Package org.apache.avro.io

Class ResolvingDecoder

java.lang.Object

org.apache.avro.io.Decoder

org.apache.avro.io.ParsingDecoder

org.apache.avro.io.ValidatingDecoder

org.apache.avro.io.ResolvingDecoder

All Implemented Interfaces:

Parser.ActionHandler, SkipParser.SkipHandler

public class ResolvingDecoder
extends ValidatingDecoder

Decoder that performs type-resolution between the reader's and writer's schemas.

When resolving schemas, this class will return the values of fields in _writer's_ order, not the reader's order. (However, it returns _only_ the reader's fields, not any extra fields the writer may have written.) To help clients handle fields that appear to be coming out of order, this class defines the method readFieldOrder().

See the parser documentation for information on how this works.

Field Summary

Fields inherited from class org.apache.avro.io.ValidatingDecoder

in

Fields inherited from class org.apache.avro.io.ParsingDecoder

parser

Method Summary

Modifier and Type	Method	Description
Symbol	doAction(Symbol input, Symbol top)	Handle the action symbol top when the input is sought to be taken off the stack.
final void	drain()	Consume any more data that has been written by the writer but not needed by the reader so that the the underlying decoder is in proper shape for the next record.
ByteBuffer	readBytes(ByteBuffer old)	Reads a byte-string written by Encoder.writeBytes(java.nio.ByteBuffer). if old is not null and has sufficient capacity to take in the bytes being read, the bytes are returned in old.
double	readDouble()	Reads a double written by Encoder.writeDouble(double).
int	readEnum()	Reads an enumeration.
final Schema.Field[]	readFieldOrder()	Returns the actual order in which the reader's fields will be returned to the reader.
final Schema.Field[]	readFieldOrderIfDiff()	Same as readFieldOrder() except that it returns null if there was no reordering of fields, i.e., if the correct thing for the reader to do is to read (all) of its fields in the order specified by its own schema (useful for optimizations).
float	readFloat()	Reads a float written by Encoder.writeFloat(float).
int	readIndex()	Reads the tag of a union written by Encoder.writeIndex(int).
long	readLong()	Reads a long written by Encoder.writeLong(long).
String	readString()	Reads a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).
Utf8	readString(Utf8 old)	Reads a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).
static Object	resolve(Schema writer, Schema reader)	Produces an opaque resolver that can be used to construct a new ResolvingDecoder(Object, Decoder).
void	skipAction()	Skips the action at the top of the stack.
void	skipBytes()	Discards a byte-string written by Encoder.writeBytes(java.nio.ByteBuffer).
void	skipString()	Discards a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).

Methods inherited from class org.apache.avro.io.ValidatingDecoder

arrayNext, configure, mapNext, readArrayStart, readBoolean, readFixed, readInt, readMapStart, readNull, skipArray, skipFixed, skipFixed, skipMap

Methods inherited from class org.apache.avro.io.ParsingDecoder

skipTopSymbol

Methods inherited from class org.apache.avro.io.Decoder

readFixed

Methods inherited from class java.lang.Object

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

Method Details

resolve

public static Object resolve(Schema writer,
 Schema reader)
                      throws IOException

Produces an opaque resolver that can be used to construct a new ResolvingDecoder(Object, Decoder). The returned Object is immutable and hence can be simultaneously used in many ResolvingDecoders. This method is reasonably expensive, the users are encouraged to cache the result.

Parameters:

writer - The writer's schema. Cannot be null.

reader - The reader's schema. Cannot be null.

Returns:

The opaque resolver.

Throws:

IOException

NullPointerException - if writer or reader is null

readFieldOrder

public final Schema.Field[] readFieldOrder()
                                    throws IOException

Returns the actual order in which the reader's fields will be returned to the reader. This method is useful because ResolvingDecoder returns values in the order written by the writer, rather than the order expected by the reader. This method allows readers to figure out what fields to expect. Let's say the reader is expecting a three-field record, the first field is a long, the second a string, and the third an array. In this case, a typical usage might be as follows:

   Schema.Fields[] fieldOrder = in.readFieldOrder();
   for (int i = 0; i < 3; i++) {
     switch (fieldOrder[i].pos()) {
     case 1:
       foo(in.readLong());
       break;
     case 2:
       someVariable = in.readString();
       break;
     case 3:
       bar(in); // The code of "bar" will read an array-of-int
       break;
     }
 

Note that ResolvingDecoder will return only the fields expected by the reader, not other fields that may have been written by the writer. Thus, the iteration-count of "3" in the above loop will always be correct. Throws a runtime exception if we're not just about to read the first field of a record. (If the client knows the order of incoming fields, then the client does not need to call this method but rather can just start reading the field values.)

