Package org.jgroups
Class Message
java.lang.Object
org.jgroups.Message
- All Implemented Interfaces:
Externalizable
,Serializable
,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:
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected Address
protected Headers
All headers are placed herestatic final byte
protected int
The number of bytes in the buffer (usually buf.length is buf not equal to null).protected static final org.apache.commons.logging.Log
static final byte
protected int
The index into the payload (usually 0)static final byte
protected Address
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
clearFlag
(byte flag) protected Object
clone()
copy()
copy
(boolean copy_buffer) Create a copy of the message.final byte[]
Returns a copy of the buffer if offset and length are used, otherwise a reference.getDest()
byte
getFlags()
Returns a reference to the headers hashmap, which is immutable.int
Returns the number of bytes in the bufferint
final Object
Uses Java serialization to create an object from the buffer of the message.int
Returns the offset into the buffer at which the data startsbyte[]
Returns a reference to the payload (byte buffer).getSrc()
boolean
isFlagSet
(byte flag) void
Puts a header given a key into the hashmap.putHeaderIfAbsent
(String key, Header hdr) Puts a header given a key into the map, only if the key doesn't exist yetvoid
void
Read the state of the current object (including superclasses) from instream Note that the input stream must not be closedremoveHeader
(String key) Deprecated.Use getHeader() instead.final void
setBuffer
(byte[] b) final void
setBuffer
(byte[] b, int offset, int length) Set the internal buffer to point to a subset of a given bufferfinal void
Note that the byte[] buffer passed as argument must not be modified.void
void
setFlag
(byte flag) final void
setObject
(Serializable obj) Takes an object and uses Java serialization to generate the byte[] buffer which is set in the message.void
long
size()
Returns the exact size of the marshalled message.toString()
Tries to read an object from the message's buffer and prints itvoid
void
writeTo
(DataOutputStream out) Streams all members (dest and src addresses, buffer and headers) to the output stream.
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Field Details
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dest_addr
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src_addr
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offset
protected transient int offsetThe index into the payload (usually 0) -
length
protected transient int lengthThe number of bytes in the buffer (usually buf.length is buf not equal to null). -
headers
All headers are placed here -
log
protected static final org.apache.commons.logging.Log log -
OOB
public static final byte OOB- See Also:
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LOW_PRIO
public static final byte LOW_PRIO- See Also:
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HIGH_PRIO
public static final byte HIGH_PRIO- See Also:
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Constructor Details
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Message
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.
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Message
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 senderbuf
- 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().
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Message
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 senderbuf
- A reference to a byte bufferoffset
- The index into the byte bufferlength
- 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
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Message
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 senderobj
- 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 serializeobj
into a byte buffer.
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Message
public Message() -
Message
public Message(boolean create_headers)
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Method Details
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getDest
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setDest
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getSrc
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setSrc
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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.
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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 nulloffset
- The initial positionlength
- The number of bytes
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setBuffer
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
Returns a reference to the headers hashmap, which is immutable. Any attempt to modify the returned map will cause a runtime exception -
printHeaders
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getNumHeaders
public int getNumHeaders() -
setObject
Takes an object and uses Java serialization to generate the byte[] buffer which is set in the message. -
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:
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setFlag
public void setFlag(byte flag) -
clearFlag
public void clearFlag(byte flag) -
isFlagSet
public boolean isFlagSet(byte flag) -
getFlags
public byte getFlags() -
putHeader
Puts a header given a key into the hashmap. Overwrites potential existing entry. -
putHeaderIfAbsent
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.)
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removeHeader
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
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getHeader
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copy
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copy
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
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clone
- Overrides:
clone
in classObject
- Throws:
CloneNotSupportedException
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makeReply
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toString
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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
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printObjectHeaders
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writeExternal
- Specified by:
writeExternal
in interfaceExternalizable
- Throws:
IOException
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readExternal
- Specified by:
readExternal
in interfaceExternalizable
- Throws:
IOException
ClassNotFoundException
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writeTo
Streams all members (dest and src addresses, buffer and headers) to the output stream.- Specified by:
writeTo
in interfaceStreamable
- Parameters:
out
-- Throws:
IOException
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readFrom
public void readFrom(DataInputStream in) throws IOException, IllegalAccessException, 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 interfaceStreamable
- Throws:
IOException
IllegalAccessException
InstantiationException
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