O'Reilly - Java Message Service

3.4.5 StreamMessage
Java Message Service
The StreamMessage carries a stream of primitive Java types (int, double, char, etc.) as its
payload. It provides a set of convenience methods for mapping a formatted stream of bytes
to Java primitives. Primitive types are read from the Message in the same order they were
written. Here's the definition of the StreamMessage interface:
public interface StreamMessage extends Message {
}
public boolean readBoolean( ) throws JMSException;
public void writeBoolean(boolean value) throws JMSException;
public byte readByte( ) throws JMSException;
public int readBytes(byte[] value) throws JMSException;
public void writeByte(byte value) throws JMSException;
public void writeBytes(byte[] value) throws JMSException;
public void writeBytes(byte[] value, int offset, int length)
throws JMSException;
public short readShort( ) throws JMSException;
public void writeShort(short value) throws JMSException;
public char readChar( ) throws JMSException;
public void writeChar(char value) throws JMSException;
public int readInt( ) throws JMSException;
public void writeInt(int value) throws JMSException;
public long readLong( ) throws JMSException;
public void writeLong(long value) throws JMSException;
public float readFloat( ) throws JMSException;
public void writeFloat(float value) throws JMSException;
public double readDouble( ) throws JMSException;
public void writeDouble(double value) throws JMSException;
public String readString( ) throws JMSException;
public void writeString(String value) throws JMSException;
public Object readObject( ) throws JMSException;
public void writeObject(Object value) throws JMSException;
public void reset( ) throws JMSException;
On the surface, the StreamMessage strongly resembles the BytesMessage, but they are not
the same. The StreamMessage keeps track of the order and types of primitives written to the
stream, so formal conversion rules apply. For example, an exception would be thrown if
you tried to read a long value as a short:
StreamMessage streamMessage = session.createStreamMessage( );
streamMessage.writeLong(2938302);
// The next line throws a JMSException
short value = streamMessage.readShort( );
While this would work fine with a BytesMessage, it won't work with a StreamMessage. A
BytesMessage would write the long as 64 bits (8 bytes) of raw data, so that you could later
read some of the data as a short, which is only 16 bits (the first 2 bytes of the long). The
StreamMessage, on the other hand, writes the type information as well as the value of the
long primitive, and enforces a strict set of conversion rules that prevent reading the long as
a short.
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