org.jgroups
Class Message

java.lang.Object
  extended by org.jgroups.Message
All Implemented Interfaces:
java.io.Externalizable, java.io.Serializable, Streamable

public class Message
extends java.lang.Object
implements java.io.Externalizable, Streamable

A Message encapsulates data sent to members of a group. It contains among other things the address of the sender, the destination address, a payload (byte buffer) and a list of headers. Headers are added by protocols on the sender side and removed by protocols on the receiver's side.

The byte buffer can point to a reference, and we can subset it using index and length. However, when the message is serialized, we only write the bytes between index and length.

Version:
$Id: Message.java,v 1.76.2.9 2008/09/16 13:09:12 belaban Exp $
Author:
Bela Ban
See Also:
Serialized Form

Field Summary
protected  Address dest_addr
           
protected  Headers headers
          All headers are placed here
static byte HIGH_PRIO
           
protected  int length
          The number of bytes in the buffer (usually buf.length is buf not equal to null).
protected static org.apache.commons.logging.Log log
           
static byte LOW_PRIO
           
protected  int offset
          The index into the payload (usually 0)
static byte OOB
           
protected  Address src_addr
           
 
Constructor Summary
Message()
           
Message(Address dest)
          Public constructor
Message(Address dest, Address src, byte[] buf)
          Public constructor
Message(Address dest, Address src, byte[] buf, int offset, int length)
          Constructs a message.
Message(Address dest, Address src, java.io.Serializable obj)
          Public constructor
Message(boolean create_headers)
           
 
Method Summary
 void clearFlag(byte flag)
           
protected  java.lang.Object clone()
           
 Message copy()
           
 Message copy(boolean copy_buffer)
          Create a copy of the message.
 byte[] getBuffer()
          Returns a copy of the buffer if offset and length are used, otherwise a reference.
 Address getDest()
           
 byte getFlags()
           
 Header getHeader(java.lang.String key)
           
 java.util.Map<java.lang.String,Header> getHeaders()
          Returns a reference to the headers hashmap, which is immutable.
 int getLength()
          Returns the number of bytes in the buffer
 int getNumHeaders()
           
 java.lang.Object getObject()
          Uses Java serialization to create an object from the buffer of the message.
 int getOffset()
          Returns the offset into the buffer at which the data starts
 byte[] getRawBuffer()
          Returns a reference to the payload (byte buffer).
 Address getSrc()
           
 boolean isFlagSet(byte flag)
           
 Message makeReply()
           
 java.lang.String printHeaders()
           
 java.lang.String printObjectHeaders()
           
 void putHeader(java.lang.String key, Header hdr)
          Puts a header given a key into the hashmap.
 Header putHeaderIfAbsent(java.lang.String key, Header hdr)
          Puts a header given a key into the map, only if the key doesn't exist yet
 void readExternal(java.io.ObjectInput in)
           
 void readFrom(java.io.DataInputStream in)
          Read the state of the current object (including superclasses) from instream Note that the input stream must not be closed
 Header removeHeader(java.lang.String key)
          Deprecated. Use getHeader() instead. The issue with removing a header is described in http://jira.jboss.com/jira/browse/JGRP-393
 void setBuffer(Buffer buf)
           Note that the byte[] buffer passed as argument must not be modified.
 void setBuffer(byte[] b)
           
 void setBuffer(byte[] b, int offset, int length)
          Set the internal buffer to point to a subset of a given buffer
 void setDest(Address new_dest)
           
 void setFlag(byte flag)
           
 void setObject(java.io.Serializable obj)
          Takes an object and uses Java serialization to generate the byte[] buffer which is set in the message.
 void setSrc(Address new_src)
           
 long size()
          Returns the exact size of the marshalled message.
 java.lang.String toString()
           
 java.lang.String toStringAsObject()
          Tries to read an object from the message's buffer and prints it
 void writeExternal(java.io.ObjectOutput out)
           
 void writeTo(java.io.DataOutputStream out)
          Streams all members (dest and src addresses, buffer and headers) to the output stream.
 
Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

dest_addr

protected Address dest_addr

src_addr

protected Address src_addr

offset

protected transient int offset
The index into the payload (usually 0)


length

protected transient int length
The number of bytes in the buffer (usually buf.length is buf not equal to null).


headers

protected Headers headers
All headers are placed here


log

protected static final org.apache.commons.logging.Log log

OOB

public static final byte OOB
See Also:
Constant Field Values

LOW_PRIO

public static final byte LOW_PRIO
See Also:
Constant Field Values

HIGH_PRIO

public static final byte HIGH_PRIO
See Also:
Constant Field Values
Constructor Detail

Message

public Message(Address dest)
Public constructor

Parameters:
dest - Address of receiver. If it is null then the message sent to the group. Otherwise, it contains a single destination and is sent to that member.


Message

public Message(Address dest,
               Address src,
               byte[] buf)
Public constructor

Parameters:
dest - Address of receiver. If it is null then the message sent to the group. Otherwise, it contains a single destination and is sent to that member.

src - Address of sender
buf - Message to be sent. Note that this buffer must not be modified (e.g. buf[0]=0 is not allowed), since we don't copy the contents on clopy() or clone().

Message

public Message(Address dest,
               Address src,
               byte[] buf,
               int offset,
               int length)
Constructs a message. The index and length parameters allow to provide a reference to a byte buffer, rather than a copy, and refer to a subset of the buffer. This is important when we want to avoid copying. When the message is serialized, only the subset is serialized.
Note that the byte[] buffer passed as argument must not be modified. Reason: if we retransmit the message, it would still have a ref to the original byte[] buffer passed in as argument, and so we would retransmit a changed byte[] buffer !

Parameters:
dest - Address of receiver. If it is null then the message sent to the group. Otherwise, it contains a single destination and is sent to that member.

src - Address of sender
buf - A reference to a byte buffer
offset - The index into the byte buffer
length - The number of bytes to be used from buf. Both index and length are checked for array index violations and an ArrayIndexOutOfBoundsException will be thrown if invalid

Message

public Message(Address dest,
               Address src,
               java.io.Serializable obj)
Public constructor

Parameters:
dest - Address of receiver. If it is null then the message sent to the group. Otherwise, it contains a single destination and is sent to that member.

src - Address of sender
obj - The object will be serialized into the byte buffer. Object has to be serializable ! The resulting buffer must not be modified (e.g. buf[0]=0 is not allowed), since we don't copy the contents on clopy() or clone().

Note that this is a convenience method and JGroups will use default Java serialization to serialize obj into a byte buffer.


Message

public Message()

Message

public Message(boolean create_headers)
Method Detail

getDest

public Address getDest()

setDest

public void setDest(Address new_dest)

getSrc

public Address getSrc()

setSrc

public void setSrc(Address new_src)

getRawBuffer

public byte[] getRawBuffer()
Returns a reference to the payload (byte buffer). Note that this buffer should not be modified as we do not copy the buffer on copy() or clone(): the buffer of the copied message is simply a reference to the old buffer.
Even if offset and length are used: we return the entire buffer, not a subset.


getBuffer

public final byte[] getBuffer()
Returns a copy of the buffer if offset and length are used, otherwise a reference.

Returns:
byte array with a copy of the buffer.

setBuffer

public final void setBuffer(byte[] b)

setBuffer

public final void setBuffer(byte[] b,
                            int offset,
                            int length)
Set the internal buffer to point to a subset of a given buffer

Parameters:
b - The reference to a given buffer. If null, we'll reset the buffer to null
offset - The initial position
length - The number of bytes

setBuffer

public final void setBuffer(Buffer buf)
Note that the byte[] buffer passed as argument must not be modified. Reason: if we retransmit the message, it would still have a ref to the original byte[] buffer passed in as argument, and so we would retransmit a changed byte[] buffer !


