ResolvingDecoder (Apache Avro Java 1.9.2 API)

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

All Methods Static Methods Instance Methods Concrete Methods
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)`.

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 Detail
  - 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
  - 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

Class ResolvingDecoder

Field Summary

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

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

Method Summary

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

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

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

Methods inherited from class java.lang.Object

Method Detail

resolve

readFieldOrder

readFieldOrderIfDiff

drain

readLong

readFloat

readDouble

readString

readString

skipString

readBytes

skipBytes

readEnum

readIndex

doAction

skipAction