org.apache.avro

Class Schema

java.lang.Object

org.apache.avro.JsonProperties

org.apache.avro.Schema

All Implemented Interfaces:

Serializable

public abstract class Schema
extends JsonProperties
implements Serializable

An abstract data type.

A schema may be one of:

• A record, mapping field names to field value data;
• An enum, containing one of a small set of symbols;
• An array of values, all of the same schema;
• A map, containing string/value pairs, of a declared schema;
• A union of other schemas;
• A fixed sized binary object;
• A unicode string;
• A sequence of bytes;
• A 32-bit signed int;
• A 64-bit signed long;
• A 32-bit IEEE single-float; or
• A 64-bit IEEE double-float; or
• A boolean; or
• null.

A schema can be constructed using one of its static createXXX methods, or more conveniently using SchemaBuilder. The schema objects are logically immutable. There are only two mutating methods - setFields(List) and addProp(String, String). The following restrictions apply on these two methods.

• setFields(List), can be called at most once. This method exists in order to enable clients to build recursive schemas.
• addProp(String, String) can be called with property names that are not present already. It is not possible to change or delete an existing property.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Schema.Field A field within a record.
static class	Schema.Parser A parser for JSON-format schemas.
static class	Schema.SeenPair Useful as key of Maps when traversing two schemas at the same time and need to watch for recursion.
static class	Schema.Type The type of a schema.

Nested classes/interfaces inherited from class org.apache.avro.JsonProperties

JsonProperties.Null

Field Summary

Fields inherited from class org.apache.avro.JsonProperties

NULL_VALUE

Method Summary

Modifier and Type	Method and Description
void	addAlias(String alias) If this is a record, enum or fixed, add an alias.
void	addAlias(String alias, String space) If this is a record, enum or fixed, add an alias.
void	addProp(String name, Object value)
void	addProp(String name, String value) Adds a property with the given name name and value value.
static Schema	applyAliases(Schema writer, Schema reader) Rewrite a writer's schema using the aliases from a reader's schema.
static Schema	create(Schema.Type type) Create a schema for a primitive type.
static Schema	createArray(Schema elementType) Create an array schema.
static Schema	createEnum(String name, String doc, String namespace, List<String> values) Create an enum schema.
static Schema	createEnum(String name, String doc, String namespace, List<String> values, String enumDefault) Create an enum schema.
static Schema	createFixed(String name, String doc, String space, int size) Create a union schema.
static Schema	createMap(Schema valueType) Create a map schema.
static Schema	createRecord(List<Schema.Field> fields) Deprecated. This method allows to create Schema objects that cannot be parsed by Schema.Parser.parse(String). It will be removed in a future version of Avro. Better use icreateRecord(String, String, String, boolean, List) to produce a fully qualified Schema.
static Schema	createRecord(String name, String doc, String namespace, boolean isError) Create a named record schema.
static Schema	createRecord(String name, String doc, String namespace, boolean isError, List<Schema.Field> fields) Create a named record schema with fields already set.
static Schema	createUnion(List<Schema> types) Create a union schema.
static Schema	createUnion(Schema... types) Create a union schema.
boolean	equals(Object o)
Set<String>	getAliases() If this is a record, enum or fixed, return its aliases, if any.
String	getDoc() If this is a record, enum, or fixed, returns its docstring, if available.
Schema	getElementType() If this is an array, returns its element type.
String	getEnumDefault() If this is an enum, return its default value.
int	getEnumOrdinal(String symbol) If this is an enum, return a symbol's ordinal value.
List<String>	getEnumSymbols() If this is an enum, return its symbols.
Schema.Field	getField(String fieldname) If this is a record, returns the Field with the given name fieldName.
List<Schema.Field>	getFields() If this is a record, returns the fields in it.
int	getFixedSize() If this is fixed, returns its size.
String	getFullName() If this is a record, enum or fixed, returns its namespace-qualified name, otherwise returns the name of the primitive type.
Integer	getIndexNamed(String name) If this is a union, return the branch with the provided full name.
LogicalType	getLogicalType()
String	getName() If this is a record, enum or fixed, returns its name, otherwise the name of the primitive type.
String	getNamespace() If this is a record, enum or fixed, returns its namespace, if any.
Schema.Type	getType() Return the type of this schema.
List<Schema>	getTypes() If this is a union, returns its types.
Schema	getValueType() If this is a map, returns its value type.
boolean	hasEnumSymbol(String symbol) If this is an enum, returns true if it contains given symbol.
int	hashCode()
boolean	isError() Returns true if this record is an error type.
boolean	isNullable() Returns true if this record is an union type containing null.
boolean	isUnion() Returns true if this record is an union type.
static Schema	parse(File file) Deprecated. use Schema.Parser instead.
static Schema	parse(InputStream in) Deprecated. use Schema.Parser instead.
static Schema	parse(String jsonSchema) Deprecated. use Schema.Parser instead.
static Schema	parse(String jsonSchema, boolean validate) Deprecated. use Schema.Parser instead.
static Object	parseJsonToObject(String s) Parses the specified json string to an object.
void	setFields(List<Schema.Field> fields) If this is a record, set its fields.
String	toString() Render this as JSON.
String	toString(boolean pretty) Render this as JSON.
protected Object	writeReplace()

Methods inherited from class org.apache.avro.JsonProperties

addAllProps, getObjectProp, getObjectProps, getProp, hasProps, putAll

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Method Detail

writeReplace

protected Object writeReplace()

create

public static Schema create(Schema.Type type)

Create a schema for a primitive type.

addProp

public void addProp(String name,
                    String value)

Description copied from class: JsonProperties

Adds a property with the given name name and value value. Neither name nor value can be null. It is illegal to add a property if another with the same name but different value already exists in this schema.

