer attribute to default
@JsonDeserialize
public class UserPOJO extends User {
}
public class UserEventDeserializer extends StdDeserializer<User> {
...
@Override
public User deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
// specify UserPOJO.class to invoke default deserializer
User deserializedUser = jp.ReadValueAs(UserPOJO.class);
return deserializedUser;
// or if you need to walk the JSON tree
ObjectMapper mapper = (ObjectMapper) jp.getCodec();
JsonNode node = oc.readTree(jp);
// specify UserPOJO.class to invoke default deserializer
User deserializedUser = mapper.treeToValue(node, UserPOJO.class);
return deserializedUser;
}
}
public class FooDeserializer extends StdDeserializer<FooBean> {
private static final long serialVersionUID = 1L;
public FooDeserializer() {
this(null);
}
public FooDeserializer(Class<FooBean> t) {
super(t);
}
@Override
public FooBean deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
JsonNode node = jp.getCodec().readTree(jp);
FooBean foo = new FooBean();
foo.setBar(ctxt.readValue(node.get("bar").traverse(), BarBean.class));
return foo;
}
}
public User deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
User user = jp.readValueAs(User.class);
// some code
return user;
}
public ObjectMapper getMapperWithCustomDeserializer() {
ObjectMapper objectMapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.setDeserializerModifier(new BeanDeserializerModifier() {
@Override
public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config,
BeanDescription beanDesc, JsonDeserializer<?> defaultDeserializer)
if (beanDesc.getBeanClass() == User.class) {
return new UserEventDeserializer(defaultDeserializer);
} else {
return defaultDeserializer;
}
}
});
objectMapper.registerModule(module);
return objectMapper;
}
public class UserEventDeserializer extends DelegatingDeserializer {
public UserEventDeserializer(JsonDeserializer<?> delegate) {
super(delegate);
}
@Override
protected JsonDeserializer<?> newDelegatingInstance(JsonDeserializer<?> newDelegate) {
return new UserEventDeserializer(newDelegate);
}
@Override
public User deserialize(JsonParser p, DeserializationContext ctxt)
throws IOException {
User result = (User) super.deserialize(p, ctxt);
// add special logic here
return result;
}
}
public MyObject deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
MyObject object = new ObjectMapper().readValue(p, MyObject.class);
// do whatever you want
return object;
}
ObjectMapper originalMapper = new ObjectMapper();
ObjectMapper copy = originalMapper.copy();//to keep original configuration
copy.setAnnotationIntrospector(new JacksonAnnotationIntrospector() {
@Override
public Object findDeserializer(Annotated a) {
Object deserializer = super.findDeserializer(a);
if (deserializer == null) {
return null;
}
if (deserializer.equals(MyDeserializer.class)) {
return null;
}
return deserializer;
}
});