io.mappedbus

Class MappedBusReader

java.lang.Object

io.mappedbus.MappedBusReader

public class MappedBusReader
extends java.lang.Object

Class for reading messages from the bus.

Messages can either be message based or byte array based.

The typical usage is as follows:

 
 // Construct a reader
 MappedBusReader reader = new MappedBusReader("/tmp/test", 100000L, 32);
 reader.open();
 
 // A: read messages as objects
 while (true) {
    if (reader.next()) {
       int type = reader.readType();
       if (type == 0) {
          reader.readMessage(priceUpdate)
       }
    }
 }

 // B: read messages as byte arrays
 while (true) {
    if (reader.next()) {
       int length = reader.read(buffer, 0);
    }
 }

 // Close the reader
 reader.close();
 
 

Constructor Summary

Constructors

Constructor and Description
MappedBusReader(java.lang.String fileName, long fileSize, int recordSize) Constructs a new reader.

Method Summary

Modifier and Type	Method and Description
void	close() Closes the reader.
boolean	hasRecovered() Indicates whether all records available when the reader was created have been read.
boolean	next() Steps forward to the next record if there's one available.
void	open() Opens the reader.
int	readBuffer(byte[] dst, int offset) Reads the next buffer of data.
MappedBusMessage	readMessage(MappedBusMessage message) Reads the next message.
int	readType() Reads the message type.
void	setTimeout(int timeout) Sets the time for a reader to wait for a record to be committed.

Methods inherited from class java.lang.Object

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

Constructor Detail

MappedBusReader

public MappedBusReader(java.lang.String fileName,
                       long fileSize,
                       int recordSize)

Constructs a new reader.

Parameters:

fileName - the name of the memory mapped file

fileSize - the maximum size of the file

recordSize - the maximum size of a record (excluding status flags and meta data)

Method Detail

open

public void open()
          throws java.io.IOException

Opens the reader.

Throws:

java.io.IOException - if there was a problem opening the file

setTimeout

public void setTimeout(int timeout)

Sets the time for a reader to wait for a record to be committed. When the timeout occurs the reader will mark the record as "rolled back" and the record is ignored.

Parameters:

timeout - the timeout in milliseconds

next

public boolean next()
             throws java.io.EOFException

Steps forward to the next record if there's one available. The method has a timeout for how long it will wait for the commit field to be set. When the timeout is reached it will set the roll back field and skip over the record.

Returns:

true, if there's a new record available, otherwise false

Throws:

java.io.EOFException - in case the end of the file was reached

readType

public int readType()

Reads the message type.

Returns:

the message type

readMessage

public MappedBusMessage readMessage(MappedBusMessage message)

Reads the next message.

Parameters:

message - the message object to populate

Returns:

the message object

readBuffer

public int readBuffer(byte[] dst,
                      int offset)

Reads the next buffer of data.

Parameters:

dst - the input buffer

offset - the offset in the buffer of the first byte to read data into

Returns:

the length of the record that was read

hasRecovered

public boolean hasRecovered()

Indicates whether all records available when the reader was created have been read.

Returns:

true, if all records available from the start was read, otherwise false

close

public void close()
           throws java.io.IOException

Closes the reader.

Throws:

java.io.IOException - if there was an error closing the file