getOffset

public int getOffset()
Returns the offset into the buffer at which the data starts


getLength

public int getLength()
Returns the number of bytes in the buffer


getHeaders

public java.util.Map<java.lang.String,Header> getHeaders()
Returns a reference to the headers hashmap, which is immutable. Any attempt to modify the returned map will cause a runtime exception


printHeaders

public java.lang.String printHeaders()

getNumHeaders

public int getNumHeaders()

setObject

public final void setObject(java.io.Serializable obj)
Takes an object and uses Java serialization to generate the byte[] buffer which is set in the message.


getObject

public final java.lang.Object getObject()
Uses Java serialization to create an object from the buffer of the message. Note that this is dangerous when using your own classloader, e.g. inside of an application server ! Most likely, JGroups will use the system classloader to deserialize the buffer into an object, whereas (for example) a web application will want to use the webapp's classloader, resulting in a ClassCastException. The recommended way is for the application to use their own serialization and only pass byte[] buffer to JGroups.

Returns:

setFlag

public void setFlag(byte flag)

clearFlag

public void clearFlag(byte flag)

isFlagSet

public boolean isFlagSet(byte flag)

getFlags

public byte getFlags()

putHeader

public void putHeader(java.lang.String key,
                      Header hdr)
Puts a header given a key into the hashmap. Overwrites potential existing entry.


putHeaderIfAbsent

public Header putHeaderIfAbsent(java.lang.String key,
                                Header hdr)
Puts a header given a key into the map, only if the key doesn't exist yet

Parameters:
key -
hdr -
Returns:
the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)

removeHeader

public Header removeHeader(java.lang.String key)
Deprecated. Use getHeader() instead. The issue with removing a header is described in http://jira.jboss.com/jira/browse/JGRP-393

Parameters:
key -
Returns:
the header assoaicted with key

getHeader

public Header getHeader(java.lang.String key)

copy

public Message copy()

copy

public Message copy(boolean copy_buffer)
Create a copy of the message. If offset and length are used (to refer to another buffer), the copy will contain only the subset offset and length point to, copying the subset into the new copy.

Parameters:
copy_buffer -
Returns:
Message with specified data

clone

protected java.lang.Object clone()
                          throws java.lang.CloneNotSupportedException
Overrides:
clone in class java.lang.Object
Throws:
java.lang.CloneNotSupportedException

makeReply

public Message makeReply()

toString

public java.lang.String toString()
Overrides:
toString in class java.lang.Object

toStringAsObject

public java.lang.String toStringAsObject()
Tries to read an object from the message's buffer and prints it


size

public long size()
Returns the exact size of the marshalled message. Uses method size() of each header to compute the size, so if a Header subclass doesn't implement size() we will use an approximation. However, most relevant header subclasses have size() implemented correctly. (See org.jgroups.tests.SizeTest).

Returns:
The number of bytes for the marshalled message

printObjectHeaders

public java.lang.String printObjectHeaders()

writeExternal

public void writeExternal(java.io.ObjectOutput out)
                   throws java.io.IOException
Specified by:
writeExternal in interface java.io.Externalizable
Throws:
java.io.IOException

readExternal

public void readExternal(java.io.ObjectInput in)
                  throws java.io.IOException,
                         java.lang.ClassNotFoundException
Specified by:
readExternal in interface java.io.Externalizable
Throws:
java.io.IOException
java.lang.ClassNotFoundException

writeTo

public void writeTo(java.io.DataOutputStream out)
             throws java.io.IOException
Streams all members (dest and src addresses, buffer and headers) to the output stream.

Specified by:
writeTo in interface Streamable
Parameters:
out -
Throws:
java.io.IOException

readFrom

public void readFrom(java.io.DataInputStream in)
              throws java.io.IOException,
                     java.lang.IllegalAccessException,
                     java.lang.InstantiationException
Description copied from interface: Streamable
Read the state of the current object (including superclasses) from instream Note that the input stream must not be closed

Specified by:
readFrom in interface Streamable
Throws:
java.io.IOException
java.lang.IllegalAccessException
java.lang.InstantiationException


Copyright ? 1998-2008 Bela Ban. All Rights Reserved.