Overrides:

addProp in class JsonProperties

Parameters:

name - The name of the property to add

value - The value for the property to add

addProp

public void addProp(String name,
                    Object value)

Overrides:

addProp in class JsonProperties

getLogicalType

public LogicalType getLogicalType()

createRecord

@Deprecated
public static Schema createRecord(List<Schema.Field> fields)

Deprecated. This method allows to create Schema objects that cannot be parsed by Schema.Parser.parse(String). It will be removed in a future version of Avro. Better use icreateRecord(String, String, String, boolean, List) to produce a fully qualified Schema.

Create an anonymous record schema.

createRecord

public static Schema createRecord(String name,
                                  String doc,
                                  String namespace,
                                  boolean isError)

Create a named record schema.

createRecord

public static Schema createRecord(String name,
                                  String doc,
                                  String namespace,
                                  boolean isError,
                                  List<Schema.Field> fields)

Create a named record schema with fields already set.

createEnum

public static Schema createEnum(String name,
                                String doc,
                                String namespace,
                                List<String> values)

Create an enum schema.

createEnum

public static Schema createEnum(String name,
                                String doc,
                                String namespace,
                                List<String> values,
                                String enumDefault)

Create an enum schema.

createArray

public static Schema createArray(Schema elementType)

Create an array schema.

createMap

public static Schema createMap(Schema valueType)

Create a map schema.

createUnion

public static Schema createUnion(List<Schema> types)

Create a union schema.

createUnion

public static Schema createUnion(Schema... types)

Create a union schema.

createFixed

public static Schema createFixed(String name,
                                 String doc,
                                 String space,
                                 int size)

Create a union schema.

getType

public Schema.Type getType()

Return the type of this schema.

getField

public Schema.Field getField(String fieldname)

If this is a record, returns the Field with the given name fieldName. If there is no field by that name, a null is returned.

getFields

public List<Schema.Field> getFields()

If this is a record, returns the fields in it. The returned list is in the order of their positions.

setFields

public void setFields(List<Schema.Field> fields)

If this is a record, set its fields. The fields can be set only once in a schema.

getEnumSymbols

public List<String> getEnumSymbols()

If this is an enum, return its symbols.

getEnumDefault

public String getEnumDefault()

If this is an enum, return its default value.

getEnumOrdinal

public int getEnumOrdinal(String symbol)

If this is an enum, return a symbol's ordinal value.

hasEnumSymbol

public boolean hasEnumSymbol(String symbol)

If this is an enum, returns true if it contains given symbol.

getName

public String getName()

If this is a record, enum or fixed, returns its name, otherwise the name of the primitive type.

getDoc

public String getDoc()

If this is a record, enum, or fixed, returns its docstring, if available. Otherwise, returns null.

getNamespace

public String getNamespace()

If this is a record, enum or fixed, returns its namespace, if any.

getFullName

public String getFullName()

If this is a record, enum or fixed, returns its namespace-qualified name, otherwise returns the name of the primitive type.

addAlias

public void addAlias(String alias)

If this is a record, enum or fixed, add an alias.

addAlias

public void addAlias(String alias,
                     String space)

If this is a record, enum or fixed, add an alias.

getAliases

public Set<String> getAliases()

If this is a record, enum or fixed, return its aliases, if any.

isError

public boolean isError()

Returns true if this record is an error type.

getElementType

public Schema getElementType()

If this is an array, returns its element type.

getValueType

public Schema getValueType()

If this is a map, returns its value type.

getTypes

public List<Schema> getTypes()

If this is a union, returns its types.

getIndexNamed

public Integer getIndexNamed(String name)

If this is a union, return the branch with the provided full name.

getFixedSize

public int getFixedSize()

If this is fixed, returns its size.

toString

public String toString()

Render this as JSON.

Overrides:

toString in class Object

toString

public String toString(boolean pretty)

Render this as JSON.

Parameters:

pretty - if true, pretty-print JSON.

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public final int hashCode()

Overrides:

hashCode in class Object

isUnion

public boolean isUnion()

Returns true if this record is an union type.

isNullable

public boolean isNullable()

Returns true if this record is an union type containing null.

parse

@Deprecated
public static Schema parse(File file)
                                throws IOException

Deprecated. use Schema.Parser instead.

Constructs a Schema object from JSON schema file file. The contents of file is expected to be in UTF-8 format.

Parameters:

file - The file to read the schema from.

Returns:

The freshly built Schema.

Throws:

IOException - if there was trouble reading the contents or they are invalid

parse

@Deprecated
public static Schema parse(InputStream in)
                                throws IOException

Deprecated. use Schema.Parser instead.

Constructs a Schema object from JSON schema stream in. The contents of in is expected to be in UTF-8 format.

Parameters:

in - The input stream to read the schema from.

Returns:

The freshly built Schema.

Throws:

IOException - if there was trouble reading the contents or they are invalid

parse

@Deprecated
public static Schema parse(String jsonSchema)

Deprecated. use Schema.Parser instead.

Construct a schema from JSON text.

parse

@Deprecated
public static Schema parse(String jsonSchema,
                                       boolean validate)

Deprecated. use Schema.Parser instead.

Construct a schema from JSON text.

Parameters:

validate - true if names should be validated, false if not.

parseJsonToObject

public static Object parseJsonToObject(String s)

Parses the specified json string to an object.

applyAliases

public static Schema applyAliases(Schema writer,
                                  Schema reader)

Rewrite a writer's schema using the aliases from a reader's schema. This permits reading records, enums and fixed schemas whose names have changed, and records whose field names have changed. The returned schema always contains the same data elements in the same order, but with possibly different names.