org.apache.avro
Class Schema

java.lang.Object
  org.apache.avro.Schema

public abstract class Schema
extends Object

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. 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.

Nested Class Summary

static class	Schema.Field A field within a record.
static class	Schema.Type The type of a schema.

Method Summary

void	addAlias(String alias) If this is a record, enum or fixed, add an alias.
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	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) Create an anonymous record schema.
static Schema	createRecord(String name, String doc, String namespace, boolean isError) Create a named record schema.
static Schema	createUnion(List<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.
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, if any.
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.
String	getProp(String name) Returns the value of the named property in this schema.
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.
static Schema	parse(File file) Constructs a Schema object from JSON schema file file.
static Schema	parse(InputStream in) Constructs a Schema object from JSON schema stream in.
static Schema	parse(String jsonSchema) Construct a schema from JSON text.
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.

Methods inherited from class java.lang.Object

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

Method Detail

create

public static Schema create(Schema.Type type)

Create a schema for a primitive type.

getProp

public String getProp(String name)

Returns the value of the named property in this schema. Returns null if there is no property with that name.

addProp

public void addProp(String name,
                    String value)

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.

Parameters:

name - The name of the property to add

value - The value for the property to add

createRecord

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

Create an anonymous record schema.

createRecord

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

Create a named record schema.

createEnum

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

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.

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.

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, if any.

addAlias

public void addAlias(String alias)

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.

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 int hashCode()

Overrides:

hashCode in class Object

parse

public static Schema parse(File file)
                    throws IOException

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

JsonParseException - if the contents are invalid

parse

public static Schema parse(InputStream in)
                    throws IOException

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

JsonParseException - if the contents are invalid

parse

public static Schema parse(String jsonSchema)

Construct a schema from JSON text.

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.