Class FormatIdOutputStream

java.lang.Object
java.io.OutputStream
java.io.FilterOutputStream
java.io.DataOutputStream
org.apache.derby.iapi.services.io.FormatIdOutputStream
All Implemented Interfaces:
Closeable, DataOutput, Flushable, ObjectOutput, AutoCloseable, ErrorInfo
public class FormatIdOutputStream extends DataOutputStream implements ObjectOutput, ErrorInfo
A stream for serializing objects with format id tags.

An ObjectOutput (henceforth 'out') preceeds objects it writes with a format id. The companion FormatIdInputStream (henceforth 'in') uses these format ids in parsing the stored data. The stream can be thought of as containing a sequence of (formatId,object) pairs interspersed with other data. The assumption is that out.writeObject() produces these pairs and in.readObject() uses the format ids to construct objects from the pairs that out.writeObject produced. The description below describes each supported pair and how in.readObject() processes it.

  1. (NULL_FORMAT_ID, nothing) in.readObject() returns null.
  2. (SRING_FORMAT_ID, UTF8 encoded string)in.readObject reads and returns this string.
  3. (SERIALIZABLE_FORMAT_ID,serialized object) in.readObject() reads the object using java serialization and returns it.
  4. (A format id for a Storable, isNull flag and object if isNull == false) (see note 1) in.readObject() reads the boolean isNull flag. If is null is true, in.readObject() returns a Storable object of the correct class which is null. If ifNull is false, in.readObject() restores the object using its readExternal() method.
  5. (A format id for a Formatable which is not Storable, the stored object) (see note 1) in.readObject restores the object using its readExternal() method.

Note 1: The FormatIdInputStream uses Monitor.newInstanceFromIdentifier(format id) to get the class.

Note 2: An object may support more than one of the following interfaces Storable, Formatable, Serializable. In this case out.writeObject use the first of these interfaces which the object supports (based on the order listed here) to determine how to write the object.

  • Constructor Details

    • FormatIdOutputStream

      public FormatIdOutputStream(OutputStream out)
      Constructor for a FormatIdOutputStream
      Parameters:
      out - output goes here.

  • Method Details

    • writeObject

      public void writeObject(Object ref) throws IOException
      Write a format id for the object provied followed by the object itself to this FormatIdOutputStream.
      Specified by:
      writeObject in interface ObjectOutput
      Parameters:
      ref - a reference to the object.
      Throws:
      IOException - the exception.

    • setOutput

      public void setOutput(OutputStream out)
      Set the OutputStream for this FormatIdOutputStream to the stream provided. It is the responsibility of the caller to flush or close (as required) the previous stream this class was attached to.
      Parameters:
      out - The new output stream.

    • getErrorInfo

      public String getErrorInfo()
      Specified by:
      getErrorInfo in interface ErrorInfo

    • getNestedException

      public Exception getNestedException()
      Specified by:
      getNestedException in interface ErrorInfo