Package org.apache.hadoop.util

Class JsonSerialization<T>

java.lang.Object

org.apache.hadoop.util.JsonSerialization<T>

Type Parameters:

T - Type to marshal.

@Private
@Evolving
public class JsonSerialization<T>
extends java.lang.Object

Support for marshalling objects to and from JSON. It constructs an object mapper as an instance field. and synchronizes access to those methods which use the mapper. This class was extracted from org.apache.hadoop.registry.client.binding.JsonSerDeser, which is now a subclass of this class.

Constructor Summary

Constructors

Constructor	Description
JsonSerialization(java.lang.Class<T> classType, boolean failOnUnknownProperties, boolean pretty)	Create an instance bound to a specific type.

Method Summary

Modifier and Type	Method	Description
T	fromBytes(byte[] bytes)	Deserialize from a byte array.
T	fromInstance(T instance)	clone by converting to JSON and back again.
T	fromJson(java.lang.String json)	Convert from JSON.
T	fromJsonStream(java.io.InputStream stream)	Read from an input stream.
T	fromResource(java.lang.String resource)	Convert from a JSON file.
com.fasterxml.jackson.databind.ObjectMapper	getMapper()	Get the mapper of this class.
java.lang.String	getName()	Get the simple name of the class type to be marshalled.
T	load(java.io.File jsonFile)	Load from a JSON text file.
T	load(FileSystem fs, Path path)	Load from a Hadoop filesystem.
T	load(FileSystem fs, Path path, FileStatus status)	Load from a Hadoop filesystem.
static com.fasterxml.jackson.databind.ObjectReader	mapReader()
void	save(java.io.File file, T instance)	Save to a local file.
void	save(FileSystem fs, Path path, T instance, boolean overwrite)	Save to a Hadoop filesystem.
byte[]	toBytes(T instance)	Convert JSON to bytes.
java.lang.String	toJson(T instance)	Convert an instance to a JSON string.
java.lang.String	toString(T instance)	Convert an instance to a string form for output.
void	writeJsonAsBytes(T instance, java.io.OutputStream dataOutputStream)	Write the JSON as bytes, then close the stream.
static com.fasterxml.jackson.databind.ObjectWriter	writer()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JsonSerialization

public JsonSerialization(java.lang.Class<T> classType,
                         boolean failOnUnknownProperties,
                         boolean pretty)

Create an instance bound to a specific type.

Parameters:

classType - class to marshall

failOnUnknownProperties - fail if an unknown property is encountered.

pretty - generate pretty (indented) output?

Method Detail

writer

public static com.fasterxml.jackson.databind.ObjectWriter writer()

Returns:

an ObjectWriter which pretty-prints its output

mapReader

public static com.fasterxml.jackson.databind.ObjectReader mapReader()

Returns:

an ObjectReader which returns simple Maps.

getName

public java.lang.String getName()

Get the simple name of the class type to be marshalled.

Returns:

the name of the class being marshalled

getMapper

public com.fasterxml.jackson.databind.ObjectMapper getMapper()

Get the mapper of this class.

Returns:

the mapper

fromJson

public T fromJson(java.lang.String json)
           throws java.io.IOException,
                  com.fasterxml.jackson.core.JsonParseException,
                  com.fasterxml.jackson.databind.JsonMappingException

Convert from JSON.

Parameters:

json - input

Returns:

the parsed JSON

Throws:

java.io.IOException - IO problems

com.fasterxml.jackson.core.JsonParseException - If the input is not well-formatted

com.fasterxml.jackson.databind.JsonMappingException - failure to map from the JSON to this class

fromJsonStream

public T fromJsonStream(java.io.InputStream stream)
                 throws java.io.IOException

Read from an input stream.

