Package org.jgroups

Class Message

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

public class Message extends Object implements 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:
  • Field Details

    • 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:
    • LOW_PRIO

      public static final byte LOW_PRIO
      See Also:
    • HIGH_PRIO

      public static final byte HIGH_PRIO
      See Also:
  • Constructor Details

    • 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, 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 Details

    • 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 Map<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 String printHeaders()
    • getNumHeaders

      public int getNumHeaders()
    • setObject

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

      public final 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(String key, Header hdr)
      Puts a header given a key into the hashmap. Overwrites potential existing entry.
    • putHeaderIfAbsent

      public Header putHeaderIfAbsent(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(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(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 Object clone() throws CloneNotSupportedException
      Overrides:
      clone in class Object
      Throws:
      CloneNotSupportedException
    • makeReply

      public Message makeReply()
    • toString

      public String toString()
      Overrides:
      toString in class Object
    • toStringAsObject

      public 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 String printObjectHeaders()
    • writeExternal

      public void writeExternal(ObjectOutput out) throws IOException
      Specified by:
      writeExternal in interface Externalizable
      Throws:
      IOException
    • readExternal

      public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
      Specified by:
      readExternal in interface Externalizable
      Throws:
      IOException
      ClassNotFoundException
    • writeTo

      public void writeTo(DataOutputStream out) throws IOException
      Streams all members (dest and src addresses, buffer and headers) to the output stream.
      Specified by:
      writeTo in interface Streamable
      Parameters:
      out -
      Throws:
      IOException
    • readFrom

      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:
      IOException
      IllegalAccessException
      InstantiationException