Throws:

AvroTypeException - If we're not starting a new record

IOException

readFieldOrderIfDiff

public final Schema.Field[] readFieldOrderIfDiff()
                                          throws IOException

Same as readFieldOrder() except that it returns null if there was no reordering of fields, i.e., if the correct thing for the reader to do is to read (all) of its fields in the order specified by its own schema (useful for optimizations).

Throws:

IOException

drain

public final void drain()
                 throws IOException

Consume any more data that has been written by the writer but not needed by the reader so that the the underlying decoder is in proper shape for the next record. This situation happens when, for example, the writer writes a record with two fields and the reader needs only the first field. This function should be called after completely decoding an object but before next object can be decoded from the same underlying decoder either directly or through another resolving decoder. If the same resolving decoder is used for the next object as well, calling this method is optional; the state of this resolving decoder ensures that any leftover portions are consumed before the next object is decoded.

Throws:

IOException

readLong

public long readLong()
              throws IOException

Description copied from class: Decoder

Reads a long written by Encoder.writeLong(long).

Overrides:

readLong in class ValidatingDecoder

Throws:

IOException

readFloat

public float readFloat()
                throws IOException

Description copied from class: Decoder

Reads a float written by Encoder.writeFloat(float).

Overrides:

readFloat in class ValidatingDecoder

Throws:

IOException

readDouble

public double readDouble()
                  throws IOException

Description copied from class: Decoder

Reads a double written by Encoder.writeDouble(double).

Overrides:

readDouble in class ValidatingDecoder

Throws:

IOException

readString

public Utf8 readString(Utf8 old)
                throws IOException

Description copied from class: Decoder

Reads a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).

Overrides:

readString in class ValidatingDecoder

Throws:

IOException

readString

public String readString()
                  throws IOException

Description copied from class: Decoder

Reads a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).

Overrides:

readString in class ValidatingDecoder

Throws:

IOException

skipString

public void skipString()
                throws IOException

Description copied from class: Decoder

Discards a char-string written by Encoder.writeString(org.apache.avro.util.Utf8).

Overrides:

skipString in class ValidatingDecoder

Throws:

IOException

readBytes

public ByteBuffer readBytes(ByteBuffer old)
                     throws IOException

Description copied from class: Decoder

Reads a byte-string written by Encoder.writeBytes(java.nio.ByteBuffer). if old is not null and has sufficient capacity to take in the bytes being read, the bytes are returned in old.

Overrides:

readBytes in class ValidatingDecoder

Throws:

IOException

skipBytes

public void skipBytes()
               throws IOException

Description copied from class: Decoder

Discards a byte-string written by Encoder.writeBytes(java.nio.ByteBuffer).

Overrides:

skipBytes in class ValidatingDecoder

Throws:

IOException

readEnum

public int readEnum()
             throws IOException

Description copied from class: Decoder

Reads an enumeration.

Overrides:

readEnum in class ValidatingDecoder

Returns:

The enumeration's value.

Throws:

IOException

readIndex

public int readIndex()
              throws IOException

Description copied from class: Decoder

Reads the tag of a union written by Encoder.writeIndex(int).

Overrides:

readIndex in class ValidatingDecoder

Throws:

IOException

doAction

public Symbol doAction(Symbol input,
 Symbol top)
                throws IOException

Description copied from interface: Parser.ActionHandler

Handle the action symbol top when the input is sought to be taken off the stack.

Specified by:

doAction in interface Parser.ActionHandler

Overrides:

doAction in class ValidatingDecoder

Parameters:

input - The input symbol from the caller of advance

top - The symbol at the top the stack.

Returns:

null if advance() is to continue processing the stack. If not null the return value will be returned by advance().

Throws:

IOException

skipAction

public void skipAction()
                throws IOException

Description copied from interface: SkipParser.SkipHandler

Skips the action at the top of the stack.

Specified by:

skipAction in interface SkipParser.SkipHandler

Overrides:

skipAction in class ParsingDecoder

Throws:

IOException