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General data-binding functionality for Jackson: works on core streaming API
package com.fasterxml.jackson.databind.deser;
import java.io.IOException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationConfig;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.jsontype.TypeIdResolver;
/**
* This is the class that can be registered (via
* {@link DeserializationConfig} object owner by
* {@link ObjectMapper}) to get called when a potentially
* recoverable problem is encountered during deserialization
* process. Handlers can try to resolve the problem, throw
* an exception or just skip the content.
*
* Default implementations for all methods implemented minimal
* "do nothing" functionality, which is roughly equivalent to
* not having a registered listener at all. This allows for
* only implemented handler methods one is interested in, without
* handling other cases.
*
* NOTE: it is typically NOT acceptable to simply do nothing,
* because this will result in unprocessed tokens being left in
* token stream (read via {@link JsonParser}, in case a structured
* (JSON Object or JSON Array) value is being pointed to by parser.
*/
public abstract class DeserializationProblemHandler
{
/**
* Marker value returned by some handler methods to indicate that
* they could not handle problem and produce replacement value.
*
* @since 2.7
*/
public final static Object NOT_HANDLED = new Object();
/**
* Method called when a JSON Object property with an unrecognized
* name is encountered.
* Content (supposedly) matching the property are accessible via
* parser that can be obtained from passed deserialization context.
* Handler can also choose to skip the content; if so, it MUST return
* true to indicate it did handle property successfully.
* Skipping is usually done like so:
*
* parser.skipChildren();
*
*
* Note: {@link com.fasterxml.jackson.databind.DeserializationFeature#FAIL_ON_UNKNOWN_PROPERTIES})
* takes effect only after handler is called, and only
* if handler did not handle the problem.
*
* @param beanOrClass Either bean instance being deserialized (if one
* has been instantiated so far); or Class that indicates type that
* will be instantiated (if no instantiation done yet: for example
* when bean uses non-default constructors)
* @param p Parser to use for handling problematic content
*
* @return True if the problem is resolved (and content available used or skipped);
* false if the handler did not anything and the problem is unresolved. Note that in
* latter case caller will either throw an exception or explicitly skip the content,
* depending on configuration.
*/
public boolean handleUnknownProperty(DeserializationContext ctxt, JsonParser p,
JsonDeserializer deserializer, Object beanOrClass, String propertyName)
throws IOException
{
return false;
}
/**
* Method called when a property name from input cannot be converted to a
* non-Java-String key type (passed as rawKeyType) due to format problem.
* Handler may choose to do one of 3 things:
*
* - Indicate it does not know what to do by returning {@link #NOT_HANDLED}
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Return actual key value to use as replacement, and continue processing.
*
*
*
* @param failureMsg Message that will be used by caller (by calling
* {@link DeserializationContext#weirdKeyException(Class, String, String)})
* to indicate type of failure unless handler produces key to use
*
* @return Either {@link #NOT_HANDLED} to indicate that handler does not know
* what to do (and exception may be thrown), or value to use as key (possibly
* null
*
* @since 2.8
*/
public Object handleWeirdKey(DeserializationContext ctxt,
Class rawKeyType, String keyValue,
String failureMsg)
throws IOException
{
return NOT_HANDLED;
}
/**
* Method called when a String value
* cannot be converted to a non-String value type due to specific problem
* (as opposed to String values never being usable).
* Handler may choose to do one of 3 things:
*
* - Indicate it does not know what to do by returning {@link #NOT_HANDLED}
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Return actual converted value (of type
targetType) to use as
* replacement, and continue processing.
*
*
*
* @param failureMsg Message that will be used by caller (by calling
* {@link DeserializationContext#weirdNumberException})
* to indicate type of failure unless handler produces key to use
*
* @return Either {@link #NOT_HANDLED} to indicate that handler does not know
* what to do (and exception may be thrown), or value to use as (possibly
* null)
*
* @since 2.8
*/
public Object handleWeirdStringValue(DeserializationContext ctxt,
Class targetType, String valueToConvert,
String failureMsg)
throws IOException
{
return NOT_HANDLED;
}
/**
* Method called when a numeric value (integral or floating-point from input
* cannot be converted to a non-numeric value type due to specific problem
* (as opposed to numeric values never being usable).
* Handler may choose to do one of 3 things:
*
* - Indicate it does not know what to do by returning {@link #NOT_HANDLED}
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Return actual converted value (of type
targetType) to use as
* replacement, and continue processing.
*
*
*
* @param failureMsg Message that will be used by caller (by calling
* {@link DeserializationContext#weirdNumberException})
* to indicate type of failure unless handler produces key to use
*
* @return Either {@link #NOT_HANDLED} to indicate that handler does not know
* what to do (and exception may be thrown), or value to use as (possibly
* null)
*
* @since 2.8
*/
public Object handleWeirdNumberValue(DeserializationContext ctxt,
Class targetType, Number valueToConvert, String failureMsg)
throws IOException
{
return NOT_HANDLED;
}
/**
* Method called when an embedded (native) value ({@link JsonToken#VALUE_EMBEDDED_OBJECT})
* cannot be converted directly into expected value type (usually POJO).
* Handler may choose to do one of 3 things:
*
* - Indicate it does not know what to do by returning {@link #NOT_HANDLED}
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Return actual converted value (of type
targetType) to use as
* replacement, and continue processing.
