com.ibm.streams.operator.state

Interface Checkpoint

public interface Checkpoint

Represents a checkpoint.

An instance of this interface will be created and passed to the operator's registered StateHandler through its checkpoint or reset methods.
The same interface will be used at checkpoint or restore time. The following example shows how an operator can save state information (in this case, an int and a string) to a back end store using this interface:

 
 public void checkpoint(Checkpoint checkpoint) throws Exception {
                // get an outputstream to write data to
                ObjectOutputStream stream = checkpoint.getOutputStream();
                
                // write an integer
                stream.writeInt(42);
 
                // write a string
                stream.writeUTF("string");
 }
 
 

The following example shows how the corresponding reset method would be used to restore the values stored above:

 
 public void reset(Checkpoint checkpoint) throws Exception {
                // get an inputstream to read data from.
                ObjectInputStream stream = checkpoint.getInputStream();
 
                // read an int (this would be 42 if the checkpoint method above is used)
                int intValue = stream.readInt();
 
                // read the string as a UTF-8 value
                String stringValue = stream.readUTF();
 
                //...
 }
 
 

Since:

InfoSphere® Streams Version 4.0

Method Summary

Methods

Modifier and Type	Method and Description
java.io.ObjectInputStream	getInputStream() Provides an ObjectInputStream object that can be used to read data stored in the checkpoint.
java.io.ObjectOutputStream	getOutputStream() Provides an ObjectOutputStream object that can be used to put data into the checkpoint.
long	getSequenceId() Sequence identifier of this checkpoint.
long	getTimestamp() Return the time (in millisecs) at which the checkpoint was created.

Method Detail

getSequenceId

long getSequenceId()

Sequence identifier of this checkpoint.

Returns:

identifier for the checkpoint

getTimestamp

long getTimestamp()
                  throws java.lang.IllegalStateException,
                         java.io.IOException

Return the time (in millisecs) at which the checkpoint was created. Only valid at restore time.

Returns:

Timestamp as long value since Jan 1, 1970.

Throws:

java.lang.IllegalStateException - if the method is called at checkpoint time.

java.io.IOException - if there is an error retrieving the checkpoint timestamp.

getInputStream

java.io.ObjectInputStream getInputStream()
                                         throws java.lang.IllegalStateException,
                                                java.io.IOException

Provides an ObjectInputStream object that can be used to read data stored in the checkpoint. The data should be read in the same order that it was put in during checkpointing. Note that the runtime will automatically call the close() method on the stream.

Returns:

Input Stream for reading data out of the checkpoint.

Throws:

java.lang.IllegalStateException - if this method is called at checkpoint time.

java.io.IOException - if a input stream could not be created.

getOutputStream

java.io.ObjectOutputStream getOutputStream()
                                           throws java.lang.IllegalStateException,
                                                  java.io.IOException

Provides an ObjectOutputStream object that can be used to put data into the checkpoint. Note that the runtime will automatically call the flush() and close() methods on the stream.

Returns:

Output Stream for writing data to the checkpoint.

Throws:

java.lang.IllegalStateException - if this method is called at restore time.

java.io.IOException - if an output stream could not be created.