Parameters:

stream - stream to read from

Returns:

the parsed entity

Throws:

java.io.IOException - IO problems

com.fasterxml.jackson.core.JsonParseException - If the input is not well-formatted

com.fasterxml.jackson.databind.JsonMappingException - failure to map from the JSON to this class

load

public T load(java.io.File jsonFile)
       throws java.io.IOException,
              com.fasterxml.jackson.core.JsonParseException,
              com.fasterxml.jackson.databind.JsonMappingException

Load from a JSON text file.

Parameters:

jsonFile - input file

Returns:

the parsed JSON

Throws:

java.io.IOException - IO problems

com.fasterxml.jackson.core.JsonParseException - If the input is not well-formatted

com.fasterxml.jackson.databind.JsonMappingException - failure to map from the JSON to this class

save

public void save(java.io.File file,
                 T instance)
          throws java.io.IOException

Save to a local file. Any existing file is overwritten unless the OS blocks that.

Parameters:

file - file

instance - instance

Throws:

java.io.IOException - IO exception

fromResource

public T fromResource(java.lang.String resource)
               throws java.io.IOException,
                      com.fasterxml.jackson.core.JsonParseException,
                      com.fasterxml.jackson.databind.JsonMappingException

Convert from a JSON file.

Parameters:

resource - input file

Returns:

the parsed JSON

Throws:

java.io.IOException - IO problems

com.fasterxml.jackson.core.JsonParseException - If the input is not well-formatted

com.fasterxml.jackson.databind.JsonMappingException - failure to map from the JSON to this class

fromInstance

public T fromInstance(T instance)
               throws java.io.IOException

clone by converting to JSON and back again. This is much less efficient than any Java clone process.

Parameters:

instance - instance to duplicate

Returns:

a new instance

Throws:

java.io.IOException - IO problems.

load

public T load(FileSystem fs,
              Path path)
       throws java.io.IOException

Load from a Hadoop filesystem.

Parameters:

fs - filesystem

path - path

Returns:

a loaded object

Throws:

PathIOException - JSON parse problem

java.io.IOException - IO problems

load

public T load(FileSystem fs,
              Path path,
              @Nullable
              FileStatus status)
       throws java.io.IOException

Load from a Hadoop filesystem. If a file status is supplied, it's passed in to the openFile() call so that FS implementations can optimize their opening.

Parameters:

fs - filesystem

path - path

status - status of the file to open.

Returns:

a loaded object

Throws:

PathIOException - JSON parse problem

java.io.EOFException - file status references an empty file

java.io.IOException - IO problems

save

public void save(FileSystem fs,
                 Path path,
                 T instance,
                 boolean overwrite)
          throws java.io.IOException

Save to a Hadoop filesystem.

Parameters:

fs - filesystem

path - path

overwrite - should any existing file be overwritten

instance - instance

Throws:

java.io.IOException - IO exception.

writeJsonAsBytes

public void writeJsonAsBytes(T instance,
                             java.io.OutputStream dataOutputStream)
                      throws java.io.IOException

Write the JSON as bytes, then close the stream.

Parameters:

instance - instance to write

dataOutputStream - an output stream that will always be closed

Throws:

java.io.IOException - on any failure

toBytes

public byte[] toBytes(T instance)
               throws java.io.IOException

Convert JSON to bytes.

Parameters:

instance - instance to convert

Returns:

a byte array

Throws:

java.io.IOException - IO problems

fromBytes

public T fromBytes(byte[] bytes)
            throws java.io.IOException

Deserialize from a byte array.

Parameters:

bytes - byte array

Returns:

byte array.

Throws:

java.io.IOException - IO problems

java.io.EOFException - not enough data

toJson

public java.lang.String toJson(T instance)
                        throws com.fasterxml.jackson.core.JsonProcessingException

Convert an instance to a JSON string.

Parameters:

instance - instance to convert

Returns:

a JSON string description

Throws:

com.fasterxml.jackson.core.JsonProcessingException - Json generation problems

toString

public java.lang.String toString(T instance)

Convert an instance to a string form for output. This is a robust operation which will convert any JSON-generating exceptions into error text.

Parameters:

instance - non-null instance

Returns:

a JSON string