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.
in
parser
Modifier and Type | Method and Description |
---|---|
Symbol |
doAction(Symbol input,
Symbol top)
Handle the action symbol top when the input is sought to be
taken off the stack.
|
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) . |
double |
readDouble()
Reads a double written by
Encoder.writeDouble(double) . |
int |
readEnum()
Reads an enumeration.
|
Schema.Field[] |
readFieldOrder()
Returns the actual order in which the reader's fields will be returned to the
reader.
|
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) . |
arrayNext, configure, mapNext, readArrayStart, readBoolean, readFixed, readInt, readMapStart, readNull, skipArray, skipFixed, skipFixed, skipMap
skipTopSymbol
public static Object resolve(Schema writer, Schema reader) throws IOException
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.writer
- The writer's schema. Cannot be null.reader
- The reader's schema. Cannot be null.IOException
NullPointerException
- if writer
or reader
is
null
public final Schema.Field[] readFieldOrder() throws IOException
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.)AvroTypeException
- If we're not starting a new recordIOException
public final Schema.Field[] readFieldOrderIfDiff() throws IOException
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).IOException
public final void drain() throws IOException
IOException
public long readLong() throws IOException
Decoder
Encoder.writeLong(long)
.readLong
in class ValidatingDecoder
IOException
public float readFloat() throws IOException
Decoder
Encoder.writeFloat(float)
.readFloat
in class ValidatingDecoder
IOException
public double readDouble() throws IOException
Decoder
Encoder.writeDouble(double)
.readDouble
in class ValidatingDecoder
IOException
public Utf8 readString(Utf8 old) throws IOException
Decoder
Encoder.writeString(org.apache.avro.util.Utf8)
.readString
in class ValidatingDecoder
IOException
public String readString() throws IOException
Decoder
Encoder.writeString(org.apache.avro.util.Utf8)
.readString
in class ValidatingDecoder
IOException
public void skipString() throws IOException
Decoder
Encoder.writeString(org.apache.avro.util.Utf8)
.skipString
in class ValidatingDecoder
IOException
public ByteBuffer readBytes(ByteBuffer old) throws IOException
Decoder
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.readBytes
in class ValidatingDecoder
IOException
public void skipBytes() throws IOException
Decoder
Encoder.writeBytes(java.nio.ByteBuffer)
.skipBytes
in class ValidatingDecoder
IOException
public int readEnum() throws IOException
Decoder
readEnum
in class ValidatingDecoder
IOException
public int readIndex() throws IOException
Decoder
Encoder.writeIndex(int)
.readIndex
in class ValidatingDecoder
IOException
public Symbol doAction(Symbol input, Symbol top) throws IOException
Parser.ActionHandler
doAction
in interface Parser.ActionHandler
doAction
in class ValidatingDecoder
input
- The input symbol from the caller of advancetop
- The symbol at the top the stack.IOException
public void skipAction() throws IOException
SkipParser.SkipHandler
skipAction
in interface SkipParser.SkipHandler
skipAction
in class ParsingDecoder
IOException
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