*
*
*
* @return Either {@link #NOT_HANDLED} to indicate that handler does not know
* what to do (and exception may be thrown), or value to use (possibly
* null)
*
* @since 2.9
*/
public Object handleWeirdNativeValue(DeserializationContext ctxt,
JavaType targetType, Object valueToConvert, JsonParser p)
throws IOException
{
return NOT_HANDLED;
}
/**
* Method that deserializers should call if the first token of the value to
* deserialize is of unexpected type (that is, type of token that deserializer
* cannot handle). This could occur, for example, if a Number deserializer
* encounter {@link JsonToken#START_ARRAY} instead of
* {@link JsonToken#VALUE_NUMBER_INT} or {@link JsonToken#VALUE_NUMBER_FLOAT}.
*
* - Indicate it does not know what to do by returning {@link #NOT_HANDLED}
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Handle content to match (by consuming or skipping it), and return actual
* instantiated value (of type
targetType) to use as replacement;
* value may be `null` as well as expected target type.
*
*
*
* @param failureMsg Message that will be used by caller
* to indicate type of failure unless handler produces value to use
*
* @return Either {@link #NOT_HANDLED} to indicate that handler does not know
* what to do (and exception may be thrown), or value to use (possibly
* null
*
* @since 2.8
*/
public Object handleUnexpectedToken(DeserializationContext ctxt,
Class targetType, JsonToken t, JsonParser p,
String failureMsg)
throws IOException
{
return NOT_HANDLED;
}
/**
* Method called when instance creation for a type fails due to an exception.
* Handler may choose to do one of following things:
*
* - Indicate it does not know what to do by returning {@link #NOT_HANDLED}
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Return actual instantiated value (of type
targetType) to use as
* replacement, and continue processing.
*
* - Return
null to use null as value but not to try further
* processing (in cases where properties would otherwise be bound)
*
*
*
* @param instClass Type that was to be instantiated
* @param argument (optional) Additional argument that was passed to creator, if any
* @param t Exception that caused instantiation failure
*
* @return Either {@link #NOT_HANDLED} to indicate that handler does not know
* what to do (and exception may be thrown), or value to use (possibly
* null
*
* @since 2.8
*/
public Object handleInstantiationProblem(DeserializationContext ctxt,
Class instClass, Object argument, Throwable t)
throws IOException
{
return NOT_HANDLED;
}
/**
* Method called when instance creation for a type fails due to lack of an
* instantiator. Method is called before actual deserialization from input
* is attempted, so handler may do one of following things:
*
* - Indicate it does not know what to do by returning {@link #NOT_HANDLED}
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Handle content to match (by consuming or skipping it), and return actual
* instantiated value (of type
targetType) to use as replacement;
* value may be `null` as well as expected target type.
*
*
*
* @param instClass Type that was to be instantiated
* @param p Parser to use for accessing content that needs handling, to either
* use it or skip it (latter with {@link JsonParser#skipChildren()}.
*
* @return Either {@link #NOT_HANDLED} to indicate that handler does not know
* what to do (and exception may be thrown), or value to use (possibly
* null
*
* @since 2.9
*/
public Object handleMissingInstantiator(DeserializationContext ctxt,
Class instClass, ValueInstantiator valueInsta, JsonParser p,
String msg)
throws IOException
{
// 16-Oct-2016, tatu: Need to delegate to deprecated method from 2.8;
// remove redirect from later versions (post-2.9)
return handleMissingInstantiator(ctxt, instClass, p, msg);
}
/**
* Handler method called if resolution of type id from given String failed
* to produce a subtype; usually because logical id is not mapped to actual
* implementation class.
* Handler may choose to do one of following things:
*
* - Indicate it does not know what to do by returning `null`
*
* - Indicate that nothing should be deserialized, by return `Void.class`
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Return actual resolved type to use for type id.
*
*
*
* @param ctxt Deserialization context to use for accessing information or
* constructing exception to throw
* @param baseType Base type to use for resolving subtype id
* @param subTypeId Subtype id that failed to resolve
* @param failureMsg Informational message that would be thrown as part of
* exception, if resolution still fails
*
* @return Actual type to use, if resolved; `null` if handler does not know what
* to do; or `Void.class` to indicate that nothing should be deserialized for
* type with the id (which caller may choose to do... or not)
*
* @since 2.8
*/
public JavaType handleUnknownTypeId(DeserializationContext ctxt,
JavaType baseType, String subTypeId, TypeIdResolver idResolver,
String failureMsg)
throws IOException
{
return null;
}
/**
* Handler method called if an expected type id for a polymorphic value is
* not found and no "default type" is specified or allowed.
* Handler may choose to do one of following things:
*
* - Indicate it does not know what to do by returning `null`
*
* - Indicate that nothing should be deserialized, by return `Void.class`
*
* - Throw a {@link IOException} to indicate specific fail message (instead of
* standard exception caller would throw
*
* - Return actual resolved type to use for this particular case.
*
*
*
* @param ctxt Deserialization context to use for accessing information or
* constructing exception to throw
* @param baseType Base type to use for resolving subtype id
* @param failureMsg Informational message that would be thrown as part of
* exception, if resolution still fails
*
* @return Actual type to use, if resolved; `null` if handler does not know what
* to do; or `Void.class` to indicate that nothing should be deserialized for
* type with the id (which caller may choose to do... or not)
*
* @since 2.9
*/
public JavaType handleMissingTypeId(DeserializationContext ctxt,
JavaType baseType, TypeIdResolver idResolver,
String failureMsg)
throws IOException
{
return null;
}
/*
/**********************************************************
/* Deprecated
/**********************************************************
*/
/**
* @since 2.8
* @deprecated Since 2.9: use variant that takes {@link ValueInstantiator}
*/
@Deprecated
public Object handleMissingInstantiator(DeserializationContext ctxt,
Class instClass, JsonParser p, String msg)
throws IOException
{
return NOT_HANDLED;
}
}