如何取消JSON字符串到对象的序列化放宽根值大小写敏感性

Question

将我的项目从Jersey移动到Spring MVC时面临问题。如何在Jackson中放松对根值的大小写不敏感？

我想支持大写和小写

我们有以下Jackson配置，它适用于属性和枚举，但不适用于根值

spring.jackson.mapper.accept-case-insensitive-properties=true
spring.jackson.mapper.accept-case-insensitive-enums=true

在我的情况下，我无法访问Car类，因此无法使用任何Jackson注释(如@JsonRootValue(将Car类的名称更新为"car">

这是我面临的带有测试的示例类来重现问题。

在jackson库中配置放松根名称不是很好吗？

public class CarTest {
public class Car {
String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}

@Test
public void testCarRootValueCaseSensitivity() throws IOException {
Car car = new Car();
car.setName("audi");
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.enable(SerializationFeature.WRAP_ROOT_VALUE);
objectMapper.enable(DeserializationFeature.UNWRAP_ROOT_VALUE);
String carAsString = objectMapper.writeValueAsString(car);
System.out.println(carAsString);
// Works fine with out any exception as the root value Car has captital 'C'
objectMapper.readValue("{"Car":{"name":"audi"}}", Car.class);
// Throws exception when lower case 'c' is provided than uppercase 'C'
objectMapper.readValue("{"car":{"name":"audi"}}", Car.class);
}
}

Answer 1

当您查看抛出的异常时：

Exception in thread "main" com.fasterxml.jackson.databind.exc.MismatchedInputException: Root name 'car' does not match expected ('Car') for type [simple type, class com.example.Car]
at [Source: (String)"{"car":{"name":"audi"}}"; line: 1, column: 2] (through reference chain: com.example.Car["car"])
at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63)
at com.fasterxml.jackson.databind.DeserializationContext.reportPropertyInputMismatch(DeserializationContext.java:1477)
at com.fasterxml.jackson.databind.DeserializationContext.reportPropertyInputMismatch(DeserializationContext.java:1493)
at com.fasterxml.jackson.databind.ObjectMapper._unwrapAndDeserialize(ObjectMapper.java:4286)
at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4200)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3205)
at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3173)

您可以注意到_unwrapAndDeserialize方法名称。

在这种方法中，你可以找到以下代码：

String actualName = p.getCurrentName();
if (!expSimpleName.equals(actualName)) {
ctxt.reportPropertyInputMismatch(rootType, actualName,
"Root name '%s' does not match expected ('%s') for type %s",
actualName, expSimpleName, rootType);
}

由于始终使用equals方法，因此无法配置此行为。

如果您真的想用不区分大小写的模式解析它，您可以覆盖_unwrapAndDeserialize方法，并用equalsIgnoreCase替换equals。示例类：

class CaseInsensitiveObjectMapper extends ObjectMapper {
protected Object _unwrapAndDeserialize(JsonParser p, DeserializationContext ctxt, DeserializationConfig config, JavaType rootType, JsonDeserializer<Object> deser) throws IOException {
PropertyName expRootName = config.findRootName(rootType);
// 12-Jun-2015, tatu: Should try to support namespaces etc but...
String expSimpleName = expRootName.getSimpleName();
if (p.getCurrentToken() != JsonToken.START_OBJECT) {
ctxt.reportWrongTokenException(rootType, JsonToken.START_OBJECT,
"Current token not START_OBJECT (needed to unwrap root name '%s'), but %s",
expSimpleName, p.getCurrentToken());
}
if (p.nextToken() != JsonToken.FIELD_NAME) {
ctxt.reportWrongTokenException(rootType, JsonToken.FIELD_NAME,
"Current token not FIELD_NAME (to contain expected root name '%s'), but %s",
expSimpleName, p.getCurrentToken());
}
String actualName = p.getCurrentName();
if (!expSimpleName.equalsIgnoreCase(actualName)) {
ctxt.reportPropertyInputMismatch(rootType, actualName,
"Root name '%s' does not match expected ('%s') for type %s",
actualName, expSimpleName, rootType);
}
// ok, then move to value itself....
p.nextToken();
Object result = deser.deserialize(p, ctxt);
// and last, verify that we now get matching END_OBJECT
if (p.nextToken() != JsonToken.END_OBJECT) {
ctxt.reportWrongTokenException(rootType, JsonToken.END_OBJECT,
"Current token not END_OBJECT (to match wrapper object with root name '%s'), but %s",
expSimpleName, p.getCurrentToken());
}
if (config.isEnabled(DeserializationFeature.FAIL_ON_TRAILING_TOKENS)) {
_verifyNoTrailingTokens(p, ctxt, rootType);
}
return result;
}
}

我从ObjectMapper类(版本2.10.1(复制了整个方法，如果您要升级Jackson版本，您需要检查此方法的实现情况，并在需要时替换它。

最后，您可以在测试中使用这种新类型：

ObjectMapper objectMapper = new CaseInsensitiveObjectMapper();

另请参阅：

• JSON区分大小写吗