我正在使用Jackson JSON将一些JSON对象转换为POJO类。这种反序列化应该不区分大小写,并且不允许具有不区分大小写重复名称的属性。
按如下所示配置ObjectMapper
可以实现不区分大小写的反序列化,并且可以使具有严格相同名称的属性失效:
final ObjectMapper objectMapper;
objectMapper.configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true);
objectMapper.enable(JsonParser.Feature.STRICT_DUPLICATE_DETECTION);
但是,当输入包含两个具有相同名称和大小写的属性时,它不会失败,例如:
{
"Name": "name01",
"NAME": "name02"
}
有什么方法可以配置ObjectMapper
在这种情况下失败?
答案 0 :(得分:1)
摘自STRICT_DUPLICATE_DETECTION
文档:
确定JsonParser是否将显式检查 不会遇到重复的JSON对象字段名称。如果启用, 解析器将检查上下文中的所有名称,并通过以下方式报告重复项 抛出JsonParseException;如果禁用,解析器将不会这样做 检查。 后一种情况的假设是呼叫者会照顾 在更高级别上处理重复项:例如,数据绑定具有 用于指定要在此处进行检测的功能。请注意,启用 由于必须存储,此功能将产生性能开销 并检查其他信息:这通常会增加20-30% 基本解析的执行时间。
JSON
默认情况下区分大小写,并且Jackson
中默认情况下未启用使其不敏感的主要原因之一。但是我们可以扩展基本实现并添加验证。我们需要扩展com.fasterxml.jackson.databind.deser.BeanDeserializerModifier
和com.fasterxml.jackson.databind.deser.BeanDeserializer
来反序列化POJO
类。下面的解决方案取决于您使用的版本,因为我从基类中复制了一些代码,这些代码尚无法拦截额外的功能。如果您的POJO
类没有任何额外的配置,则将调用vanillaDeserialize
方法,我们将尝试改进这一方法。让我们实现它:
class InsensitiveBeanDeserializerModifier extends BeanDeserializerModifier {
@Override
public JsonDeserializer<?> modifyDeserializer(DeserializationConfig config, BeanDescription beanDesc, JsonDeserializer<?> deserializer) {
JsonDeserializer<?> base = super.modifyDeserializer(config, beanDesc, deserializer);
if (base instanceof BeanDeserializer) {
return new InsensitiveBeanDeserializer((BeanDeserializer) base);
}
return base;
}
}
class InsensitiveBeanDeserializer extends BeanDeserializer {
public InsensitiveBeanDeserializer(BeanDeserializerBase src) {
super(src);
}
public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
// common case first
if (p.isExpectedStartObjectToken()) {
if (_vanillaProcessing) {
return vanillaDeserialize(p, ctxt, p.nextToken());
}
// 23-Sep-2015, tatu: This is wrong at some many levels, but for now... it is
// what it is, including "expected behavior".
p.nextToken();
if (_objectIdReader != null) {
return deserializeWithObjectId(p, ctxt);
}
return deserializeFromObject(p, ctxt);
}
return _deserializeOther(p, ctxt, p.getCurrentToken());
}
protected Object vanillaDeserialize(JsonParser p, DeserializationContext ctxt, JsonToken t) throws IOException {
final Object bean = _valueInstantiator.createUsingDefault(ctxt);
// [databind#631]: Assign current value, to be accessible by custom serializers
p.setCurrentValue(bean);
Map<String, String> names = new HashMap<>();
if (p.hasTokenId(JsonTokenId.ID_FIELD_NAME)) {
String propName = p.getCurrentName();
do {
String oldName = names.put(propName.toLowerCase(), propName);
if (oldName != null) {
String msg = "Properties '" + propName + "' and '" + oldName + "' are the same!";
throw new DuplicateInsensitiveKeysException(p, msg);
}
defaultImplementation(p, ctxt, bean, propName);
} while ((propName = p.nextFieldName()) != null);
}
return bean;
}
private void defaultImplementation(JsonParser p, DeserializationContext ctxt, Object bean, String propName) throws IOException {
p.nextToken();
SettableBeanProperty prop = _beanProperties.find(propName);
if (prop != null) { // normal case
try {
prop.deserializeAndSet(p, ctxt, bean);
} catch (Exception e) {
wrapAndThrow(e, bean, propName, ctxt);
}
return;
}
handleUnknownVanilla(p, ctxt, bean, propName);
}
public static class DuplicateInsensitiveKeysException extends JsonMappingException {
public DuplicateInsensitiveKeysException(Closeable processor, String msg) {
super(processor, msg);
}
}
}
用法示例:
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.core.JsonTokenId;
import com.fasterxml.jackson.databind.BeanDescription;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.MapperFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.BeanDeserializer;
import com.fasterxml.jackson.databind.deser.BeanDeserializerBase;
import com.fasterxml.jackson.databind.deser.BeanDeserializerModifier;
import com.fasterxml.jackson.databind.deser.SettableBeanProperty;
import com.fasterxml.jackson.databind.module.SimpleModule;
import java.io.Closeable;
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
public class JsonApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
SimpleModule module = new SimpleModule();
module.setDeserializerModifier(new InsensitiveBeanDeserializerModifier());
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(module);
mapper.enable(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES);
System.out.println(mapper.readValue(jsonFile, User.class));
}
}
对于以上JSON
个有效负载打印:
Exception in thread "main" InsensitiveBeanDeserializer$DuplicateInsensitiveKeysException: Properties 'NAME' and 'Name' are the same!